In this paper, a metasurface-based multiple-input multiple-output (MIMO) antenna with high isolation between antenna elements is presented. The main patch radiator is sandwiched between a metasurface and a ground plane to achieve performance enhancement. The fabricated single element antenna has a compact size of $0.85\lambda _{0} \times 0.85\lambda _{0} \times 0.038\lambda _{0}$ . The antenna exhibits a wideband operational bandwidth from 3.27 to 3.82 GHz for $\vert \text{S}_{11}\vert < -10$ , which corresponds to a fractional bandwidth of 15.5%. Moreover, stable radiation patterns with a peak gain of 8.1 dBi are also achieved across the operating band. The proposed single element antenna is characterized for $2 \times 2$ MIMO system by translating each antenna element orthogonal to each other. A decoupling structure consisting of slots and metallic strip with shorting pins is used to improve the isolation between the MIMO elements. The shorting pins connect the metallic strips (located between MIMO elements) on the metasurface and ground plane. These slots on ground plane and shorting pins affect the electromagnetic field distribution and consequently reduce the mutual coupling. The fabricated MIMO antenna has a compact size of $1.75\lambda _{0}\times 1.75\lambda _{0} \times 0.038\lambda _{0}$ . The proposed 4 port ( $2\times 2$ ) MIMO antenna provides 15.9% of 10 dB impedance bandwidth from 3.3 to 3.87 GHz with a peak gain of 8.72 dBi. Moreover, the proposed MIMO antenna offers excellent diversity performance, isolation between antenna elements is very high (>32dB), ECC is lower than 0.001, and diversity gain is 9.99 dB very close to the ideal value of 10dB. Owing to these features, the proposed MIMO antenna can be a good candidate for 5G Sub-6 GHz (n78 band) smart devices and sensors.

This paper presents an AMC (artificial magnetic conductor)-based wideband circularly polarized printed monopole antenna for unidirectional radiation. The antenna includes an AMC reflector, a coplanar waveguide (CPW) feed structure to excite the antenna, a ground plane with a rectangular slot on the left side of feedline, and an asymmetrical ground plane on its right side. The induced surface currents on CWP feedline, rectangularly slotted, and asymmetrical ground planes cause circularly polarized radiations. The AMC reflector consisting periodic metallic square patches is used instead of the conventional PEC (perfect electric conductor) reflector, the distance between the antenna and reflector is reduced from 0.25λ0 to 0.18λ0 with performance improvement. By incorporating AMC layer with the monopole antenna, the gain of antenna is increased from 3.3 dBic to 8.7 dBic while the axial ratio bandwidth (ARBW) of antenna is increased from 27.27% to 51.67%. The simulated and measured results show that the proposed antenna has an overlapping 10-dB |S11| and 3-dB ARBW of 51.67% (3.0–5.09 GHz). The overall dimensions of monopole antenna backed by AMC reflector is 1.20λ0 × 1.20λ0 × 0.21λ0 and covers 5G sub-6 GHz new radio bands (n77/n78/n79) for wireless communication systems.

In this paper, a wideband circularly polarized (CP) magnetoelectric (ME) dipole antenna operating at 28 GHz band was proposed for 5G millimeter-wave (mm-wave) communications. The antenna geometry included two metallic plates with extended hook-shaped strips at its principal diagonal position, and two corners of truncated metallic plates at the secondary diagonal position. The pair of metallic vias connected the modified strips to the ground plane to create the magnetic dipole. The L-shaped probe feed between the strips was used to excite the antenna. The antenna showed stable gain and wideband characteristics. The simulated and measured results showed that the proposed CP ME dipole antenna had an overlapping (|S₁₁|< −10 dB impedance and 3 dB axial ratio) bandwidth of 18.1% (25–30 GHz), covering the frequency bands dedicated for 5G new radio communications. Moreover, an average gain of 8 dBic was achieved by the antenna throughout the operating bandwidth. The measured data verified the design concept, and the proposed antenna had a small footprint of 0.83 λ_o × 0.83 λ_o × 0.125 λ_o (λ_o is free space wavelength at the lowest operating frequency), suitable for its application in 5G smart devices and sensors.

This paper presents a detailed study on 2D flattened Luneburg lenses using quasi-conformal transformation optics (QCTO) and their performance at 30 GHz. This analysis reveals that QCTO transformations distort the focal circle of the original 2-D circular Luneburg lens, resulting in degraded performance, particularly for severe flattening angles and large sizes. Two different transformations are compared in terms of their resulting focal plane aberration and far field performance. Furthermore, we introduce two methods to correct the focal plane aberration and improve the directivity of the flattened lenses by over 3 dB in select directions.