PIER C | PIER Journals

2026-04-03

PIER C

Vol. 168, 82-88, 2026

doi:10.2528/PIERC26011901

download: 11

Parametric Model for Coaxial Cavity Filter Using Deep Learning Neural Networks

Nour El Houda Sara Senasli, Bouhafs Bouras, Mohammed Chetioui, Lamia Senasli and Mehdi Damou

This study introduces a deep neural network architecture tailored for accurately modeling the parameters of microwave components, with a specific focus on waveguide filters. Unlike simpler neural networks, this architecture is designed to handle the complex relationships that are prevalent in microwave engineering. The model's inputs include the filter's geometric variables and frequency, whereas the S-parameters serve as outputs. To effectively capture these relationships, the Rectified Linear Unit (ReLU) activation function was employed, which is known for its efficiency in managing a significant number of training parameters. This choice allowed the model to better grasp the intricate connection between the S-parameters and geometric variables, and the relationship was found to be more complex than that with frequency. The primary goal is to reduce the overall count of training parameters within the deep neural network while maintaining a level of accuracy similar to that of fully connected neural networks. This study demonstrates the effectiveness of this approach through waveguide filter parametric modeling, highlighting its capacity to accurately model and optimize the electromagnetic response of the filter.

Parametric Model for Coaxial Cavity Filter Using Deep Learning Neural Networks

2026-04-02

PIER C

Vol. 168, 75-81, 2026

doi:10.2528/PIERC26012203

download: 20

Compact Elliptical Multi-Band Microstrip Sensor for Thumb-Tissue Glucose Sensing

Amjad Hussein Yousif, Saad Wasmi Osman Luhaib and Mohammed Younis Thanoun

A new compact tri-band elliptical microstrip resonator is proposed for noninvasive microwave-based glucose sensing using a thumb-contact configuration. The sensor consists of concentric elliptical copper rings with a localized outer-ring slot and capacitive feed coupling, implemented on an FR-4 substrate to enhance electric-field confinement beneath the thumb-loading region. A multilayer cylindrical thumb phantom incorporating dispersive tissue models and glucose-dependent blood permittivity is employed to emulate realistic on-body conditions. Full-wave simulations in the 2-6 GHz band demonstrate three dominant glucose-sensitive resonant modes. Over a concentration range of 0-600 mg/dL, the resonances shift monotonically from 2.054 to 2.142 GHz, 2.83 to 3.214 GHz, and 5.128 to 5.75 GHz, respectively. The corresponding frequency-deviation rates are 0.147, 0.64, and 1.037 MHz/(mg/dL), with the highest linearity reaching R² ≈ 0.98. By distributing sensing across three coupled resonant modes, the proposed approach enables frequency-diverse feature extraction suitable for multivariate calibration, improving robustness against contact variability and modeling uncertainties compared with single-band configurations.

Compact Elliptical Multi-Band Microstrip Sensor for Thumb-Tissue Glucose Sensing

2026-04-02

PIER C

Vol. 168, 64-74, 2026

doi:10.2528/PIERC26012501

download: 19

Suppressing Torque Ripple of PMa-SRM Based on Variable Hysteresis Threshold in Sub-Divided Region

Junwu Zhu, Junxin Xu and Yan Chen

To address the issue of significant torque ripple in traditional direct instantaneous torque control strategies for permanent magnet assisted switched reluctance motors, which stems from the use of fixed hysteresis thresh-olds, this paper proposes a variable hysteresis threshold pulse width modulation (PWM) method based on subdivided regions. First, based on the torque-current ratio curve features, the two-phase exchange (TpE) region is subdivided into two-phase exchange I (TpE I) and two-phase exchange II (TpE II), using the angle of equal torque-current ratio as the dividing point. PWM control was applied within these two intervals to ensure a smoother transition of the total torque during commutation. Second, the hysteresis threshold is optimized by a BP neural network tuned via the dung beetle optimizer (DBO) algorithm under different speeds and loads, thereby enhancing the system's flexibility. Finally, simulations and experiments were performed using a 6/20 three phases permanent magnet-assisted switched reluctance motor. Experimental results show that the torque ripple is reduced from 30.4% to 11% under 500 r/min and 5 N.m, and PWM with a variable hysteresis threshold can effectively suppress torque ripple.

