As an integral part of the electromagnetic system, antennas are becoming more advanced and versatile than ever before, thus making it necessary to adopt new techniques to enhance their performance. Machine Learning (ML), a branch of artificial intelligence, is a method of data analysis that automates analytical model building with minimal human intervention. The potential for ML to solve unpredictable and non-linear complex challenges is attracting researchers in the field of electromagnetics (EM), especially in antenna and antenna-based systems. Numerous antenna simulations, synthesis, and pattern recognition of radiations as well as non-linear inverse scattering-based object identifications are now leveraging ML techniques. Although the accuracy of ML algorithms depends on the availability of sufficient data and expert handling of the model and hyperparameters, it is gradually becoming the desired solution when researchers are aiming for a cost-effective solution without excessive time consumption. In this context, this paper aims to present an overview of machine learning, and its applications in Electromagnetics, including communication, radar, and sensing. It extensively discusses recent research progress in the development and use of intelligent algorithms for antenna design, synthesis and analysis, electromagnetic inverse scattering, synthetic aperture radar target recognition, and fault detection systems. It also provides limitations of this emerging field of study. The unique aspect of this work is that it surveys the state-of the art and recent advances in ML techniques as applied to EM.

In the context of implantable bioelectronics, this work provides new insights into maximizing biomedical wireless power transfer (BWPT) via the systematic development of inductive links. This approach addresses the specific challenges of power transfer efficiency (PTE) optimization within the spatial/area constraints of bio-implants embedded in tissue. Key contributions include the derivation of an optimal self-inductance with S-parameter-based analyses leading to the codesign of planar spiral coils and L-section impedance matching networks. To validate the proposed design methodology, two coil prototypes— one symmetric (type-1) and one asymmetric (type- 2)— were fabricated and tested for PTE in pork tissue. Targeting a 20 MHz design frequency, the type-1 coil demonstrated a state-of-the-art PTE of ~ 4% (channel length = 15 mm) with a return loss (RL) > 20 dB on both the input and output sides, within an area constraint of < 18×18 mm². In contrast, the type-2 coil achieved a PTE of ~ 2% with an RL > 15 dB, for a smaller receiving coil area of < 5×5 mm² for the same tissue environment. To complement the coils, we demonstrate a 65 nm test chip with an integrated energy harvester, which includes a 30-stage rectifier and low-dropout regulator (LDO), producing a stable ~ 1V DC output within tissue medium, matching theoretical predictions and simulations. Furthermore, we provide a robust and comprehensive guideline for advancing efficient inductive links for various BWPT applications, with shared resources in GitHub available for utilization by the broader community.

In this paper, a novel analytical design technique is presented to implement a coupled-line wideband Wilkinson power divider (WPD). The configuration of the WPD is comprised of three distinct coupled-line and three isolation resistors. A comprehensive theoretical analysis is conducted to arrive at a set of completely new and rigorous design equations utilizing the dual-band behavior of commensurate transmission lines. Further, the corresponding S-parameters equations are also derived, which determine the wideband capability of the proposed WPD. To validate the proposed design concept, a prototype working at the resonance frequencies of 0.9 GHz and 1.8 GHz is designed and fabricated using 60 mils thick Rogers’ RO4003C substrate. The measured result of the fabricated prototype exhibits an excellent input return loss > 16.4 dB, output return loss > 15 dB, insertion loss < 3.30 dB and a remarkable isolation > 22 dB within the band and with a 15 dB and 10 dB references provide a fractional bandwidth of 110% and 141%, respectively.

In this paper, we present a novel analytical design technique to implement a miniaturized 3-way power divider (3PD) supporting a wideband operation with a band ratio from 1-6.5. The proposed 3PD configuration comprises four distinct commensurate transmission lines and two different isolation resistors. A comprehensive theoretical analysis is conducted to arrive at a set of completely new and rigorous design equations by utilizing the dual-band behavior of the commensurate transmission line and the recombinant approach. Additionally, corresponding S-parameter equations are derived, which manifest the wideband capability of the proposed 3PD, as validated through several design examples. A fabricated prototype of the proposed technique exhibits excellent input return loss (>15 dB), output return loss (>15 dB) as well as insertion loss (16 dB) from 0.94-2.24 GHz and even achieves a fractional bandwidth of 132% (band ratio=4.96) considering a 10 dB reference. The different features and performance provided by this simple yet compact planar structure make the design an ideal choice for applications such as microwave ICs, antenna feed networks, and Doherty power amplifiers.

In this paper, a new analytical design technique for a three-section wideband Wilkinson power divider is presented. The proposed design technique utilizes the dual-frequency behavior of commensurate transmission lines for the even-mode analysis and contributes a set of completely new and rigorous design equations for the odd-mode analysis. Measurement of a fabricated prototype utilizing the proposed technique shows an excellent return-loss (>16 dB), insertion loss (22.7 dB) over 104% fractional bandwidth extending beyond the minimum requirements.

This article presents a Mid-section crossed dual-band Branch-Line Coupler (MBLC) with port extensions, along with a new design methodology for both complex and conventional structured branch-Line couplers. The proposed MBLC structure features a conventional branch-line coupler with a crossed line at the center, as well as an L-section impedance matching network at all four ports, which facilitates analysis and design. A comprehensive theoretical analysis is performed to derive closed-form design equations for determining the coupler’s design parameters using a perturbation factor. The analysis demonstrates that the proposed MBLC can support a wide band ratio of up to 11, indicating a broad operating frequency range. To evaluate the performance of the proposed MBLC, two prototypes were fabricated on a 62 mil Rogers 4003C substrate, operating at 1 GHz and 2 GHz for equal and unequal power division cases. The simulated and measured results for both prototypes showed an excellent match, with a magnitude imbalance of less than 4% and a phase imbalance of less than 2%. Overall, the proposed MBLC with port extensions in conjunction with the new design methodology demonstrates promising results in the development of efficient and effective dual-band branch-line couplers.