九州大学 研究者情報
論文一覧
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/


原著論文
1. 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..
2. 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.
3. 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..
4. 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..
5. 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..
6. 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..
7. 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..
8. 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, [URL], 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..
9. Mohamed Aboualalaa, Islam Mansour, Hala Elsadek, Adel B. Abdel-Rahman, Ahmed Allam, Mohammed Abo-Zahhad, Kuniaki Yoshitomi, Ramesh K. Pokharel, Independent Matching Dual-Band Compact Quarter-Wave Half-Slot Antenna for Millimeter-Wave Applications, IEEE Access, 10.1109/ACCESS.2019.2940273, 7, 130782-130790, 2019.01, [URL], A dual-band mm-wave compact antenna is proposed in this paper. A quarter-wave half-slot resonator is used instead of a half-wave slot to achieve miniaturization of the antenna size. The antenna consists of two stacked half-slot resonators to radiate at two frequencies, f1=24GHz and f2=28.5GHz, with the same microstrip line feed. By using this stacked structure, a dual-band is obtained and the two resonant frequencies become independently matched with a minor effect on each other. Measurements show the proposed antenna has an impedance bandwidths of 6.3% and 15% at f{1} and f{2} , respectively; furthermore, the antenna has good radiation characteristics. The antenna gains in addition to the radiation efficiencies at f{1} and f{2} , are 3.5dBi , 92%, 4dBi , and 95% respectively. The equivalent circuit model for the proposed antenna is introduced to show the electrical behavior of the antenna. Finally, the antenna design is inserted in multiple-input multiple-output (MIMO) system. The proposed antenna is analyzed and optimized using ANSYS HFSS EM simulator and its equivalent circuit is performed by Agilent Advanced Design System (ADS). The simulated as well as measured results show good agreement. The designated antenna resembles good candidate for 5G wireless communication systems..
10. 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, [URL], 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..
11. Nusrat Jahan, Adel Barakat, Ramesh K. Pokharel, A −192.7-dBc/Hz FOm Ku-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, [URL], 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 KU-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..
12. 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, [URL], 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..
13. 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, [URL], 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..
14. 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, [URL], 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..
15. 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.
16. 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, [URL], 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 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..
17. Manal M. Mohamed, Ghazal A. Fahmy, Adel B. Abdel-Rahman, Ahmed Allam, Adel Barakat, Mohammed Abo-Zahhad, Hongting Jia, Ramesh Pokharel, High-Efficiency CMOS RF-to-DC Rectifier Based on Dynamic Threshold Reduction Technique for Wireless Charging Applications, IEEE Access, 10.1109/ACCESS.2018.2866457, 6, 46826-46832, 2018.08, [URL], This paper presents a high-efficiency CMOS rectifier based on an improved dynamic threshold reduction technique (DTR). The proposed DTR consists of a clamper circuit that biases the gates of pMOS diode switches through a capacitor and diode-connected pMOS transistor. The clamper is used to insert a negative dc level to the input RF signal; therefore, more negative RF signal can be obtained to bias the gates of the main rectifying pMOS devices during its conduction phase. This mechanism reduces the threshold voltage of the main pMOS transistors and increases their sensitivity to the RF input signal. The proposed rectifier is implemented in a 0.18-μm CMOS technology and tested. The measurement shows a peak power conversion efficiency of 86% and an output voltage of 0.52 V at an input power of-16.5 dBm and an input frequency of 402 MHz. The core area of chip excluding measurement pads is 0.024 mm
2.
18. Omnia M. Nawwar, Hossam M.H. Shalaby, Ramesh Pokharel, Photonic crystal-based compact hybrid WDM/MDM (De)multiplexer for SOI platforms, Optics Letters, 10.1364/OL.43.004176, 43, 17, 4176-4179, 2018.09, [URL], A compact hybrid wavelength- (WDM) and mode-division (de)multiplexer (MDM) is proposed, and its performance is evaluated. The design of the device is based on 2D photonic crystals with a square lattice and Si rods. The device can multiplex two eigenmodes, TM
0
and TM
1
, and two wavelengths, 1550 and 1300 nm. Two identical multimode interference couplers and an asymmetric directional coupler are used in implementing both the wavelength- and mode-division multiplexing functions, respectively. To avoid back-reflections, tapers are used at waveguide junctions. The structure is compact with dimensions of 29 μm × 12 μm, which is suitable for on-chip integration. Simulation results reveal that the insertion losses and crosstalks are less than −1.0927 and −11.9024 dB, respectively, for all four channels..
