Circular Polarization Diversity Implementation for Correlation Reduction in Wideband Low-Cost Multiple-Input-Multiple-Output Antenna

In this paper, a multiple-input-multiple-output (MIMO) antenna featuring circular polarization diversity, and designed on a common coplanar ground is presented. The proposed antenna design utilizes a coplanar waveguide (CPW) feeding technique with three parallel coplanar ground planes, and two feedlines in-between. For circular polarization (CP), quasi-loops are created by etching slots on the outermost ground planes. With this configuration, circular polarization diversity is induced in the MIMO antenna with the left-hand CP (LHCP) from one antenna and the right-hand CP (RHCP) from the other. The total footprint of the antenna radiator is only <inline-formula> <tex-math notation="LaTeX">$0.78\lambda _{0} \times 0.55\lambda _{0} = 0.42\lambda _{o}^{2}$ </tex-math></inline-formula>. Experimental results show perfectly overlapping impedance and axial ratio bandwidths of 39.3% (4.5 GHz to 6.7 GHz). In addition, average in-band isolation <inline-formula> <tex-math notation="LaTeX">$\vert S_{21}\vert \le -15$ </tex-math></inline-formula> dB without any added complexity or active circuit elements. The peak realized gain of the antenna is 5.8 dBic with broadside radiation pattern in the +z- direction and envelope correlation coefficient (ECC) of 0.005. The antenna is suitable for multiple applications in the C-band that includes WLAN (5 GHz, 5.2 GHz and 5.8 GHz) and WiMAX (5.5 GHz).