I. Introduction
Frequency selective surfaces (FSS) find extensive applications in defense technology, wireless network, RF energy harvesting, satellite communication, antenna parameter enhancement, etc. [1]–[6], owing to their ability to exhibit various electromagnetic (EM) characteristics, such as filter, absorber, polarizer, reflector, and so on. These FSSs are made of periodic structures arranged in two-dimensional (2-D) arrays, where the shapes of the unit cells regulate the EM operation.[7], [8] Along with displaying various types of passive EM behavior, these FSSs are also used in reconfigurable devices due to their ease of integration with PIN diodes, varactor diodes, and other lumped components. [9]–[12] One of the primary applications of FSS is its highly selective shielding properties, which are often exploited to protect any electronic/ electrical device from its nearby interference. Over the last decade, several types of FSS-based shielding operations have been reported in the literature [13], [14]. A few geometries are used for single-band shielding, whereas a few others are focused on multi-band and wideband shielding [15]. Researchers have also achieved wide band coverage, polarization insensitivity, and angular stability in those shielding devices. A four-fold symmetrical topology helps an FSS geometry to achieve polarization insensitivity, [16], [17] whereas miniaturized elements can produce good angular stability [18]. Multi-layer or/and resistive-conductive ink patterns can achieve wide bandwidth. Reconfigurable shielding operations have also been found in various works, where PIN diodes and varactors diodes are used to regulate the shielding operations across various frequency ranges.