Reducing mutual coupling for a square UWB MIMO antenna using various parasitic structures

In this study, a compact ultra-wideband (UWB) multiple input multiple output (MIMO) antenna system is designed for mobile terminals. The antenna system consists of two symmetrical 8×8 mm2 square antenna elements fed by a 50 Ohm microstrip transmission line (MTL). The UWB MIMO antenna operates at large frequency range of 2.5-13.3 GHz with an isolation level of about 9 dB less than 5 GHz and 15 dB greater than 5 GHz in average. In fact, the isolation level is almost sufficient for MIMO operation especially for high frequency. Nevertheless, various techniques are then investigated, and additional parasitic structures (PSs) such as monopole, V-shaped, plus-shaped, T-shaped PSs and neutralization line are thus designed on the square UWB MIMO for further reducing the mutual coupling. Among the PSs, T-shaped PS shows better return loss and isolation performance. Moreover, the proposed UWB MIMO antenna with T-shaped structure is investigated in terms of resonant bandwidth, radiation pattern, peak gain and envelope correlation coefficient (ECC). According to the results, the compact MIMO antenna has nearly omnidirectional patterns, stable gain and better diversity performance.