Compact decoupling structure for improving isolation of MIMO antennas

In this paper, a compact planar spiral line (PSL) structure between two closely packed PIFAs is proposed for enhancing port isolation and reducing size. The decoupling structure has the dimensions of less than 0.1λ×0.1λ, and can be flexibly applied to various practical MIMO systems. For two closely placed PIFAs with distance of 0.1λ, a high isolation (better than 20 dB) within the WLAN band is achieved by employing this structure. Meanwhile, the 10dB return loss bandwidth of the PIFAs is doubled (2.34-2.63 GHz). The decoupling mechanism and design requirement of PSL are discussed. Influences of the proposed PSL to the efficiency, gain and radiation pattern of PIFAs were also studied. Good agreement between the simulated results and measured results is obtained.