Kyushu University [Ramesh Kumar Pokharel (Professor) Faculty of Information Science and Electrical Engineering, Department of I&E Visionaries]

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Ramesh Kumar Pokharel
Professor
http://rfic.ed.kyushu-u.ac.jp/en.html
Department of I&E Visionaries
Faculty of Information Science and Electrical Engineering
Last modified date：2024.05.03

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Department of Electronics
Graduate School of Information Science and Electrical Engineering

Department of Electrical and Electronic Engineering
Graduate School of Information Science and Electrical Engineering

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電子情報基礎(Fundamentals of Electronics and Information Engineering)

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Center for Japan-Egypt Cooperation in Science and Technology（E-JUST Center）

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Director of the Center for Egypt-Japan Coordination in Science and Technology

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Total Priod of education and research career in the foreign country

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1.	Mohamed Aboualalaa, Hala Elsadek and Ramesh K. Pokharel, WPT, Recent Techniques for Improving System Efficiency, Online, 10.5772/intechopen.96003, 1-26, 2021.03, [URL], This book addresses the design challenges in near-field wireless power transfer (WPT) systems, such as high efficiency, compact size, and long transmission range. It presents new low-profile designs for the TX/RX structures using different shapes of defected ground structures (DGS) like (H, semi-H, and spiral-strips DGS). Most near-field WPT systems depend on magnetic resonant coupling (MRC) using 3-D wire loops or helical antennas, which are often bulky. This, in turn, poses technical difficulties in their application in small electronic devices and biomedical implants. To obtain compact structures, printed spiral coils (PSCs) have recently emerged as a candidate for low-profile WPT systems. However, most of the MRC WPT systems that use PSCs have limitations in the maximum achievable efficiency due to the feeding method. Inductive feeding constrains the geometric dimensions of the main transmitting (TX)/receiving (RX) resonators, which do not achieve the maximum achievable unloaded quality factor. This book will be of interest to researchers and professionals working on WPT-related problems..
2.	Sherif Hekal, Ahmed Allam, Adel Abdel-Rahman, Ramesh K. Pokharel , Compact Size Wireless Power Transfer Using Defected Ground Structures, Singapore, 10.1007/978-981-13-8047-1, 1-91, 2019.09, [URL], This book addresses the design challenges in near-field wireless power transfer (WPT) systems, such as high efficiency, compact size, and long transmission range. It presents new low-profile designs for the TX/RX structures using different shapes of defected ground structures (DGS) like (H, semi-H, and spiral-strips DGS). Most near-field WPT systems depend on magnetic resonant coupling (MRC) using 3-D wire loops or helical antennas, which are often bulky. This, in turn, poses technical difficulties in their application in small electronic devices and biomedical implants. To obtain compact structures, printed spiral coils (PSCs) have recently emerged as a candidate for low-profile WPT systems. However, most of the MRC WPT systems that use PSCs have limitations in the maximum achievable efficiency due to the feeding method. Inductive feeding constrains the geometric dimensions of the main transmitting (TX)/receiving (RX) resonators, which do not achieve the maximum achievable unloaded quality factor. This book will be of interest to researchers and professionals working on WPT-related problems..
3.	Ramesh Kumar Pokharel, Adel Barakat, Innovative Techniques for 60 GHz On-Chip Antennas on CMOS Substrate , (In press), 2017.03, The 60 GHz band has a 7 GHz of bandwidth enabling high data rate wireless communication. Also, it has a short wavelength allowing for passive devices integration into a chip; i.e. fully integrated system-on-chip (SOC) is possible. This chapter features the design, implementation, and measurements of 60 GHz on-chip antennas (OCAs) on Complementary-Metal-Oxide-Semiconductor (CMOS) technology. OCAs are the primary barrier for the SOC solution due to their limited performance. This degraded performance comes from the low resistivity and the high permittivity of the CMOS substrate. We present here two innovative techniques to improve the CMOS OCAs’ performance. The first method utilizes Artificial Magnetic Conductors to shield the OCA electromagnetically from the CMOS substrate. The second methodology employs the PN-Junction properties to create a high resistivity layer. Both approaches target the mitigation of the losses of the CMOS substrate; hence, the radiation performance characteristics of the OCAs are enhanced..
4.	Ramesh K. Pokahrel, H. Kanaya, and K. Yoshida, Microwave and Millimeterwave Technologies, Viena, Austria, ISBN 978-953-7619-X-X, IN-TECH Publications, 2010.1 (In Press)., 2010.01, [URL].

1.	Xin Jiang; Ramesh K. Pokharel; Adel Barakat, An Efficient Inverse Modeling Method Using Translator-inspired Neural Network and Dual-annealing for a Compact WPT System, IEEE Transactions on Antennas and Propagation, 10.1109/TAP.2024.3372149, 72, 4, 3282-3291, 2024.04, [URL], This article proposes a novel prediction method for efficient inverse modeling of a compact wireless power transfer (WPT) system. Impedance matching circuit analysis with admittance (J-) inverter theory is used for coupling analysis. Then, a simple translator-inspired neural network is proposed to predict scattering (S-) parameters from 100 MHz to 1 GHz for each coupling case. The training dataset comprises 2900 randomly generated dimensions and the corresponding S-parameters via full-wave simulation. Consequently, the power transfer efficiency (PTE) can be figured out using the S-parameter, which varies from different coupled modes. Then, a dual-annealing algorithm is leveraged to find the best dimensions. The predicted dimensions, including the transmitter (Tx) and receiver (Rx) layouts, values of the etched capacitors, and WPT distances, meet the design purposes. Compared to the state-of-the-art approaches, the proposed method can efficiently optimize the WPT system with desired frequencies. The proposed inverse model reveals new insights and understanding of the prediction and optimization of inductively coupled WPT..
2.	Mohamed Aboualalaa; Ramesh K. Pokharel, Reliable Multiple Cascaded Resonators WPT System Using Stacked Split-Ring Metamaterial Passive Relays, IEEE Transactions on Instrumentation and Measurement, 10.1109/TIM.2023.3324672, 72, xx, xx-xx, 8006710, 2023.10, [URL], A new cascaded structure is proposed to improve the coupled KQ -product ( K is the coupling coefficient, and Q is the unloaded quality factor) and boost the power transfer efficiency (PTE) of the wireless power transfer (WPT) system. The structure consists of four small resonators cascaded together and fed with a single excitation; each consists of two concentric rectangular rings. This cascaded structure can achieve a high PTE of 89.5% at a transfer distance of 20 mm. Afterward, a passive relay system made of stacked metamaterial (MTM) lenses is utilized to extend power transfer distance and address misalignment issues. The proposed WPT system increases the transfer distance up to 80 mm with a PTE of 50%, i.e., the integration with the MTM achieves a 300% improvement in the transfer distance with a reasonable PTE. Then, an assembly of two stacked MTMs is utilized for further extension of the transfer distance. The two stacked MTMs provide an additional 200% enhancement without affecting PTE. A thorough study of the misalignment was executed, showing that the proposed system is capable of transferring power independently of the position of receiver (Rx) with a reasonable PTE. To the best of authors’ knowledge, the proposed structure is the first structure that employed multiple cascaded resonators integrated with the stacked MTM structure for WPT applications..
3.	Adel Barakat and Ramesh K. Pokharel, Low Pass Filtering Admittance Inverter for High out-of-band Rejection Millimeter-Wave on-Chip BPF, IEEE Transactions on Circuits and Systems II: Express Brief, 10.1109/TCSII.2023.3283532, 2023.08, [URL], This brief proposes an on-chip bandpass filter (BPF) that achieves low loss and reduced out-of-band rejection by cascading two resonators and a low pass filtering admittance (J) inverter between them. The proposed J-inverter uses a Tnetwork with negative mutual coupling to generate a transmission zero, and the design equations for this component are provided and verified through circuit simulations. Additionally, a resonator is proposed that utilizes a high impedance line loaded capacitor, and its poles and zeros are thoroughly investigated. Finally, the efficacy of the proposed approach is demonstrated through an on-chip prototype. The measured results show an insertion loss of 3.3 dB at 61 GHz, a 3-dB fractional bandwidth of 25%, and an extended rejection of less than 30 dB between 82 GHz and 115 GHz..
4.	O. Algnar, A. Barkat, and R. K. Pokharel, High PAE CMOS power amplifier with 44.4% FBW using superimposed dual-band configuration and DGS inductors, IEEE Microwave and Wireless Components Letters, 10.1109/LMWC.2022.3189347, 32, 7, 1423-1426, 2022.12, [URL], A two-stage 180-nm CMOS wideband (14–22 GHz) power amplifier (PA) with a superimposed staggered technique and defected-ground-structure (DGS) inductors is introduced, where a wideband peaking main stage is designed at the center frequency; then, a superimposed dual-band (SDB) driver stage is proposed to obtain the optimally flat gain response over the whole bandwidth (BW). Also, DGS inductors are used to enhance the power added efficiency (PAE) of the implemented PA by decreasing the matching circuits’ insertion losses. The proposed PA achieved a power gain of 12 dB at a total chip area of 0.564 mm2. Also, at the center frequency, it achieved a saturated output power of 16.6 dBm exhibiting the smallest reported amplitude-to-phase (AM-PM) distortion (2.1°) and group delay (GD) variations (±66 ps). Finally, it gives among the highest fractional bandwidth (FBW) (44.4%) and the PAE (18.7%) so far. Also, it achieves an error vector magnitude of −25 dB at 9.3-dBm output power for a 400-MHz 5G-NR signal..
5.	Xin Jiang, Ramesh K. Pokharel, Adel Barakat, Kuniaki Yoshitomi, Hybrid SRR-based Stacked Metamaterial for Miniaturized Dual-band Wireless Power Transfer System, IEEE Transactions on Antennas and Propagation, 10.1109/TAP.2023.3262977, 71, 6, 5014-5024, 2023.07, [URL], A novel stacked wideband metamaterial is proposed for a robust and compact dual-band wireless power transfer (WPT) system. The proposed metamaterial employs split-ring resonator (SRR) unit cells loaded by nonuniform capacitors. First, two types of unit cells that exhibit two resonance frequen- cies are analyzed. The results show that it can only improve the coupling between the transmitter (Tx) and the receiver (Rx) at the single band. Then, each unit cell is sandwiched with each other, and a hybrid unit cell that indicates three resonance frequencies is finally proposed. The hybrid SRR exhibits near- zero permeability within the wide frequency range of interest. Therefore, the proposed metamaterial is effective at both bands simultaneously. The system was fabricated and tested, including a compact dual-band WPT system. The size of the Tx (Rx) and the metamaterial is 15 × 15 and 20 × 20 mm, respectively. The measured figures of merit (FOM) are 0.92 at 390 MHz and 0.85 at 770 MHz at a power transfer distance of 20 mm, which is a significant improvement over recently proposed dual-band WPT systems with metamaterials..
6.	N. Jahan and R. K. Pokharel, Design of a K-Band VCO Implementing T-Type LC Network in 0.18-um CMOS Technology, IEEE MICROWAVE AND WIRELESS TECHNOLOGY LETTERS, 10.1109/LMWT.2023.3266315, 33, 7, 1039-1042, 2023.07, [URL], A symmetrical T-type LC network is presented to design a low-noise quasi-millimeter-wave voltage-controlled oscillator (VCO) for the first time. For the same value of inductance, the T-type LC network obtains an enhanced resonant frequency compared to the conventional parallel LC resonator. This characteristic relaxes the capacitance budget while designing quasi-millimeter wave VCO utilizing the proposed network. The network is realized by connecting a ground capacitor to a U-shape inductor. Finally, the symmetrical T-type LC network is implemented in a K -band VCO and prototyped in a 0.18-μm CMOS technology. The chip area is only 0.1 mm2. The proposed VCO achieves a frequency tuning range of 14.5%, from 21.8 to 25.2 GHz. The measurement result shows that the VCO has a phase noise of −112.9 dBc/Hz at a 1-MHz offset of 23.12-GHz oscillation frequency while consuming 4.1 mW. This results in a figure of merit (FoM) of the proposed VCO to be −194.9 dB..
7.	M. Ali and Ramesh K. Pokharel, Energy Harvesting Rectenna Using High-gain Triple-band Antenna for Powering Internet-of-Things (IoT) Devices in a Smart Office, IEEE Trans. on Instrumentation and Measurement, 10.1109/TIM.2023.3238050, 72, 1, 2001312, 2023.01, [URL], A new rectenna that can be utilized for sending/receiving data and scavenging radio frequency (RF) waves for linking and powering the Internet-of-Things (IoT) devices is proposed. The rectenna has three operating frequency bands; the lower frequency band is used for energy harvesting, and the other two frequency bands are assigned for data communication. It comprises a stacked four-layer antenna integrated with a voltage doubler rectifier. The antenna consists of a driven element, a planar reflector, and a planar director composed of a periodic structure of a square patch with a hexagonal slot in its center. The measurement results show that the proposed antenna covers 1.86–2.65, 2.84–3.64, and 5.34–6 GHz with an impedance bandwidth of 35%, 24.7%, and 11.64%, respectively. The antenna exhibits a high measured gain of 8.1, 8.9, and 9 dBi at 2.3, 3.5, and 5.7 GHz, respectively. The Industrial, Scientific and Medical (ISM) 2.45-GHz frequency band is selected for energy harvesting. Moreover, specific absorption rate (SAR) calculations are done for the antenna using the Hugo model to ensure lower absorption operation. The proposed antenna provides acceptable values of SAR; the values are under the safety standard limits for RF exposure. Then, a rectifier circuit is designed, fabricated, and tested separately. Finally, the rectifier is integrated with the proposed enhanced-gain antenna to produce a rectenna system. The rectenna presents a power conversion efficiency (PCE) of 69.7% and a dc output voltage of 1.9 V at an input power of 2 dBm. The PCE of the proposed rectenna is over 50% at a range of input power from −6.5 to 4.7 dBm..
8.	O. Algnar, A. Barkat, and R. K. Pokharel, Capacitive Feedbacked Cold-Phase Compensator Analog Pre-Distorter and PAE Enhancer for 5G-NR K-Band CMOS PAs, IEEE Transactions on Circuits and Systems I: Regular Papers., 10.1109/TCSI.2022.3205367, 69, 12, 4969-4980, 2022.12, [URL], A K-band two-stage power amplifier (PA) with capacitive-feedbacked cold-phase compensator (cold-PC) linearizer and power-added-efficiency (PAE) enhancer is introduced in 180-nm CMOS technology. This cold-PC consists of two parts. First, a cold-FET analog pre-distorter (APD) with a new capacitive-feedbacked technique is proposed to improve the linear behavior of the PA by enhancing the corresponding APD’s compensation slope. The proposed implementation has a reduced insertion loss and a minimal chip area overhead. Second, a low-pass two-tunable inductive and capacitive PC is proposed to solve the phase shift problem at intermediate nodes that would enhance the PAE of the stacked-transistors configuration. The implemented PA achieves, at 23.5-GHz, a maximum measured PAE of 21.2%, output power at the 1-dB compression point (OP1dB) of 13.4-dBm, and saturated output power of 15-dBm using a total chip area of 0.58 mm2. Employing the proposed cold-PC results in a decrease of the measured error vector magnitude (EVM) of the 400-MHz 5G-NR of 64-QAM modulated signal and an increase of the OP1dB and its PAE by 2.5-dB and 7%, respectively (enhancement by 78% and 72% from the original case, respectively), which, to the best of authors’ knowledge, is the highest reported enhancement of the linearizers of k-band PAs..
9.	M. Ali, Islam Mansour, and R. K. Pokharel, Experimental Study of Effectiveness of Metasurface for Efficiency and Misalignment Enhancement of Near-Field WPT System, IEEE Antennas and Wireless Propagation Letters, 10.1109/LAWP.2022.3188297, 21, 10, 2010-2014, 2022.10, [URL], Unlikely for a far-field wireless power transfer (WPT) system, designing a metasurface is critical for a near-field WPT system. First, a robust near-field WPT system using open-loop spiral resonators and a metasurface are designed, and then, the effectiveness of the metasurface is investigated in improving the power transfer efficiency (PTE) and misalignment effects. Furthermore, a study of planar and angular misalignments is also executed experimentally to prove the WPT system immunity. The proposed WPT system offers a PTE of 30% when the Rx shifts by the lateral length of the Rx that means the Rx does not remain in front of the Tx. Moreover, the efficiency is almost unchanged due to the angular misalignment..
