PIER C | PIER Journals

2026-01-25

PIER C

Vol. 165, 108-117, 2026

doi:10.2528/PIERC25111801

download: 43

High-Efficiency Broadband GaN Power Amplifier with Algorithmic Gate-Bias Optimization

Ahmed Elrefaey, Fathi A. Faragb, Azhar A. Hamdi and Amir Almslmany

Achieving simultaneous wideband operation and high output power efficiency remains a major challenge in modern GaN HEMT power amplifier (PA) design, particularly for broadband communications and radar systems. This paper presents a systematic design methodology for a broadband PA that integrates radial-stub (RS)-based bias/matching networks with an algorithmic gate-bias (V_GS) optimization, alongside load-pull-derived device termination and compact layout. Starting with theWolfspeed CMPA0530002S GaN HEMT, which features intrinsic broadband stability and an integrated input match, we replace conventional narrowband bias lines with a radial-stub network that ensures broadband bias isolation and low-loss matching. A thorough load-pull study identifies the optimum load impedance for concurrent maximization of power-added efficiency (PAE), gain, and output power. Subsequently, an automated V_GS sweep across the full 1.16-1.6 GHz band determines the optimal bias point for broadband and efficiency trade-off. The PA achieves a simulated result of output power of 34.28 dBm , flat gain of approximately 13.28 dB, and a peak PAE of 58.69% in a fractional bandwidth of 37% (1.16-1.6 GHz). A key novelty of this work lies in the proposed algorithmic V_GS sweep technique, which enables optimization of broadband efficiency throughout the entire 1.16-1.6 GHz operating band and can be easily extended to other frequency ranges. Unlike conventional bias optimization methods that are limited to a single frequency, the proposed algorithm systematically identifies the optimal gate bias across multiple frequencies to maintain high efficiency and consistent output power over a wide bandwidth. The simulated results confirm that this algorithmic bias optimization approach achieves superior broadband efficiency and stable output performance, providing a scalable and adaptable design methodology for next-generation wireless communication and electronic warfare systems.

High-Efficiency Broadband GaN Power Amplifier with Algorithmic Gate-Bias Optimization

2026-01-25

PIER C

Vol. 165, 97-107, 2026

doi:10.2528/PIERC25112602

download: 12

Compact Four-Port Conformal MIMO Antenna with Asymmetric Ground for Wideband X-Band Applications

Velraju Prithivirajan, Kannan Vishnulakshmi, Palaniselvan Sundaravadivel, Muthu Manickam Anbarasu, Dhanushkodi Siva Sundhara Raja and Dhandapani Rajeshkumar

This paper presents a compact four-port conformal multiple-input multiple-output (MIMO) antenna designed on a 0.1-mm-thick transparent flexible polyimide substrate for wideband X-band wireless applications. Each antenna element is composed of an annular ring radiator and an asymmetric coplanar ground to achieve low mutual coupling and high diversity performance. The proposed MIMO antenna covers an impedance bandwidth of 7.9-14 GHz, with isolation greater than 20 dB and a maximum reflection coefficient of 32.5 dB at 10.5 GHz. The experimental results are in good agreement with the simulated results in terms of reflection, transmission, and radiation characteristics. The measured gain ranges from 4.5 to 6 dBi, with stable radiation patterns across the operating band. The MIMO performance metrics, including the envelope correlation coefficient (ECC = 0.002), diversity gain (≈10 dB), channel capacity loss (<0.3 bits/s/Hz), and total active reflection coefficient (TARC), confirm the suitability of the design for robust high-data-rate communication. Furthermore, the antenna maintains stable operation under various bending configurations, ensuring its potential for X-band conformal and wearable applications.

Compact Four-Port Conformal MIMO Antenna with Asymmetric Ground for Wideband X-Band Applications

2026-01-24

PIER C

Vol. 165, 89-96, 2026

doi:10.2528/PIERC25121602

download: 18

CSRR-Loaded Reconfigurable SIW Bandpass Filter Using PIN Diodes for S-Band and 5G n79/C-Band Applications

Amjad A. Al-Rahmah and Bashar J. Hamza

Modern wireless systems require filters that can tune multiple bands independently, but conventional designs cannot achieve this and suffer from limited flexibility and higher loss. The proposed filter solves this problem by providing compact, low-loss, and independently reconfigurable dual-band operation for multi-standard applications. Therefore, in this paper, a reconfigurable substrate-integrated waveguide bandpass filter is proposed. The filter is suitable for a broad range of wireless applications. The first band has a centre frequency of 2.7 GHz and attains a tuning percentage of 13.4%. The second band achieves 26.35% at a centre frequency of 4.7 GHz. The lower band targets S-band applications, whereas the upper band is appropriate for 5G band n79 applications and can be reconfigured to cover the C-band. The proposed design has complementary split-ring resonator slots on the top layer with four p-i-n diodes. It has compact dimensions of 0.21λ_g × 0.48λ_g, a minimal insertion loss of less than 1 dB, and a substantial return loss of 14 dB. Advanced design methods, including eigenmode analysis, are used to attain precise selectivity and computation of the coupling matrix. The filter demonstrates superior performance and guarantees low interference, with suppression up to 9 GHz. A prototype filter was fabricated and measured, with the results closely agreeing with the simulations.

