Metasurfaces are two-dimensional artificial structures which have extraordinary electromagnetic properties. They have been used in myriad of devices such as nano-antennas, cloaking coatings, imaging devices, flat lenses, and Polarization converters over a wide range of frequency. Due to high dependency of many devices on incident wave Polarization, manipulating the Polarization of electromagnetic waves would be useful, especially in the THz regime. In this study, we propose a linear to circular Polarization converter (LTC-PC) based on a THz reflective Metasurface. For a TE linear Polarization incident wave, this structure has two distinct bands; the first one lays in a wideband frequency range of 0.5-1.41 THz, in which the reflected wave would be a left-handed circular Polarization (LHCP) with minimum efficiency of 89% and maximum efficiency of more than 95% in 80% of the bandwidth. The second band lays in the narrowband frequency range of 1.45-1.55 THz, resulting a right-handed circular Polarization (RHCP) wave with a minimum efficiency of 82%. The proposed Polarization converter can be used in optical communication and electronic devices.

The mutual coupling issue between two Right Hand Circularly Polarized (RHCP) Magneto-electric (ME) dipole antennas is addressed in this study. To mitigate this issue, a Metasurface Polarization-Rotator (MPR) Wall is employed, resulting in effective minimization of the coupling effects. The innovative antenna design, with high gain, shows promise for 5G applications. It consists of two electric dipole plates with triangular corners positioned at the top, along with two plates acting as magnetic dipoles perpendicular to the ground plane. Additionally, the presence of four plates on the outer periphery of the antenna contributes to the improvement of the circular Polarization (CP) performance of the antenna. The feeding structure is configured in a V-shape. Integration of the Metasurface Polarization-Rotator led to a significant reduction in mutual coupling. On average, the mutual coupling is decreased by more than -20.5 dB, reaching impressive values of -45 dB at 2 GHz, -55 dB at 3.1 GHz, and -40 dB at 3.7 GHz when the MPR wall is placed between the ME antennas. The antenna demonstrates promising performance in terms of impedance bandwidth, with a remarkable value of 61.4% for |S11| < [-10dB]. Furthermore, the axial ratio bandwidth for AR < [3 dB] is 63.36%, representing an 11% increase compared to the configuration without the MPR Wall. The maximum right-hand circular Polarization gain achieved by the antenna is 9.91 dB at a frequency of 3 GHz. Additionally, the maximum front-to-back ratio (FBR) is 37.6 dB at a frequency of 2.5 GHz. By comparing and analyzing the simulation results for the scenarios with and without the MPR Wall, it becomes evident that the MPR Wall does not significantly affect the parameters of gain, front-to-back ratio, and impedance bandwidth.

In this paper, a novel low-profile and low cross-Polarization Metasurface antenna is proposed for 5G mm-wave applications. The proposed antenna consists of two layers, with a slot antenna as the base and a novel Metasurface layer on top. The Metasurface layer is a 3×3 array of patches. By strategically incorporating slits and stubs within the middle patches, the undesired degenerate mode is separated from the fundamental mode, and higher-order modes are suppressed that typically appear in conventional Metasurfaces. Additionally, rectangular slots are added in the middle of the corner patches to shift higher-order modes to frequencies beyond the desired operating bandwidth, mitigating issues such as beam splitting and beam squint in the radiation patterns. Experimental measurements demonstrate that the proposed Metasurface antenna operates over a bandwidth of 25.14% (23.3 GHz to 30 GHz), with a return loss better than 10 dB, a peak gain of 8.1 dB, and an XP level lower than -26 dB and -53 dB at  and  planes, respectively. Compared to conventional Metasurface antennas, our design reduces the antenna dimension by 62%, resulting in a compact size of 0.72λ0 × 0.72λ0 × 0.08λ0. Furthermore, we validate the performance of the single-element antenna by employing it in a 2×2 Multiple Input-Multiple Output (MIMO) configuration without requiring additional inter-element spacing. The MIMO antenna exhibits promising performance as well. Overall, our proposed low-profile and low cross-Polarization Metasurface antenna shows great potential for 5G mm-wave applications, offering improved efficiency and reduced size compared to conventional designs.

This paper presents a 2-bit programmable digital Metasurface for real-time beam steering applications at X-band. Tunability of the Metasurface is provided by employing a varactor in the unit cell structure to control each unit cell independently. This ability leads to achieve beam steering capability in both elevation and azimuth directions. The structure is designed so that the biasing circuit has no electrical connection to the MS ground. The equivalent circuit model of the unit cell is also presented to better investigate its physical behaviour. Furthermore, the effects of number of unit cells and states of reflection phase on far-field pattern are investigated. Finally, the numerical results are compared to analytical ones, where a good agreement between them is observed.