19. Hany A. Atallah, Adel B. Abdel-Rahman, Kuniaki Yoshitomi, Ramesh 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, 10.1017/S1759078717001556, 10, 4, 487-496, 2018.05, [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..
20. Nessim Mahmoud, Adel Barakat, Mohamed E. Nasr, Ramesh Pokharel, Performance enhancement of 60 GHz CMOS band pass filter employing oxide height virtual increase, Progress In Electromagnetics Research M, 10.2528/pierm18101608, 77, 125-134, 2019.01, [URL], A high selectivity compact size coupled open-loop resonator (OLR-) band pass filter (BPF) in 0.18 µm TSMC Complementary Metal Oxide Semiconductor (CMOS) with low insertion (IL) is presented in this manuscript. First, shape optimization and folding are used to guarantee compact size. Then, high performance of the proposed BPF is obtained by virtually increasing the height of the oxide between the OLR’s traces and their ground plane. This virtual increase in the oxide height is realized by etching large slot areas below each of the OLRs. Consequently, the traces are characterized by wider width which in return exhibit lower attenuation constant and hence lower IL. The simulated and measured responses have a very good agreement. The fabricated BPF shows an IL of 3.5 dB at 59 GHz with a return loss of 15 dB and a fractional bandwidth of 16.5%. The fabricated chip has an area of 378 × 430 µm
2
including the measurements pads..
21. Basma E. Abu-Elmaaty, Mohammed S. Sayed, Ramesh Pokharel, Hossam M.H. Shalaby, General silicon-on-insulator higher-order mode converter based on substrip dielectric waveguides, Applied Optics, 10.1364/AO.58.001763, 58, 7, 1763-1771, 2019.03, [URL], A general silicon mode-converter waveguide that converts a fundamental mode to any higher-order mode is proposed. Specifically, dielectric substrip waveguides are inserted in the fundamental mode propagation path so that the conversion is done directly in the same propagation waveguide, without coupling the power into another waveguide as it happens in traditional mode converters. The device has a very small footprint compared to traditional converters. A mathematical model is developed to determine the design parameters of the used dielectric material and analyze the whole performance of the proposed device. Both the effective index method (EIM) and the perturbative mode-coupled theory are used in our mathematical analysis to get exact values for both the coupling coefficient and the length of the used dielectric material, so as to ensure a maximum coupled power transfer to the higher-order mode. In addition, full vectorial 3D-FDTD simulations are performed to validate our mathematical model. Our results show good agreement between the approximate EIM method and accurate full vectorial 3D-finite-difference time-domain (FDTD) simulations in characterizing the device parameters and performance. In order to validate the design model, two mode converters are simulated, fabricated, and tested for converting a fundamental TE
0
mode into both first- and second-order (TE
1
and TE
2
) modes, respectively. Good insertion losses and low crosstalks are obtained. Good agreement between simulated and fabricated results are achieved..
22. 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, [URL], 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..
23. 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..
24. Ibrahim L Abdalla, Hongting Jia, Ramesh K Pokharel, A DC-2.5 GHz high linearity CMOS attenuator in a 0.18 µm technology, Procedia Manufacturing, 22, 591-597, 2018.11, [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..
25. 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)..
26. 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..
27. #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..
28. 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..
29. 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..
30. 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..
31. 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..
32. Omnia M. Nawwar, Hossam M.H. Shalaby, Ramesh Pokharel, Modeling, simulation, and fabrication of bi-directional mode-division multiplexing for silicon-on-insulator platform, Applied Optics, 10.1364/AO.57.000042, 57, 1, 42-51, 2018.01, [URL], A strip waveguide-based bi-directional mode-division multiplexer is proposed. A mathematical model has been proposed to analyze the performance, and the results are simulated. The design concept of this device to (de) multiplex three modes simultaneously has been studied previously for slab waveguides, both mathematically using the perturbative mode-coupled theory and by simulation using 2D FDTD Solutions (FDTD, finite difference time domain). As slab waveguides are not suitable for extracting fabrication parameters for most silicon-on-insulator applications, we apply the concept to a more practical device that involves strip waveguides rather than slab waveguides. The effective index method (EIM) has been used to develop the mathematical model and to get approximate forms for both the profiles and coupling coefficients. The return loss of different modes is taken into consideration to fully characterize the device performance. Simple formulas for both insertion and return losses of all multiplexing modes have been derived. In addition, full vectorial 3D FDTD simulations are performed so as to validate our mathematical model. Different design parameters have been used to get numerical results of the proposed device. Our results reveal that the EIM has enough accuracy to characterize the performance of our device compared to that of the complex full vectorial simulation. In order to validate the used model, the device has been fabricated and tested. Good insertion losses and crosstalks for all modes have been obtained..
