Volume 79, Issue 9-10

This paper presents a comprehensive review highlighting the progress made over the last few years, illuminating the state of the art in antenna designs based on characteristic modes theory and its application. The ultimate objective of this review is to provide an inclusive study of the recent advancements in characteristic mode analysis to design and optimize various antenna structures. The study will provide a broad coverage of characteristic modes theory, the underlying theoretical framework, and its significance in designing effective antenna structures. Additionally, the step-by-step methodology for antenna design using characteristic mode theory in commercial EM solvers has been extensively discussed. This article will be beneficial for beginners to explore the potential of characteristic modes and its applications enable them to embark on innovation working in this exciting field.

This study delves various nature inspired soft computing optimization and their applications for solving complex electromagnetics optimization problems. As the discipline advances, the integration of soft computing and electromagnetics is expected to drive innovation and broaden the scope of various engineering fields. In the past, there have been efforts to exploit various nature based optimization techniques like Genetic Algorithm (GA), Ant Colony Optimization (ACO), Particle Swarm Optimization (PSO), Differential Evolution (DE), Evolutionary Strategy, Simulated Annealing (SA), Memetic Algorithm (MA), Bacteria Foraging Optimization (BFO), Comprehensive Learning Particle Swarm Optimization (CLPSO), Wind Driven Optimization (WDO) Technique and many more, for solving multi-modal and multi-dimension in area of electromagnetcis, communications, system identifications, power flow optimization, pattern recognition, biomedical, health-care and marketing management etc. Incorporating soft computing techniques – such as Neural Networks (NN), Wind Driven Optimization (WDO), and Genetic Algorithms (GA) etc. – into electromagnetics has demonstrated significant potential in overcoming complex challenges where traditional methods fall short. These methods enhance resilience against the inherent uncertainties and nonlinear characteristics of electromagnetic systems, leading to notable progress in design optimization, antenna pattern synthesis, and mitigating electromagnetic interference.

This letter presents a class of wideband filtering phase shifters using end coupled short-circuit resonators (ECSCRs). By employing parallel coupled line, transmission zero (TZ) can be introduced. The proposed ones have some advantages such as intrinsic wideband characteristic, steep filtering property, wide stopband bandwidth, and low phase deviation in phase shift. The synthesis method for designing the proposed wideband filtering phase shifters with a prescribed phase shift value and bandwidth is presented. To verify the design method, 45° and 90° wideband filtering phase shifters are designed, fabricated, and measured. Good performances are achieved with small insertion loss and low phase deviation of ± 2.2° over bandwidth of 56.64 %, and 62.69 %, respectively.

In this paper, two novel balanced bandpass filters (BPFs) with wideband common-mode (CM) suppression and high selectivity are proposed based on the out-of-phase double-sided parallel strip-line (DSPSL) structure. The out-of-phase DSPSL structure is composed of a pair of out-of-phase transmission lines as the balanced ports and a λ/2 resonator placed in the center. Based on the DSPSL structure with out-of-phase characteristics, a wideband CM suppression without affecting the differential-mode (DM) performance is achieved in two BPFs. By using a pair of shorted-coupled lines in BPF I and introducing a ring resonator in BPF Ⅱ, two transmission zeros are attained, achieving high selectivity in both BPF designs. For experimental demonstration purposes, two balanced BPFs are designed and fabricated. The measured results are in good agreement with the simulated ones.

In this paper, a balanced dual-band bandpass filter (BPF) with enhanced differential-mode (DM) selectivity and stopband suppression is proposed. The design utilizes four half-wavelength stepped impedance resonators (SIRs) with mixed electromagnetic couplings to generate two DM passbands at 2.47 GHz and 3.53 GHz. By optimizing resonator dimensions ( L r 4 , L r 13 ) and coupling gaps ( g 1 , g 2 ), the center frequencies and fractional bandwidths (FBWs) of both passbands are independently controlled. A U-type transition structure enables intrinsic common-mode (CM) suppression exceeding 42 dB, while source-load coupling introduces four transmission zeros (TZs) to sharpen DM selectivity. Measured results show insertion losses (ILs) of 1.72 dB and 1.70 dB, return losses >17 dB, and a wide out-of-band suppression up to 6.7 GHz. The design outperforms the existing works in TZ count and flexibility, validated through rigorous simulation and measurement.

In this paper, a balanced dual-wideband BPF based on a novel quad-mode slotline resonator is proposed, achieving flexible, wide differential-mode (DM) bandwidths and high intrinsic common-mode (CM) suppression. With the application of the quad-mode slotline resonator, four transmission poles (TPs) are generated, leading to the creation of two wide DM passbands. The positions of these TPs can be flexibly adjusted by controlling the length of resonator. Meanwhile, utilizing quad-mode slotline resonator avoids multiple energy conversions between the slotline and microstrip line, simplifying the design and reducing overall size. In order to achieve intrinsic CM suppression, the BPF utilizes a microstrip/slotline structure, enabling the DM circuit to be designed independently of the CM circuit model, which greatly simplified the design procedure and thereby achieving excellent CM suppression. For the purpose of demonstrating the theoretical design, a dual-band BPF operating at 1.60 GHz and 3.75 GHz with bandwidths of 1,072 MHz and 1,088 MHz is fabricated. The results show good agreement between the simulations and measurements.

