Ultraminiaturized, Wideband and Flexible Square Ring-Shaped MIMO Antenna for Sub-6 GHz 5G (n77/n78/n79) Communications

This investigation presents a wideband, flexible, and ultraminiaturized square ring multiple-input multiple-output (MIMO) antenna made for sub-6 GHz applications. The design incorporates a semicircular ground plane with a neutralization line and two orthogonally positioned feed ports, together with two square ring radiating elements connected by four short strips, to enhance isolation between the two ports. To enhance isolation and MIMO performance, a 50 Ω microstrip line positioned orthogonally feeds each ring. The antenna achieves a wideband resonant with a center frequency of 4.2 GHz, maintains the S11 under -10 dB, and achieves port isolation of up to 18 dB across the frequency span from 3.2 to 5.8 GHz and a fractional bandwidth of 61.9% with maximum peak gain of 3.21 dBi. Detailed evaluations of the radiation patterns, surface current distributions, and S-parameters of the antenna are provided. Built on a flexible PDMS substrate, the antenna's observed findings closely match estimates, proving its efficiency. This design method consequently provides a dependable solution and has significant potential for 5G sub-6 GHz MIMO systems.