Correlation Reduction in Closely-Spaced MIMO Antenna With Circular Polarization Diversity

Radiator correlation in multiple-input-multiple-output (MIMO) antenna has always been a serious concern for MIMO systems. In this paper, an antenna consisting of two parallel-placed coplanar waveguide (CPW)-fed radiators engineered on a common coplanar ground plane is presented. The antenna is designed with three parallel coplanar ground planes and two feed lines. The two outermost ground planes are systematically modified by etching a slot to form a quasi-loop, whereas the middle ground plane is made asymmetric along the feeding line. The current flowing on the edges of the quasi-loops generates opposite senses of circular polarization due to switched positioning of the slotted ground plane with respect to the feedline. This induces polarization diversity in the antenna. The proposed structure with circular polarization diversity features a low level of envelop correlation coefficient (ECC), < 0.005. Moreover, a wide impedance bandwidth ( |S11|≤−10 dB ) and axial ratio (AR) bandwidth of approximately 38.5% from 4.7 GHz to 6.7 GHz. The average in-band isolation is ( |S21|≤−15 dB ) with the peak realized gain of 3.15 dBic when operated with the bi-directional radiation characteristics in the ±z -direction