A Planar Printed Four-Element Pattern Diversity MIMO Antenna Based on Novel Quasi-Yagi Elements

In this paper, a new planar printed quasi-Yagi antenna with compact size and wide bandwidth is presented for a multiple-input-multiple-output (MIMO) antenna system. Antenna element consists of a rectangular driven monopole, a strip director, and a coplanar ground shorted reflector. A planar rectangular monopole is used for the first time as a driven element instead of a dipole to avoid the implementation complexity of BALUN as it can be fed directly by an unbalanced coaxial feed. It has been shown that the antenna element has an impedance bandwidth (|S-11| < -10 dB) of 60.5% ranging from 1.59 to 2.97 GHz. Based on this element, a four-element pattern diversity MIMO antenna is proposed. By utilizing the ground of one element as a reflector for the successive element, a compact size of 109 mm x 109 mm (0.54 lambda(0) x 0.54 lambda(0) at 1.5 GHz) has been obtained. Measured bandwidth of 65.9% (1.5-2.97 GHz) with minimum isolation of 13 dB has been achieved. The measured directional patterns and an average gain of 4 dBi, remain stable in the operating band with cross-polarization levels less than -25 dB. The envelope correlation coefficient and channel capacity loss show good diversity performance.