This paper presents RF/Microwave rectangular waveguide bandpass filter integrated with two-layer of periodical metamaterial SRR unit cell structure excited by proper EM wave boundary conditions. A properly constructed PCB-based metamaterial unitcell is integrated as a resonating circuit within a rectangular waveguide WR229. In order to achieve bandpass response, the metamaterial unit cell in the metallic waveguide of the designed RF bandpass filter is kept at λ g /4 spacing. Two open-ring resonators connected by a short stub are used to design the metamaterial unit-cell, which is fabricated on a Rogers 48350B substrate with a dielectric constant of ε r =3.48 and thickness of 1.52 mm. In addition, the metallic cavity generated with the CNC milling technology is zinc-coated to resist oxidation. The experimental results of the final prototype show good agreement with the overall wave modeling results. The proposed RF/microwave waveguide filters operated in the S-band frequency range; therefore, their applicability is recognized in RF sensing device for material characterization.

In this paper, we propose an ultra-wideband (UWB) Fabry–Perot cavity (FPC) antenna with dual-notch (DN) bands, utilizing a partially reflective surface (PRS) as a superstrate and an artificial magnetic conductor (AMC) reflector to support and enhance a DN band UWB antenna. The antenna components work synergistically to improve gain and provide directional radiation characteristics, while effectively mitigating interference from 5G and WLAN signals in urban environment. The proposed FPC design is executed in two main steps. First, a planar monopole UWB antenna is designed to operate within the frequency range of 2.69 GHz–12.27 GHz, incorporating a DN at 5G-3.5 GHz and 5 GHz WLAN bands through a single-slotted electromagnetic bandgap (EBG) unit-cell placed near the feedline. Second, a 5 × 5 array of AMC reflector elements and a PRS are strategically placed at specific distances from the UWB antenna to increase the gain. The resulting FPC structure was designed, optimized in HFSS, fabricated, and experimentally validated. Both measured and simulated results confirm that the proposed FPC structure achieves a peak gain of 10.21 dBi at 8.8 GHz, highlighting its potential to address challenges in meeting UWB application requirements, including Radar systems dedicated to high-resolution infrastructure monitoring and microwave medical imaging.

In this research, an L shaped four port MIMO antenna with chip resistor assisted H decoupling is designed. The proposed four port Multiple Input Multiple Output (MIMO) antenna can be applied over both 5G and 6G communication systems in the frequency range of 10 GHz–300 GHz. The antenna can resonate at three different frequencies such as 68.6667 GHz, 90 GHz, and 106.20 GHz. The MIMO antenna is intended on the Rogers RT DUROID 5880 substrate with a thickness of 0.5 mm, the relative permittivity of ε r = 2.2, and loss tangent of tan δ  = 0.0009 and a Coplanar waveguide feed line is employed. The whole dimensions of the proposed antenna model is 20.6 × 22.5 × 0.5 mm 3 . To attain better isolation, T shaped defected ground structure (TDGS) is used in this research. The proposed antenna is analyzed under different parameters such as gain, return loss, Voltage Standing Wave Ratio (VSWR), axial ratio, and other diversity performances of MIMO antenna like Envelope correlation coefficient (ECC), Total Active Refection Coefficient (TARC), Mean Effective Coefficient (MEG) and Diversity Gain (DG). The proposed antenna can obtain return loss values of −18.5540 dB, −31.1488 dB, and −42.0233 dB at the resonating frequencies of 68.667 GHz, 90 GHz, and 105.2 GHz.

This paper presents a new approach in microwave antenna-based non-ionizing contactless breast tumor detection system. A low-profile compact circular slotted microstrip antenna is designed with a 40 × 36 mm 2 structure, operating in 3.54 GHz–5.34 GHz. The radiation characteristics of the design are optimized by carefully adjusting the placements of the circular slots. To verify the functioning, the model is investigated using a breast phantom with an early-stage deep-seated tumorous region. Differences in various antenna parameters are used to claim the presence of a tumor. Also, the impact of the electrical characteristics of the breast layers on antenna performance is studied. The physical antenna measurements show good agreement with the simulated performance. This allows deep signal penetration and ease of tumor detection. With a peak realized gain of 6.9 dBi, radiation efficiency of 99.07 %, and three S 11 peaks below −20 dB, the antenna shows strong sensitivity across frequencies for the detection of tumors. Further, by processing the reflected signals using a modified delay multiply and sum algorithm, a 2D image is created for tumor localization. The findings of this work demonstrate the ability of the suggested antenna to perceive early-stage deep-seated breast tumors.

Bio implants are popularized in health care industry for patient monitoring. This article presents an ultraminiaturized flexible slotted patch antenna with superstrate for bio implantable applications. The radiator is designed on Roger 6010 with dimension 5 × 6.2 × 0.508 mm 3 which is 0.130 × 0.161 × 0.012 λ g at 2.45 GHz. The superstrate ensures protection of body tissues and reduces SAR. Achieved gain and bandwidth of the antenna in free space are −27.07dBi and 30 MHz, respectively. Antenna bandwidth on body tissues like stomach, heart and liver are 124 MHz, 138 MHz and 175 MHz, respectively. SAR analysis is carried out using both homogeneous and heterogeneous human body models for 1 g and 10 g tissues during simulation. Head, heart, liver and stomach phantom shows simulated SAR value of 33.53 W/Kg, 52.49 W/Kg, 32.49 W/Kg and 31.37 W/Kg, respectively for 1 g tissue with 1 W input power and is within IEEE standard limit of 1.6 W/Kg with maximum allowable power of 47 mW, 30 mW, 48 mW and 50 mW. Performance validation of antenna is done with liver, heart and minced meat of pork for body tissues. Brain tissue is mimicked with saline solution. The link budget analysis is performed using NI-USRP 2920 module and LabVIEW with data transfer at a transmission rate of 1/2/5 Mbps and shows a wireless transmission link of 15 m for bio telemetry.