The multiple-input-multiple-output (MIMO) system consisting of multiple antenna elements faces issue of isolation performance between antenna elements. In this paper, isolation is improved by inserting a thin parasitic slit between antennas on the upper side and a plus-shaped stub in the ground plane. The proposed MIMO antenna consists of two bevelled circular antennas with a common partial ground. It is designed on FR-4 substrate having 12.5 mm x 24 mm x 1.6 mm dimensions. Bevelling is applied at the bottom of a circular patch to attain wideband performance. This antenna achieved bandwidth from 5.22 GHz to 14.89 GHz and offers isolation better than 15 dB in most of the operational bands while isolation more than 20 dB in the entire X-band. The Envelope Correlation Coefficient (ECC) of the antenna is less than 0.017 and DG is more than 9.9175. It offers an acceptable gain between 1.12 to 3 dBi and radiation efficiency between 57 to 75 %. The simulation and measurement results show good agreement. The designed MIMO antenna is compatible with WLAN (5.2 GHz to 5.8 GHz), upper C-band (5.22 GHz to 8 GHz), X-band (8 GHz to12 GHz) and lower Ku-band (12 GHz to 14.89 GHz) applications.
