九州大学 研究者情報
発表一覧
POKHAREL RAMESH KUMAR(ぽかれる らめしゆ くまーる) データ更新日:2021.08.06

教授 /  システム情報科学研究院 I&Eビジョナリー特別部門 http://rfic.ed.kyushu-u.ac.jp/


学会発表等
1. 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, [URL], 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.
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2. 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..
3. 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..
4. 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..
5. 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, [URL], 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..
6. 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..
7. 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..
8. Fairus Tahar, Sumin Chalise, Adel Barakat, Kuniaki Yoshitomi, Ramesh K. Pokharel, Dual-Band Defected Ground Structure Resonators Wireless Power Transfer System Connected to Voltage-Doubler Circuit, 2019 IEEE Topical Conference on Wireless Sensors and Sensor Networks, WiSNet 2019, 2019.05, [URL], Recently, research on multiband wireless power transfer (WPT) systems has drawn attention high efficiency in the air with a small package of WPT size for the possible bio-related application. However, the WPT system itself is not complete without complementary circuit to convert the received RF power to DC. Thus, this paper presents a design method of integrating a predesigned dual-band WPT system to a voltage-doubler (VD) without external circuit configuration. The method proved to be working as experiment RF-DC conversion efficiency recorded to be 35.2% and 37.9% in both bands, respectively with 20 mm working distance through skin,-1.27% and-1.6% dropped from air condition..
9. M. Mahmoud, G. Fahmy, A. B. Abdel-Rahman, A. Allam, M. Abo-Zahhad, H. Jia, R. K. Pokharel, Enhancing Dynamic Range of RF-to-DC Rectifier using Leakage Current Reduction Technique, 7th International Japan-Africa Conference on Electronics, Communications and Computations, JAC-ECC 2019, 2019.12, [URL], In this paper, the dynamic range of the conventional differential drive rectifier is enhanced based on leakage current reduction technique, to solve the narrow dynamic range problem of the input power and improve the output rectifier performance. The proposed design uses auxiliary transistors to control the conductivity of the rectifying PMOS devices dynamically to reduce the reverse leakage current. Post layout simulations have been performed using 0.18 μm CMOS technology at 402 MHz with 10kΩ load resistor. The proposed rectifier increases the range of the RF input power about ten times compared to a conventional rectifier's dynamic range and reduces the reverse leakage current from 98 μA to 22 μA. It also boosts the output average voltage at high input power. In addition, the developed rectifier exhibits good performance over wide band of input frequencies up to 2.4 GHz. The proposed rectifier has a small area of about 0.19 mm2..
10. 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..
11. 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, [URL], 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.
12. 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, [URL], 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..
13. 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, [URL], 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..
14. Omnia M. Nawwar, Hossam M.H. Shalaby, Ramesh Pokharel, First-Order Mode Compact Focusing Grating Coupler for SOI Interconnect, 2018 IEEE Photonics Society Summer Topicals Meeting Series, SUM 2018, 2018.07, [URL], Compact on-chip grating coupler for first-order TE-like mode in a strip waveguide is proposed. The grating coupler is used in mode-division multiplexing (MDM) systems to couple light from a single-mode fiber to desired on-chip mode without the need of intermediate mode converters..
15. 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, [URL], 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..
16. Mohamed Aboualalaa, Islam Mansour, Mohamed Mansour, Adel Bedair, Ahmed Allam, Mohammed Abo-Zahhad, Hala Elsadek, Kuniaki Yoshitomi, Ramesh Pokharel, Dual-band Rectenna Using Voltage Doubler Rectifier and Four-Section Matching Network, 2018 IEEE Wireless Power Transfer Conference, WPTC 2018, 2019.02, [URL], A dual-frequency rectenna is introduced in this paper. An enhanced-gain antenna is integrated with the rectifying circuit for increasing the rectenna capability for scavenging. A voltage doubler circuit is used for the rectification. Moreover, a four-section matching network is employed for the matching between the antenna and the rectifier. The measured results reveal that the RF-to-DC conversion efficiency is more than 50% over wide range of the input power, from-3.5dBm to 10. 5dBm at f1 and from -4.5dBm to 11dBm at f2, with maximum conversion efficiency of 63% and 69% at input power of 7dBm and 3. 5dBm, respectively with resistive load of 1KΩ. Further-more, the measurements illustrate good agreement between the simulated and measured results..
17. 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, [URL], 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..
18. 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, [URL], 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..
19. Ramy Sharaf, Sherif Hekal, Anwer Abd El-Hameed, Adel B. Abdel-Rahman, Ramesh Pokharel, A new compact wireless power transfer system using C-shaped printed resonators, 23rd IEEE International Conference on Electronics, Circuits and Systems, ICECS 2016, 2017.02, [URL], This paper presents a simple and compact design for an efficient short-range wireless power transfer (WPT) system. The proposed design is composed of two identical transmitting (TX) and receiving (RX) substrates. Each substrate has a micro strip feed line and C-shaped edge coupled resonator. A partial ground plane is added under the feeding line to guide the transmitted/received signals. The C-shaped resonator is loaded by chip capacitor for miniaturization. A circuit model has been extracted for verification of the design theory. The proposed design achieves a WPT efficiency of 69% at 1 GHz and a transmission distance of 15mm..
