Design of a dual-polarized MIMO antenna with high isolation

Abstract

Multipolarized MIMO antennas can effectively increase the channel capacity of wireless communication systems and also provide a compact design of the MIMO antenna for the space limited applications. However, if the dual-polarized antenna is composed of a coplanar loop and dipole, the mutual coupling between the two antennas are generally very high, which causes the decrease of the performance of MIMO antenna. In this paper, a dual-polarized MIMO antenna with a dual-layer mushroom EBG structure is presented working at 2.4 GHz bands. The MIMO antenna consists of a loop and a coplanar dipole placed in the middle of the loop In order to retain the radiation characteristics of a magnetic dipole, the electric loop should have a constant current distribution, thus the loop is constructed based on a structure of dash line which is an artificial zerophase transmission line and can ensure that the current is of equal magnitude and in-phase along the loop. The antenna elements are printed on an FR4 (relative dielectric constant of 4.4, loss tangent of 0.02) substrate with dimensions of 70mm × 75mm × 1.6 mm. Isolation enhancements are achieved by introducing a dual-layer mushroom EBG structure. Based on the concept of slow-wave propagation, the dual-layer mushroom EBG structure performs well in both antenna miniaturization and mutual coupling mitigation. Its upper layer acts as a band-stop filter at the antenna's resonant frequency and reduces the unwanted surface waves occurs in the substrate, while the inner layer aids in the antenna miniaturization. Simulation results show that the amplitude of S 21 is below −17 dB at the resonant frequency, which is 12.1 dB lower than that of the MIMO antenna without an EBG structure.