10.	Islam Mansour, Marwa Mansour, Mohamed Aboualalaa, Ahmed Allam, Adel B Abdel-Rahman, Ramesh K Pokharel, Mohammed Abo-Zahhad, Dual-Band VCO Using High Quality Factor Two Orthogonally Located Inductors in 0.18-m CMOS Technology, IEEE Microwave and Wireless Components Letters, 10.1109/LMWC.2022.3179002, 32, 12, 1431-1434, 2022.07, [URL], This work introduces a new topology for designing low-phase noise (PN) dual-band voltage-controlled oscillator (VCO) by proposing orthogonally located inductors in 0.18- μ m CMOS. The inductors are implemented using five metal layers keeping the lowest layer empty to maximize the quality ( Q) factor. The first inductor is two halves shunted octagonal loops using the top layer (M 6) and utilized in cross-coupled VCO, while the second inductor is formed by four C-shaped shunted inductors using the lower four layers M 5−2 and used in current-reuse (CR) VCO. The M 6 inductor improves the Q -factor by more than 25%over one loop inductor in the frequency band of interest, while the M 5−2 inductor uses four shunt layers to boost the Q -factor by 28% in K -band compared to the single-layer inductor. The VCO oscillates from 22.36 to 23.4 GHz with PN of − 112.4 dBc/Hz at 1 MHz and figure of merit (FoM) of − 188.8 dBc/Hz, while the CR VCO has tuning range from 23.8 to 25.7 GHz with a PN of − 107 dBc/Hz at 1 MHz and FoM − 185.8 dBc/Hz..
11.	Samundra K Thapa, Ramesh K Pokharel, Baichuan Chen, Adel Barakat, On-Chip Millimeter-Wave DGS Based Bandstop Filter in 0.18-mu m CMOS Process, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS II-EXPRESS BRIEFS, 10.1109/TCSII.2022.3158995, 69, 6, 2732-2736, 2022.06, [URL], Defected Ground Structure (DGS) based on-chip bandstop filter (BSF) design is proposed for millimeter-wave applications. In the proposed structure, a capacitively loaded T-shape resonator is embedded in the original DGS resonator, which forms two high quality ( Q -) factor small loop resonators. Moreover, this structure, in combination with the feedline and series capacitor, independently realizes the position of two transmission poles: one at each side of the parallel resonance without increasing the layout size. The proposed BSF presents a sharp scattering (S-) parameter response due to the appearance of two transmission poles. As a result, the loaded Q -factor and negative group delay of the BSF are improved. The prototype of the proposed BSF is fabricated in 0.18- μm Complementary Metal-Oxide-Semiconductor (CMOS) process and measured. The measurement result shows a return loss of 1.78 dB at 53.2 GHz center stopband frequency with the negative group delay of 161 pS. The measurement results also agree well with the electromagnetic simulation results. Without pads, the active area of the prototyped BSF is only 0.024 mm2..
12.	Baichuan Chen, Ramesh K Pokharel, Samundra K Thapa, Nusrat Jahan, Adel Barakat, Design of 50-GHz Low Phase Noise VCO Employing Two-Branches DGS Resonator in 0.18-mu m CMOS Technology, IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, 10.1109/LMWC.2022.3171405, 2022.05, [URL], This letter presents a V-band low phase noise voltage-controlled oscillator (VCO) design using a novel integrated two-branches defected ground structure (DGS) resonator in 0.18-μm complementary metal-oxide-semiconductor (CMOS) technology. The proposed DGS resonator is realized in the top metal layer (M6) which has not only a higher quality factor than its predecessors but is also effective to reduce the length of interconnects. The measured carrier frequency and phase noise are 49 GHz and -122.05 dBc/Hz (-102.58 dBc/Hz) at 10-MHz (1-MHz) offset frequencies, respectively. The VCO core consumes 5.5 mW of dc power from the dc supply, which results in a figure of merit (FoM) of -189 dBc/Hz. The proposed VCO using the two-branches DGS resonator may give an alternative low-cost solution for designing a high-performance VCO or frequency synthesizer at V-band and beyond..
13.	Islam Mansour, Marwa Mansour, Mohamed Aboualalaa, Ahmed Allam, Adel B Abdel-Rahman, Ramesh K Pokharel, Mohammed Abo-Zahhad, Ku-Band Low Phase Noise VCO Using High-Quality Factor Transformer in 0.18-mu m CMOS Technology, IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, 10.1109/LMWC.2022.3167705, 2022.05, [URL], This work introduces a low phase-noise (PN) wideband voltage-controlled-oscillator (VCO) by proposing five ports transformer in 0.18-μm CMOS technology. The proposed VCO uses five ports transformer and operates in the low band when all the pMOS-nMOS cross-coupled VCO components are activated, whereas this VCO operates in the high band using only part of the transformer, and an nMOS cross-coupled core. The transformer is designed using the top metal layer (M6) and the first inductor is meander line U-shaped center tap inductor, while the second inductor consists of two shunted octagonal loops to increase the quality (Q-) factor compared with using a single-loop inductor. The wideband switched transformer VCO achieves a measured frequency tuning range (FTR) of 16.4-17.1 GHz with a PN of -113.3 dBc/Hz at 1-MHz offset, and from 17 to 17.9 GHz with a PN of -110.3 dBc/Hz at 1-MHz offset in the low and high bands, respectively. The achieved figure-of-merit (FoM) is -189 and -186.4 dBc/Hz in the low and high bands, respectively..
14.	Baichuan Chen, Samundra K Thapa, Adel Barakat, Ramesh K Pokharel, A W-Band Compact Substrate Integrated Waveguide Bandpass Filter With Defected Ground Structure in CMOS Technology, IEEE Transactions on Circuits and Systems II: Express Briefs, 10.1109/TCSII.2021.3123655, 69, 3, 889-893, 2022.03, [URL], This brief proposes the first on-chip bandpass filter (BPF) based on substrate integrated waveguide (SIW) for W-band applications. Slot-loaded, folded ridge and quarter mode technology is used to reduce the cavity size. The coupling characteristic of two folded ridged quarter mode substrate integrated waveguide (QMSIW) cavities implemented in CMOS technology is investigated. A simplified equivalent lumped-element circuit model of the proposed wide-band BPF approach is provided and applied to study the coupling characteristic of slot-loaded folded ridged QMSIW cavity. Then, a novel coupling method using a defected ground structure is proposed to realize a proper coupling intensity for BPF design. Finally, the proposed BPF design is implemented in a commercial complementary metal-oxide-semiconductor (CMOS) technology, fabricated, and measured. The active size of the proposed cavity resonator is only 405 μm×185μm ( 0.22λg×0.1λg ), and the measured insertion loss ( \|\|S21 \|\| ) is 3.15 dB with a central frequency of 85.5 GHz..
15.	Shimaa Alshhawy, Adel Barakat, Kuniaki Yoshitomi, Ramesh K Pokharel, Compact and Efficient WPT System to Embedded Receiver in Biological Tissues Using Cooperative DGS Resonators, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS II-EXPRESS BRIEFS, 10.1109/TCSII.2021.3123954, 69, 3, 869-873, 2022.03, [URL], This brief presents a compact and efficient resonance-shift insensitive wireless power transfer (WPT) system. This is possible by using a small electrical length defected ground structure (DGS) resonator, which is found effective against the resonance-shift phenomenon resulted from the higher permittivity of the tissue. Tissue has two undesired effects on a WPT system: (i) reduced coupled quality factor, and (ii) self-resonance shifting that leads to mismatch loss. So, the efficiency of a WPT system degrades in a tissue environment. Then, using the small electrical length DGS, we build a WPT transmitter (TX) using three cooperative DGS resonators to mitigate both issues. The fabricated prototype operates at 49 MHz in the air and tissue. This shows no change in operating frequency when the same receiver (Rx) is kept in the air or embedded inside tissues, which proves the effectiveness of the proposed cooperative DGS-WPT system against the resonance shift. The measured efficiency is 62% when the RX is embedded inside the tissue and is 68% in the air..
16.	Baichuan Chen, Samundra K Thapa, Adel Barakat, Ramesh K Pokharel, A W-Band 0.01 mm2 Cavity Resonator Employing Slot-Loaded Shielded Folded Ridged Quarter-Mode in CMOS Technology, IEEE Microwave and Wireless Components Letters, 10.1109/LMWC.2021.3122149, 32, 2, 113-116, 2022.02, [URL], This letter proposes a W -band compact cavity resonator for future applications of on-chip bandpass filters (BPFs), oscillators, phase shifters, and so on. To mitigate the leakage from the open sides of a folded ridged quarter-mode substrate integrated waveguide (SIW) cavity, shielding structures made of vias are employed. Two parallel inductive slots are etched on the top metal layer for further size reduction. Later, the one-port cavity is converted to a two-port cavity resonator and utilized in the design of W -band BPF. The proposed design is implemented in a commercial complementary metal-oxide-semiconductor (CMOS) technology, fabricated, and measured. The active size of the proposed cavity resonator is only 99 μm×99μm ( 0.054λg×0.054λg ), and the measured insertion loss ( \|S21\| ) is 2.26 dB..
17.	Xin Jiang, Ramesh K Pokharel, Adel Barakat, Kuniaki Yoshitomi, A multimode metamaterial for a compact and robust dualband wireless power transfer system, Scientific Reports, 10.1038/s41598-021-01677-6, 11, 1, 2021.12, [URL], o release more flexibility for users to charge their portable devices, researchers have increasingly developed compact wireless power transfer (WPT) systems in recent years. Also, a dual-band WPT system is proposed to transfer power and signal simultaneously, enriching the system’s functionality. Moreover, a stacked metasurface has recently been proposed for a single band near-field WPT system. In this study, a novel multimode self-resonance-enhanced wideband metasurface is proposed for a robust dual-band WPT system, which significantly improves the performance of both bands. The size of the transmitter (Tx) and the receiver (Rx) are both 15 mm × 15 mm only. The proposed metasurface can improve efficiency from 0.04 up to 39% in the best case. The measured figure of merit (FoM) is 2.09 at 390 MHz and 2.16 at 770 MHz, respectively, in the balanced mode. Especially, the FoM can reach up to 4.34 in the lower mode. Compared to the previous state-of-the-art for similar applications, the WPT performance has significantly been improved..
18.	Islam Mansour, Marwa Mansour, Mohamed Aboualalaa, Ahmed Allam, Adel B Abdel-Rahman, Ramesh K Pokharel, Mohammed Abo-Zahhad, A multiband VCO using a switched series resonance for fine frequency tuning sensitivity and phase noise improvement, IEEE Transactions on Very Large Scale Integration (VLSI) Systems, 10.1109/TVLSI.2021.3115050, 29, 12, 2163 -2171, 2021.10, [URL], This work proposes a new technique to reduce the phase noise (PN) and improve the tuning sensitivity of -band voltage-controlled oscillators (VCOs) by increasing the quality ( -) factor of the switched resonator. The proposed switched resonator consists of a high -factor half-circle inductor in parallel with an improved switched varactor and operates in four different frequency bands using a single switching voltage pin. The proposed switched resonator introduces one pole before the parallel resonance frequency, which sharpens the skirt characteristics of the scattering parameters of the resonator. The chip is implemented in the 0.18- CMOS technology, and the proposed VCO operates in four different frequency bands, with a total frequency tuning range (FTR) of 10.7%. The first band ranges from 19.4 to 19.84 GHz, the second band ranges from 19.8 to 20.3 GHz, the third band ranges from 20.25 to 20.
19.	Babita Gyawali, Samundra K Thapa, Adel Barakat, Kuniaki Yoshitomi, Ramesh K Pokharel, Analysis and design of diode physical limit bandwidth efficient rectification circuit for maximum flat efficiency, wide impedance, and efficiency bandwidths, SCIENTIFIC REPORTS, 10.1038/s41598-021-99405-7, 11, 1, 2021.10, [URL], Generally, a conventional voltage doubler circuit possesses a large variation of its input impedance over the bandwidth, which results in limited bandwidth and low RF-dc conversion efficiency. A basic aspect for designing wideband voltage doubler rectifiers is the use of complex matching circuits to achieve decade and octave impedance and RF-dc conversion efficiency bandwidths. Still, the reported techniques till now have been accompanied by a large fluctuation of the RF-dc conversion efficiency over the operating bandwidth. In this paper, we propose a novel rectification circuit with minimal inter-stage matching that consists of a single short-circuit stub and a virtual battery, which contributes negligible losses and overcomes these existing problems. Consequently, the proposed rectifier circuit achieves a diode physical-limit-bandwidth efficient rectification. In other words, the rectification bandwidth, as well as the peak efficiency, are controlled by the length of the stub and the physical limitation of the diodes..
20.	Nusrat Jahan, Adel Barakat, and Ramesh K. Pokharel, Design of Low Phase Noise VCO Considering C/L Ratio of LC Resonator in 0.18-μm CMOS Technology, IEEE Transactions on Circuits and Systems II: Express Briefs, 10.1109/TCSII.2021.3079309, 2021.05, [URL], A voltage-controlled oscillator (VCO) is usually designed by maximizing the quality (Q-) factor of the LC-tank resonator to realize a low phase noise. For the same frequency, the ratio of C/L affects the loaded Q-factor (QL) and then phase noise of the VCO. This affect has not been considered so far in the design of VCO because the conventional on-chip spiral inductor cannot be optimized for C/L ratio. This brief first investigates the effects of C/L ratio on the phase noise, and a design methodology for optimized C/L ratio using defected ground structure (DGS) resonator is presented. Then, the resonators were further evaluated based on LgL-product simulation for a fixed Ibias. Employing the proposed resonator, a very low phase noise KUband VCO is designed and implemented in 0.18-lm CMOS technology. The measurement result shows that the proposed VCO has a phase noise of -110.77 dBc/Hz at 1 MHz offset of 17.5 GHz carrier frequency and a frequency tuning range of 8.7%. The VCO consumes 2.3 mW power, which results in a figure of merit (FoM) of -191.95 dB..
21.	Samundra K Thapa, Baichuan Chen, Adel Barakat, Kuniaki Yoshitomi, Ramesh K Pokharel, X-Band Feedback Type Miniaturized Oscillator Design With Low Phase Noise Based on Eighth Mode SIW Bandpass Filter, IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, 10.1109/LMWC.2021.3064602, 31, 5, 485-488, 2021.05, [URL], A standard substrate integrated waveguide (SIW)-based bandpass filter (BPF) suffers from bulkiness that limits its application in the implementation of compact size low phase noise oscillator. Instead, in this letter, an eighth mode SIW (EMSIW) resonator-based BPF is utilized to realize a miniaturized low phase noise oscillator for X -band applications. Additionally, an equivalent circuit model of EMSIW-BPF is presented. A compact feedback-type oscillator prototype using EMSIW-BPF is designed and fabricated for the first time with a circuit area of just 1092 mm 2 . The experimental results of the prototype show a phase noise of −126.13 dBc/Hz at 1 MHz offset from 9.97 GHz oscillation frequency with an output power of 3.17 dBm..
22.	Ramesh K Pokharel, Adel Barakat, Shimaa Alshhawy, Kuniaki Yoshitomi, Costas Sarris, Wireless power transfer system rigid to tissue characteristics using metamaterial inspired geometry for biomedical implant applications, Scientific Reports, /10.1038/s41598-021-84333-3, 11:5868, 11:5868, 1-10, 2021.03, [URL], Conventional resonant inductive coupling wireless power transfer (WPT) systems encounter performance degradation while energizing biomedical implants. This degradation results from the dielectric and conductive characteristics of the tissue, which cause increased radiation and conduction losses, respectively. Moreover, the proximity of a resonator to the high permittivity tissue causes a change in its operating frequency if misalignment occurs. In this report, we propose a metamaterial inspired geometry with near-zero permeability property to overcome these mentioned problems. This metamaterial inspired geometry is stacked split ring resonator metamaterial fed by a driving inductive loop and acts as a WPT transmitter for an in-tissue implanted WPT receiver. The presented demonstrations have confirmed that the proposed metamaterial inspired WPT system outperforms the conventional one. Also, the resonance frequency of the proposed metamaterial inspired TX is negligibly affected by the tissue characteristics, which is of great interest from the design and operation prospects. Furthermore, the proposed WPT system can be used with more than twice the input power of the conventional one while complying with the safety regulations of electromagnetic waves.