20. Adel Barakat, Nessim Mahmoud, Ramesh Pokharel, Low insertion loss 60 GHz CMOS H-shaped resonator BPF, 2017 IEEE Radio and Wireless Symposium, RWS 2017, 2017.03, [URL], This paper presents a low insertion less 60 GHz on-chip bandpass filter (BPF) on 0.18 μm standard CMOS technology. For insertion loss minimization, this BPF uses the H-shaped resonator which couples through two branches and the rectangular defected ground structures (DGS) which reduce the external quality factor. Besides, this BPF employs metal-insulator-metal capacitor to ensure size compactness. The fabricated BPF chip size is 240 μm × 650 μm. The simulation results agree well with the measured ones. The measured insertion loss is 2.1 dB at 60GHz..
21. Manal Mahmoud, Adel B. Abdel-Rahman, Ghazal A. Fahmy, Ahmed Allam, Hongting Jia, Ramesh Pokharel, Dynamic threshold compensated, low voltage CMOS energy harvesting rectifier for UHF applications, 59th IEEE International Midwest Symposium on Circuits and Systems, MWSCAS 2016, 2017.03, [URL], A new differential drive CMOS rectifier topology has been provided for RF wireless energy harvesting of low input power applications as implantable devices. It applies a dynamic threshold compensation technique by gate biasing of selected MOS switches with external bootstrapping circuit. The proposed architecture has been simulated in 0.18μm CMOS technology. The performance of the circuit is evaluated in terms of the power conversion efficiency (PCE), and the voltage conversion ratio (VCR). The proposed architecture has achieved a maximum power conversion efficiency of 75% and a voltage conversion ratio of 83.9% at 402MHz and -15.4dBm RF input power. The DC output power exceeds 21μW with a parallel combination of 10kOhm and 2pF load. The design layout has 0.085mm2 chip area..
22. H. Mosalam, A. Allam, Adel Abdel-Rahman, T. Kaho, Hongting Jia, Ramesh Pokharel, A high-efficiency good linearity 21 to 26.5 GHz fully integrated power amplifier using 0.18 μm CMOS technology, 59th IEEE International Midwest Symposium on Circuits and Systems, MWSCAS 2016, 2017.03, [URL], This paper presents the design and implementation of a 21- 26.5 GHz broadband, two stages CMOS power amplifier (PA) for quasi-millimeter wave band wireless communication systems. The proposed PA is designed using staggered tuning method [1], which is employed for the first time in quasi-millimeter wave band. Moreover, source and load-pull simulation, in addition to, impedance analysis are employed to optimize the input, output, and inter-stage impedance matching circuits for maximum power added efficiency (PAE) and better linearity. The measurement results on a chip fabricated using 0.18 μm CMOS technology shows a power gain of 10.2 ± 0.8 dB, a maximum PAE and output gain compression point (POut1dB ) of 10.5 dBm and 18 %, respectively, at 24 GHz while consuming 42 mW only. In addition, the PA achieved excellent low measured group delay variations of 75 ± 22 ps..
23. Ibrahim L. Abdalla, Hongting Jia, Ramesh Pokharel, A DC-2.5 GHz high linearity CMOS attenuator in a 0.18μm technology, 11th International Conference on Interdisciplinarity in Engineering, INTER-ENG 2017, 2018.01, [URL], A CMOS attenuator with high linearity has been designed and measured in a 0.18-μm CMOS process, to be used for a variable gain amplifier of RF wireless transceiver. The design is based on four cascaded Bridge-T attenuator stages that are consecutively activated to adjust the attenuation level and improve linearity. The design operates in the frequency band of DC-2.5 GHz with 2 - 3.5 dB insertion loss and 14 dB maximum attenuation in the entire frequency range. Measured and simulated results are in good agreement over the frequency band of interest. Measured worst case S11 and S22 are -10 and -8.8 dB, respectively, across the frequency band. The measured 1-dB compression point is +22 dBm at maximum-attenuation..