Suppressing Torque Ripple of PMa-SRM Based on Variable Hysteresis Threshold in Sub-Divided Region

2026-04-01

PIER C

Vol. 168, 56-63, 2026

doi:10.2528/PIERC26010806

download: 34

Fabry-Perot Resonator Antenna Design Based on Phased Array Feed

Zechen Li, Zibin Weng, Yahong Li, Youqian Su and Jingnan Guo

To address the issues of narrow gain bandwidth and severe element coupling faced by traditional Fabry-Perot resonant antennas in phased array feed systems, this paper proposes a decoupling design method based on highly optimized resonant mode height. By analyzing electric field distributions and coupling mechanisms under multi-feed conditions, an improved resonator height calculation formula suitable for phased array feeds is derived, achieving mutual suppression of energy between reflected wave coupling and inter-element coupling. A 2 × 2 microstrip antenna array was employed as the feed source. Combined with a multilayer positive phase gradient partially reflective surface, a Fabry-Perot antenna prototype operating at 28 GHz was designed and fabricated. Simulated and experimental results demonstrate that compared to conventional designs, this antenna achieves a maximum gain at 28 GHz increased from 21.80 dBi to 23.15 dBi, with the 3-dB gain bandwidth expanded from 1350 MHz to 1730 MHz. This study provides an effective approach for achieving a broadband high-gain design in phased array-fed Fabry-Perot resonant antennas.

Fabry-Perot Resonator Antenna Design Based on Phased Array Feed

2026-04-01

PIER C

Vol. 168, 45-55, 2026

doi:10.2528/PIERC26020603

download: 17

Wideband Circularly Polarized Dielectric Resonator Antenna with Wide Stopband Characteristics

Chuanyun Wang, Yi Ouyang, Pin Wen, Zhiyong Tan and Tianle Zheng

A wideband circularly polarized (CP) dielectric resonator antenna (DRA) with integrated harmonic suppression is proposed. The design transforms the original rectangular coupled slot into a branched configuration to perturb the electric field distribution within the dielectric resonator (DR) and ground plane, thereby obtaining wideband circular polarization characteristic. For harmonic suppression, a double-ended feeding structure integrated with a π-shaped stub and a transverse stub is introduced, generating four radiation nulls. Furthermore, a stepped-impedance feeding line is employed to extend the upper stopband bandwidth. A prototype is fabricated and measured; the experimental results and simulations are generally consistent. The antenna achieves a -10 dB impedance bandwidth of 40.2% (2.86-4.3 GHz), a 3 dB axial ratio bandwidth of 26.13% (3.06-3.98 GHz), an average gain of 5.3 dBi, and harmonic suppression of 2.7f₀ (where f₀ is the center frequency). The out-of-band suppression in both upper and lower stopbands exceeds 15 dB.

Wideband Circularly Polarized Dielectric Resonator Antenna with Wide Stopband Characteristics

2026-03-31

PIER C

Vol. 168, 39-44, 2026

doi:10.2528/PIERC26012305

download: 41

Printed Compact Monopole with Multiband Operation for Wi-Fi 8, 5G NR79, and 6G Upper Mid-Band Applications

Saou-Wen Su and Guan-Lin Chen

A compact yet simple, printed monopole design targeted at providing multiband operation in the 2.4/5/6 GHz Wi-Fi 8 (2400-2484/5150-7125 MHz) bands and also the 5G new radio (NR79) (4.4-5.0 GHz) band and 6G upper mid-band in the 7.125-8.4 GHz range is demonstrated. The antenna is composed of longer and shorter radiating arms, as well as a matching stub that protrudes from the longer arm around the antenna port and extends toward the shorter arm. The two arms and the stub are all printed on a low-cost single-layer substrate. Four resonant modes of the antenna are excited, with the lower mode covering the 2.4 GHz band and the three upper modes forming a wide 7.4-dB return-loss bandwidth of about 4.3-8.6 GHz, covering the 5G NR79 band, 5/6 GHz Wi-Fi bands, and 6G upper mid-band. Additionally, the design can be fed by a commercially available coaxial cable, allowing the antenna to have considerable flexibility in installation within wireless devices.

Printed Compact Monopole with Multiband Operation for Wi-Fi 8, 5G NR79, and 6G Upper Mid-Band Applications

2026-03-30

PIER C

Vol. 168, 26-38, 2026

doi:10.2528/PIERC26011102

download: 43

A Low-Current Pulsed Electric Field Treatment System for Fruit Juices: Air-Gap Optimisation and Assessment of Microbial Inactivation

Thomas Mohan, Aswini Sivadas Choolangal, Noorul Haque Mohamed Noor, Krishnan Jagada Suja, Karakkat Mana Sunitha and Tharamel Vasu Suchithra

The use of electromagnetic fields to preserve food items by inactivating microorganisms is gaining increasing popularity. Among the different electromagnetic treatments used for fruit juice preservation, Pulsed Electric Field treatment is a prominent method. However, in the Pulsed Electric Field treatment chambers used today, the current flow and energy dissipation within the juice are very high. These high currents cause unwanted electrochemical reactions inside the juice and also raise its temperature. This work introduces a method to prevent these by reducing the current flow with the help of an air gap inside the Pulsed Electric Field treatment chamber. A mathematical model of the proposed system was created, and the reduced current values were calculated. Simulations using COMSOL Multiphysics software were conducted to analyse the electric field distribution and the increase in juice temperature. The optimum value of air gap that can be provided inside the chamber without the risk of electrical breakdown was determined through simulations of electric field intensities and later confirmed through experiments. The effectiveness of the proposed system in inactivating microbes was assessed through microbiological experiments using Escherichia coli bacteria in watermelon juice. According to the experimental results, the proposed system successfully achieved bacterial inactivation with a low current value and without any measurable increase in juice temperature. To the best of our knowledge, there are very limited studies addressing the reduction of current flow within a Pulsed Electric Field treatment chamber through the incorporation of air gaps. In the future, this novel method for preserving fruit juices could prove highly beneficial to the food processing industry.

