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The present work describes a unique planar low-profile wideband circularly polarized Multiple-Input and Multiple-Output (MIMO) antenna operating in the X-band, with pattern and polarization diversity over the entire axial-ratio bandwidth (ARBW). The design is unique in the sense that a simple grounded stub introduced between two linearly polarized monopole antennas has been used to realize wideband circular polarization, pattern diversity, and high isolation between antennas. The ARBW of the MIMO antenna is 2.45 GHz (8.11–10.56) 3 dB and its impedance matching bandwidth is 3.52 GHz (8.07–11.59). The isolation is better than 20 dB. The antenna can be easily adapted to operate other frequency bands by simple frequency scaling. It has been fabricated on an FR-4 substrate and its performance has been compared against several existing available antennas.

In this study, the authors propose a new type of metasurface, namely a sandwiched anisotropic metasurface, for converting a linearly polarised elliptical patch antenna into a wideband circularly polarised antenna. A partially reflecting surface (PRS) as a superstrate is further used to enhance the gain of the antenna. The design rules of the antenna are also presented. The combined metasurface and the PRS‐based patch antenna is designed on a low‐cost substrate FR‐4. The realised 3 dB axial ratio bandwidth (ARBW) of the antenna is 1.01 GHz (3.55–4.56 GHz), its impedance matching bandwidth is 1.33 GHz (3.08–4.41 GHz), and its peak gain varies from 7 to 7.84 dB within the band. By placing the PRS superstrate above the antenna, gain further improves to 9.32 dBi without degrading the performance of the antenna. Measured results are presented to validate the antenna performance and results are compared against a large number of similarly available antenna.

The present work describes a unique planar wideband circularly polarized MIMO antenna for 4G and Sub-6 5G band (1.35-2.75 GHz), with pattern diversity over the entire axial-ratio bandwidth. The design consists of two tri-branch planar inverted-F antenna (PIFA) antennas with a ground T-stub between the antennas, which is used to realize circular polarization and high isolation. The third antenna is an integrated Sub-6 5G (4.45-4.7 GHz) and LTE band (786.7-807.7 MHz) antenna, which is folded above the ground and placed vertically around the side. It also provides circular polarization at LTE band. The 3 dB axial ratio bandwidth (ARBW) of the MIMO antenna is 1.08 GHz (1.47-2.55 GHz); impedance matching bandwidth (IMBW) is 1.4 GHz (1.35-2.75 GHz); and its isolation is better than 13.4 dB in the whole band. It is fabricated on an FR-4 substrate and is suitable for mobile handset.

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