24. A. Gadallah, A. Allam, A. B. Abdel-Rahman, Hongting Jia, Ramesh Pokharel, A high-efficiency, low-power 2.4 GHz class AB PA for WBAN applications using load pull, 2017 Japan-Africa Conference on Electronics, Communications, and Computers, JAC-ECC 2017, 2018.03, [URL], A low-power, 2.4 GHz, class AB power amplifier (PA) for Wireless Body Area Network (WBAN) applications was designed using load-pull te chniques in TSM C 0.18 μm pr ocess. Measurement results show ed a power gain of 14 dB, an input return loss Su of -14.5 dB, and an output return loss S22 of -26 dB at 2.4 GHz. The PA achieved a maximum power-added efficiency (PAE) of39.5 % while delivering 9.5 dBm of power at an input 1 dB compression of-1 dBm. The PA consumed 6 mW from a 1.8V supply. In addition, a class F PA with maximum PAE of 47 % at 2.4 GHz was designed using the third harmonic peaking technique in T SMC 0.18 μm technology. Although class F PA achieved better PAE, it consumed 50% more area compared to the designed class AB PA..
25. Nusrat Jahan, Chen Baichuan, Ramesh Pokharel, Adel Barakat, A K-Band VCO Employing High Active Q-factor Defected Ground Structure Resonator in 0.18pm CMOS Technology, 2018 IEEE International Symposium on Circuits and Systems, ISCAS 2018, 2018.04, [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..
26. M. Aboualalaa, Adel B. Abdel-Rahman, A. Allam, Ramesh Pokharel, Kuniaki Yoshitomi, H. Elsadek, Compact 24GHz half-slot antenna for energy combining, 2018 International Applied Computational Electromagnetics Society Symposium in Denver, ACES-Denver 2018, 2018.05, [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..
27. Sumin Chalise, F. Tahar, M. R. Saad, A. Baraket, Kuniaki Yoshitomi, Ramesh Pokharel, High efficiency wireless power transfer system using spiral DGS resonators through biological tissues, 2018 IEEE/MTT-S International Microwave Biomedical Conference, IMBioc 2018, 2018.08, [URL], This paper presents a wireless power transfer (WPT) system to transfer power through the tissues using Defected Ground Structure (DGS) resonators. The proposed DGS resonator is made of a spiral structure at the ground plane to increase the quality (Q-) factor, and when two DGS resonators are coupled back to back, it transforms to a bandpass filter resulting in the wireless power transfer. Experiment on the proposed WPT system shows an efficiency of 67.7% in air and 61% when placed in the tissue environment at 20MHz frequency..
28. Ramesh Pokharel, Adel Barakat, Fairus Tahar, Sherif Hekal, Degree of freedom to select coupling coefficent and quality factor in near-field wireless power transfer
A case study of using DGS Structures, 2017 IEEE MTT-S International Microwave and RF Conference, IMaRC 2017, 2018.08, [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..
29. S. A.Enche Ab Rahim, Adel Barakat, Ramesh Pokharel, Design of 5.5GHz LC oscillator using distributed grid of N-well in P-substrate inductor, 2016 IEEE Asia Pacific Conference on Circuits and Systems, APCCAS 2016, 2017.01, [URL], This paper presents the design of low noise LC oscillator that employs an enhanced inductor, where a distributed grid of N-well in P-substrate of the inductor was design to improve the quality factor of the inductor, therefore improves the phase noise of the oscillator. The electromagnetic (EM) simulation shows that the total equivalent resistance of an inductor is reduced, which results in a higher quality factor. A 5.5GHz cross-coupled CMOS LC oscillator is designed by using this new inductor. Based on the simulation results, the oscillator shows an improvement of 0.7 dBc/Hz in phase noise at 1MHz offset from the carrier, which results a FOM of 189..
30. Hany A. Atallah, Adel B. Abdel-Rahman, Kuniaki Yoshitomi, Ramesh Pokharel, Compact frequency tunable filtenna with wide continuous tuning range using capacitively loaded folded arms open loop resonator for interweave cognitive radio applications, 33rd National Radio Science Conference, NRSC 2016, 2016.04, In this paper, a compact microstrip planar monopole antenna with a wide tunable frequency band is proposed and developed for interweave cognitive radio (CR) communication applications. Tunability is achieved by integrating a tunable folded arms open loop resonator bandpass filter with an ultra-widband (UWB) microstrip monopole antenna. The technique depends on centrally loading the folded arms open loop resonator with a single lumped varactor diode, decreasing the varactor capacitance results in increasing the miniaturized even resonant mode of the folded arms open loop resonator while keeping the odd-mode fixed. The filter-antenna is adaptable and compact in terms of the availability of several tunable bands. Moreover, the simple biasing of the varactor diode does not have a significant effect on the filtenna performance. Simulation results show that the proposed design is capable of tuning over a continuous wide operating band of 3.18 GHz covering a large band for interweave CR communication with a 52 % frequency tuning range from 4.6 to 7.8 GHz. Furthermore, the normalized radiation patterns are steady over the operating frequency bands. The frequency parameters and radiation patterns of the proposed filter-antenna are successfully optimized with numerical experimentation approaches using 3D full-wave electromagnetic simulator..
