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

In this letter, a wideband circularly polarized four element multiple-input–multiple-output (MIMO) antenna is reported. The impedance and the axial ratio bandwidth (ARBW) of wideband circular polarization (CP) MIMO antenna are 82% and 81.5%, respectively. The ARBW 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 3.4 GHz to 8.25 GHz. The MIMO diversity performances are investigated using measured S-parameter. The diversity gain, channel capacity loss, envelope correction coefficient and total active reflection coefficients 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 2.3 ns variation. The high overlapping factor of 0.99, wider ARBW of 81.5% without using additional feeding network makes the wideband CP MIMO antenna compact in size.