Antenna synthesis is becoming increasingly challenging given the tight requirements for C-SWAP (cost, size, weight and power) reduction while maintaining stringent electromagnetic performance specifications. While recent reports have investigated developments in AI (primarily deep learning) to address this challenge, such methods have limited capability for multi-objective constrained inverse design and the ability to handle large shape sets. We present a multi-objective antenna synthesis methodology employing deep neural network surrogate-driven evolutionary algorithm. Specifically, we propose a branched-output convolutional neural network architecture for creating the surrogate model and showing its ability to predict multiple electromagnetic parameters over an operating frequency range. The proposed methodology and its synthesis capabilities are showcased by considering the set of polygonal-patch antennas for operation in the 2 to 3 GHz spectral band. Specifically, we report the design, fabrication and experimental characterization of three polygon-shaped patch antennas, each fulfilling different objectives, one being a single band with resonance at 2.45 GHz, the second antenna is dual-band with resonance at 2.2 GHz and 2.9 GHz, and the third one being wide-band centered around 2.7 GHz. The reported methodology enables rapid synthesis (in seconds), produces verifiable sound designs and is promising for furthering data-driven design methodologies for electromagnetic wave device synthesis.

In this letter, we propose the designs of 1-bit and 2-bit digitally coded metasurfaces, which achieve anomalous reflection-based beam-steering. First, we demonstrate the systematic design flow of coded metasurface using phase gradient digital unit cells to achieve anomalous reflection in the preferred direction for a normally incident plane wave. Initially, the design procedure is analytically implemented  to get the phase profiles for 1-bit and 2-bit digitally coded metasurfaces having equal sizes of $10\lambda_0 \times 10\lambda_0$ (where $\lambda_0$ is the free space wavelength at $5.9$ GHz) for a specific reflection angle, $(\theta_r=30^0,\phi_r=0^0)$, and subsequently, the far-field plots are generated. Furthermore, these phase profiles are used to generate 3D-CAD models of the 1-bit and 2-bit metasurfaces using CST, and the desired far-field patterns are obtained having half-power beamwidth (HPBW) of $5^0$. It is observed that the 1-bit coded metasurface produces additional side-lobe levels, which are minimized by use of 2-bit coding. Finally, the proposed 1-bit and 2-bit coded metasurfaces are fabricated, and the anomalously reflected far-field beam is detected by the received power at desired reflection angle and comparing the results with a perfect electric conductor (PEC). The proposed design is suitable for V2X communications and can be scaled to other frequencies.

In this paper, we propose a parasitic patch-based method to improve the power transfer efficiency of radiative wireless power transfer (WPT) systems involving implanted biomedical devices. The proposed WPT system uses circularly polarised antennas, having a four-element sequentially rotated antenna array, as the Tx and a miniaturized circularly polarized antenna implanted inside a body mimicking gel as the Rx with a parasitic patch placed in close vicinity. The design guidelines for the dimensions of the parasitic patch and its distance from the implanted antenna are discussed in-depth based on rigorous parametric studies and analysis. The proposed parasitic patch-based method improves the implantable antenna gain by 7.83 dBic, thereby increasing the power transfer efficiency at 2.4 GHz operating frequency. Improvement in power transfer is experimentally demonstrated with the help of a low-cost experimental setup having a software-defined radio (SDR) and a spectrum analyzer. Further to analyze the effect of interfering signals on the performance of the WPT system, power received by the implantable antenna is measured in presence of a secondary transmitter.

This paper presents, a mutual coupling reduction technique between a very closely spaced (1.8 mm) two-element microstrip based MIMO antennas using a modified inverted-fork shaped decoupling (m-IFSD) structure. The m-IFSD consists of an inverted fork and a cross shaped structure with a shorted via. The combined effect of inverted-fork and shorted cross shaped structure results in mutual coupling reduction below −35 dB between adjacent antenna elements. The decoupling technique is analyzed using an approximate transmission-line model and field distribution. Further, the two-element MIMO antenna design is extended to 8-element MIMO configuration to improve the MIMO diversity. To verify the proposed isolation technique a two-element MIMO antenna prototype is fabricated and measured. The proposed MIMO antenna exhibits a low mutual coupling (< −35 dB) with good impedance matching (< −10 dB) at 5.45 GHz. The MIMO antenna provided a total active reflection coefficient (TARC) less than −10 dB and envelop correlation coefficient (ECC) (for isotropic propagation scenario) less than 0.5. Finally, the ECC of the proposed MIMO antenna system is analyzed for a realistic Gaussian/Uniform propagation scenario for various incidence angles and angular spreads to better understand the effect of the mutual coupling reduction technique.

In this paper, MATLAB based computational approaches for the design and analysis of time-varying capacitors using the finite-difference time-domain (FDTD) technique and the Simulink design environment are presented. The FDTD formulation for multiple lumped capacitors loaded in series on a transmission line is discussed and extended to include time variation of capacitance. The design methodology for the same is also discussed using MATLAB’s Simulink using the RF Blockset Library. The developed FDTD formulation and the Simulink method are then used to design a mixer with time-varying capacitors loaded transmission line.