33. 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..
34. Hany A. Atallah, Adel B. Abdel-Rahman, Kuniaki Yoshitomi, Ramesh Pokharel, CPW-Fed UWB antenna with sharp and high rejection multiple notched bands using stub loaded meander line resonator, AEU - International Journal of Electronics and Communications, 10.1016/j.aeue.2017.08.022, 83, 22-31, 2018.01, [URL], This paper presents a CPW-fed UWB filter-antenna with sharp and high rejection multiple band notches for band-notched UWB communication applications. The band notch operation is achieved by employing a sharp bandstop filter (BSF) with multiple reject bands using only one element meander line resonator at the bottom layer through theoretical calculations and parametric studies. The adjustment of the notched bands is successfully accomplished by loading the meander line with open ended stubs to modify the harmonic frequencies to the desired bands. The structure of the proposed BSF is simple and compact so that the proposed filter-antenna is achieved with the same size of the reference UWB antenna without an extra area. Measurement results show that the proposed filter-antenna has two notches at the WiMAX systems operating in the 5.8 GHz (5.725–5.85 GHz) and at the international telecommunication union (ITU) operating in the 8.2 GHz (8.025–8.4 GHz). Also, it has sharp rejection characteristics at the edges of the federal communication commission (FCC) band for UWB communications. The experimental measurements are in good agreement with theoretical and simulation results for the BSF and the filter-antenna. Moreover, the filter-antenna exhibits stable omnidirectional radiation patterns except at the notched bands..
35. POKHAREL RAMESH KUMAR, Class-C architecture for cross-coupled FBAR oscillator to further improve phase noise, IEICE Electronics Express, 10.1587/elex.14.20170056, 14, 5, 1-5, 2017.03, [URL], In this letter, a class-C architecture for an oscillator employing
film bulk acoustic resonator (FBAR) is presented to improve the phase noise
significantly in 1/f 3 region. The advantages offers by class-C operation are
exploited in order to reduce the noise contributed by the current-source
transistor in cross-coupled topology. An adaptive biasing circuit is used in
order to ensure the oscillation start-up. The post-layout simulation incorporating
all parasitic and representing FBAR by modified Butterworth
Van Dyke (MBVD) model illustrates the phase noise improvement by
17 dBc/Hz at 100 kHz offset of a 1.9 GHz carrier compared to the FBAR
based cross-coupled topology presented by the authors [1].
36. 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..
37. Atallah, Hany A, Ahmed Allam, Kuniaki Yoshitomi, Ramesh Kumar Pokharel, Mutual Coupling Reduction in MIMO Patch Antenna Array Using Complementary Split Ring Resonators Defected Ground Structure, APPLIED COMPUTATIONAL ELECTROMAGNETICS SOCIETY JOURNAL, 31, 7, 737-743, 2016.07.
38. Adel Barakat, Ramesh Kumar Pokharel, Miniaturized low loss 60 GHz CMOS mixed coupled BPF with patterned ground shield, MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, 10.1002/mop.29650, 58, 3, 697-699, 2016.03.
39. 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 ....
40. 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.
41. 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..
42. 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.
43. 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.
44. 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..
45. 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..
46. 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. .
47. 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..
48. 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..
49. 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..
50. 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..
51. 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%..
52. 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.
53. 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.
54. Toru Okazaki, Kanemoto Daisuke, POKHAREL RAMESH KUMAR, 金谷 晴一, A design methodology for SAR ADC optimal redundancy bit, IEICE Electronics Express , Vol. 11 (2014), No. 10, 1-6, 2014.04.