23.	Adel Barakat, Shimaa Alshhawy, Kuniaki Yoshitomi, Ramesh K Pokharel, Simultaneous Wireless Power and Information Transfer Using Coupled Co-Existing Defected Ground Structure Resonators, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS II-EXPRESS BRIEFS, 10.1109/TCSII.2020.3016385, 68, 2, 632-636, 2021.02, [URL], In this brief, we realize a simultaneous wireless power and information transfer (WPIT) system using co-existing coupled defected ground structure (DGS) resonators. First, co-existing DGS resonators are utilized in the design of simultaneous band stop filter (BSF) responses. Then, coupling two sets of co-existing DGS-BSFs achieves simultaneous WPIT. The DGS resonators have spiral elliptical-shape and share the same ground plane. The coupling characteristics are studied to improve the kQ-product of power carrier and reduce the cross-coupling with the Information carrier. A prototype is fabricated having a size 30 mm × 15 mm for both transmitter (TX) and receiver (RX). The separation between TX and RX is 15 mm. At this separation, the measured efficiencies are 71% and 66% at 49.6 MHz and 149 MHz, respectively, and the isolation between the power channel TX and the information channel RX is 39 dB at 49.6 MHz..
24.	Mohamed Aboualalaa, Islam Mansour, Adel Barakat, Kuniaki Yoshitomi, Ramesh K Pokharel, Improvement of Magnetic Field for Near-Field WPT System Using Two Concentric Open-Loop Spiral Resonators, IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, 10.1109/LMWC.2020.3016136, 30, 10, 993-996, 2020.10, [URL], This letter introduces two concentric open-loop spiral resonators (OLSRs) that are used to improve magnetic field for nonradiative wireless power transfer (WPT) systems. OLSRs are fed through metal-insulator-metal (MIM) capacitive coupling using a 50-Ω microstrip transmission line. First, a single OLSR is designed and implemented for WPT, then two OLSRs are used instead of a single OLSR to emphasize the surface current on the spiral resonators. Therefore, it helps to intensify the electromagnetic field in order to get a high transmission distance or higher efficiency. The proposed WPT system operates at 438.5 MHz with a measured power transfer efficiency (PTE) of 70.8% at a transmission distance of 31 mm and a design area of 576 mm 2 . An equivalent circuit of the proposed WPT system is presented as a heuristic approach to show the electrical behavior of the WPT system..
25.	Mohamed Aboualalaa, Islam Mansour, Adel B Abdelrahman, Ahmed Allam, Mohamed Abo-zahhad, Hala Elsadek, Ramesh K Pokharel, Dual-band CPW rectenna for low input power energy harvesting applications, IET CIRCUITS DEVICES & SYSTEMS, 10.1049/iet-cds.2020.0013, 14, 6, 892-897, 2020.09, [URL], A dual-frequency band low input power rectenna is proposed in this study. The rectenna is comprised of a co-planar waveguide (CPW) rectifier integrated with a rectangular split ring antenna loaded by a spiral strip line. A single diode series connection topology is used to miniaturise the losses at low input power. A spiral coil in addition to two short circuit stubs are used as a matching network for maximum power transfer between the antenna and the rectifying circuit. The proposed rectenna operates at low input power with relatively high measured RF-DC conversion efficiency up to 74% at input power of −6.5dBm at the first resonant frequency f1=700MHz and 70% at −4.5dBm at the second operating frequency f2=1.4GHz with a resistive load of 1.9kΩ. The measured rectenna sensitivity (the rectenna ability to receive low power with acceptable conversion efficiency) reaches up to −20dBm with a conversion efficiency of 47 and 36% at f1 and f2, respectively, and a DC output voltage of 0.18V. The measured efficiency is over 50% from −18 to −3.5dBm and from −15 to −1.5dBm at f1 and f2, respectively..
26.	Islam Mansour, Mohamed Aboualalaa, Adel Barakat, Ahmed Allam, Adel B Abdel-Rahman, Mohammed Abo-Zahhad, Ramesh K Pokharel, Analysis and Implementation of High-Q CT Inductor for Compact and Wide-Tuning Range Ku-Band VCO, IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, 10.1109/LMWC.2020.3004753, 30, 8, 802-805, 2020.08, [URL], This work presents a new structure of center tap (CT) inductor to improve the performance of Ku-band voltage-controlled oscillators (VCOs). Conventional CT inductor provided by the foundry suffers from a poor-quality (Q-) factor large area and low self-resonance frequency. These problems are solved by introducing a coupling structure. For the proposed CT inductor, despite its size is miniaturized by 51%, the Q-factor is increased by 41% in the frequency range of 5-30 GHz compared to a conventional CT inductor. The measured differential inductance and quality factor of the proposed inductor are 385 pH and 22 at 12 GHz. The proposed CT inductor is used to design a compact and wide-tuning-range VCO at Ku-band in 0.18-μm complementary metal-oxide-semiconductor (CMOS) technology, and this leads to 5.8 dB phase noise improvement compared to the use of a conventional CT inductor. The fabricated VCO has a compact core size of 140 μm × 400 μm only. The VCO chip oscillates from 11.7 to 13.7 GHz. The measured phase noise is -107.7 dBc/Hz at 1-MHz offset frequency at a carrier frequency of 13.7 GHz, and the dc power consumption of the VCO core is 4 mW which results in a figure of merit (FoM) normalized to the die area (FoMA) to be -197 dBc/Hz..
27.	Nusrat Jahan, Chen Baichuan, Adel Barakat, Ramesh K. Pokharel, Utilization of Multi-Resonant Defected Ground Structure Resonators in the Oscillator Feedback for Phase Noise Reduction of K-Band VCOs in 0.18-μ m CMOS Technology, IEEE Transactions on Circuits and Systems I: Regular Papers, 10.1109/TCSI.2020.2965007, 67, 4, 1115-1125, 2020.04, This work proposes a new theory to reduce the phase noise of K-band Voltage-Controlled Oscillators (VCOs) in Complementary Metal Oxide Semiconductor (CMOS) process by introducing one or more transmission poles around the parallel resonance of an LC-tank circuit. Introduction of transmission poles beside the parallel resonance of the LC-tank circuit sharpens the skirt characteristics of the Scattering (S) parameters of the resonators. In return, sharp S-parameters slope enhances the resonator loaded quality (Q) factor without compromising the unloaded Q-factor. In addition, the transmission pole can be realized near the second harmonic of the oscillation. This allocation of the transmission pole leads to the cancellation of this second harmonic and a further reduction of the phase noise. The proposed theory is verified by three different designs based on defected ground structure (DGS) resonators. These designs realized a low-band transmission pole before the parallel resonance, a high-band transmission pole after the parallel resonance, and dual-band transmission poles around the parallel resonance. First, each design is verified and compared to the others using circuit and electromagnetic simulations to establish the Q-factor improvement. Then, each of the resonators is utilized in a differential VCO topology and the phase noise reduction in post-layout simulations is confirmed. Finally, two chips are fabricated in 0.18-μ m CMOS technology and measured. The measurement results are in good agreement with the simulations, which confirm our claim about the proposed theory..
28.	Nusrat Jahan, Adel Barakat, Ramesh K. Pokharel, A −192.7-dBc/Hz FOm K_u-band VCO using a DGS resonator with a high-band transmission pole in 0.18-μm CMOS technology, IEEE Microwave and Wireless Components Letters, 10.1109/LMWC.2019.2950525, 29, 12, 814-817, 2019.12, This letter presents the improvement of the phase noise (PN) of a voltage-controlled oscillator (VCO) by using a defected ground structure (DGS) resonator with a high-band transmission pole. The proposed DGS resonator has two loops in a coplanar stripline topology. The outer loop is loaded by a series capacitance, which produces the high-band transmission pole. The overall combination has a parallel capacitor to generate the necessary parallel resonance for the VCO operation. This proposed DGS resonator has a sharper impedance and frequency response slope, which results in an improved quality factor. In return, utilization of this DGS resonator into a K_U-Band VCO reduces its PN. The prototyped VCO in 0.18-µm CMOS oscillates at 15.52 GHz and shows a PN of −111.27 and −134.07 dBc/Hz at 1- and 10-MHz offset, respectively, while consuming 3.3-mW power. The VCO has a frequency tuning range of 9.5%, which results in a figure of merit (FoM) of −192.7 dB..
29.	Shimaa Alshhawy, Adel Barakat, Kuniaki Yoshitomi, Ramesh K. Pokharel, Separation-Misalignment Insensitive WPT System Using Two-Plane Printed Inductors, IEEE Microwave and Wireless Components Letters, 10.1109/LMWC.2019.2935621, 29, 10, 683-686, 2019.10, This letter presents a separation-misalignment insensitive wireless power transfer (WPT) system. This insensitivity is possible by minimizing the variation of mutual inductance. The transmitter (TX) of the proposed WPT system uses a two-plane printed inductor, and the receiver (RX) is a single-plane one. The TX encloses the RX to achieve minimal mutual inductance variations. Hence, the lost mutual inductance due to the misalignment between the RX and one of the TX inductors is compensated by getting close to/moving away from the other TX inductor. Furthermore, admittance inversion and compensation networks are designed to compensate for the remaining variations. Then, we design and fabricate a prototype at 50 MHz. Each TX inductor has an area of 50 text {mm} × 50 mm and an initial separation of 30 mm from the 25 text {mm} × 25 mm RX. The measured efficiency ranges between 72.5% and 80.5% for the separation of ±20 mm from the initial position..
30.	Hamed Mosalam, A. Allam, Hongting Jia, A. B. Abdel-Rahman, Ramesh Pokharel, High Efficiency and Small Group Delay Variations 0.18-μ m CMOS UWB Power Amplifier, IEEE Transactions on Circuits and Systems II: Express Briefs, 10.1109/TCSII.2018.2870165, 66, 4, 592-596, 2019.04, A new staggered tuning technique, by optimizing the inter-stage matching circuit, is proposed to realize a power amplifier (PA) with small group delay (GD) variations and excellent gain flatness across the full bandwidth of ultra-wideband (UWB) system. The proposed PA consists of two stages where the first stage is constructed by a current-reuse with shunt RC feedback topology to realize gain flatness and low power consumption. The design is implemented in 0.18 μ m commentary metal-oxide semiconductor (CMOS) technology, fabricated, and tested. The proposed PA has a measured power gain (\|S ₂₁ \|) of 11.5 ± 0.7 dB, maximum power-added efficiency (PAE) of 26% and an output 1-dB compression point of 9 dBm, respectively, and this is the maximum PAE among CMOS PAs that cover the full bandwidth of UWB system. Besides, the PA has a small GD variations of ± 68 ps which is the lowest till date..
31.	Adel Barakat, Kuniaki Yoshitomi and Ramesh K. Pokharel, Design Approach for Efficient Wireless Power Transfer Systems during Lateral Misalignment, IEEE Transactions on Microwave Theory and Techniques, (In press), 2018.12, This paper methodizes the efficiency improvement during lateral misalignment for the wireless power transfer (WPT) system using two coupled semi-elliptic defected ground structure (DGS) resonators. We design the WPT system using a scaled value of the available mutual coupling between the resonators at perfect alignment. This scaled mutual coupling value enforces over-coupling regime, and the WPT efficiency is lower than the peak one. Then, during lateral misalignment, WPT efficiency improves until it peaks at critical coupling. Next, with further misalignment, the efficiency drops as the system enters loose coupling regime. The proposed method consists of two steps. First, we derive an analytical approach to determine the scaled mutual coupling value for the efficiency design during lateral misalignment, and second, we improve the maximum obtainable efficiency by a careful designing of the DGS structures’ profile. We verify the proposed method by implementing the WPT system at 300 MHz, which shows a peak efficiency of 80% for a size Do × Do = 40 × 40 mm2 with a transfer distance d = Do. During misalignment, the efficiency is higher than 50% for a lateral shift up to ±0.75 Do..
32.	Elsayed Elsaidy, Adel Barakat, Member, Adel B. Abdel, Rahman, Ahmed Allam, and Ramesh K. Pokharel, Ultra Compact 60 GHz Tapped Line Combline BPF with Two Transmission Zeros Using Defected Ground Structures, IEEE TRANSACTIONS ON COMPONENTS, PACKAGING AND MANUFACTURING TECHNOLOGY, 1-7, 2018.12, In this paper, we propose a compact on-chip 60 GHz band-pass filter (BPF) in Complementary Metal Oxide Semiconductor (CMOS) Technology. This CMOS-BPF employs a tapped-line Combline configuration with folding and overlapping to achieve a compact size. The Combline BPF is realizable with low insertion loss (IL) due to the capacitive loading, which reduces the physical length of the resonators and in consequence reduce the resulting attenuation. Finally, defected ground slots are implemented in the ground plane under the coupled arms for an additional enhancement of the performance and more size compactness. The measured IL and return loss of the fabricated prototype BPF are 3.2 dB and 31 dB, respectively at a center frequency of 59 GHz with a 14 GHz of bandwidth. The chip area including measurements pads is 189.5 µm × 354.9 µm (0.01×𝝀𝒈𝟐) which is almost 50% compact compared to that of the smallest BPF so far proposed in same technology.
33.	Anwer Sayed Abd El-Hameed, Adel Barakat, Adel B. Abdel-Rahman, Ahmed Allam, Ramesh K. Pokharel, Design of Low-Loss Coplanar Transmission Lines Using Distributed Loading for Millimeter-Wave Power Divider/Combiner Applications in 0.18-μm CMOS Technology, IEEE Transactions on Microwave Theory and Techniques, 10.1109/TMTT.2018.2873381, 66, 12, 5221-5229, 2018.12, This paper presents a new type of a low-loss miniaturized coplanar-waveguide (CPW) transmission line (TL) by employing distributed loading, capacitors and inductors, in 0.18-μm complementary metal-oxide-semiconductor (CMOS) technology. The capacitors are realized by vertical parallel plates made of vias, and a group of open stubs inserted to the signal line, whereas the inductors are realized by high impedance lines. Then, the proposed CPW-TL is employed to design a miniaturized millimeter wave ultra-wideband low-loss Wilkinson power divider/combiner (WPD/C). The proposed distributed loading results in reducing each WPD/C arm length by more than 50% without changing its characteristic impedance and insertion loss (IL). The design is fabricated in 0.18-μm CMOS technology and tested. The measured results show a wideband performance from dc to 67 GHz with 1-dB IL and isolation greater than 15 dB from 36 to 67 GHz. In addition, the fabricated WPD/C achieves an excellent amplitude imbalance and phase imbalance of less than 0.16 dB and 0.45°, respectively. The core chip size is 336 × 165 μm ² , which is almost 32.8% compact compared to the recently proposed WPD in the same technology..
34.	Adel Barakat, Kuniaki Yoshitomi, Ramesh Pokharel, Design and Implementation of Dual-Mode Inductors for Dual-Band Wireless Power Transfer Systems, IEEE Transactions on Circuits and Systems II: Express Briefs, 10.1109/TCSII.2018.2883671, 2018.12, We propose a dual-band wireless power transfer (WPT) system employing a dual-mode inductor. The dual-mode inductor is possible through enforcing a self-resonance condition by loading an inductor in series by a tank circuit. In return, two distinct resonances are achieved, simultaneously, utilizing a single compensation capacitor as the inductance of the dual-mode inductor appears with a smaller value after its self-resonance. Also, by maintaining the same mutual coupling, the coupling coefficient becomes larger at the higher resonance, which allows for the employment of the same source/load admittance inversion network to achieve maximum power transfer at both of the operating frequency bands, concurrently. We verify the operation by fabricating a dual-band WPT system, which shows measured efficiencies of 70% and 69% at 90.3 MHz and 138.8 MHz, correspondingly. The size of the WPT system is 50 50 mm2 and has a transfer distance of 40 mm..