31. Hany A. Atallah, Adel B. Abdel-Rahman, Kuniaki Yoshitomi, Ramesh Pokharel, New compact tunable filter-antenna using varactor loaded ring resonator for cognitive radio front end system, IEEE/ACES International Conference on Wireless Information Technology, ICWITS 2016 and System and Applied Computational Electromagnetics, ACES 2016, 2016.05, In this paper, a novel compact filter-antenna with tunable frequency band is proposed and developed for interweave cognitive radio (CR) system. The antenna is fed by a microstrip line integrated with a ring resonator bandpass filter. Reconfiguration is achieved by centrally loading the ring resonator with only a single varactor diode. Furthermore, the simple biasing of the varactor diode has a small effect on the filter-antenna performance. The proposed design is fabricated and measured for verification purposes. Experimental results show that the proposed filter-antenna is capable of tuning over a wide operating band of 1.43 GHz covering continuous bands for interweave CR from 4.65 to 6.08 GHz. Moreover, the radiation patterns are stable over the operating frequency range. Good agreement is found between simulated and measured results..
32. Anwer S.Abd El-Hameed, Nessim Mahmoud, Adel Barakat, Adel B. Abdel-Rahman, Ahmed Allam, Ramesh Pokharel, A 60-GHz on-chip tapered slot Vivaldi antenna with improved radiation characteristics, 10th European Conference on Antennas and Propagation, EuCAP 2016, 2016.05, This paper presents a design of 60-GHz exponential tapered slot Vivaldi antenna-on-chip (AOC). The antenna is designed using standard 0.18μm six metal-layers CMOS technology. A double-Y balun feeding structure is used to make transition from coplanar waveguide to slot-line. Two techniques are investigated for improving antenna radiation properties. The first technique incorporates equal corrugations on the edges of exponential flaring section and other on the backed-edge of antenna to enhance the antenna gain. Second, a planar arc reflector is constructed using metal vias between M6 and M1 to inhibit the back lobe, contributing to the enhancement of gain and efficiency. The overall antenna size is compact and equal to 785μm×930μm. The influence of the antenna position on the radiation properties is also studied. The proposed antenna offers endfire radiation pattern with a simulated peak gain and a radiation efficiency of -0.4 dBi and 32%, respectively..
33. Elsayed Elsaidy, Adel Barakat, Adel B. Abdel-Rahman, Ahmed Allam, Ramesh Pokharel, Radiation performance enhancement of a 60 GHz CMOS Quasi-Yagi antenna, 17th IEEE Annual Wireless and Microwave Technology Conference, WAMICON 2016, 2016.06, This paper presents a study on 60 GHz CMOS Quasi-Yagi antenna for radiation performance enhancement. The driven element is meandered for size compactness and is fed by a coplanar waveguide to coplanar stripline transition. Moreover, the ground plan was corrugated to serve as the reflecting element. Furthermore, the director was designed from multi-element which led to gain and efficiency enhancement. Finally, the effect of the antenna location on the radiation characteristics was studied. The simulated gain and efficiency are-0.746 dBi and 21.4%, respectively at 60 GHz, and The design has an area of 1 × 0.87 mm2..
34. Hany A. Atallah, Adel B. Abdel-Rahman, Kuniaki Yoshitomi, Sherif Hekal, Ramesh Pokharel, Design of frequency tunable CPW-Fed UWB antenna using varactor diodes for cognitive radio and future software defined radio, 17th IEEE Annual Wireless and Microwave Technology Conference, WAMICON 2016, 2016.06, In this paper, a novel compact coplanar waveguide (CPW) ultra-wideband (UWB) antenna with an electronically reconfigurable band is developed for interweave cognitive radio (CR) system and future software defined radio (SDR). The center frequency of the tunable band can be electronically altered by adjusting the electrical length of the microstrip resonator at the bottom layer, which is accomplished by incorporating two varactor diodes at the resonator edges. Simulation results show that the proposed design is capable of tuning over a continuous wide operating band of 1.15 GHz covering a wide band for interweave CR communication from 4.54 to 5.69 GHz. Furthermore, the radiation patterns are steady over the interesting frequency bands. The proposed antenna is fabricated and measured at a fixed capacitance for verification purposes. Good agreement is found between the simulated and the measured results..
35. 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..
36. 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.
37. 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..
38. Nusrat Jahan, Adel Barakat, Ramesh Pokharel, Ku-band oscillator using integrated defected ground structure resonator in 0.18μm CMOS technology, 47th European Microwave Conference, EuMC 2017, 2017.12, In the paper, we propose a novel voltage-controlled oscillator (VCO) employing defected ground structure (DGS) band stop filter (BSF). The VCO operates from 15.24 GHz to 15.86 GHz. A square shaped DGS etched at the lowest metal layer (M1) below 50-Ohm microstrip line on the top metal layer (M6) of 0.18 μm 1P6M CMOS process. The proposed square-shaped DGS resonator achieves smaller size and higher quality factor than those of a conventional spiral inductor resonator at Ku band frequency. The power dissipation of the VCO is 4 mW. The measured carrier frequency and phase noise are 15.76 GHz and-127.57 dBc/Hz (104.25 dBc/Hz) at 10 MHz (1 MHz) offset frequency, respectively. The measured figure of merit (FoM) is 182.9 dB. The fabricated chip core VCO size is only 0.084mm2 which increases figure of merit (FoMa) to 194 dB..