CSRR-Loaded Reconfigurable SIW Bandpass Filter Using PIN Diodes for S-Band and 5G n79/C-Band Applications

2026-01-23

PIER C

Vol. 165, 79-88, 2026

doi:10.2528/PIERC25110401

download: 36

An Improved Equivalent-Input-Disturbance Method Based on Enhanced Estimators for Wideband Disturbance Suppression in PMSM

Jiacheng Tong, Kaihui Zhao, Yunzhen Chen, Jinnan Cao, Youzhuo Duan and Jie Xiong

This paper presents an improved equivalent-input-disturbance (IEID) method based on enhanced estimators. This method addresses the degradation performance in a permanent magnet synchronous motor (PMSM) drive system caused by multi-source disturbances in different frequency bands. First, a PMSM model is established that considers these disturbances and categorizes them as control inputs for both current and speed-loops. Next, the estimated compensation structures of the dual-loop equivalent-input-disturbance (EID) are designed. To address the differing sensitivities of the dual-loop anti-disturbance frequency bands, enhanced estimators are designed to expand their respective bandwidths. This reduces the sensitivity of the system to uncertainty, and parameter-adjusting conditions are derived to ensure stability. Finally, the simulation results demonstrate that, when PMSM operates under the nominal condition, the IEID method suppresses steady-state speed fluctuation by approximately 63% compared to the method without EID compensation, by approximately 35% compared to the conventional EID method, and by approximately 25% compared to improved sliding mode observer-based EID (ISMO-EID) method; when PMSM parameters are perturbed, the suppression rates can further reach to 65%, 44%, and 32%, respectively. The findings indicate that the proposed method exhibits superior steady-state tracking accuracy and disturbance suppression performance, while also exhibiting enhanced robustness in transient scenarios.

An Improved Equivalent-Input-Disturbance Method Based on Enhanced Estimators for Wideband Disturbance Suppression in PMSM

2026-01-21

PIER C

Vol. 165, 68-78, 2026

doi:10.2528/PIERC25082003

download: 77

High-Resolution Brain Source Localization for BCI Applications Using a Deep Learning-Based Direct Inversion Approach on EEG Data

Babak Ojaroudi Parchin, Mehdi Nooshyar and Mohammad Ojaroudi

This paper presents a novel high-resolution brain source reconstruction method for Brain-Computer Interface (BCI) applications using a deep learning-based direct inversion approach. The proposed framework integrates electroencephalography (EEG) data simulated via the FieldTrip toolbox and leverages a modified U-Net architecture trained to directly estimate the active and inactive cortical source regions. Unlike traditional inverse methods such as Minimum Norm Estimation (MNE), LORETA, and Lasso the proposed method bypasses the computational complexity of analytical solutions and offers faster inference times once trained. Experimental results using a database of 50,000 synthetic models demonstrate a reconstruction accuracy of up to 61.66% under optimized conditions, with a validation loss of 0.6372 and an F1 score of 61.12%. The method shows improved detection of active brain regions in central cortical areas and delivers robust spatial reconstructions compared to conventional numerical techniques. Although performance on certain edge cases remains limited, the proposed framework offers a promising direction for scalable, real-time source localization in diagnostic and neurorehabilitation applications.

High-resolution Brain Source Localization for BCI Applications Using a Deep Learning-based Direct Inversion Approach on EEG Data

2026-01-21

PIER C

Vol. 165, 61-67, 2026

doi:10.2528/PIERC25102703

download: 52

GPR-SAR Imaging of Underground Pipelines Using Adaptive Threshold-Enhanced CBP Algorithm

Qiang Guo, Peng-Ju Yang, Rui Wu and Yuqiang Zhang

An adaptive threshold enhanced-Cross-correlation Back Projection (CBP) imaging algorithm is presented for artifacts suppression and accuracy improvement of Synthetic Aperture Radar (SAR) imaging in Ground Penetrating Radar (GPR) applications. B-Scan profiles of underground pipelines are obtained by using the open-source GprMax simulator, and they are then preprocessed with the method of background subtraction to remove direct waves. Adaptive threshold scheme using Hilbert transform is adopted to obtain the envelopes of B-Scan profiles after removing direct waves. GPR-SAR imaging of underground pipelines is simulated and discussed in detail for different pipe parameters and soil environment. The simulated results demonstrate that the adaptive threshold enhanced-CBP algorithm achieves focused pipeline images with sub-wavelength localization accuracy, enabling geometric contour reconstruction for non-metallic pipelines with strong robustness in Peplinski's soil and multiple target scenarios.

