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2026-01-25

PIER Letters

Vol. 129, 9-14

Characterization of Complex Permittivity Using Microwave Diffraction of Spheres

Elio Samara , Jean-Michel Geffrin and Amelie Litman

The determination of the complex permittivity of materials is a fundamental aspect of experimental electromagnetics. This study introduces a method that estimates the complex permittivity by comparing the measured bistatic field diffracted by spherical samples in an anechoic chamber with fields computed using Mie theory. The approach is applied to a molded PMMA sphere and two 3D-printed materials (Clear Resin V4.1 and Rigid 10K) over the 2-18 GHz band. The retrieved permittivity values show excellent agreement with reference data for PMMA and enable reliable characterization of low-loss 3D-printed materials, with uncertainties quantified from both experimental and numerical contributions. These results confirm the effectiveness of microwave-diffraction-based characterization and highlight promising perspectives for future investigations on an even larger frequency band.

2026-01-24

PIER C

Vol. 165, 89-96

doi:10.2528/PIERC25121602

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.

2026-01-23

PIER C

Vol. 165, 79-88

doi:10.2528/PIERC25110401

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.

2026-01-21

PIER C

Vol. 165, 68-78

doi:10.2528/PIERC25082003

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.

2026-01-21

PIER C

Vol. 165, 61-67

doi:10.2528/PIERC25102703

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.

2026-01-21

PIER B

Vol. 117, 29-42

doi:10.2528/PIERB25111901

Adapting Operational Volume Scanning to Low-Power FMCW: System Development and Physically-Informed ML Calibration

Asif Awaludin , Dwiyanto , Rahmat Triyono , Yunus Subagyo Swarinoto , Erwin Makmur , Beno Kunto Pradekso , Oktanto Dedi Winarko , Muhammad Farras Archi Maggaukang , Liarto , Donaldi Sukma Permana , Roni Kurniawan , Rezky Yunita , Mohamad Husein Nurrahmat , Thahir Daniel Foreigner Hutapea , Agung Majid , Muhamad Rifki Taufik , Warjono , Ferdinandus Edwin Penalun , Bobby Harnawan , Dodi Dian Patriadi , Muhammad Rendi Anggara , Hastuadi Harsa , Alfan Sukmana Praja , Fatkhuroyan , Wido Hanggoro , Muhammad Najib Habibie , Welly Fitria , Rahayu Sapta Sri Sudewi , Asteria Satyaning Handayani , Sri Noviati and Vestiana Aza

This study presents the development and evaluation of a transportable X-band frequency-modulated continuous-wave (FMCW) weather radar (WR) that successfully adapts operational volumetric scanning strategies typically reserved for high-power to low-power pulsed systems. The radar integrates a complete radio-frequency chain, a carbon graphite antenna, and a dedicated real-time processing unit designed for operational volumetric scanning. It performs rapid 4-minute volume scans across seven elevation angles (0.00˚-15.88˚) with non-uniform spacing optimized for low-level atmospheric sampling, while a 2 RPM rotation provides full azimuthal coverage every 30 s. The resulting Column Maximum (CMAX) product synthesizes reflectivity from all elevation angles to depict three-dimensional precipitation structure, demonstrating a spatial observational capability distinct from traditional profiling FMCW radars. A three-stage hierarchical physically-informed architecture calibration framework was implemented to ensure quantitative accuracy in the FMCW WRs measurements, using collocated C-band Doppler Weather Radar (CDWR) observations as reference data. Validation through internal five-fold Group K-Fold cross-validation, Leave-One-Pair-Out (LOPO) testing, and external evaluation using independent radar pairs demonstrated the frameworks robustness. The case study of localized urban convection observed by the FMCW WR shows that the developed low-cost radar offers much finer range resolution and can reveal detailed structures within convective cells.

2026-01-20

PIER C

Vol. 165, 48-60

doi:10.2528/PIERC25092906

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.

2026-01-20

PIER C

Vol. 165, 35-47

doi:10.2528/PIERC25100103

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.

2026-01-18

PIER C

Vol. 165, 25-34

doi:10.2528/PIERC25120101

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.

2026-01-18

PIER C

Vol. 165, 18-24

doi:10.2528/PIERC25111306

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).

2026-01-16

PIER C

Vol. 165, 11-17

doi:10.2528/PIERC25101503

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

doi:10.2528/PIERC25102603

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.