A Low-Current Pulsed Electric Field Treatment System for Fruit Juices: Air-Gap Optimisation and Assessment of Microbial Inactivation

2026-03-29

PIER C

Vol. 168, 21-25, 2026

doi:10.2528/PIERC25122802

download: 35

Microstrip Dual-Frequency Voltage Doubling Rectifier Circuit

Jia-Feng Zhou, Yu-Li Yang and Jiu-Sheng Li

We present a microstrip dual-frequency rectifier circuit, which includes a voltage-doubling rectifier circuit, a sector-shaped dual-frequency harmonic suppression network, and a Π-shaped dual-frequency impedance matching network. Four fan-shaped microstrip stubs were utilized to suppress the fundamental and higher-order harmonics in the two frequency bands. A microstrip line is employed to form a Π-shaped impedance matching network to achieve impedance matching in both frequency bands. The measured results show that at input power of 15 dBm, the rectification efficiencies are 50% and 43% at frequencies of 2.45 GHz and 5.80 GHz, respectively. This dual-frequency rectifier circuit can be applied to scenarios such as powering passive RFID tags and IoT sensors.

Microstrip Dual-frequency Voltage Doubling Rectifier Circuit

2026-03-28

PIER C

Vol. 168, 11-20, 2026

doi:10.2528/PIERC26010602

download: 83

Intelligent RF Signal Monitoring and Threat Detection

Chinmay Kumar, Gourav Kumar, Sehejdeep Singh, Vritant Sood and Naveen Jaglan

The problem of Radio Frequency (RF) jamming is a significant threat to any current wireless communication network, since a low-power source may seriously diminish or disrupt legitimate conditions of a transmission. Traditional methods of detection based generally on a fixed threshold or packet-level cues cannot be effectively sustained in the presence of adaptive and reactive jamming behavior as observed in real-world deployments. This paper introduces a system of RF signal monitoring and threat detection integrating frequency-domain feature extraction, supervised machine learning, and statistical signal characterization. Both time-domain (such as Received Signal Strength Indicator (RSSI) and Signal to Interference plus Noise Ratio (SINR) metrics and spectral quantities calculated with the Fast Fourier Transform (FFT) are being used to capture both temporary and persistent interference patterns. The hybrid ensemble approach in the form of Random Forest and XGBoost classifiers is implemented to achieve a balance among robustness, interpretability, and classification performance of various jammer types. Empirical testing with actual RF data demonstrates that the suggested method has an initial detection rate of 98 percent, and its performance does not degrade in the low signal-to-noise ratio regime. These findings imply that the combination of lightweight spectral analysis and ensemble learning is a feasible and scalable solution to real-time RF threat detection in dynamic wireless systems.

Intelligent RF Signal Monitoring and Threat Detection

2026-03-28

PIER C

Vol. 168, 1-10, 2026

doi:10.2528/PIERC26012006

download: 39

An Integrated Ray Tracing and Variable-Step Fourier Transform-Based Split-Step Parabolic Equation Modeling Approach for UAV-Assisted Channel Characterization in Mountainous Environments

Jihui Shi and Jian Song

To enhance communication performance in mountainous environments, unmanned aerial vehicle (UAV)-assisted communication systems have emerged as a mainstream solution. Channel modeling for UAV-assisted communication is a critical research focus, confronting prominent challenges, including balancing computational efficiency and modeling accuracy. This paper proposes a hybrid modeling approach that combines ray tracing (RT) and the variable-step Fourier transform-based Split-Step Parabolic Equation (V-FSSPE) to address the issue. The proposed method fully leverages the strengths of RT in accurately calculating direct, reflected, and diffracted propagation paths, as well as the advantages of V-FSSPE in efficiently modeling long-distance and large-scale areas. A hierarchical model suitable for low-altitude UAV communication is thereby established. Simulation results demonstrate that, compared with traditional modeling methods, the proposed method in this study effectively balances accuracy and efficiency in terrain-dominated air-to-ground channels, making it suitable for millimeter wave (mmWave) communication and emergency communication network planning in terrain-dominated propagation environments. Since factors such as vegetation and atmospheric effects have not yet been incorporated, practical deployment requires case-specific corrections based on the actual environment. Nonetheless, this framework is expected to provide important theoretical references and foundational support for the design and optimization of communication systems in related fields.