GPR-SAR Imaging of Underground Pipelines Using Adaptive Threshold-Enhanced CBP Algorithm

2026-01-20

PIER C

Vol. 165, 48-60, 2026

doi:10.2528/PIERC25092906

download: 71

Design and Fabrication of a New Triple-Band Bandpass Filter with Adjustable Bandwidth Passbands Depending on Coupling

Obaida Oulad Haddar, Mohammed Boulesbaa and Tarek Djerafi

In this research, a simple design with a compact size of a triple-band bandpass filter (BPF) based on SIW is proposed. The proposed design consists of a main SIW cavity combined with two others-secondary SIW cavities. The three passbands of the proposed BPF are formed based on the center frequencies (CFs) of the four modes given by the main SIW cavity and two transmission poles (TP₁ and TP₂) achieved with the secondary SIW cavity. The SIW modes achieved with the main SIW cavity are TE₁₀₁, TE₂₀₁, and TE₃₀₁ addition to the suppressed mode, and those modes are realized by the perturbation of seven metallic vias. The coupling of the TP₁ with the suppressed mode realizes the first passband of the filter proposed with a bandwidth of 0.53 GHz. Vertical CPW slots are etched at the main SIW cavity for coupling TE₁₀₁ and TE₂₀₁ to form the second passband with a bandwidth of 1.3 GHz. Horizontal CPW slots are etched in the two rectangular secondary SIW cavities to join the TP₂ with TE₃₀₁ mode for realizing the third passband with a bandwidth of 1.2 GHz. Finally, an adjustable bandwidth filter with CFs of 6.9/10.1/13.3 GHz, respectively, has been achieved. Also, six transmission zeros (TZs) are achieved in the operation frequency range (6-16 GHz), which improves the selectivity of the filter. The proposed filter is modeled with an approximate equivalent circuit, and the prototype of the filter is fabricated and tested to demonstrate its excellent performance. A good agreement was realized among simulation, equivalent circuit LC model, and measurement S-parameters, which proves and validates the operation of the proposed triple-band BPF. The multiple advantages of the proposed filter, such as a simple structure, compactness (1.29λ_g × 1.62λ_g), selectivity, and high performance, make it a promising candidate for multi-tasking communication systems.

Design and Fabrication of a New Triple-Band Bandpass Filter with Adjustable Bandwidth Passbands Depending on Coupling

2026-01-20

PIER C

Vol. 165, 35-47, 2026

doi:10.2528/PIERC25100103

download: 67

Corporate-Fed Inclined Patch Arrays for Meteorological Direct Broadcast Reception

Paramasivam Jothilakshmi and Rajendran Mohanasundaram

This work codesigns and validates a compact microstrip patch array with a corporate feed for meteorological direct broadcast at 7.5 GHz, comparing 1×4 to 1×64 arrays. Square patches with rounded corners are rotated 45° to suppress modes, reduce coupling, and preserve broadside radiation. The feed network delivers equal amplitude to four ports. A neural network surrogate trained on full-wave samples accelerates exploration of edge length, corner radius, spacing, rotation, and feed-line dimensions while enforcing limits on S₁₁ and coupling. The 1×4 prototype uses Rogers RT Duroid 5880, ε_r 2.2, thickness 0.787 mm, with a substrate size of 120 mm by 75 mm. Photolithography and anechoic measurements confirm a 7.5 GHz center frequency, broadside radiation, peak gain above 14 dBi, and a 450 MHz bandwidth. Scaling to 1×64 shows 3 dB gain per doubling, reduced beamwidth, stable bandwidth, and coupling; sensitivity studies verify robustness.

Corporate-fed Inclined Patch Arrays for Meteorological Direct Broadcast Reception

2026-01-18

PIER C

Vol. 165, 25-34, 2026

doi:10.2528/PIERC25120101

download: 73

Optimized NCP MIMO Antenna with Dual Diamond Slots for Enhanced Isolation in 5G Applications

Rama Lakshmi Gali and Madhavi Tatineni

This research paper presents a novel two-element Notched Circular Patch (NCP) antenna tailored for n78 5G NR band communication, resonating at a frequency of 3.5 GHz. The primary focus of this study is to enhance isolation using a simple antenna design with advanced optimization techniques. The proposed NCP antenna incorporates two diamond-shaped slots within a circular patch, designed to operate at n78 band or C-band. Through meticulous design and fabrication processes, the antenna achieves an inter-element spacing that is optimized with GA algorithm, and 1/4 of the ground structure is considered at the center of the patch, significantly improving its performance at 3.5 GHz, maintaining a VSWR of 1.1. The proposed 60 × 30 mm² NCP antenna exhibits remarkable characteristics, including > -30 dB isolation, a reflection coefficient of -27 dB, and a gain of 4 dBi. These results underscore the effectiveness of the antenna design in reducing mutual coupling and enhancing isolation, which are essential for achieving reliable and efficient communication in 5G. The NCP MIMO antenna is thoroughly analyzed using characteristic mode analysis (CMA), and CMA parameters' influence on antenna performance is discussed. The design further highlights its practicality and potential for implementation in various wireless communication systems.