2026-01-16

PIER C

Vol. 164, 271-278

doi:10.2528/PIERC25111502

Wide-Angle Scanning Phased Array Based on Phase Mode Antenna Element

Ming-Qi Yi and Shen-Yun Wang

To address the significant gain degradation that conventional phased arrays suffer during wide-angle scanning, a linear antenna array based on phase mode antenna elements is proposed. The phase mode antenna element is three-layer structure with two feeding ports. It can operate in odd mode, even mode, and hybrid mode by using different excitation strategies, and continuous beam scanning is achieved using hybrid mode, which results in a wide-angle beam scanning performance of the antenna array. The maximum beam gain can be obtained by using the method of maximum power transmission efficiency (MMPTE) compared with the traditional beam scanning method. The optimal excitation distributions calculated by MMPTE lead to a significant improvement in wide-angle beam scanning for the phase mode antenna array.

2026-01-15

PIER C

Vol. 164, 263-270

doi:10.2528/PIERC25071008

A Compact Time-Domain Reflectometry (TDR)-Based Microwave Nondestructive Testing Circuit

Nadine Adnan Shaaban and Ghassan Nihad Jawad

This paper proposes a proof-of-concept circuit of a time-domain reflectometry (TDR)-based non-destructive testing (NDT) circuit. The circuit consists of a broadband six-port reflectometer with an end-fire antenna probe. The broadband operation is achieved by a reduced-size six port reflectometer that uses a special algorithm to extend the frequency of operation beyond the limits between which a normal reflectometer usually used. In addition, a highly-directive antenna probe is proposed to provide a near-constant gain across the bandwidth of operation. By operating the circuit within the frequency range 2.5-7 GHz, it is used to detect gaps of various widths between the back of a polystyrene sample and a metallic plate. Results show clear indication of the gaps' existence in addition to a shift that is associated with the gap width. The proposed circuit proves the possibility of implementing the TDR-based microwave NDT system using a low-cost and compact circuit without the need for bulky and expensive vector network analyzers. This paves the road towards utilizing this technology in real-life scenarios.

2026-01-15

PIER C

Vol. 164, 253-262

doi:10.2528/PIERC25101603

Design of a High Gain Low SAR Microstrip Antenna Array with AMC Structure for Wearable Applications

Jialin Zhang , Chengzhu Du and Xu Wu

In this paper, a novel wearable antenna array backed by an AMC reflector is presented for high gain and low side-lobe levels. The presented antenna consists of a four-element array. The impedance bandwidth (≤ -10 dB) of the proposed antenna is from 5.6 to 6.8 GHz. After adding an AMC structure on the back side of the antenna array, the maximum measured gain reaches 13.8 dBi at 6.7 GHz; the front-to-back ratio (FBR) value is raised by 25.3 dB; and the sidelobe level is less than -20.51 dB. When the antenna array is on the human body model, the simulated SAR value is only 0.05 W/Kg/10 g, significantly lower than the international standard. These good measured results demonstrate that the proposed antenna is suitable for modern wearable applications.

2026-01-14

PIER C

Vol. 164, 243-252

doi:10.2528/PIERC25111004

A Wearable CPW-Fed Quad-Band-Notched Two-Port MIMO Antenna for IoT Applications

Jiali Wang , Chengzhu Du , Jun Chu and Ruomeng Li

This paper introduces a wearable quad-band-notched two-port Multiple Input Multiple Output (MIMO) antenna with coplanar waveguide (CPW)-fed for 5G applications. The antenna uses a liquid crystal polymer (LCP) flexible substrate with dimensions of 30 mm * 54 mm * 0.1 mm. The proposed antenna achieves four notched bands by etching four C-shaped slots on the patch and introduces a fence structure in the middle to enhance the isolation between the antenna elements, which ultimately achieves a band coverage of 3.26-10.8 GHz, with the notched-band coverage of 4.0-4.57 GHz (C-band radar Note7), 4.8-5.0 GHz (N79 mobile), 5.62-6.0 GHz ( WLAN downlink), and 8.08-8.79 GHz (ITU-R), peak gain of 6.9 dBi, radiation efficiency of above 70%, and isolation greater than 20 dB. In addition, the important performance parameters of the designed MIMO antenna include envelope correlation coefficient (ECC), diversity gain (DG), channel capacity loss (CCL) and total active reflection coefficient (TARC). The antenna is subjected to bending and human body experiments, and all the results show that the antenna has the advantages of small size, multiple notched bands, and high isolation, which has a good prospect of application in the field of wearable antennas for the Internet of Things (IoT).

