Systematic Inverse Design of Miniaturized Frequency Selective Surfaces Based on Microwave Network Theory and NSGA-III

As an efficient method for characterizing device properties, microwave network theory plays a critical role in microwave techniques. In this article, inspired by the equivalent circuit model (ECM) of the gridded square loop, a simple but systematic inverse design method is proposed for miniaturizing frequency selective surfaces (FSSs) based on the integrated internal and external microwave network theory. The microwave network model as well as its numerical calculation method under the isotropic FSS architecture are described in detail. Finally, a carefully designed multiobjective optimization problem is established, which is solved by nondominated sorting genetic algorithm III (NSGA-III) autonomously. Following the method, with the single-layered third-order gridded square loop structure and several lumped elements at specific locations, three extremely miniaturized FSSs are achieved, including single-band transmissive FSS, single-band reflective FSS, and multiband transmissive FSS. The realized dimensions for these FSSs are 0.014 λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub>, 0.012 λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub>, and 0.064 λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub>, respectively. Such compact FSSs also enable excellent angular stability, further expanding their applications in electromagnetic shields. A prototype of the miniaturized tri-band transmission FSS was fabricated and measured to validate the effectiveness of the proposed method, with the measured results agreeing well with the simulated ones.