PIER C | PIER Journals

2026-03-11

PIER C

Vol. 167, 39-49, 2026

doi:10.2528/PIERC26011705

download: 17

Mode Analysis for Prediction of Heating Patterns in Microwave Cavities Powered by Magnetron

Freda Carvalho, Ashwini Kotrashetti and Kaustubh Bhattacharyya

Microwave heating, widely employed in the food industry, offers significant advantages due to its volumetric heating capabilities. However, its efficiency is often hindered by non-uniform heating patterns. This study aims to analyse heating patterns in a rectangular, single-fed domestic microwave oven, leveraging cost-effective methodologies. Theoretical analyses, electromagnetic simulations, and experimental measurements were conducted to characterise the resonant modes within an empty cavity and with a load. The mathematical computation of multiple mode superposition within the cavity was performed for two domestic microwave ovens. Mathematical and experimental analyses demonstrate a close agreement in results. The findings reveal that mode distribution, influenced by cavity dimensions, load properties, load placement, and magnetron characteristics, significantly impacts heating patterns. This study helps us understand that in spite of the dynamic nature of magnetron, it is important to superimpose multiple resonant modes prevalent within the cavity to understand influences on microwave heating pattern of any food materials.

Mode Analysis for Prediction of Heating Patterns in Microwave Cavities Powered by Magnetron

2026-03-08

PIER C

Vol. 167, 32-38, 2026

doi:10.2528/PIERC25122306

download: 49

Design of a π-Type Broadband Flat Negative Group Delay Circuit

Aixia Yuan, Zhiyang Feng, Junzheng Liu, Yuwei Meng, Niannan Chang and Hongjun Zhang

This study proposes a novel π-type circuit topology designed to achieve broadband and flat negative group delay (NGD) characteristics. Featuring a simple structure composed entirely of passive lumped elements, the proposed design offers significant advantages in terms of ease of fabrication, low cost, and seamless integration into larger microwave systems. First, a comprehensive theoretical analysis was conducted to establish the operational principles and derive the design equations. We then systematically investigated the sensitivity of the circuit's performance to variations in individual component values, which provides crucial guidelines for practical implementation. To validate our theoretical findings, a physical prototype with compact dimensions of 32 mm × 35 mm was designed and fabricated. Experimental results demonstrate that at the center frequency of 107.5 MHz, the circuit achieves an NGD of -2.27 ns with an insertion loss of 19.5 dB. Notably, the circuit maintains a wide flat NGD bandwidth of 151 MHz, exhibiting a group delay fluctuation of merely 4.1% across the band. These results confirm the effectiveness and robustness of the proposed circuit for broadband microwave applications.

Design of a π-type Broadband Flat Negative Group Delay Circuit

2026-03-06

PIER C

Vol. 167, 21-31, 2026

doi:10.2528/PIERC25120702

download: 89

Optimized Hierarchical Nested Array for Enhanced Uniform Degrees of Freedom in Sparse Array DOA Estimation

Guibao Wang, Keyi Yu, Xianghui Wang and Shuzhen Wang

Sparse arrays have been extensively investigated for their capability to enhance degrees of freedom (DOFs). However, conventional nested array configuration is susceptible to strong mutual coupling (MC), while its achievable uniform DOFs (uDOFs) remains limited. To address these challenges, this paper proposes two optimized hierarchical nested arrays, designated as OHNA-I and OHNA-II. OHNA-I reconstructs the spatial arrangement of subarrays through a hierarchical shifting operation, effectively extending the continuous segment of the difference co-array (DCA). Building on this, OHNA-II further optimizes the subarray geometry via sensor displacement, achieving a better balance between uDOF enhancement and MC suppression, thereby maintaining higher uDOFs while reducing inter-sensor coupling interference. Numerical simulation results demonstrate that, under the same number of physical sensors, the proposed structures - particularly OHNA-II - achieve a greater number of uDOFs than existing classical sparse arrays. Furthermore, in scenarios with strong MC, the proposed structure exhibits superior robustness and lower root mean square error (RMSE) in DOA estimation.

Optimized Hierarchical Nested Array for Enhanced Uniform Degrees of Freedom in Sparse Array DOA Estimation

2026-03-06

PIER C

Vol. 167, 15-20, 2026

doi:10.2528/PIERC25123001

download: 33

Ac Losses Modeling in ReBCO Superconducting Coils Using the Volume Integral Method

Sara Fawaz and Hocine Menana

This paper presents a fast and efficient modeling approach based on the volume integral method for the characterization of AC losses in high-temperature superconducting coils made of second-generation Rare-earth Barium Copper Oxide (ReBCO) tapes. Three modeling strategies are investigated and compared, considering the detailed multilayer tape configuration, the homogenized tape configuration, and the simplified single-layer superconducting tape representation. These approaches aim to evaluate the impact of geometrical and electromagnetic simplifications on the accuracy of the results while significantly reducing computational time. In particular, the homogenization of the electromagnetic properties of the tape is explored to accelerate simulations without compromising the accuracy of key physical quantities such as AC losses and current density distribution. The modeling results are compared to measurements.

AC Losses Modeling in ReBCO Superconducting Coils Using the Volume Integral Method

2026-03-04

PIER C

Vol. 167, 4-14, 2026

doi:10.2528/PIERC26011606

download: 105

High Gain Circularly Polarized Dual-Band Antenna Array Using Hybrid Couplers

Qurratul Ayn, Yuvaraj Sivasubramanian and Kiran Kumar Gurrala

This work presents a dual-band circularly polarized antenna array in which adjacent elements are excited with quadrature phase progression using a cascaded hybrid-coupler feeding network comprising one rat-race coupler and two branch-line couplers. Double-T monopole elements enable dual-band operation, achieving impedance bandwidths of 300 MHz (2.4-2.7 GHz) and 975 MHz (5.025-6 GHz) with corresponding axial-ratio bandwidths of 110 MHz and 525 MHz. The array provides peak gains of 9.19 dB and 9.49 dB with simulated radiation efficiencies of 90% and 87% in the respective bands. The array yields peak realized gains of 9.19 dBic and 9.49 dBic with simulated total efficiencies of 90% and 87% in the corresponding bands. Unlike sequential rotation or multilayer CP arrays, the proposed single-layer planar hybrid-coupler network ensures frequency-stable dual band circular polarization. An analytical formulation of the array factor and axial ratio sensitivity is provided to clarify the CP synthesis mechanism and its suitability for compact vehicular platforms.

High Gain Circularly Polarized Dual-band Antenna Array Using Hybrid Couplers

2026-03-04

PIER C

Vol. 167, 1-3, 2026

doi:10.2528/PIERC25101605

download: 58

Phase Noise Experimental Characterization of CRLH Distributed Oscillators

Walter Ciccognani, Antonio Serino, Giancarlo Bartolucci, Lucio Scucchia and Stefan Simion

The phase noise levels of the output signals provided by two CRLH (Composite Right-/Left-Handed) distributed oscillator configurations are measured and compared. The first CRLH oscillator configuration provides two output signals, drain-line and gate-line output signals, available at the ends of the drain-line and gate-line that are not used for connecting the oscillator feedback. The second CRLH oscillator configuration is obtained by adding a Wilkinson power combiner to the first configuration that sums the drain-line and gate-line output signals for a single-output signal, a combined output signal. The experimental results show that the best performance in terms of output power and spectral purity can be obtained for the single-output CRLH oscillator.