39. Adel Barakat, Sherif Hekal, Ramesh Pokharel, Simple design approach for asymmetric resonant inductive coupled WPT systems using J-inverters, 2016 Asia-Pacific Microwave Conference, APMC 2016, 2017.05, 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 between the analytical design procedure, the circuit and the EM simulations, and the measurements. The measured efficiency is 75% at a transmission distance of 38 mm, and the sizes of the TX and RX are 50×50 mm2 and 30×30 mm2, respectively..
40. Ankit Goel, Abhishek Tomar, Navneet Kumar, Ramesh Pokharel, Low phase noise high switching ring VCO with quadrature output, 2016 Asia-Pacific Microwave Conference, APMC 2016, 2017.05, In this paper, novel two loop architecture of ring type voltage controlled oscillator (VCO) with low phase noise and low power dissipation in 0.18 μm CMOS technology is presented. To reduce phase noise and power dissipation, transistors in sub-feedback loop are operated in linear and cut off region and transistors in main loop of inverter are designed for fast switching with large voltage swing to minimize the switching current. The VCO has a frequency tuning range from 2.40 to 3.45GHz. The simulated result shows a phase noise of -107.56 dBc/Hz @ 1MHz offset from 2.6 GHz center frequency with a power consumption of 32 mW..
41. Omnia M. Nawwar, Hossam M.H. Shalaby, Ramesh Pokharel, Design and fabrication of a Bi-directional Mode-Division Multiplexer (BMDM) for optical interconnects, 30th Annual Conference of the IEEE Photonics Society, IPC 2017, 2017.11, A bi-directional mode-division multiplexer (BMDM) based on strip waveguides is presented. The device is fabricated and tested to prove the concept. Insertion losses less than −3.5 dB with crosstalks less than −15 dB are measured for all multiplexed modes at 1550 nm..
42. Nusrat Jahan, Adel Barakat, Ramesh Pokharel, Study of phase noise improvement of K-band VCO using additional series resonance realized by DGS resonator on CMOS technology, 2017 IEEE Asia Pacific Microwave Conference, APMC 2017, 2018.01, In this paper, we propose a K-band voltage controlled oscillator (VCO) using defected ground structure (DGS) that realizes the series resonant and parallel resonant characteristic. An H-shaped DGS etched at the lowest metal layer (M1) below microstrip line (MSL) on the top metal layer (M6) of 0.18 μm 1P6M CMOS process. The MSL is etched in the middle to realize series capacitance, which produces series resonance characteristics and sharpens the response of magnitude of Z11 (mag|Z11|). The proposed DGS resonator achieved smaller size and high quality (Q-) factor. The post-layout simulation result shows that VCO has a tuning range of 3.4%, and a low phase noise with -110.9 dBc/Hz @1 MHz offset at 21.02 GHz oscillation. The VCO consumes 7.5 mW power resulting in a FoM of 188.7 dB..
43. M. R. Saad, Fairus Tahar, Adel Barakat, Kuniaki Yoshitomi, Ramesh Pokharel, Analysis of near field wireless power transfer using bow-tie defected ground structure, 2017 IEEE Asia Pacific Microwave Conference, APMC 2017, 2018.01, This paper describes the design of a couple of a bow-tie Defected Ground Structure (DGS) resonator with high efficiency and compact size for near field Wireless Power Transfer (WPT) system. The proposed WPT is experimentally measured. The resonant frequency is at 0.26GHz, with low insertion loss, |S21| = -1.9dB and low return loss, |S11| < -17dB. The Measured result shows that the proposed WPT has a power efficiency of 65% at distance 10mm..
44. Anwer S.Abd El-Hameed, Adel Barakat, Adel B. Abdel-Rahman, Ahmed Allam, Ramesh Pokharel, Kuniaki Yoshitomi, Broadband printed-dipole antenna for future 5G applications and wireless communication, 2018 IEEE Radio and Wireless Symposium, RWS 2018, 2018.02, In this paper, a broadband printed dipole antenna (PDA) with improved radiation characteristics is presented for the next fifth-generation (5G) applications. A broadband integrated balun is used to feed the dipole, which consists of a folded microstrip line and an elliptical slot. Antenna radiation characteristics improvement is obtained thanks to triangle shaped dipole, which stimulates the electromagnetic fields to gather in the end-fire direction and consequently enhances the antenna gain. The proposed design is validated by experimental measurements. The designed antenna bandwidth covers from 26.3 to 40 GHz including the dual 5G bands of 28/38 GHz. The proposed antenna provides almost end-fire patterns, relatively flat gain, and high radiation efficiency through the frequency band..
