A 4-Element Wideband MIMO Antenna using Quarter-Mode SIW and 90-Degree Bent Planar Dipole

In this paper, a wideband, multiple-input-multiple-output (MIMO) antenna with good isolation based on the complementary antenna concept is proposed. The complementary antenna is based on a quarter-mode substrate integrated waveguide (QMSIW) and a 90-degree bent planar dipole, with the former acting as a magnetic dipole and the latter as an electric dipole. The proposed complementary antenna is fed coaxially. Good isolation between the antenna elements is obtained without any decoupling network throughout the operating bandwidth even though they are in electrical contact with each other. A fabricated prototype achieves a measured impedance bandwidth of 27.6%, an envelope correlation coefficient (ECC) of less than 0.004 and, stable gain higher than 4.8 dBi. The port to port isolation is higher than 18.7 dB, and 33.2 dB for adjacent antennas and diagonally opposite antennas, respectively, throughout the operating band. The effect of the substrate thickness on the bandwidth and the isolation is studied. It is observed that a bandwidth of 47% with good isolation is achieved for a substrate thickness of 3.8 mm.