35.	Adel Barakat, Kuniaki Yoshitomi, Ramesh Pokharel, Design Approach for Efficient Wireless Power Transfer Systems during Lateral Misalignment, IEEE Transactions on Microwave Theory and Techniques, 10.1109/TMTT.2018.2852661, 66, 9, 4170-4177, 2018.09, This paper methodizes efficiency improvement during lateral misalignment for the wireless power transfer (WPT) system using two coupled semielliptic defected ground structure (DGS) resonators. We design the WPT system using a scaled value of the available mutual coupling between the resonators at perfect alignment. This scaled mutual coupling value enforces over-coupling regime, and the WPT efficiency is lower than the peak one. Then, during lateral misalignment, WPT efficiency improves until it peaks at critical coupling. Next, with further misalignment, the efficiency drops as the system enters loose coupling regime. The proposed method consists of two steps. First, we derive an analytical approach to determine the scaled mutual coupling value for efficiency design during lateral misalignment, and second, we improve the maximum obtainable efficiency by careful designing of the DGS structures' profile. We verify the proposed method by implementing the WPT system at 300 MHz, which shows a peak efficiency of 80% for a size D_o × D_o = 40 × 40 mm² with a transfer distance d = D_o. During misalignment, the efficiency is higher than 50% for a lateral shift up to ±0.75 D_o..
36.	Nusrat Jahan, Siti Amalina Enche Ab Rahim, Hamed Mosalam, Adel Barakat, Takana Kaho, Ramesh Pokharel, 22-GHz-Band Oscillator Using Integrated H-Shape Defected Ground Structure Resonator in 0.18-μ m CMOS Technology, IEEE Microwave and Wireless Components Letters, 10.1109/LMWC.2018.2801031, 28, 3, 233-235, 2018.03, [URL], A novel 22-GHz-band oscillator using an integrated defected ground structure (DGS) resonator is presented for quasi-millimeter waveband applications. The DGS is etched on the first metal layer (M1) below a 50-Ω microstrip line on the top metal layer (M6) of 0.18-μm one-poly six-metal (1P6M) complementary metal-oxide-semiconductor (CMOS) technology. The proposed oscillator is fabricated using 0.18-μm CMOS technology, and the measured carrier frequency and phase noise are 22.88 GHz and-129.21 dBc/Hz (-108.05 dBc/Hz) at 10-MHz (1 MHz) offset frequency, respectively. The power dissipation is 6 mW that results in a figure of merit to be-188.8 dB. As the DGS resonator could be designed at any high frequency, it may give an alternative design approach of high performance voltage controlled oscillator and frequency synthesizers at K-band and beyond, thus alleviates the problem of self-resonance that a spiral inductor usually encounters at higher frequency..
37.	Islam Mansour, Mohammed Abou Alalaa, Ahmed Allam(その他）, Adel B. Abdel-Rahman(その他）, Mohammed Abo-Zahhad(その他）, Ramesh Pokharel, Dual Band VCO based on High Quality factor Switched Interdigital Resonator for Ku band using 180 nm CMOS Technology, IEEE Transactions on Circuits and Systems II: Express Briefs, 10.1109/TCSII.2018.2817499, 2018.03, [URL], A dual band and low phase noise Ku-band voltage-controlled oscillator (VCO) using 180 nm CMOS technology is presented in this brief. The proposed VCO employs a switched notch filter that can operate in the low and high band depends on the state of nmos transistor and has a quality factor that is higher than that of a conventional inductor-capacitor (LC) resonator. The proposed resonator doubles the quality factor compared to LC in the technology and reduces the total die area. The first band is realized by the switched interdigital resonator when nmos transistor is in the off state. Furthermore, the second band is realized by turning nmos transistor to the on state which is located between two fingers in the proposed resonator. The chip is implemented in 180nm CMOS technology, and found that the proposed VCO operates from 15.5 16.7Hz (low band) and 16.6 17.4 GHz (high band). At 1.8 V power supply, the power consumption of the oscillator core is 5.4mW and 7.2mW in the low and high-frequency bands respectively. The measured phase noise is –107 dBc/Hz at 1MHz offset from 16.7 GHz carrier frequency..
38.	Hany A. Atallah(その他）, Adel B. Abdel-Rahman(その他, Kuniaki Yoshitomi, and Ramesh K. Pokharel , Design of compact frequency agile filter-antenna using reconfigurable ring resonator bandpass filter for future cognitive radios, International Journal of Microwave and Wireless Technologies, DOI: 10.1017/S1759078717001556, 83, 22-31, 2018.01, [URL], In this paper, a new miniaturized frequency agile filter-antenna with a wide reconfigurable frequency band is proposed for interweave cognitive radios (CRs). A tunable bandpass filter (BPF) composed of a symmetrical ring resonator is cascaded to the feed line of an ultra-wideband planar antenna. The structure of the proposed ring resonator BPF is simple and compact so that the total size of the proposed filter-antenna is smaller than that of a conventional system made of a separate antenna and BPF. The reconfigurability of the proposed filter-antenna is achieved by changing the operating frequency of the BPF by loading the ring resonator with a single varactor diode at its center. The fabricated prototype has successfully achieved a wide operational bandwidth of 1.43 GHz which covers continuous narrow bands from 4.65 to 6.08 GHz. Moreover, the operating tunable narrow bands have stable radiation characteristics. Good agreement between measurement and simulation results is demonstrated..
39.	Fairus Tahar, Adel Barakat, Redzuan Saad, Kuniaki Yoshitomi, Ramesh Pokharel, Dual-Band Defected Ground Structures Wireless Power Transfer System with Independent External and Inter Resonator Coupling, IEEE Transactions on Circuits and Systems II: Express Briefs, 10.1109/TCSII.2017.2740401, 64, 12, 1372-1376, 2017.12, [URL], This brief proposes a design methodology based on the admittance (J-) inverters for a dual-band wireless power transfer (WPT) system that employs two cascaded circulars defected ground structure (DGS) resonators with different capacitive loading to guarantee distinct resonances. A single microstrip line excites the two DGSs, and when two DGS resonators are coupled back to back, it transforms to a dual band pass filter leading to wireless power transfer at both bands. Each of the DGS resonators has independent coupling. Thus, the realized J-Inverters are designed independently. Also, we employ a single stub for the matching. This stub appears with a different length according to the operating frequency; hence, an independent external coupling is achieved at both frequencies. A compact size of 30 mm × 15 mm is fabricated achieving a WPT efficiency of more than 71% at a power transfer distance of 16 mm for both bands (0.3 GHz and 0.7 GHz)..
40.	F. Tahar, R. Saad, A. Barakat, Ramesh Pokharel, 1.06 FoM and Compact Wireless Power Transfer System Using Rectangular Defected Ground Structure Resonators, IEEE Microwave and Wireless Components Letters, 10.1109/LMWC.2017.2750032, 27, 11, 1025-1027, 2017.11, [URL], This letter proposes a wireless power transfer (WPT) system using coplanar waveguide fed rectangular defected ground structure (DGS) resonators. One of the advantages of rectangular DGS resonator is that it has higher quality (Q-) and coupling (K-) factor compared to the H-shape or semi-H-shape DGS resonators. When two DGS resonators are coupled back-to-back, it transforms to a bandpass filter with tight coupling, resulting in the transfer of power wirelessly. The fabricated WPT system of size 35.8 mm × 20 mm achieves, for the first time, a figure of merit of more than one at a WPT distance from 40 to 44 mm..
41.	Nusrat Jahan, Siti Amalina Enche Ab Rahim, Adel Barakat, Takana Kaho, Ramesh Pokharel, Design and Application of Virtual Inductance of Square-Shaped Defected Ground Structure in 0.18-$\mu \text{m}$ CMOS Technology, IEEE Journal of the Electron Devices Society, 10.1109/JEDS.2017.2728686, 5, 5, 299-305, 2017.09, [URL], This paper investigates a possibility of application of a virtual inductor realized by an integrated defected ground structure (DGS) to design a front-end circuit in CMOS technology. Two types of DGS are analyzed and found that the inductance realized by a square-shaped DGS achieves smaller size and higher quality factor than an H-shaped DGS. Then, a 15-GHz low phase noise voltage-controlled oscillator (VCO) employing the proposed square-shaped DGS in 0.18-$\mu \text{m}$ 1P6M CMOS technology is designed. The fabricated VCO operates from 15.2 to 16.12 GHz and consumes 5-mW power. The measured phase noise is-132.08 dBc/Hz at 10-MHz offset frequency, and this results in the figure of merit (FoM) and FoM taking account of the area to be 189.1 and 199.9 dB, respectively..
42.	Anwer S.Abd El-Hameed, Adel Barakat, Adel B. Abdel-Rahman(その他）, Ahmed Allam(その他）, Ramesh Pokharel, Ultracompact 60-GHz CMOS BPF Employing Broadside-Coupled Open-Loop Resonators, IEEE Microwave and Wireless Components Letters, 10.1109/LMWC.2017.2734771, 27, 9, 818-820, 2017.09, [URL], This letter presents a 60-GHz ultracompact on-chip bandpass filter (BPF). The designed filter is based on a unique structure, which consists of two overlapped broadside-coupled open-loop resonators, achieving a high level of miniaturization. Moreover, each resonator is loaded by a metal-insulator-metal capacitor to get further miniaturization. Defected ground structure pattern is constructed under the filter structure to enhance the insertion loss (IL). This BPF is designed and fabricated using a standard 0.18- μ complementary metal-oxide-semiconductor technology for millimeter-wave applications. The fabricated BPF chip size is 240 × 225-μ 2 including pads. The measured results agree well with the simulation ones and show that the BPF has an IL of 3.3 dB at 59.5-GHz center frequency, and a bandwidth of 12.9 GHz..
43.	＃Ruibing Dong, Haruichi Kanaya, Ramesh Pokharel, A CMOS ultrawideband pulse generator for 3-5 GHz applications, IEEE Microwave and Wireless Components Letters, 10.1109/LMWC.2017.2701306, 27, 6, 584-586, 2017.06, [URL], A low-power ultrawideband (UWB) pulse generator based on pulsed oscillator architecture for 3-5 GHz applications is proposed. The pulsed oscillator is improved, so it realizes binary phase shift keying (BPSK) modulation. Unlike ON-OFF keying or pulse-position modulation (PPM), BPSK can scramble the spectrum, so it can be used in high pulse rate applications without having spectral line problem. The signal structure in this design is burst mode of PPM+BPSK. The proposed UWB pulse generator was successfully implemented on 0.18-μm CMOS technology. The peak-to-peak amplitude of output pulse is about 220 mV with 50-ω load, the maximum power consumption is 4 mW at a raw data rate of 7.8 Mbps and the energy consumption is 32 pJ/pulse at a pulse rate of 125 Mpulses/s..
44.	Guoqiang Zhang, Awinash Anand, Kousuke Hikichi(その他）, Shuji Tanaka(その他）, Masayoshi Esashi(その他）, Ken Ya Hashimoto(その他）, Shinji Taniguchi(その他）, Ramesh Pokharel, A 1.9 GHz low-phase-noise complementary cross-coupled FBAR-VCO without additional voltage headroom in 0.18 μm CMOS technology, IEICE Transactions on Electronics, 10.1587/transele.E100.C.363, E100C, 4, 363-369, 2017.04, [URL], A 1.9 GHz film bulk acoustic resonator (FBAR)-based low-phase-noise complementary cross-coupled voltage-controlled oscillator (VCO) is presented. The FBAR-VCO is designed and fabricated in 0.18 μ m CMOS process. The DC latch and the low frequency instability are resolved by employing the NMOS source coupling capacitor and the DC blocked cross-coupled pairs. Since no additional voltage headroom is required, the proposed FBAR-VCO can be operated at a low power supply voltage of 1.1 V with a wide voltage swing of 0.9 V. An effective phase noise optimization is realized by a reasonable trade-off between the output resistance and the trans-conductance of the cross-coupled pairs. The measured performance shows the proposed FBAR-VCO achieves a phase noise of-148 dBc/Hz at 1 MHz offset with a figure of merit (FoM) of-211.6 dB..
45.	, [URL].
46.	Adel Barakat, Ahmed Allam, Ramesh Kumar Pokharel, 60 GHz CMOS Circular Patch Antenna-on-Chip, Microwave Journal, 60, 2, 90-100, 2017.02, [URL], This article presents a 60 GHz circular patch Antenna-on-Chip (AoC) on asymmetric Artificial Magnetic Conductor (AMC) designed and fabricated using the TSMC 0.18 pm CMOS process. An AMC plane allows a positive reflection coefficient within the bandwidth of interest so incident and reflected waves are in phase. At the AMC frequency o f operation, a high impedance is generated which reduces surface waves and thus enhances gain. At first, circular AoC performance is enhanced using a square AMC. However, square AMC cells suffer from discontinuities that affect performance when using lengthy feed lines to connect the AoC to a front-end circuit. To overcome this problem, an asymmetric rectangular (R-AMC) is employed. A modified asymmetric AMC is used with a circular AoC for further gain enhancement. The area of the fabricated design is only 1715 μm × 710 μm. Measured ∣S11∣, gain and radiation patterns are reported.
47.	Hekal Sherif, Adel Barakat, Ahmed Allam, Adel B. Abdel-Rahman, Hongting Jia, Ramesh Kumar Pokharel, A Novel Technique for Compact Size Wireless Power Transfer Applications Using Defected Ground Structures, IEEE Transactions on Microwave Theory and Techniques., 10.1109/TMTT.2016.2618919, 65, 2, 591-599-599, 2017.02, [URL], This paper presents a novel technique for high efficiency and compact size wireless power transfer (WPT) systems. These systems are based on coupled defected ground structure (DGS) resonators. Two types of DGSs (H-shape and semi-H-shape) are proposed. The semi-H-shaped DGS realizes larger inductance value, and this results in higherWPT efficiency. Instead of using an inductive-fed resonant coupling, we propose capacitive-fed resonant coupling, which reduces the design complexity and enhances the.
48.	Mohamed Ali, Ahmed Allam, Adel B. Abdel-Rahman, Ramesh Kumar Pokharel, Design of Dual Band Microstrip Antenna with Enhanced Gain for Energy Harvesting Applications, IEEE Antennas and Wireless Propagation Letters, 0.1109/LAWP.2017.2654353, 2017.01, [URL], In this paper, a dual band circular patch antenna is introduced. The antenna consists of a circular patch with a direct feed through microstrip feed line, that designed to radiate at 2.45 GHz with fractional bandwidth of 4.5%. A circular slot is inserted into the ground plane that radiates by capacitive coupling between the patch and the ground plane. This slot radiates at 1.95 GHz with fractional impedance bandwidth of 5%. The antenna achieves good radiation characteristics by inserting a reflecting plane at optimum position behind it. The antenna has gain of 8.3 and 7.8 dBi at 1.95 and 2.45 GHz, respectively. This antenna is proposed for the rectenna; then it is designed to direct the main beam in a certain direction by increasing Front to Back (F/B) ratio with low cross polarization levels by using Defected Reflector Structure (DRS) in reflecting plane. The equivalent circuit of the proposed antenna is introduced to model the electrical behavior of the antenna. The proposed antenna can be used to harvest the energy from Wi-fi and widely spread mobile networks. The proposed antenna was designed using CST Microwave Studio. The simulated and measured results show good agreement..
49.	Sherif Hekel, Adel Barakat, Ahmed Allam, Adel B. Adel-Rahman, Hongting Jia, Ramesh Kumar Pokharel, Compact Wireless Power Transfer System Using Defected Ground Bandstop Filters, IEEE Microwave and Wireless Components Letters, 10.1109/LMWC.2016.2601300, 99, 10, 2016.10, This letter presents a new design for wireless power transfer (WPT) applications using two coupled bandstop filters (BSF). The stopband is created by etching a defected structure on the ground plane, and the power is transferred through electromagnetic (EM) resonant coupling when the two BSFs are coupled back to back. An equivalent circuit model of the proposed WPT system is extracted. Verification of the proposed design is performed through a good agreement between the EM simulation, circuit simulation, and measurement results. The proposed system achieves a measured WPT efficiency of 68.5% at a transmission distance of 50 mm using a compact size (40 x 40mm²). This results in a figure of merit of the proposed system to be 0.856 and the ratio of transmission distance/lateral size is 1.25 that is the highest among the WPT systems proposed so far using planar structures..
