This work presents a new technique to reduce the correlation coefficient value between adjacent antenna elements in multiple-input-multiple-output (MIMO) configurations. Unlike the conventional works which utilize port isolation enhancement methods for this purpose, the proposed approach adopts decorrelation of the radiation patterns of individual elements. To achieve this, a phase-gradient frequency selective surface (FSS) is used as a superstrate above the antenna elements in a low profile Fabry- Perot (FP) cavity configuration. The effectiveness of the method is demonstrated by designing the system for a two-element MIMO antenna at 5.25 GHz. The proposed technique results in more than 95% reduction in the correlation coefficient value, thus projecting better MIMO performance.

Intelligent reflecting surfaces (IRS), also known as reconfigurable intelligent surfaces (RIS), have currently received much attention for their applications in wireless communication. The n-bit RISs presented in the literature are restricted to a single resonance and single polarization. These shortcomings create hurdles to engage more number of users and design a low-cost system (i.e., a separate hardware is required for each desired frequency band and each polarization). However, these issues can be solved if frequency reconfigurability and multiple polarization states (i.e., TE and TM) can be achieved in one structure. This paper presents a new multi-bit reconfigurable reflecting surface (RRS) with frequency-reconfigurable functionality working for both TE and TM polarized waves. The proposed design is tunable between 1.8-2.3 GHz and 2.95-3.9 GHz for TE and TM polarized electromagnetic (EM) waves, respectively. To simultaneously achieve the frequency reconfigurability and phase tailoring (varied from 0 ^$\circ$ to 315 ^$\circ$ ) in the proposed structure, the super-cell technique is used. This latter is incorporated in a phase gradient metasurface with different digital coding patterns to perform beam scanning and splitting functionalities. The simultaneous frequency reconfigurability and phase controlling for both TE and TM polarized waves, make this RRS a potential candidate for future RIS and reconfigurable devices.

In this letter, a novel bianisotropic omega frequency selective surface (FSS) is presented. The distinctive feature of the surface is that it offers simultaneous absorptive and partial reflective operation at seven frequency bands that range from the C-band to the K-Band. The maximum absorption (~ 99%) from one side is obtained at 14.312 GHz, while reflection from the other side remains between 75% and 99%. Moreover, the FSS provides the same behavior for any arbitrarily oriented linear polarized wave as well as circularly polarized waves. Furthermore, the surface is stable against oblique incidences of up to 60° at the lower frequency bands. The proposed FSS has potential applications in Fabry-Perot cavity antennas with reduced radar cross-section (RCS).

Platforms with low radar signatures require compatible antennas (low scattering) for communication purposes. Under this context, the article presents two Fabry-Perot (FP) Cavity antennas (Ant-1 and Ant-2). Ant-1's aperture is an integrated design of artificial magnetic conductor (AMC) surface and a phase gradient metasurface (PGM), incorporating three unit-cell structures. The antenna achieves reduced monostatic scattering over broad bandwidth, and simultaneously obtains high gain as well as tilted beam peak radiation. Patch radiating at 7 GHz forms excitation source of the cavity, and cavity height is 0.33λ, smaller than the heights of conventional cavity designs ( λ/2). RCS reduction is obtained over a bandwidth of 105.8% (4-13 GHz) for arbitrary polarizations, covering C/X bands. Antenna gain is 12 dB, and peak radiation tilt is -60° in elevation plane. Simulations have been verified through fabricated prototype. Ant-2 is a modification of Ant-1. Ant-2's aperture is constructed from two unit-cell structures, and its aperture size is 41% smaller than Ant-1. Its cavity height is 0.3λ. Ant-2 also achieves wideband backscattering reduction; however, due to asymmetric layout of unit-cell elements over the aperture, radar cross section (RCS) reduction bandwidth is different for the two polarizations. For vertically polarized (VP) incident wave, RCS reduction bandwidth is 105.8% (4-13 GHz), but for horizontally polarized (HP) wave, it is 85.7% (5.2-13 GHz). Nevertheless, broadband RCS reduction is still achieved for both polarizations. Peak gain is 11.73 dB, achieved at -37° tilt angle. Simulations are presented for Ant-2. Compared to literature, both antennas show various improved results.

In a recent publication, Lu et al