In this work two-port multiple input multiple output (MIMO) antenna with self-isolation between antenna elements is presented. Initially, the proposed antenna is constructed as a single-port square-shaped radiating patch connected diagonally with a stub to operate the antenna in frequency reconfigurable mode. A 2×2 mm slot is cut at the middle part of the stub for implementing reconfigurability on the radiating patch to operate the antenna in multi-functional mode. Later the proposed antenna is converted to two-port frequency reconfigurable MIMO antenna that realizes an S11 below -10 dB intended for two resonant bands operating at 3.79 GHz (3.41-4.04 GHz) with pin-diode off-mode and 4.53 GHz (4.69-4.88 GHz) in on-mode with maximum peak realized gain of 4.93 dB at diode off-mode and 4.55 dB in pin diode on-mode. moreover, the gain is enhanced by 1.5 dB after converting to the two-port antenna. The two feeding ports of the proposed antenna are positioned orthogonal to each other to permit the antenna in self-isolation mode without connecting any de-coupling circuit and maintaining the mutual coupling (S21) below-21 dB in off-mode and -29.50 dB in diode on-mode. The distance between antenna elements is 0.12 λ0. In addition to that, two-port MIMO of envelope correlation coefficient (ECC), channel capacity loss (CCL), total active reflection coefficient (TARC), mean effective gain (MEG), and diversity gain (DG) are simulated. The designed antenna is applicable for 5G new radio (NR) bands of n48, n78 in off-mode, and n79 in on-mode respectively.
