A compact four-port UWB MIMO antenna with connected ground and wide axial ratio bandwidth

A new design method of an ultra-wideband circularly-polarized planar multiple-input-multiple-output (MIMO) antenna is presented in this paper. The proposed MIMO antenna consists of four unit cell antennas, being comprised of a microstrip feed line and a square slotted ground plane. In the proposed unit cell design, a circular stub is protruded from the ground plane strip for achieving circular polarization. The unit cell of the MIMO antenna is optimized by adjusting design parameters. The compact four-port MIMO antenna prototype is designed on the FR4 substrate with the overall dimensions of 45 x 45 x 1.6 mm(3). The proposed four-port MIMO antenna design provides an impedance bandwidth (S-11 < -10 dB) of 112% (3.1-11 GHz) and a 3 dB axial ratio bandwidth of 36% (4.8-6.9 GHz). The performance of the fabricated MIMO antenna shows good agreement between the EM simulation and measurement results.