50.	Hamed Mosalam, Ahmed Allam, Hongting Jia, Adel Abdelrahman, Ramesh Kumar Pokharel, A 12 to 24 GHz High Efficiency Fully Integrated 0.18 μm CMOS Power Amplifier, The Institute of Electronics, Information and Communication Engineers, 13, 14, 20160551, 0160551, 2016.10, This letter presents a high efficiency, and small group delay variations 12–24GHz fully-integrated CMOS power amplifier (PA) for quasi-millimeter wave applications. Maximizing the power added efficiency (PAE), and minimizing the group delay variations in a wideband frequency range are achieved by optimizing the on-chip input, output, and inter- stage matching circuits. In addition, stagger tuning is employed for realizing excellent gain flatness. A two-stage CMOS PA using the proposed methodology is designed and ....
51.	Nessim Mahmoud, Adel Barakat, Adel B. Abdel-Rahman, Ahmed Allam, Ramesh Kumar Pokharel, Compact Size On-Chip 60 GHz H-Shaped Resonator BPF, IEEE Microwave and Wireless Components Letters, 10.1109/LMWC.2016.2597219, 26, 9, 681-683, 2016.09.
52.	ADEL TAWFIK MOHAMED MOHAMED BARAKAT, Hala Elsadek, Adel Abdelrahma, POKHAREL RAMESH KUMAR, Takana Kaho, Improved Gain 60 GHz CMOS Antenna with N-well Grid, IEICE Electronics Express　（In press), 2016.03, [URL], This paper presents a novel technique to enhance Antenna-on-Chip gain by introducing a high resistivity layer below it. Instead of using the costly ion implantation method to increase resistivity, the N-well that is available in the standard CMOS process is used. A distributed grid structure of N-well on P-type substrate is designed such that the P and N semiconductors types are fully depleted forming a layer with high resistivity. By an electromagnetic simulation, the using depletion layers enhance the antenna gain and radiation efficiency without increasing the occupied area. The simulated and measured \|S11\| are in fair agreement. The measured gain is –1.5 dBi at 66 GHz..
53.	Hany A. Atallah, Adel B. Abdel-Rahman, Kuniaki Yoshitomi, Ramesh Kumar Pokharel, Compact frequency reconfigurable filtennas using varactor loaded T-shaped and H-shaped resonators for cognitive radio applications, IET Microwaves Antennas & Propagation, 10.1049/iet-map.2015.070, 4, 4, 2016.03, [URL], In this study, novel compact filtennas with large tunable frequency band are proposed for cognitive radio (CR) applications. .
54.	Adel Barakat, Ramesh Kumar Pokharel, 60 GHz on-chip mixed coupled BPF with H-shaped defected ground structures, Electronics Letters, 10.1049/el.2015.4465, 2016.03, [URL], A 60 GHz miniaturised, low loss on-chip bandpass filter (BPF) based on open-loop resonators is presented. Overlapping of the BPF's resonators leads to miniaturisation and introduces a mixed coupling configuration..
55.	Ramesh Kumar Pokharel, Performance Analysis of Multicode OCDM Networks Supporting Elastic Transmission With QoS Differentiation, IEEE TRANSACTIONS ON COMMUNICATIONS, 10.1109/TCOMM.2015.2512922, 64, 2, 741-752, 2016.02, [URL], A multicode optical code-division multiplexing (OCDM) is proposed to support the dynamic changes in the requested traffic demand in OCDM networks by adapting the number of allocated codes according to the requested transmission rate..
56.	Lechang Liu, POKHAREL RAMESH KUMAR, Compact Modeling of Phase-Locked Loop Frequency Synthesizer for Transient Phase Noise and Jitter Simulation, IEEE TRANSACTIONS ON COMPUTER-AIDED DESIGN OF INTEGRATED CIRCUITS AND SYSTEMS, 10.1109/TCAD.2014.2354291, 35, 1, 166-170, 2016.01, [URL], Compact modeling of phase-locked loop (PLL) frequency synthesizer is proposed to reduce transient phase noise and jitter simulation time. Conventional small-signal noise assumption based frequency-domain simulation approach produces inaccurate results for nonlinear PLLs. Accurate analysis of nonlinear PLL are possible through time-domain, or transient noise simulation but time-domain simulation is computationintensive and time-consuming. This research presents a practical solution for transient phase noise and jitter analysis using compact modeling techniques. It features an autoregressive moving average process modeled voltage-controlled oscillator with fractional calculus and wavelet transform for phase noise decomposition and reconstruction, thereby reducing the phase noise and jitter simulation time to 25.8% of the transistor-level simulation with 0.4dB@1MHz phase noise error and 0.3ps long-term jitter error for a 2GHz PLL frequency synthesizer in a 65nm CMOS process. with a lookup table for nonlinearity compensation and a radial basis function neural network for the voltage-controlled oscillator with nonlinear frequency-voltage relationship, thereby reducing the post-layout simulation time to 26% of the original circuits with the accuracy of 93%..
57.	Adel Barakat, Ramesh Kumar Pokharel, Miniaturized low loss 60 GHz CMOS mixed coupled BPF with patterned ground shield, Microwave and Optical Technology Letters, 58, 3, 697-699, 2016.01, This letter presents a miniaturized low loss mixed coupled on-chip band-pass filter using overlapped open loop ring resonators and using patterned ground shields. The fabricated prototype shows an insertion loss of 3.7 dB, a return loss> 20 dB, a bandwidth of 13 GHz, and a chip size of 700 μm× 450 μm..
58.	Adel Barakat, A. B. Adel, Ahmed Allam, POKHAREL RAMESH KUMAR, 60 GHz CMOS Circular Patch AoC Modified Asymmetric AMC, Microwave Journals, (In Press) (採録決定）, 2015.12, This paper presents a small size 60 GHz circular Antenna-on-Chip (AoC) designed and fabricated using 0.18 µm Taiwan Semiconductor Manufacturing Company (TSMC) Complementary Metal Oxide Semiconductor (CMOS) process. AoC performance is enhanced using Artificial Magnetic Conductor (AMC) because the AMC allows a positive reflection coefficient at the bandwidth of interest so incident and reflected waves are in phase. To illustrate this, several shapes of symmetric AMC have been investigated and the performances employed in the circular AoC are then compared, and it is found that symmetric AMC cells suffer from discontinuity which affects the performance in case of using lengthy feed lines to connect AoC to a front-end circuit. To overcome this problem, asymmetric AMC is proposed and implemented using 0.18 CMOS process with operating bandwidth from 50 to 67 GHz. The area of AoC including the asymmetric AMC is only 1715 µm by 710 µm.
59.	Ahmed E. Farghal, Hossam M. H. Shalaby, Kazutoshi Kato, Ramesh Kumar Pokharel, Optical Code-Division Multiplexing (OCDM) Networks Adopting Code-Shift Keying/Overlapping PPM Signaling: Proposal and Performance Analysis, IEEE Transactions on Communications , 63, 10, 3779 -3788, 2015.10, Optical code-division multiplexing (OCDM) systems use short pulses compared with bit-duration to achieve high transmission rate. The use of short pulses poses several problems as a result of group velocity dispersion (GVD), intersymbol interference (ISI) (due to avalanche photodiode (APD) buildup time), and receivers limited bandwidth. In this paper, an OCDM system employing code-shift keying (CSK) and overlapping pulse-position modulation (OPPM) signaling is proposed and theoretically investigated. By using CSK while maintaining same data rate, the chip duration can be increased to counteract the GVD effect in 2D OCDM systems. Moreover, by increasing the chip duration, the chip rate is decreased and the stringent requirement on receiver bandwidth is relaxed. In addition, using overlapping property in OPPM allows for further chip duration increase. We consider using correlation receivers with hard-limiters and APDs at the receiver side. The bit error probability (BEP) of the proposed system is derived taking into account the impacts of APD noise, thermal noise, GVD, ISI, and multiple-access interference (MAI). A performance comparison between OOK-, PPM-, OPPM-OCDM and the proposed system is carried out. Our results reveal that the use of CSK/OPPM-OCDM with data rate constraint allows the reduction of MAI, GVD and ISI effects with improved spectral efficiency..
60.	Sho Asano, ANAND AWINASH, Ramesh Kumar Pokharel, Hideki Hirano, Shuji Tanaka, Monolithic Integration of BST Thin Film Varactors and Au Electroplated Thick Film Inductors above IC, 電気学会論文誌Ｅ（センサ・マイクロマシン部門誌） , 138, 8, 323-329, 2015.08, [URL], This paper presents an integration process of barium strontium titanate (BST) thin film varactors and Au thick film inductors above an integrated circuit (IC) by film transfer technology and Au electroplating process. A high-quality BST film grown on a Si substrate at 650°C was patterned into MIM (Metal-Insulator-Metal) structures, and transferred to an IC substrate at 270°C by BCB (Benzocyclobutene) polymer bonding and Si lost wafer process. Thick film inductors fabricated by Au electroplating were also integrated above the IC substrate to realize high Q factor. The capacitance tunability of the BST varactors did not decrease by transfer process. The Q factor of the fabricated inductor was higher than that of conventional inductors on IC chips. The resonant frequency of an LC series resonance circuit composed of the transferred BST varactor and the Au electroplated inductor changed from 0.76 GHz to 1.19 GHz by applying a DC bias voltage of 8 V to the BST varactor. Monolithic integration technology developed in this research will be useful for tunable radio frequency circuits like tunable power amplifiers..
61.	JIA HONGTING, POKHAREL RAMESH KUMAR, 金谷晴一, Strong resonant coupling for short-range wireless power transfer using defected ground structures, Proc. 3rd International Japan-Egypt Conference on Electronics, Communications and Computers, 100-101, 2015.03.
62.	POKHAREL RAMESH KUMAR, G. Zhang, S. A. Enche Ab Rahim, Design of High Performance of Oscillator using Film Bulk Acoustic Resonator, 2014 Korea-Japan Microwave Workship, 1-2, 2014.12.
63.	Lechang Liu, POKHAREL RAMESH KUMAR, Post-Layout Simulation Time Reduction for Phase-Locked Loop Frequency Synthesizer Using System Identification Techniques, IEEE TRANSACTIONS ON COMPUTER-AIDED DESIGN OF INTEGRATED CIRCUITS AND SYSTEMS, 10.1109/TCAD.2014.2354291, 33, 11, 1751-1755, 2014.11, [URL], Compact model extraction of phase-locked loop (PLL) frequency synthesizer using system identification techniques is proposed to reduce post-layout simulation time. This is the first published compact model for PLL using system identification techniques. It features an autoregressive exogenous model for the charge pump and the loop filter with a lookup table for nonlinearity compensation and a radial basis function neural network for the voltage-controlled oscillator with nonlinear frequency-voltage relationship, thereby reducing the post-layout simulation time to 26% of the original circuits with the accuracy of 93%..
64.	POKHAREL RAMESH KUMAR, 金谷晴一, A. Barakat, Small Size 60 GHz CMOS Antenna-on-Chip, Proc. 44th European Microwave Conference, 104-107, 2014.10.
65.	POKHAREL RAMESH KUMAR, 金谷晴一, A. Barakat, Back radiation reduction of 60 GHz CMOS slot Antenna-on-Chip (AoC) using Artificial Dielectric Layer (ADL) for Area Reuse, Proc. 2014 IEEE International Symposium on Antennas and Propagation and USNC-URSI National Radio ScienceMeeting, 1-1, 2014.07.
66.	W. Yamamoto, D. Kanemoto, POKHAREL RAMESH KUMAR, 金谷晴一, 吉田啓二, A Low Power 2.4GHz LNA Operated in Subthreshold Region, Future Information Engineering Volume I, WIT Transactions on Communications and Information Technologie, 199-196, 2014.05.
67.	兼本大輔, POKHAREL RAMESH KUMAR, 吉田啓二, 金谷晴一, Keigo Oshiro, A 10-bit 50MS/s 350 μW Small Die Area Capacitive Digital-to-Analog Converter for Bluetooth Applications, IEEJ Transactions on Electronics, Information and Systems,Vol.134 No.2 pp.328.329,2014.02., 134, 2, 328-329, 2014.02.
68.	Guoqiang Zhang, 金谷晴一, 吉田啓二, Tanaka Shuji, POKHAREL RAMESH KUMAR, A low phase noise FBAR based multiband VCO design, IEICE Electronics Express, 10, 13, 1-6, 2013.07.
69.	金谷晴一, S. Tsukamoto, T. Hirabaru, POKHAREL RAMESH KUMAR, 兼本大輔, 吉田啓二, Energy Harvesting Circuit on a One-Sided Directional Flexible Antenna, IEEE Microwave and Wireless Components Letters, 23, 3, 164-166, 2013.03.
70.	POKHAREL RAMESH KUMAR, Prapto Nugroho, ANAND AWINASH, Abhishek Tomar, 金谷晴一, 吉田啓二, Low Phase Noise 14-Bit Digitally Controlled CMOS Quadrature Ring Oscillator, IEICE Trans. on Electronics, Vol E-96, No. 2, 262-269, 2013.02, High phase noise is a common problem in ring oscillators. Continuous conduction of the transistor in an analog tuning method degrades the phase noise of ring oscillators. In this paper, a digital control tuning which completely switches the transistors on and off, and a 1/f noise reduction technique are employed to reduce the phase noise. A 14-bit control signal is employed to obtain a small frequency step and a wide tuning range. Furthermore, multiphase ring oscillator with a sub-feedback loop topology is used to obtain a stable quadrature outputs with even number of stages and to increase the output frequency. The measured DCO has a frequency tuning range from 554 MHz to 2.405 GHz. The power dissipation is 112 mW from 1.8 V power supply. The phase noise at 4 MHz offset and 2.4 GHz center frequency is -134.82 dBc/Hz. The FoM is -169.9 dBc/Hz which is a 6.3 dB improvement over the previous oscillator design..
71.	Rohana Sapawi, POKHAREL RAMESH KUMAR, Dayang Azra Awang Mat, 金谷晴一, 吉田啓二, A 0.9-3.5 GHz high linearity, good efficiency CMOS broadband power amplifier using stagger tuning technique, Microwave and Optical Technology Letters, Vol. 54, Issue: 12, 2881-2884, 2012.12, A simple CMOS broadband power amplifier design with high linearity and good efficiency is proposed.The proposed power amplifier design employed stagger tuning technique that consist of two stages amplifier with different resonant frequencies to obtain a wider bandwidth from 0.9 to 3.5 GHz and low power consumption. To obtain high linearity self-biased circuit is employed at the first stage of amplifier. The measurement results indicated that the proposed design achieves average gain of 8.5 dB, an input return loss (S11) less than −3 dB and output return loss (S22) less than −5 dB. High linearity, that is, IIP3 of 13.4 dBm at 2 GHz, power added efficiency of 34% is obtained while consuming 24.4 mW power from 1.5 V supply voltage..
72.	ANAND AWINASH, Nischal Koirala, POKHAREL RAMESH KUMAR, 金谷晴一, 吉田啓二, Analytical method to determine optimal out-of-band gain in multi-bit delta-sigma modulator, IEICE Electronics Express, vol. 9, no. 20, 1598-1603, 2012.10.
73.	R. K. Pokharel, K. Uchida, A. Tomar, H. Kanaya, and K. Yoshida, Low phase noise, 18 kHz frequency tuning step, 5 GHz, 15 bit digitally controlled oscillator in 0.18 um CMOS technology, IEICE Trans. on Electronics, Vol. E93-C, no. 7, pp. xx-xxx, July 2010. (In press), 2010.07.
74.	R. K. Pokharel, H. Kanaya, and K. Yoshida, Design and evaluation of -117dBc/Hz phase noise voltage-controlled oscillator using on-chip CPW resonator for 5 GHz-band WLAN, Microwave and Optical Technology Letters. , 52, 3, pp. 763-766, 2010.03.
75.	O. Nizhnik, R. K. Pokharel, H. Kanaya, and K. Yoshida, Low noise wide tuning range quadrature ring oscillator for multi-standard transceiver, IEEE Microwave and Wireless Components Letters, vol. 19, no. 7, pp. 470-472, July 2009. , 2009.07.
76.	A. I. A. Galal, R. K. Pokharel, H. Kanaya, and K. Yoshida, Linearization Technique using Bipolar Transistor at 5GHz Low Noise Amplifier, Int. Journal of Electronic and　Communications (AEU), (Elsevier publication), (2009), doi: 10.1016/j.aeue.2009.07.008., 2009.07.