55. 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.
56. 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.
57. 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.
58. POKHAREL RAMESH KUMAR, 金谷 晴一, G. Zhang, A. Anand, A 1.9 GHz Low Phase Noise Complementary Cross-coupled FBARVCO in 0.18 um CMOS Technology, Proc. 44th European Microwave Conference, 253-256, 2014.10, A 1.9 GHz film bulk acoustic resonator (FBAR) based complementary cross-coupled voltage-controlled oscillator (VCO) designed in 0.18 μm CMOS is presented. DC latch and low frequency instability problems have been solved by the cross-coupled pairs with DC block capacitors. The open loop gain has been analyzed and optimized by considering the effect of transistors' size on enhancement of the stability at low frequencies and the loop gain at the desired oscillation frequency. The optimization of the phase noise has been done by considering the effect of PMOS transistors' size on the quality (Q-) factor and the impedance of FBAR. The final fabricated chip is packaged in dual in-line package (DIP) and the measured performance shows that the proposed FBAR-VCO achieves a phase noise of -148 dBc/Hz at 1 MHz offset with a figure of merit (FOM) of -212 dBc/Hz..
59. K. I. Yousef, 金谷 晴一, POKHAREL RAMESH KUMAR, A 0.18 CMOS Current Reuse Ultra-Wideband Low Noise Amplifier (UWB-LNA) with Minimized Group Delay Variations, Proc. 44th European Microwave Conference, 1392-1392, 2014.10.
60. Y. Esaki, POKHAREL RAMESH KUMAR, 金谷 晴一, Design of a Tunable CMOS PA for TV White Space Application, 2014 Korea-Japan Microwave Workshop., 1, 1-4, 2014.12.
61. 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%..
62. 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.
63. 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.
64. 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.
65. 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.
66. 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..
67. 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.
68. POKHAREL RAMESH KUMAR, Dayang A.A. MAT, DONG RUIBING, 金谷 晴一, 吉田 啓二, 60 GHz Millimeter-Wave CMOS Integrated On-Chip Open Loop Resonator Bandpass Filters on Patterned Ground Shields, IEICE TRANSACTIONS on Electronics, Vol E-96, No. 2, 270-276, 2013.02, This paper presents the design of second-order and fourth-order bandpass filters (BPFs) for 60 GHz millimeter-wave applications in 0.18 μm CMOS technology. The proposed on-chip BPFs employ the folded open loop structure designed on pattern ground shields. The adoption of a folded structure and utilization of multiple transmission zeros in the stopband permit the compact size and high selectivity for the BPF. Moreover, the pattern ground shields obviously slowed down the guided waves which enable further reduction of the physical length of the resonator, and this, in turn, results in an improvement of the insertion losses. A very good agreement between the electromag¬netic (EM) simulations and measurement results has been achieved. As a result, the second-order BPF has the center frequency of 57.5 GHz, insertion loss of 2.77 dB, bandwidth of 14 GHz, return loss less than 27.5dB and chip size of 650 μm x 810 μm (including bonding pads) while the fourth-order has the center frequency of 57 GHz, insertion loss of 3.06 dB, bandwidth of 12 GHz, return loss less than 30 dB with chip size of 905 μm x 810 μm (including bonding pads), respectively..
69. 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..
70. 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.
71. 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.
72. 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.
73. 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.
74. 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.
75. 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.
76. 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.
77. 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.
78. 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].
79. O. Hashimoto and R. K. Pokharel, Analysis of error due to exclusion of higher modes on complex permittivity measurement using waveguide with flange, Trans. of IEICE, vol. E88-C, no. 1, pp. 139-142., 2005.01.
80. 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.
81. 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].
82. K. Suga, O. Hashimoto, R. K. Pokharel, and K. Wada, Analysis of temperature distribution and absorption characteristics of single layer radio wave absorber, IEEE Trans on Electromagnetic Compatibility, vol. 47, no. 3, pp. 866-871., 2005.11.
83. 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].
84. 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].
85. 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.
86. 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.
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, Realization of attenuation poles, spurious resonance Suppression and size reduction by microstrip SIR loaded with dielectric rods, IEICE Trans. on Electronics, 10.1093/ietele/e88-c.12.2302, vol. E88-C, no. 12, 2302-2309, 2005.12.

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