Design of a Frequency Selective Surface Backed Wideband Sub-6 GHz Band MIMO Antenna with High Isolation for 5G Applications

In this paper, a stub-loaded 2-port MIMO antenna is introduced for applications across the n77 (3.30–4.20 GHz), n78 (3.30–3.80 GHz), n79 (4.40–5.00 GHz), Wi-Fi-5 (5.15–5.85 GHz), and 7–7.83 GHz bands. It comprises a microstrip line feed, a two-port stub-loaded MIMO antenna, and an FSS (frequency selective surface) filter. The antenna designed with dimensions of 37.5 × 32 mm
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on an FR-4 epoxy substrate PCB with a thickness of 1.6 mm. The FSS structure contains 16 circular vertex square-shaped unit cells arranged in a 4×4 array, with a size of 50×50×1.6 mm
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, and due to stub and FSS loading, gain, bandwidth, and isolation improved significantly. The design process utilizes the ANSYS HFSS tool, and the antenna operates within the frequency ranges of 3.36–5.76 GHz and 7–7.83 GHz. Moreover, the isolation value achieves a minimum of −18 dB and −15 dB for nearly simulated and measured results across the entire band. Peak gain reaches a maximum of 6 dBi and a minimum of 3.35 dBi due to FSS loading. Radiation patterns exhibit high directivity at lower and higher frequencies and nearly omnidirectional behavior at middle frequencies, attributed to the passband filter characteristics of the FSS. The MIMO diversity parameters ECC and CCL are verified to be within acceptable limits. This innovative antenna can envisaged for sub-6 GHz band 5G applications.