77.	S. A. Z. Murad, R. K. Pokharel, H. Kanaya, K. Yoshida, and O. Nizhnik, A 2.4 GHz 0.18µm CMOS Class E Single-Ended Switching Power Amplifier with Self Biased Cascode, Int. Journal of Electronic and　Communications (AEU), (Elsevier publication), doi: 10.1016/j.aeue.2009.06.002., 2009.06.
78.	Ramesh K. Pokharel, H. Kanaya and K. Yoshida, Design of 5GHz-band power amplifier with on-chip matching circuits using CPW impedance (K) inverters, Trans. of IEICE, vol. E91-C, no. 11, pp. 1824-1827, November, 2008. , 2008.11.
79.	Haruichi Kanaya, Ramesh K. Pokharel, Sangtae Kim, Akihiro Imada, and Keiji Yoshida, Design of Power Amplifier with On-Chip Matching Circuits using CPW Line Impedance (K) Inverters, 11th WSEAS CSCC, Crete island, Greece, July 2007., paper number: 561-265, 2007.07, [URL].
80.	Haruichi KANAYA, Ramesh K. POKHAREL, Fuminori KOGA, Keiji YOSHIDA , Design and Verification of On-Chip Impedance-Matching Circuit Using Transmission-Line Theory for 2.4 GHz-Band Wireless Receiver Front-End, IEICE Trans. On Electronics., Vol.E89-C No.12 pp.1888-1895,December 2006., 2006.12.
81.	R. K. Pokharel, K. Wada, O. Hashimoto, and T. Takahashi, Fundamental characteristics of microstrip resonators loaded with dielectric rods for suppression of spurious responses, IEE Proc. Microwaves, Antennas, & Propagation, vol. 153, issue 4, pp. 341-346., 2006.08, [URL].
82.	R. K. Pokharel, O. Hashimoto, and M. Toyota, Analysis of EM environment for DSRC system on express highway with wave absorbers on sidewalls and pavement, IEICE Trans. Electron.,, Vol. 89-C, no. 1, pp 61-68., 2006.01, [URL].
83.	Ramesh K. Pokharel, K. Wada and O. Hashimoto, Out-of-band improvement by BPFs with multiple attenuation poles using a condition of variable coupling length of a parallel partially coupled-line section, Microwave and optical Technology Letters, vol. 47, no. 1, pp.4-9, October 2005, 2005.09.
84.	Ramesh K. Pokharel, K. Wada and O. Hashimoto, Improvement of spurious responses of coupled-line BPFs using interdigital-type resonators, Microwave and optical Technology Letters, vol. 44, no. 2, pp. 126-130, Jan. 2005., 2005.01.
85.	R. K. Pokharel, K. Wada, O. Hashimoto, and T. Takahashi, A method for LTCC resonators to improve spurious responses on reduced-size microstrip structure, Trans. of IEICE, Vol. E87-C, pp. 1517-1523., 2004.09.
86.	R. K. Pokharel, K. Wada, O. Hashimoto and T. Takahashi, A method for LTCC resonators to improve spurious responses on reduced-size microstrip structure, IEICE Trans. on Electronics, Vol. E87-C, no. 9, pp. 1517-1523, Sept. 2004., 2004.09.
87.	Ramesh K. Pokharel, M. Toyota and O.Hashimoto, Analysis of EM wave absorbers for improvement of DSRC EM environment on express highway, IEEE Trans. on Microwave Theory and Techniques, vol. 53, no. 9, pp. 2726-2731, Sept. 2005.
88.	R. K. Pokharel, K. Wada, O. Hashimoto, and T. Takahashi, Improvement of spurious responses with attenuation poles in stopband by microstrip resonator, IEE Electronics Letters, vol. 40, no. 8, pp. 481-482., 2004.04, [URL].

1.	S.K. Thapa, R.K. Pokharel, A. Barakat, Ruibing Dong; Shuhei Amakawa; Shinsuke Hara; I. Watanabe, and A. Kasamatsu, Implementation of SIW Cavity in Commercial CMOS Technology for Sub-Terahertz Band Applications, 2023 International Microwave Symposium (IMS), 2023.06, [URL], For sub-terahertz band applications, two compact and low-loss on-chip substrate integrated waveguide (SIW) cavities are designed in CMOS technology. Compact size cavity is achieved by utilizing the folded ridge structure in the quarter mode SIW (QMSIW) structure which is loaded with complementary split-ring resonators (CSRRs). Two prototypes of the proposed QMSIW cavities with and without CSRR are fabricated in 1P6M CMOS technology. From the measurement, both cavities present return losses higher than 27 dB and external Q-factors higher than 140. The proposed work shows that even at such high frequencies, compact and low-loss SIWs can be fabricated in commercial CMOS technology and opens a window to utilizing such cavities for other low-loss components such as oscillators, on-chip bandpass filters and on-chip antennas for sub-terahertz band applications..
2.	Ramesh K. Pokharel, T. Fukuda, Samundra K. Thapa, Adel Barakat, Ruibing Dong, Shinsuke Hara, Issei Watanabe, and A. Kasamatsu, 200 GHz-band Low-loss Half-Mode SIW CMOS Interconnects and Transmission Lines for Sub-Terahertz Frequency Band Applications, 2023 International Microwave Symposium (IMS), 2023.06, [URL], Low-loss half-mode substrate integrated waveguide (HMSIW)-based interconnects and transmission lines are designed and implemented in Complementary Metal-Oxide Semiconductor (CMOS) technology. In HMSIW interconnects, complementary split ring resonators (CSRR) whose self-resonance is much higher than the cut-off frequency of the SIW are etched on, due to which matching is improved. By controlling the parameters of the CSRRs, the losses due to microstrip to SIW transition are substantially improved, and no extra external matching circuit is required. A prototype was fabricated in 1P6M CMOS technology and tested. The measured cut-off frequency of the proposed HMSIW transmission line is 110 GHz, and the measured attenuation constant at frequencies of 175–220 GHz is less than 1.4 dB/mm. This work confirms a significant performance improvement of the CMOS interconnects in the sub-terahertz frequency band..
3.	M. Ali, R.K. Pokharel, and T. Kaho, Extended Embedded Depth Using Cascaded Resonators Near-field WPT System with High Efficiency for Biomedical Implants, 2023 International Microwave Symposium (IMS), 2023.06, [URL], A novel multiple cascaded resonators wireless power transfer (WPT) design is proposed to provide an extended implanted depth for biomedical implants. Symmetrical four cascaded resonators are utilized in Tx/Rx to obtain high power transfer efficiency (PTE); each resonator consists of two concentric rectangular loops. KQ-product is calculated for a single resonator and compared with the four resonators WPT; four cascaded resonators achieve higher KQ-product value and produce a maximum measured PTE of 89.5% at a transfer distance of 20 mm. Then, the proposed WPT is tested with human tissue to provide a measured PTE of 76% and 63% at a transfer distance of 15 and 20mm, respectively. Specific absorption rate (SAR) is calculated to estimate the maximum operating power of the source and receiver that guarantees working within the safety standard levels of RF exposure..
4.	Ramesh K. Pokharel, MetaTx-introduction of metamaterial-assisted WPT system for biomedical implants, 2022Asian Wireless Power Transfer Workshop, 2022.12, [URL], Wireless charging of biomedical implants will make the life of patients with implants much easier. However, it is associated with significant design challenges - efficiency degradation and the need to meet standards for exposure to electromagnetic fields. Tissue's dielectric and conductive properties affect the electrical performance of an inductor, which appears on increased effective inductance, reduced quality factor, and reduced self-resonance. Building a wireless power transfer (WPT) system using such inductors leads to low efficiency and low power that limit specific absorption rate. In this work, we will introduce the characteristics of inductance in biomedical tissue and its problems. Finally, to overcome these issues, we propose a metamaterial-assisted geometry for transmitter side, called meta-Tx. The effects of losses of metamaterial and their design approach will be disused in detail in this lecture..
5.	M. Ali and Ramesh K. Pokharel, Dual-band split-ring antenna with high-gain end-fire radiation characteristics for 5G MM-wave applications, 2022 IEEE International Symposium on Antennas and Propagation & USNC-URSI Radio Science Meeting, 2022.07, [URL], A dual-frequency band high-gain split-ring antenna is proposed for 5G mm-wave applications. The antenna consists of three split ring resonators (SRRs), one is the main SRR which radiates at the first resonant frequency (f 1 =24.5 GHz). The other two resonators are parasitic SRRs which act as directors to get end-fire radiation characteristics for the proposed antenna at f 1 . In addition, the two parasitic SRRs are fed by capacitive coupling with the main SRR to radiate at the second resonant frequency (f 2 =28.5 GHz). The antenna has better radiation characteristics. It has high gain values of 7.9, and 7.5 dBi with radiation efficiencies of 92% and 95% at f 1 , and f 2 , respectively. The proposed antenna is a good candidate for MIMO array at 5G frequency bands utilizing the antenna high gain to improve the system performance..
6.	S. K. Thapa, B. Chen, A. Barakat, and R. K. Pokharel, A Compact Millimeter-Wave On-chip DGS-based Bandstop Filter with Two Transmission Poles in CMOS Technology, 2022 European Microwave Conference (EuMW), 2022.09, [URL].
7.	B. Gyawali, Adel Barakat, Kuniaki Yoshitomi, Ramesh Pokharel, Broadband and Compact 3-Bit Digitally-Controlled Reconfigurable Rectification Circuit , 2022 IEEE Wireless Power Transfer Conference, WPTC 2022, 2022.07, [URL].
8.	X. Sun, Adel Barakat, Kuniaki Yoshitomi, Ramesh Pokharel, STUDY OF METAMATERIAL ON EFFICIENCY OF DGS-BASED MISO-WPT SYSTEM, 2022 IEEE Wireless Power Transfer Conference, WPTC 2022, 2022.07, [URL].
9.	S.K. Thapa, R.K. Pokharel, T. Fukuda, B. Chen, and A. Barakat, Millimeter-Wave High Q-factor Sixteenth Mode SIW Cavity Resonator Implemented in 0.18-µm CMOS Technology, 2022 International Microwave Symposium (IMS), 2022.06, [URL], Millimeter-wave miniaturized Substrate Integrated Waveguide (SIW) cavity resonator is proposed in 0.18-µm CMOS technology. Miniaturization of the SIW cavity resonator is achieved first by taking 1/16 th parts of the standard SIW and employing folded ridge structure. Later this folded ridge sixteenth mode SIW cavity is inductively loaded by a complementary split-ring resonator, which provides internal matching within the cavity resonator. This improved matching enhances the return loss, the external Q-factor, and ultimately, the loaded Q-factor of the proposed cavity resonator. At 60 GHz resonance frequency, the fabricated prototype of the proposed cavity resonator presents a measured reflection coefficient of −33.42 dB, with the external Q- factor 112. Moreover, the active area of the fabricated cavity without measuring pads is only 0.019 mm2 ..
10.	S. Alshhawy, A. Barakat, R.K. Pokharel, K. Yoshitomi, Low Magnetic Loss Metamaterial Based Miniaturized WPT System for Biomedical Implants, 2022 International Microwave Symposium (IMS), 2022.06, We propose a low magnetic loss multi-ring resonator (MRR) metamaterial. Then, we utilize this MRR metamaterial in a stacked configuration as the WPT transmitter (TX) for a miniaturized receiver (RX) embedded in biomedical tissue. A prototype is fabricated, and the measurement shows an efficiency of 51% at 50 MHz when the TX/RX separation distance is 9 mm. The TX/RX sizes are 20 mm × 20 mm and 7 mm × 7 mm, respectively. Hence, the proposed system has a figure-of- merit of 0.42, which is a significant improvement over the previously reported WPT systems. Also, the simulated specific absorption rate is within the recommended level when the input power is 21 dBm..
11.	X. Jiang, R.K. Pokharel, A. Barakat, K. Yoshitomi, Wideband Stacked Metamaterial for a Compact and Efficient Dual-Band Wireless Power Transfer, 2022 International Microwave Symposium (IMS), 2022.06, A novel wideband stacked metamaterial is proposed for a dual-band wireless power transfer (WPT) system. Firstly, two types of split-ring resonators (SRRs) of different self-resonance frequencies are proposed. Then we sandwiched each type of the unit cell. Consequently, the proposed metamaterial exhibits wideband near-zero characteristics on both the real part and imaginary part of the permeability. Also, compared with conventional 1-D metamaterial [2], the proposed metamaterial can significantly empower both bands simultaneously of the dual-band WPT system. An experiment shows that the proposed metamaterial of size (20 mm x 20 mm 5.468 mm) has improved the efficiencies of both bands from 18.6%, 22.9% to 51.8% and 47.8%, respectively, at a wireless power transfer distance of 20 mm..
12.	TBaichuan Chen; Samundra K. Thapa; Nusrat Jahan; Adel Barakat; Ramesh K. Pokharel, Design Methodology of Wide Tuning Range DGS-based VCO for K-band Applications in 0.18-µm CMOS Technology, 2021 51st European Microwave Conference (EuMC), 2022.04, [URL], Recently, defected ground structure (DGS) resonators have been employed to design a low phase noise Voltage-Controlled Oscillator (VCO) for quasi-millimeter wave applications [10]. A few advantages of such VCOs are that a DGS resonator has a higher Q-factor than an on-chip spiral inductor, and it has a higher self-resonance frequency compared to a conventional LC resonator so that a stable inductance value with respect to the frequency can be realized. However, one of its drawbacks is that the tuning range of DGS-based VCOs is limited. In this paper, a method to realize a wide tuning range of DGS-based VCOs has been proposed using two interconnected DGS resonators. As a result, the designed VCO implemented in 0.18-µm 1P6M CMOS technology achieves a 19.8% tuning range with the best phase noise performance of -109.43dBc/Hz at 1-MHz offset frequency in simulations. The experiment result shows that the fabricated VCO has a phase noise of -108.41dBc/Hz at 1-MHz offset frequency with the carrier frequency of 18.51GHz, which exhibits good agreement with the simulation..
13.	Tomoki Fukuda, Baichuan Chen, Samundra K Thapa, Adel Barakat, Ramesh K Pokharel, Design of Compact and High Q-Factor W-Band Cavity in 0.18-µm CMOS Technology, 2021 51st European Microwave Conference (EuMC), 2022.04, [URL], This paper proposes a compact, high-quality (Q-) factor cavity in commercial CMOS technology for terahertz band applications. The proposed cavity consists of a folded quarter-mode substrate integrated waveguide (QMSIW) topology. It also outlines some guidelines for creating layouts with specific foundries, particularly for building vertical walls using an array of vias. The cavity was implemented in 0.18 µm CMOS technology and measurements were taken. The measurements showed that the resonant frequency and reflection coefficients were 96.9 GHz and -30.14 dB, respectively, in good agreement with the simulation results. The area of the proposed cavity was 0.0506 mm2 without measurement pads, which is only 2.4% and 8.9% when compared to the standard full-mode SIW cavity and the recently proposed 87 GHz..
14.	Yutaro Ikeda, Xin Jiang, Mohamed Aboualalaa, Adel Barakat, Kuniaki Yoshitomi, Ramesh K Pokharel, Stacked Metasurfaces for Misalignment Improvement of WPT System Using Spiral Resonators, 2021 51st European Microwave Conference (EuMC), 2022.04, [URL], A miniaturized shielded folded ridged quarter-mode Substrate Integrated Waveguide (FRQMSIW) resonator in 1P6M CMOS technology is presented for millimetre wave applications. By adding a capacitive ridge and folded it inside the resonator, a significant miniaturization is realized. An additional shielded structure is employed to mitigate the leakage from the effective perfect conductor of the conventional quarter-mode SIW cavity. The characteristics of the proposed resonator are investigated first and then employed to design a 100GHz bandpass filter (BPF) with two transmission zeros. Finally, the proposed filter is implemented in 1P6M CMOS technology and measured. The active size of the proposed BPF without pads is , and the measured insertion loss (\|S21\|) is 2.06dB..
