Compact Decoupling Network for Closely Spaced Microstrip Antennas

In this paper, a compact decoupling network is proposed to improve the isolation between the closely spaced MIMO elements. It consists of a quarter wavelength open-circuited microstrip line, which is connected to the ground plane using a via at the other end. The decoupling network is placed in between the closely spaced rectangular microstrip patch antennas without using any additional space. The proposed design has been compared with that of using a half-wavelength short-circuited microstrip line as a decoupling network and without any decoupling network. The results show an isolation better than 28 dB over the entire frequency range. The proposed design provides an ECC of less than 0.001, a diversity gain greater than 9.9 dB, and a multiplexing efficiency of better than -0.5 dB.