45. Omnia M. Nawwar, Hossam M.H. Shalaby, Ramesh Pokharel, Design and fabrication of a Bi-directional Mode-Division Multiplexer (BMDM) for optical interconnects, 30th Annual Conference of the IEEE Photonics Society, IPC 2017, 2017.11, A bi-directional mode-division multiplexer (BMDM) based on strip waveguides is presented. The device is fabricated and tested to prove the concept. Insertion losses less than −3.5 dB with crosstalks less than −15 dB are measured for all multiplexed modes at 1550 nm..
46. 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..
47. 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.
48. 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..
49. 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..
50. 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..
51. I. L. Abdalla, A. Allam, JIA HONGTING, Ramesh Kumar Pokharel, A broadband high linearity inductorless CMOS variable gain amplifier for square kilometer array, 2015 International Conference on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design (SMACD), 2015.09, [URL], This paper presents a high-bandwidth 2 GHz CMOS variable gain amplifier (VGA) for using in the band of square kilometer array (SKA) range that achieves an 18 dB dynamic range (DR) while powered from a single 1.8 V supply. This VGA capability is obtained by employing a passive digital T-bridge attenuator followed by a fixed amplifier, the use of attenuator in the front end of the VGA results in a high linearity of 28 dBm to 34 dBm over the full DR. In contrast to traditional VGAs [5], [6], the VGA exhibits 30-50 dB more in DR while its bandwidth and IP3 extends below the presented..
52. 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.
53. 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..
54. 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..
55. 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.
56. 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.
57. 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..
58. 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..
59. A. Gadallah, A. B. Abdel-Rahman, Ramesh Kumar Pokharel, Hongting Jia, A High Efficiency 3-7 GHz Class AB CMOS Power Amplifier for WBAN Applications
, 2014 IEEE International Symposium on Radio-Frequency Integration Technology, 2015.08, [URL], The design of 3-7 GHz class AB two stages power amplifier (PA) for wireless body area network (WBAN) applications in TSMC 0.18 µm is presented. Source and Load-pull contours are employed in order to maximize power added efficiency. The post-layout simulation results of the proposed UWB-PA indicated that the power gain (S 21) is 12 dB ± 0.8; the input return loss (S 11) and the output return loss (S 22) are less than-10 dB and-11 dB respectively over the frequency range from 3 GHz to 7 GHz. In addition, The PA achieved maximum power added efficiency (PAE) of 38.5% at 5 GHz and an output 1-dB compression of 7.21 dBm at the same frequency. Moreover, a group delay variation of ± 32.5 ps was achieved through the frequency band of interest..
60. 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..
61. 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..
62. Haruichi Kanaya, 兼本 大輔, 吉田 啓二, POKHAREL RAMESH KUMAR, 吉富 邦明, Multi-Band Miniaturized Slot Antenna with Two-Stage Bandpass Filter,, IEEE International Symposium on Antennas and Propagation and USNC-URSI National Radio ScienceMeeting, 2013.07, [URL], This paper presents the design and implementation of
miniaturized slot antenna with two-stage impedance matching
circuit for 800MHz and 2GHz up/down link multiband application. Our proposed multi-band antenna is designed and simulated by using commercial three-dimensional electromagnetic (EM) field simulator. Also, we fabricated this multi-band antenna on FR4 substrate and measured the frequency characteristics. .
63. 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].
64. 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].
65. 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].
66. 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].
67. 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..
68. A. I. A. Galal, R. K. Pokharel, K. Uchida, H. Kanaya, and K. Yoshida, Ultra-wideband Low Noise Amplifier with Shunt Resistive Feedback in 0.18um CMOS Process, IEEE 10th Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems, 2010.01.
69. S. A. Z. Murad, R. K. Pokharel, K. Uchida, H. Kanaya, and K. Yoshida, A 2.4 GHz 0.18 um CMOS Class E Single-Ended Power Amplifier without Spiral Inductors, IEEE 10th Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems, 2010.01.
70. R. K. Pokharel, K. Uchida, H. Kanaya, and K. Yoshida, Low Phase Noise 18 kHz Frequency Tuning Step 5 GHz DCO Using Tiny Capacitors Based on Transmission Lines, IEEE 10th Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems, 2010.01.
71. H. Kanaya, N. Koga, M. A. Abdelghany, R. K. Pokharel, and K. Yoshida, Low Flicker-Noise and Low Leakage Direct Conversion CMOS Mixer for 5GHz Application, Proc. of 2009 Asia Pacific Microwave Conference (APMC), Singapore, December 2009. , 2009.12.
72. M. A. Abdelghany, R. K. Pokharel, H. Kanaya, and K. Yoshida, A Low Flicker Noise Direct Conversion Receiver for the IEEE 802.11a Wireless LAN Standard, Proc. of 2009 Asia Pacific Microwave Conference (APMC), Singapore, December 2009. , 2009.12.