15.	Baichuan Chen, Samundra K Thapa, Adel Barakat, Ramesh K Pokharel, A 100GHz Bandpass Filter Employing Shielded Folded Ridged Quarter-Mode SIW Resonator in CMOS Technology, 2021 51st European Microwave Conference (EuMC), 2022.04, [URL], A miniaturized shielded folded ridged quarter-mode Substrate Integrated Waveguide (FRQMSIW) resonator in 1P6M CMOS technology is presented for millimetre wave applications. By adding a capacitive ridge and folded it inside the resonator, a significant miniaturization is realized. An additional shielded structure is employed to mitigate the leakage from the effective perfect conductor of the conventional quarter-mode SIW cavity. The characteristics of the proposed resonator are investigated first and then employed to design a 100GHz bandpass filter (BPF) with two transmission zeros. Finally, the proposed filter is implemented in 1P6M CMOS technology and measured. The active size of the proposed BPF without pads is , and the measured insertion loss (\|S21\|) is 2.06dB..
16.	X. Jiang, Adel Barakat, Kuniaki Yoshitomi, Ramesh Pokharel, Design of Three Layers-stacked Metasurface and its Application to Compact Dual-band WPT System, 2021 IEEE Wireless Power Transfer Conference, WPTC 2021, 2021.06, This paper proposes a three-layers stack metasurface first, and then employed it to a compact double-band wireless power transfer (WPT) system. For the proposed dual-band WPT system, the metasurface exhibits the wide-band characteristic of the negative-near-zero permeability from 222 MHz to 889 MHz, where the transmission efficiency improves significantly at longer WPT distance at the lower band. Only a unit cell is stacked in three layers so that the size of the proposed metasurface has significantly reduced compared to a conventional metasurface where several unit cells are arranged in 1-D topology. The size of the proposed WPT system and the metasurface is 15 x 15 mm and 20 x 20 mm, respectively. Also, capacitors with the value of 0.1pF are etched on the gaps of the metasurface. The measured efficiencies’ improvement ratios are 1.13 at 390 MHz in the air, where the WPT distance is significantly improved from 19 mm to 23 mm. .
17.	X. Jiang, Adel Barakat, Kuniaki Yoshitomi, Ramesh K. Pokharel, Efficient and Compact Dual-band Wireless Power Transfer System through Biological Tissues Using Dual-Reference DGS Resonators, 2021 IEEE MTT-S International Microwave Symposium, (IMS 2021), 2021.06, [URL], This paper presents a novel design for a compact dual-band wireless power transfer (WPT) system through biological tissues using dual-reference defected ground structure (DGS) resonators. Overlapping is used to minimize the size to be suitable for biomedical applications. The proposed DGS resonator exhibits bandstop characteristics at two different frequencies depending on the excitation reference plane. Then, two coupled sets of the proposed dual-reference DGS, in a back-to-back configuration, achieves a dual-band WPT system. The sizes of the receiver and transmitter are 15 mm × 15 mm and 18 mm × 18 mm, respectively. The measured efficiencies are 60.3% at 381MHz and 54.3% at 750MHz when the receiver is embedded in chicken breast within a depth of a 10mm, while the overall WPT distance of 11 mm..
18.	S. Thapa, B. Chen, Adel Barakat, and Ramesh Pokharel, Miniaturized Slot-Loaded SIW Resonator and Its Application to C-band Low Phase Noise Oscillator, 2020 50th European Microwave Conference, EuMC 2020, 2021.01, [URL], This paper presents a C-band low phase noise oscillator using a small size low-profile substrate integrated waveguide (SIW) resonator for RF applications. A compact 6 GHz SIW resonator size is possible by introducing λ g /4 resonating slots. A size reduction of 29.87% is achieved while maintaining the quality factor. Also, the impedance of the SIW resonator is controlled by appropriate selection of the location of these introduced slots; which advantages for the conjugate matching between the SIW resonator and the active device and removes the need of a matching circuit between them. Then, a C-band oscillator prototype utilizing the proposed compact SIW resonator is designed, fabricated and measured. The measured results show a phase noise of -122.11 dBc/Hz at 1 MHz offset with an output power of -4.2 dBm at 5.96 GHz oscillation frequency. This will help to make a next-generation wireless transceiver..
19.	Adel Barakat, Shimaa Alshhawy, Kuniaki Yoshitomi, Ramesh K. Pokharel, High Isolation Simultaneous Wireless Power and Information Transfer System Using Coexisting DGS resonators and Figure-8 Inductors, 2020 IEEE MTT-S International Microwave Symposium, (IMS 2020), 2020.08, [URL], For the first time, we propose a combination of coupled defected ground structure (DGS) resonators for wireless power transfer and coupled Figure-8 inductors for information transfer. This combination allows the realization of a simultaneous compact wireless power and information transfer (WPIT). Each set of the DGS resonators and the Figure-8 inductors are located on the same plane. However, they show negligible coupling due to the coupling cancellation mechanism of the Figure-8 inductors. Hence, high isolation can be achieved between the power and information channels. A prototype is fabricated for operation at 50 MHz and 100 MHz. The overall area of the TX/RX is 30 mm × 30 mm and are separated by 14 mm. The measured efficiencies are 78% and 76% at 50 MHz and 100 MHz, respectively, and the isolation is more than 34 dB..
20.	Nusrat Jahan, Chen Baichuan, Adel Barakat, Ramesh K. Pokharel, Analysis and application of dual series resonances for low phase noise K-band VCO design in 0.18-μm CMOS technology, 2019 IEEE International Symposium on Circuits and Systems, ISCAS 2019, 2019.01, This work proposes a new theory to improve the phase noise of a Voltage-Controlled Oscillator (VCO) by introducing dual series resonances around the parallel resonance of an LC-tank circuit. The overall circuit has an improved susceptance slope parameters, which results in the improvement of quality (Q-) factor. Later, its effectiveness is demonstrated to design a low phase noise K-band VCO. The proposed characteristics are realized by a compact defected ground structure (DGS) resonator in a coplanar strip line (CPS) topology. The DGS is loaded by a capacitor, and this combination introduces the parallel resonance. The CPS signal line is implemented with high characteristic impedance to introduce a series inductance. Then, a gap in the CPS is introduced with a loading series capacitance forming a series resonance circuit with the CPS inductance. The overall combination of the series and parallel resonance circuits allowed the targeted two series resonances before and after the parallel resonance. The design is implemented in 0.18-μm CMOS technology, and the post-layout simulation shows that the VCO has a phase noise of -112.31 dBc/Hz @1 MHz offset of 22.07 GHz oscillation, which is 2.3 dB improvement compared to single series resonance VCO. The VCO consumes 4 mW power resulting in a figure of merit (FoM) of -193.2 dB..
21.	Adel Barakat, Shimaa Alshhawy, Kuniaki Yoshitomi, Ramesh K. Pokharel, Triple-Band Near-Field Wireless Power Transfer System Using Coupled Defected Ground Structure Band Stop Filters, 2019 IEEE MTT-S International Microwave Symposium, IMS 2019, 2019.06, For the first time, a triple-band near-field wireless power transfer (WPT) system is presented using coupled triple-band defected ground structure (DGS) bandstop filters (BSF). A triple-band DGS-BSF is possible through creating a frequency dependent effective inductance, which appears with lower inductance at higher frequencies. When we couple two triple-band DGS-BSFs in a back-to-back configuration, a triple-band DGS-WPT system is created. We verify the proposed DGS-WPT system through good agreements between electromagnetic simulations and measurements. The measured WPT efficiencies are 68%, 60%, and 65% at 100.8 MHz, 140.7 MHz, and 182.2 MHz, respectively at a WPT separation distance of 30 mm. Each of the WPT transmitter and receiver has a size of 50 × 50 mm..
22.	Sumin Chalise, Mitsuki Nakao, Fairus Tahar, Adel Barakat, Kuniaki Yoshitomi, Ramesh K. Pokharel, 45% RF-to-DC Conversion Efficiency Wireless Power Transfer System Through Biological Tissues Using Complex Conjugate Impedance Matching Taking Account of Tissue's Properties, 2019 IEEE MTT-S International Microwave Symposium, IMS 2019, 2019.06, This paper presents a complex conjugate impedance matching technique taking account of the electric properties of biological tissues during power transfer. Output impedance of a wireless power transfer (WPT) system depends on the electrical property of tissues where the system is being used. So, impedance mismatch between Rx and rectifier occurs when the system optimized for air is used in biological tissues. First, the system is matched in the air and later, impedance mismatch is estimated when the same system is being used in chicken which is later compensated. The proposed matching technique will bring back the rf-dc power conversion efficiency (PCE) very close to that of the system being used in the air. Experiment was carried out in three different cases where PCE is 49.53% in the air, 30% in chicken with the conventional conjugate matching and 45.5% in the chicken using the proposed matching technique..
23.	Baichuan Chen, Nusrat Jahan, Adel Barakat, Ramesh K Pokharel, Experimental Study of the Effect of Interconnects on Phase Noise of K-Band VCO in CMOS Technology, 2019 IEEE Asia-Pacific Microwave Conference (APMC), 2019.12, [URL], In this paper, to characterize the effect of interconnects inductance on VCO's phase noise precisely, two K-band VCO circuits that employ DGS as an inductor are designed and analyzed. It's shown that not only the quality factor of the inductor in resonator has a significant effect on VCO's phase noise, the parasitic inductance of the interconnecting transmission lines will also inflect the phase noise severely. To get the Quantitative analysis, a K-band (25 GHz) VCO is implemented in the 1P6M CMOS process and measured..
24.	Islam Mansour, Marwa Mansour, Mohamed Aboualalaa, Ahmed Allam, Adel B. Abdel-Rahman, Mohammed Abo-Zahhad, Ramesh Pokharel, 70% Improvement in Q-factor of spiral inductor and its application in switched K-band VCO using 0.18 um CMOS technology, 30th Asia-Pacific Microwave Conference, APMC 2018, 2018.11, A novel technique for increasing the quality factor of the on-chip inductor is proposed in this paper. A high-quality factor shunt inductor is designed using the lower layers 5 and 3 in 0.18 um CMOS technology so the top layer is valid for other circuit components. The quality factor is improved by 70 % in the Ku, K and Ka-band compared to the single layer inductor. Furthermore, the proposed inductor has a compact area of about 0.0089 mm2. This shunt inductor is used with a switched MOS varactor capacitors to construct a switched notch filter which has a sharp skirt characteristic and can be used in the VCO circuits. Using this switched shunt inductor resonator, the phase noise of the VCO is enhanced by 8 dB compared to single layer inductor resonator, moreover, the frequency tuning range is doubled. The VCO achieves a wide tuning range of 2.5 GHz, the first band from 18.8 to 19.97 GHz while the second band from 19.96 to 21.3 GHz. The phase noise at 1MHz is -112.4 and -112.5 dBc/Hz at the low and high band and this results FoM of-192.2 and -192.5 at 19.9 GHz and 21.3 GHz, respectively. The figure of merit considering the frequency tuning range (FoM ^T ) is -194.4 dBc/Hz and the active VCO core area is 0.039 mm ².
25.	Ramesh Pokharel, Nusrat Jahan, Adel Barakat, Dual Resonance Circuits by Defected Ground Structure Resonators for Low Phase Noise K-Band CMOS VCO, 2018 IEEE International Symposium on Radio-Frequency Integration Technology, RFIT 2018, 2018.08, We analyze the quality factor (Q_U/Q_K) of three different types of defected ground structure (DGS) resonators including a series resonance in addition to the parallel one. Then, we implement the resonators to design high-performance K-band VCOs in 0.18μ CMOS Technology and finally, a low phase noise VCO at K-band is introduced..
26.	Islam Mansour, Mohamed Aboualalaa, Nusrat Jahan, Adel Barakat, Ramesh Pokharel, Ahmed Allam, Adel B. Abdel-Rahman, Mohammed Abo-Zahhad, Design of multi-layers DGS resonator for phase noise improvement of K-Band VCOs in 0.18 µm CMOS technology, 61st IEEE International Midwest Symposium on Circuits and Systems, MWSCAS 2018, 2018.08, A novel technique for a low phase noise and compact K-band Voltage-Controlled Oscillator (VCO) using multi-layers DGS resonator is proposed. The proposed DGS resonator realizes an additional series resonance at the higher side of parallel resonance frequency, and this results in improving both the active and loaded quality factor of the resonator. The proposed resonator has active quality factor of 130 and a compact size of 0.009 mm ² (0.000459 ? ² ). Using the proposed DGS resonator in the VCO causes 9 dB improvement in the phase noise compared the VCO implemented using the conventional LC resonator. Two VCOs are designed using the method to illustrate the effect of the series resonance. The first VCO is designed three layers DGS resonator and the other VCO using two layers DGS resonator. The designs are implemented in 0.18 µm CMOS technology and consume 2.9 mW power, and from the post layout results, the first proposed VCO oscillates from 19.6 to 21.3 GHz (8.3 %) and has a phase noise of -113.2 dBc/Hz at 1 MHz offset frequency, and this results in the figure of merit (FoM) and FoM taking account of the tuning range to be -194.4 and -192.7 dB, respectively. The second VCO has a tuning range of 6.1 % and phase noise of -114 dBc/Hz @ 1 MHz offset at 19.6 GHz oscillation..
27.	M. R. Saad, Fairus Tahar, Sumin Chalise, Adel Barakat, Kuniaki Yoshitomi, Ramesh Pokharel, High FOM Dual Band Wireless Power Transfer using Bow-tie Defected Ground Structure Resonators, 2018 IEEE Wireless Power Transfer Conference, WPTC 2018, 2018.06, This work presents a dual-band wireless power transfer (WPT) system with high figure of merit (FoM). One band can be used for power transfer and another for data transfer in biomedical applications. A Bow-tie Defected Ground Structure (DGS) resonators with high quality (Q-) factor and coupling (k-) factor is utilized for ensuring high efficiency. An equivalent circuit model using the admittance (J-) inverters is utilized to design the admittance inversion and compensation networks. The measured result shows that the proposed WPT system is able to transfer the power at both of the bands with a highFoM, making a suitable candidate for compact near filed WPT applications..
28.	Fairus Tahar, Sumin Chalise, Kuniaki Yoshitomi, Adel Barakat, Ramesh Pokharel, Compact Dual-Band Wireless Power Transfer Using Overlapped Single Loop Defected Ground Structure, 2018 IEEE Wireless Power Transfer Conference, WPTC 2018, 2018.06, This paper presents a compact dual-band wireless power transfer (WPT) system using overlapped defected ground structure for biomedical applications. One band for power and another for data transfer. The proposed defected ground structure can channel two distinct resonant frequencies. As a result, the fabricated WPT device has almost 50% reduction in the size without changing other performances compared to ref. [9]. The fabricated device is 15 mm ×15 mm. The measured efficiency is 71% and 73%, respectively at 0.45 GHz and 0.95 GHz at WPT distance of 12.5mm..
29.	Basma E. Abu-Elmaaty, Omnia M. Nawwar, Mohammed S. Sayed, Hossam M.H. Shalaby, Ramesh Pokharel, Silicon-on-insulator first-order mode converter based on binary phase plate, 2018 Japan-Africa Conference on Electronics, Communications, and Computations, JAC-ECC 2018, 2018.12, A silicon-on-insulator fundamental to first-order mode converter is proposed based on binary phase plate. The device can be operated in both polarizations simultaneously as it converts both fundamental TE and TM modes to first-order TE and TM modes, respectively which will be very useful in implementing PDM-MDM systems. The proposed device has a simple and compact structure. It has a low insertion loss of -2 dB and low crosstalk..
30.	Ramesh K. Pokharel, Adel Barakat, and Fairus Tahar, K and Q Factors in Near-Field Wireless Power Transfer: A Case Study of DGS Resonators, 2017 IEEE MTT-S International Microwave and RF Conference, 2017.12, [URL], This paper discusses the probability of improving the degree of freedom in implementing wireless power transfer (WPT) systems. This is possible by utilizing the defected ground structures (DGSs). The WPT efficiency can be increased by optimizing the coupling coefficient (K) between the transmitter and the receiver, and the quality (Q-) factor of them. DGSs can be implemented in different shapes; hence, the K and Q-factor of these DSGs are realized with different values depending on the DGS shape. In return, the achievable WPT efficiency can be maximized by careful selection of the DGS shape and dimensions depending on the system efficiency and distance requirements..