Optimized NCP MIMO Antenna with Dual Diamond Slots for Enhanced Isolation in 5G Applications

2026-01-18

PIER C

Vol. 165, 18-24, 2026

doi:10.2528/PIERC25111306

download: 45

Transmission-Line Dual-Band Absorptive Bandstop Filter with Two Input Lossy Step-Impedance Stubs

Jiapei Dong, Xiaoying Zuo, Mengxin He, Yajian Li, Juntao Cao and Zelin Sun

In this paper, a novel planar dual-band absorptive bandstop filter (ABSF) based on transmission lines is proposed. The filter structure is composed of multiple transmission lines and two chip resistors, which endows it with distinct advantages including multiple transmission zeros, high-selectivity dual-bandstop performance. Through formula derivations, the specific positions of the four transmission zeros within the operating frequency are precisely determined. Experimental measurement results demonstrate that the -10 dB fractional bandwidth of the first stopband is 50.27% (from 0.7 GHz to 1.17 GHz), while that of the second stopband reaches 13.18% (from 3.33 GHz to 3.8 GHz). Across the entire frequency, the insertion loss S₂₁ achieves a minimum of -45.20 dB at 1 GHz, and the return loss S₁₁ attains a maximum of -10.27 dB at 3.94 GHz. The physical dimensions of the filter are 102 mm × 26 mm (0.77λ₀ × 0.20λ₀).

Transmission-line Dual-band Absorptive Bandstop Filter with Two Input Lossy Step-impedance Stubs

2026-01-16

PIER C

Vol. 165, 11-17, 2026

doi:10.2528/PIERC25101503

download: 59

An Asymmetric Miniaturized Single-Layer Bandpass Filter Based on Interdigital Capacitors and Microstrip Inductors

Juntao Cao, Xiaoying Zuo, Mengxin He, Yajian Li and Jiapei Dong

This paper proposes an asymmetric miniaturized single-layer bandpass filter based on interdigital capacitors and microstrip inductors with miniaturization and a wide bandwidth. It is composed of three series of LC resonator pairs and two parallel LC resonator pairs, and this asymmetric structure enhances design flexibility. The measured results indicate that the center frequency is 1.48 GHz, and the passband covers 0.88~2.08 GHz, with a return loss better than 12.6 dB, whereas the insertion loss is less than 0.58 dB. The physical size is 31 mm × 13 mm, which is smaller than that of traditional LC filters.

2026-01-16

PIER C

Vol. 165, 1-10, 2026

doi:10.2528/PIERC25102603

download: 53

Design and Experimental Evaluation of a Compact Half-Shaped Printed-Monopole Antenna with Short Stub for UWB Systems

Nobuyasu Takemura

A compact, half-shaped, planar-monopole antenna optimized for ultra-wideband (UWB) communication systems was proposed, numerically analyzed, and experimentally validated. The proposed antenna is configured as a bell-shaped monopole structure fabricated on an FR-4 dielectric substrate, which is bisected along its axis of symmetry to achieve a reduced footprint. To ensure broadband impedance matching, a short-circuited stub is integrated between the monopole and the ground conductor through a plated via. The antenna dimensions are 30 × 12 × 1.6 mm³, which represent a significant reduction compared with those of conventional UWB monopole antennas. Full-wave electromagnetic simulations demonstrate that the antenna covers the FCC-authorized UWB band of 3.1-10.6 GHz with a voltage standing-wave ratio (VSWR) of ≤ 2. Experimental measurements of properties of a fabricated prototype of the proposed antenna agree well with the simulation results. In addition to the analysis of frequency-domain performance, time-domain analysis is conducted using two identical antennas in both face-to-face and side-by-side arrangements. According to the results of the time-domain analysis, the calculated correlation coefficient between signals received by the proposed antenna is 0.986, which confirms high waveform fidelity. Group-delay analysis of the proposed antenna verified stable temporal characteristics with an average delay of approximately 0.2 ns across the UWB range. These results demonstrate that the proposed antenna is a promising candidate for compact and high-performance integration in short-range, high-speed, wireless-communication devices.