73. H. Kanaya, K. Tsumura, R. K. Pokharel, H. Kanaya, K. Yoshida, A. Ishikawa, S. Fukagawa, and A. Tahira, Development of a One-Sided Directional Thin Planar Antenna with Quarter Wavelength Top Metal, Proc. of 2009 Asia Pacific Microwave Conference (APMC), Singapore, December 2009. , 2009.12.
74. H. Urabe, R. K. Pokharel H. Kanaya, K. Yoshida, A. Ishikawa, S. Fukagawa, A. Tahira, Design and performance of 800MHz/2GHz dual band small planar antenna, Proc. of 2009 Asia Pacific Microwave Conference (APMC), Singapore, December 2009. , 2009.12.
75. R. Dong, R. K. Pokharel, H. Kanaya, and K. Yoshida, An UWB Bandpass Filter with Large Notch Suppression, Proc. of 2009 Asia Pacific Microwave Conference (APMC), Singapore, December 2009. , 2009.12.
76. S. A. Z. Murad, R. K. Pokharel, H. Kanaya, and K. Yoshida, A 3.0-7.5 GHz CMOS UWB PA for Group 1~3 MB-OFDM Application Using Current-Reused and Shunt-Shunt Feedback, the first International Conference on Wireless Communications & Signal Processing, WCSP2009., 2009.11.
77. R. K. Pokharel, K. Uchida, H. Kanaya, and K. Yoshida, 10 Bit 2/5 GHz Dual Band Digitally-Controlled LC-Oscillator in 0.18 um CMOS Process, Proc. of 2009 Asia Pacific Microwave Conference (APMC), Singapore, December 2009. , 2009.12.
78. S. A. Z. Murad, R. K. Pokharel, H. Kanaya, and K. Yoshida, A 3.1 - 4.8 GHz CMOS UWB Power Amplifier Using Current Reused Technique, the 5th International conference on wireless communications, networking, and mobile computing networks, 2009.09.
79. R. K. Pokharel, H. Kanaya, and K. Yoshida, Low Phase Noise 10 bit 5 GHz DCO Using On-Chip CPW Resonator in 0.18 mm CMOS Technology, First Asian Himalayas International Conference on Internet AH-ICI2009, The next generation of mobile, wireless and Optical communications networks, 2009.11.
80. R. K. Pokharel, O. Nizhinik, H. Kanaya, and K. Yoshida, Wide Tuning Range CMOS Quadrature Ring Oscillator of Lowest Figure of Merit, 2009 IEEE European Microwave Integrated Circuits (EuMIC), 2009.09, [URL].
81. H. Kanaya, R. K. Pokharel, Y. Nakamura, and K. Yoshida, Development of one-sided thin planner antenna for 5GHz wireless communication applications, 20009 IEEE Symposium on Antenna and Propagation, 2009.06, [URL].
82. M. A. Abdelghany, R. K. Pokharel, H. Kanaya, and K. Yoshida, A low flicker noise high conversion gain RF-CMOS mixer with differential active inductor, Proc. of 2009 Korea-Japan Microwave Conference (KJMW), 2009.04.
83. Abhishek Tomar, R. K. Pokharel, Haruichi Kanaya, Keiji Yoshida, Design of Digitally Controlled LC Oscillator with Wide Tuning Range in 0.18um TSMC CMOS Technology, Design of Digitally Controlled LC Oscillator with Wide Tuning Range in 0.18um TSMC CMOS Technology, 2008.12.
84. A. I. A. Galal, R. K. Pokharel, H. Kanaya, and K. Yoshida, Comparison between Bipolar and NMOS Transistors in Linearization Technique at 5GHz Low Noise Amplifier, Proc. of 2008 Asia-Pacific Microwave Conference (APMC), 2008.12.
85. Y. Nakamura, H. Kanaya, R. K. Pokharel, and Keiji Yoshida, Design and performance of electrically small planar antennas with matching circuit at 2.4GHz band, Proc. of 2008 Asia-Pacific Microwave Conference (APMC) , 2008.12.
86. R. K. Pokharel, A. Tomar, H. Kanaya, and K. Yoshida, Design of Highly linear, 1GHz 8-bit digitally controlled ring oscillator with wide turning range in 0.18um CMOS process, The Proc. of China-Japan Microwave conference (CJMW), 2008.09.
87. R. K. Pokharel, A. I. A. Galal, O. Nizhnik, H. Kanaya and K. Yoshida, Design of flat gain and low noise figure LNA for 3.1-10.2GHz band UWB applications in 0.18um CMOS process, The 2008 IEEJ international workshop on AVLSI, 2008.07.
88. R. K. Pokharel, S. Sasaki, O. Nizhnik, H. Kanaya, and K. Yoshida, Design of VCO Using On-Chip CPW Resonator for 5 GHz-Band Wireless Applications, Proc. of 2008 Asia-Pacific Microwave Conference (APMC), 2008.12, [URL].