31.	Nusrat Jahan, Chen Baichuan, Ramesh K Pokharel, Adel Barakat, A K-Band VCO Employing High Active Q-factor Defected Ground Structure Resonator in 0.18 pm CMOS Technology, 2018 IEEE International Conference in Circuits and Systems (ISCAS2018), 2018.05, [URL], In this paper, a new theory to improve the phase noise of a Voltage-Controlled Oscillator (VCO) utilizing dual series and parallel resonance to improve the susceptance slope parameter of the resonator circuit is proposed, and its effectiveness is demonstrated to design a low phase noise K-band VCO. The proposed dual resonance is realized using a compact defected ground structure (DGS) resonator, which achieve the additional series resonance by loading its transmission line by a series capacitor. The resulting susceptance slope, and active quality (Qk-) factor of the resonator circuit enhance that, in returns, improves the phase noise by 3.2dB of the same circuit without the series resonance. The design is implemented in 0.18 μm CMOS technology, and the post-layout simulation results show that VCO has a tuning range of 3.4%, and low phase noise with − 111.9 dBc/Hz @1 MHz offset at 21.04 GHz oscillation. The VCO consumes 7.5 mW power resulting in a FoM of −188.7 dB.
32.	M Aboualalaa, Adel B Abdel-Rahman, A Allam, Ramesh K Pokharel, Kuniaki Yoshitomi, H Elsadek, Compact 24GHz half-slot antenna for energy combining, 2018 International Applied Computational Electromagnetics Society Symposium (ACES), 2018.03, [URL], A compact half-slot microstrip antenna is proposed in this paper. The antenna consists of microstrip line-fed half slot, and an open-circuited stub is connected to the microstrip feed line to adjust the matching at the operated frequency band. A half slot is used for miniaturization, as well as due to concentrating the field at only half slot; consequently, it decreases the resonance frequency and improves the antenna radiation characteristics. The antenna radiates at 24 GHz with measured fractional impedance bandwidth of 9%. The antenna gain at the resonant frequency is 5.2 dBi. The proposed antenna shows about 60% length reduction. Therefore, the proposed half slot antenna could be used for energy harvesting applications, at 24 GHz ISM band, due to its compact size with improved gain value. The proposed antenna was designed using ANSYS high-frequency structure simulator (HFSS). The simulated and measured results show good agreement..
33.	F. Tahar, A. Barakat, R. Saad, K. Yoshitomi, and R. K. Pokharel, Dual-Band Wireless Power Transfer System Using Circular Defected Ground Structure Resonators for Biomedical Applications, 2017 International Conference in Circuits and Systems (ISCAS2017), 2017.05, [URL], In this paper, we proposed and developed a compact dual-band wireless power transfer system for future wireless power supply to embedded sensors and implants. This was fabricated in the commercial substrate, so it is low cost but it has high efficiency..
34.	Adel Barakat, Sherif Hekal, Ramesh Kumar Pokharel, Simple design approach for asymmetric resonant inductive coupled WPT systems using J-inverters, 2016 Asia Pacific Microwave Conference, 2016.12, [URL], This paper presents a simple and precise design method for asymmetric resonant inductive coupled wireless power transfer (WPT) systems without the involvement of circuit or electromagnetic (EM) simulators. The design method is based on the generalized second- order band-pass filter (BPF). First, the values of the BPF's J-inverters are computed based on the mutual coupling between the transmitter (TX) and the receiver (RX). Then, the required components are extracted from the J-inverters values. We achieved good agreements.
35.	ADEL Barakat, N Mahmoud, POKHAREL RAMESH KUMAR, Low insertion loss 60 GHz CMOS H-shaped resonator BPF, 2017 IEEE Radio and Wireless Symposium (RWS), 2017.01, [URL], In this paper, a new theory to realize low loss of an on-chip bandpass filter at 60GHz band is proposed and experimentally verified..
36.	Nessim Mahmoud, Adel B Abdel-Rahman, Adel Barakat, Ramesh Kumar Pokharel, Performance enhancement of 0.18 um CMOS on chip bandpass filters using H-shaped parasitic element, 2015 27th International Conference on Microelectronics (ICM), 2015.12, [URL], A design of an improved open loop resonator on-chip bandpass filter for 60 GHz millimeter-wave applications using 0.18 µm CMOS technology is presented..
37.	Ramesh Kumar Pokharel, B. Amalina, Comparative Design of Extremely Low Phase Noise Oscillator in Class-B and Class-C by Integrating Film Bulk Acoustic Resonator (FBAR) on CMOS Wafer for Low Power Applications , 2015 IEEE MTT-S International Microwave and RF Conference (IMaRC), 2015.12, This paper presents the comparative design of a CMOS cross-coupled oscillator in class-B and Class-C topology, respectively using film bulk acoustic resonator (FBAR) in order to improve the phase noise and power consumption. The design issues such as low frequency stability, phase noise issues and optimization method of FBAR on a CMOS wafer will will be discussed. Experiment results and performance comparison will be discussed..
38.	M. Hanif, ADEL TAWFIK MOHAMED MOHAMED BARAKAT, POKHAREL RAMESH KUMAR, A gain enhanced 60 GHz CMOS antenna-on-chip using off-chip Mu near zero metamaterial lens, , 2015 IEEE 4th Asia-Pacific Conference on Antennas and Propagation (APCAP), 2015.07, (MNZ-MM) lens to enhance the gain of a 60 GHz Antenna-on-Chip (AoC). First, a MNZ-MM unit cell is designed to ensure the near zero characteristics at the 60 GHz band. Furthermore, a 3 by 3 matrix of the MNZ-MM is placed in the desired direction of radiation such that the radiated waves are coupled and the gain is enhanced and the AoC's\| S11\| is negligibly affected. The simulated gain and efficiency of the AoC with MNZ-MM lens are 2.8 dBi and 35%, respectivel.
39.	Khalil Yousef, A. B. Abdel-Rahman, Ramesh Kumar Pokharel, Hongting Jia, An eight-phase CMOS injection locked ring oscillator with low phase noise, 2014 IEEE International Conference on Ultra-WideBand (ICUWB), 2014.09, [URL], This paper presents the design of a low DC power, low phase noise single-ended ring oscillator (RO) in 0.18 μm CMOS technology. It introduces a new RO output phase control technique. This RO uses a voltage pull-down circuit to produce different output signal phases. The proposed RO employs the pulse injection (PI) technique for phase noise and spurious signals suppression. The proposed injection locked ring oscillator (ILRO) can be used for phase shift keying (PSK) implementation. The proposed ILRO has an oscillation frequency of 4.5 GHz with a fine tuning range of 540 MHz. It consumes only a 4.25 mW of power while having a phase noise of -130.9 dBc/Hz @ 1MHz offset. Through this ILRO design, a figure of merit (FoM) of -197.68 dBc/Hz has been achieved..
40.	H. Hekel, A. B. Abdel-Rahman, M. Hanif, Ramesh Kumar Pokharel, Strong resonant coupling for short-range wireless power transfer applications using defected ground structures, 2015 IEEE Wireless Power Transfer Conference (WPTC), 2015.05, [URL], This paper presents a new structure for highly efficient short-range wireless power transfer. The proposed structure is based on strongly coupled resonators using H-slot defected ground structures. An equivalent circuit model for H-slot coupled resonators is introduced. Measurement results for the new proposed structure show a power transfer efficiency of 70% at 15 mm distance between driver and load resonators. Experimental measurements have shown good agreement with electromagnetic and circuit simulations..
41.	Adel Barakat, A. B. Abdel-Rahman, M. Hanif, Ramesh Kumar Pokharel, Miniaturized 60 GHz triangular CMOS Antenna-on-Chip using asymmetric artificial magnetic conductor, 2015 IEEE 15th Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems (SiRF), 2015.01, [URL], This paper presents a miniaturized triangular Antenna-on-Chip (AoC) designed and fabricated on a 0.18 μm CMOS process using asymmetric rectangular artificial magnetic conductor (R-AMC). An AMC acts as a shield plane between the AoC and the lossy CMOS substrate. AoC using asymmetric R-AMC presents a smaller overall area than that of the previous reported AoC with symmetric AMCs. The triangular AoC area including the asymmetric AMC cells is only 0.81mm2 with a simulated gain of -0.2 dBi at 60 GHz. Measurements confirm the wide impedance bandwidth of the AoC.
42.	Ibrahim Abdalla, M. Ragab, Ramesh Kumar Pokharel, Hongting Jia, A DC-2.5GHz voltage variable attenuator in 0.18-μm CMOS technology, 2014 IEEE Asia Pacific Conference on Circuits and Systems (APCCAS), 2014.11, [URL], A CMOS variable voltage attenuator(VVA) with wide bandwidth has been designed and fabricated in a 0.18-μm CMOS process. Four bridge-T stages are cascaded to achieve 12 dB of dynamic range attenuation over a frequency range from DC up to 2.5 GHz. Cascaded bridge-T stages can be programmed to achieve the full scale attenuation and ensure good input and output matching. The design operates with 1.5-dB step size and with a maximum input power of -13 dBm in the entire frequency DC-2.5 GHz range. Worst case S11 is -11.5 dB across the frequency band. The design achieves an input third order intercept point (IIP3) of+31 dBm at maximum-attenuation.
43.	Hamed Mosalam, M. Ragab, Ramesh Kumar Pokharel, Hongting Jia, A 5–9 GHz CMOS Ultra-wideband power amplifier design using load-pull, 2013 IEEE 20th International Conference on Electronics, Circuits, and Systems (ICECS), 2013.08, [URL], The design of 5-9 GHz, two stages CMOS power amplifier (PA) for Ultra-wideband (UWB) is presented in this paper. Post-layout simulation results indicated a power gain S21 of 16± 0.5dB, an input return loss S11 less than -4 dB and an output return loss S22 less than -5 dB over the frequency range of interest. Source-pull contours were used to design the inter stage matching of the PA. The proposed two stages PA achieves an average Power Added Efficiency (PAE) of 12.4% and an output 1-dB compression above 0 dBm over the same frequency band. Moreover, the proposed UWB PA achieves group delay of 170±20 ps with power consumption of 25 mW from a 1.8V supply voltage. The UWB PA is designed in TSMC 0.18 μm CMOS technology..
44.	Hamed Mosalam, A. B. Adel, Ramesh Kumar Pokharel, Hongting Jia, 5.0 to 10.6 GHz 0.18 µm CMOS power amplifier with excellent group delay for UWB applications, 2015 IEEE MTT-S International Microwave Symposium (IMS), 2015.05, [URL], The optimization technique to realize the minimum group delay (GD) of a 5-10.6 GHz, two stages CMOS Ultra Wideband power amplifier (UWB-PA) is presented and implemented in 0.18 μm CMOS technology. The fabricated UWB-PA has a power gain (\|S21\|) of 14± 1 dB, maximum power added efficiency and an output 1-dB compression of 10 %, and 2 dBm, respectively at 6 GHz. In addition, the PA has an excellent small group delay variation of 147± 40 ps with power consumption of 20 mW and this is the smallest variations among CMOS PAs so far reported..
45.	Adel Barakat, Ramesh Kumar Pokharel, Haruichi Kanaya, Small size 60 GHz CMOS Antenna-on-Chip: Gain and efficiency enhancement using asymmetric Artificial Magnetic Conductor, 2014 44th European Microwave Conference (EuMC), 2014.10, [URL], This paper presents a small size 60 GHz Antenna-on-Chip (AoC) designed and fabricated using 0.18 um TSMC Complementary Metal Oxide Semiconductor (CMOS) process. AoC performance is enhanced using asymmetric Artificial Magnetic Conductor (AMC). The AoC area including the AMC is 1715 um by 710 um. As AMC shields AoC from the lossy CMOS substrate, simulated gain of -0.25 dBi is achieved at 60 GHz for design rule compatible circular AoC with 12.8 dB front-to-back ratio (FBR) due to removal of AMC cells below the AoC. Measurements agree well with simulation results and confirm operation at the 60 GHz band with a peak measured gain of -3 dBi at 64 GHz..
46.	Adel Barakat, POKHAREL RAMESH KUMAR, 吉田啓二, Ahmed Allam, Compact size high gain AoC using rectangular AMC in CMOS for 60 GHz millimeter wave applications, 2013 IEEE MTT-S International Microwave Symposium, 2013.06, [URL], This paper presents a compact size, high gain triangular Antenna-on-Chip (AoC), designed and fabricated using a 0.18 μm CMOS process and optimized over different cells' configurations of rectangular artificial magnetic conductor (R-AMC). An AMC acts as a shield plane between the AoC and the lossy CMOS substrate. R-AMC shows better shielding characteristics than previously reported AMCs. Measurement results confirm the wide impedance bandwidth of the AoC..
47.	Khalil Ismail Khalil Yousef, POKHAREL RAMESH KUMAR, JIA HONGTING, 金谷晴一, 吉田啓二, Ahmed Allam, CMOS Ultra-Wideband Low Noise Amplifier (UWB-LNA) Using Symmetric 3D RF Integrated Inductor, IEEE International Conference on Ultra-Wideband , 2013.09, [URL].
48.	POKHAREL RAMESH KUMAR, Daisuke Kanemoto, 金谷晴一, 吉田啓二, Design Technique for a High-speed SAR ADC Using Non-binary Search Algorithm and Redundancy, 2013 Asia-Pacific Microwave Conference Proceedings, 2013.11, [URL].
49.	Tomoya Ijiguchi,, Daisuke Kanemoto, POKHAREL RAMESH KUMAR, Yoshida Keiji, 金谷晴一, Development of Circularly Polarized Planar Slot Antenna for 5.8 GHz-DSRC Application, 2013 Asia-Pacific Microwave Conference Proceedings, 2013.11, [URL].
50.	POKHAREL RAMESH KUMAR, Prapto Nugroho, ANAND AWINASH, Haruichi Kanaya, Keiji Yoshida, Digitally Controlled CMOS Quadrature Ring Oscillator with Improved FoM for GHz Range All-Digital Phase-Locked Loop Applications , Dig. of 2012 IEEE International Microwave Symposium (IMS), 2012.06, [URL].
51.	Prapto Nugroho, POKHAREL RAMESH KUMAR, ANAND AWINASH, 金谷晴一, 吉田啓二, A Low Power 8-bit Digitally Controlled CMOS Ring Oscillator, Proc. of 2012 European Microwave Conference, 2012.10, [URL], High phase noise is a common problem in ring oscillators. Continuous conduction of the transistor in an analog tuning method degrades the phase noise of ring oscillators. In this paper, a digital control tuning which completely switches the transistors on and off, and a 1/f noise reduction technique are employed to reduce the phase noise. A 14-bit control signal is employed to obtain a small frequency step and a wide tuning range. Furthermore, multiphase ring oscillator with a sub-feedback loop topology is used to obtain a stable quadrature outputs with even number of stages and to increase the output frequency. The measured DCO has a frequency tuning range from 554 MHz to 2.405 GHz. The power dissipation is 112 mW from 1.8 V power supply. The phase noise at 4 MHz offset and 2.4 GHz center frequency is -134.82 dBc/Hz. The FoM is -169.9 dBc/Hz which is a 6.3 dB improvement over the previous oscillator design..
52.	, [URL].
53.	, [URL].
54.	High Dynamic Range Mixer in 0.18 um Technology for WLAN Direct Conversion Receiver .
55.	Development of a One-Sided Directional Planer Antenna with Matching Circuit.
56.	Discussion on the method of the performance improvement of 5.2GHz-Band VCO.
57.	Development of an Electrically Small One-Sided Directional Antenna with Matching Circuit.
58.	Design of VCO for 2.4GHz Wireless Applications Using Transmission Line Resonators.
59.	Study of A CPW-Fed Slot Dipole One-Sided Directional Antenna for UWB Systems.
60.	Design and Performance of an Electrically Small Antenna with Matching Circuit.
61.	Design of High-Linearity Amplifier for Wireless LAN Transceiver.
62.	Design of 1.1 GHz Highly Linear Digitally-Controlled Ring Oscillator with Wide Tuning Range.
63.	Design and Measurement of RF Frontend LSI with CPW Impedance Circuit.
64.	Design of Power Amplifier with On-Chip Matching Circuits using CPW Line Impedance (K) Inverters.
65.	, [URL].
66.	Development of high conversion gain double balanced mixer for high performance direct conversion receiver.