Circularly Polarized Wide-Band Quad-Element MIMO Antenna With Improved Axial Ratio Bandwidth and Mutual Coupling

In this letter, a wide band Circularly polarized four element multiple input multiple output (MIMO) antenna is reported. The impedance and the axial ratio bandwidth (ARBW) of wide-band CP MIMO antenna are 82% and 81.5% respectively. The axial ratio bandwidth of single element is controlled by modifying the ground plane. The design steps are illustrated with characteristics mode analysis. The four elements are arranged orthogonal in MIMO configuration and also the plus shaped decoupling structure (PSDS) is placed to reduce inter element coupling. The measured results are presented and compared with simulated results which shows both are in good agreement. According to measured S-Parameter and axial ratio, the operating frequency of fabricated quad port MIMO antenna is 3.4GHz to 8.25GHz. The MIMO diversity performances are investigated using measured S-Parameter. The diversity gain (DG), channel capacity loss (CCL), envelope correction coefficient (ECC) and total active reflection coefficients (TARC) are reported to provide MIMO performance. The linear phase characteristics are confirmed with the group delay performances of fabricated antenna.It is found that the almost constant group delay within 2.3ns variation. The high overlapping factor (OF) of 0.99, wider ARBW of 81.5% without using additional feeding network makes the wide band CP MIMO antenna compact in size.