89. Oleg Nizhnik, Ramesh Pokharel, Haruichi Kanaya, Keiji Yoshida, High Dynamic Range Mixer in 0.18 um Technology for WLAN Direct Conversion Receiver , Proceedings of 2008 International Conference on Microwave and Millimeter Wave Technology (ICMMT 2008), 2008.04.
90. 中村優太・鍋嶋隆介・ポカレル ラメシュ・金谷晴一・吉田啓二, 片面指向性をもつ整合回路一体型平面アンテナの開発, 電子情報通信学会技術研究報告, 2008.04.
91. 佐々木慎一・今田明寛・ポカレル ラメシュ・金谷晴一・吉田啓二, 5.2GHz帯VCOの開発と高性能化の検討, 電子情報通信学会技術研究報告, 2008.04.
92. Haruichi Kanaya, Ryusuke Nabeshima, Ramesh Pokharel, Keiji Yoshida, Masato Tsujii, and Ryoichi Iino, Development of an Electrically Small One-Sided Directional Antenna with Matching Circuit, 2008 IEEE Radio and Wireless Symposium Proceedings, 2008.01.
93. R. K. Pokharel, A. Imada, S. Sasaki, H. Kanaya, and K. Yoshida, Design of VCO for 2.4GHz Wireless Applications Using Transmission Line Resonators, 2007APMC (2007 Asia-Pacific Microwave Conference) Proceedings, 2007.12.
94. H. Kanaya, T. Hashiguchi, R. K. Pokharel, and K. Yoshida, Study of A CPW-Fed Slot Dipole One-Sided Directional Antenna for UWB Systems, 2007APMC (2007 Asia-Pacific Microwave Conference) Proceedings, 2007.12.
95. H. Kanaya, R. Nabeshima, R. K. Pokharel, and K. Yoshida, Design and Performance of an Electrically Small Antenna with Matching Circuit, 2007APMC (2007 Asia-Pacific Microwave Conference) , 2007.11.
96. O. Nizhnik, R.K. Pokharel, H. Kanaya, and K. Yoshida, Design of High-Linearity Amplifier for Wireless LAN Transceiver, 2007APMC (2007 Asia-Pacific Microwave Conference), 2007.12.
97. A. Tomar, R. K. Pokharel, O. Nizhnik, H. Kanaya, and K. Yoshida, Design of 1.1 GHz Highly Linear Digitally-Controlled Ring Oscillator with Wide Tuning Range, IEEE International Workshop on Radio-Frequency Integration Technology, 2007.12.
98. Akihiro IMADA, Sangtae, KIM, Ramesh POKHAREL, Haruichi KANAYA and Keiji YOSHIDA, CPWインピーダンス回路を用いたRFフロントエンドLSIの設計・評価, 電子情報通信学会技術研究報告, 2007.04.
99. H. Kanaya, R. K. Pokharel, S. Kim, A. Imada, K. Yoshida, Design of Power Amplifier with On-Chip Matching Circuits using CPW Line Impedance (K) Inverters, 11th WSEAS International Conference on CIRCUITS, 2007.07.
100. H. Kanaya, R. K. Pokharel, , F. Koga, D. Arima, S. Kim, and K .Yoshida, Design of Coplanar Waveguide on-chip impedance matching circuit for wireless receiver front-end, IEEE Radio Frequency Integrated Circuit Conference (2006), 2006.06, [URL].
101. R. K. Pokharel and M. Ishii, Accuracy and Applications of Time-Domain Numerical Electromagnetic Code to Lightning Surge Analysis: Survey and Comparative Study in Time- and Frequency-Domain Codes, International Conference on Lightning Protection (ICLP), 2006, 2006.08.
102. R. K. Pokharel, H. Kanaya, and K. Yoshida, Development of high conversion gain double balanced mixer for high performance direct conversion receiver, 電子情報通信学会、ソサェティ大会, 2006.08.
103. H. Kanaya, R. K. Pokharel, K. Yoshida,, “Design of CMOS design circuit connected to a transmission line for high speed and low power optical switch,” China-Japan Joint Microwave Conferrence, 23-25 Aug, 2006., China-Japan Joint Microwave Conferrence, 23-25 Aug, 2006., 2006.08.
104. R. K. Pokharel, K. Wada, and O. Hashimoto, Improvement of out-of band characteristics of BPFs using partially coupled lines, Asia Pacific Microwave Conference (APMC'04), 2004.12.
105. R, K. Pokharel, K. Wada, O. Hashimoto, and T. Takahashi, Experimental study on LTCC resonators loaded with dielectric rods, 2005 IEEE International Symposium on AP-S/USRI, 2005.06.
106. R. K. Pokharel, M. Toyota, and O. Hashimoto, Comparative study of 5.8 GHz DSRC EM environment in a rectangular and semi-circular tunnel, 2005 IEEE International EMC Symposium, 2005.08.

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