A Compact Single-Layer Four-Port Orthogonally Polarized Yagi-Like MIMO Antenna System

A wideband compact Yagi-like directional multiple-input- multiple-output (MIMO) antenna system is presented based on a slot loop excitation. Four orthogonally polarized beams are generated by orthogonally feeding the slot loop elements using microstrip lines. The proposed design is based on a single-layer geometry with an overall size of 35 × 90 × 0.76 mm3, which is suitable for compact wireless handheld devices. The conventional vertically polarized omnidirectional beams from each slot loop element are made directional and horizontally polarized by using two passive complementary slot reflector (CSR) elements. The antenna system has a wide measured bandwidth of 620 MHz (3.26-3.88 GHz) targeting the 3.6 GHz WiMAX band. It has a maximum realized gain of 4 dBi and front to back ratio (FBR) of more than 7 dB within the band of operation. The proposed antenna system shows good MIMO performance with a minimum measured isolation of 10 dB between the adjacent ports and more than 20 dB between other ports. The orthogonal beams of the antenna system help in achieving low envelope correlation coefficient (ECC) values of less than 0.1. The measured total efficiency of the antenna system is more than 75% for all the ports of the antenna system.