2026-01-14

PIER B

Vol. 117, 16-28

doi:10.2528/PIERB25112704

Multispectral Optical Emission Modeling of Sprites Using Plasma Streamer Simulations: A Computational Electromagnetics Approach for Remote Sensing Applications

Carlos Antonio Gómez Vargas and Francisco José Román Campos

We present a computational framework for the multispectral synthesis of optical emissions in Transient Luminous Events (TLEs), specifically sprites, based on plasma fluid simulations obtained with the Afivo Streamer tool. Using the simulated electric field and electron density, we compute quasi-stationary excitation, quenching, and radiative emission rates for four key spectral bands: first positive 1PN₂ and second positive 2PN₂ band systems of nitrogen, Lyman-Birge-Hopfield (LBH) band system, and Optical emission images OI (Ionized Atomic Oxygen) at 777.4 nm (OI 777.4 nm). The model incorporates electron-impact excitation coefficients k(E/N), non-radiative losses due to collisional quenching Q = Σ_iα_in_i, and atmospheric attenuation (especially relevant for LBH). It also produces 2D emission maps and vertical brightness profiles, showing the spatial localization of each band as a function of the reduced electric field, electron density, and non-radiative losses. The results capture the temporal evolution of the discharge, from the early propagation phase to advanced branching, enabling direct comparisons with spaceborne instrumentation (e.g., ASIM). The developed scheme provides a reproducible diagnostic tool that links plasma physical variables with observed signals across multiple spectral bands.

2026-01-13

PIER C

Vol. 164, 232-242

doi:10.2528/PIERC25111807

Electromagnetic Performances Comparison of Partitioned Stator Flux Modulation Machines with Different Auxiliary Rotor Structures

Yifei Hu , Meimei Xu , Zhijian Ling , Wenxiang Zhao and Zhaowei Wang

In this paper, the electromagnetic performances of partitioned stator flux modulation (PSFM) machines with different rotor structures are compared to highlight the advantages of the auxiliary rotor structures. Two novel auxiliary rotors are proposed to suppress electromagnetic vibration in PSFM machine. First, the PSFM machine topology and the analytical models for the outer air-gap permeance of the different rotors are introduced. Furthermore, a comparative analysis of the electromagnetic and vibrational performance between the different auxiliary rotor machines and the conventional rotor machine are conducted to validate the advantages of the proposed designs. Finally, machines with different auxiliary rotors are mounted onto the experimental platform for testing to validate the effectiveness of the theoretical analysis.

2026-01-13

PIER C

Vol. 164, 224-231

doi:10.2528/PIERC25120905

Compact Wideband Antenna Design Incorporating DGS, Slots and Tiny Reflectors for Wireless Applications

Nirav Jashvantkumar Chauhan , Chandulal Harilal Vithalani and Jagdish M. Rathod

To achieve wideband operation while maintaining a small overall footprint (26 mm × 27 mm × 1.6 mm) and electrical size of 0.46λ × 0.47λ × 0.03λ, this paper presents a compact wideband MPA (Microstrip Patch Antenna) that uses a DGS (Defected Ground Structure) and internal slots on a radiating patch and ground plane. The proposed antenna was designed on FR-4 with loss tangent = 0.02, ε_r = 4.4 & h = 1.6 mm, which achieves a wide bandwidth covering key wireless bands (sub-6 GHz 5G, Wi-Fi, WiMAX) with acceptable gain and radiation stability. The upper and lower edges of the band were tuned by the slot geometry and DGS, as demonstrated by parametric analysis. Full-wave electromagnetic simulation results are reported, and the fabrication and measurement procedure is described. The stated antenna achieves a peak radiation efficiency of 95.46%, a fractional bandwidth of 64.39%, a maximum gain of 4.8 dB, and an S₁₁ below -10 dB over the range of frequency 3.57-6.96 GHz, all in a small size similar to a coin. The antenna is particularly suitable for compact wireless devices, IoT modules, and sub-6 GHz applications.

2026-01-12

PIER C

Vol. 164, 214-223

doi:10.2528/PIERC25113001

ADMM-Based Sparse SAR Imaging Algorithm with Cholesky Decomposition and Dual-Momentum Coupling

Enchen Wang , Xuechen Zhang , Daming Lin and Shumao Qiu

To address the challenges of high computational complexity in linear system solving and slow convergence of the Alternating Direction Method of Multipliers (ADMM) for compressed sensing Synthetic Aperture Radar (SAR) imaging, this study proposes a precomputation strategy based on Cholesky decomposition. Specifically, the system matrix is decomposed once during the initialization phase and reused across subsequent iterations, substantially reducing the computational overhead associated with the primal variable update. Furthermore, a novel dual-momentum coupling mechanism is designed, and building on Nesterov extrapolation, this mechanism integrates cross-momentum interactions between the real and imaginary components of dual variables, along with the historical variation trends of primal variables, thereby effectively accelerating overall convergence. Both simulated and measured data results demonstrate that the proposed method achieves a significant improvement in computational efficiency while ensuring high imaging quality.

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