Reduction of mutual coupling between closely spaced microstrip antennas with H-shaped isolation wall

This paper presents a novel H-shaped isolation wall structure (called as H-wall in this paper) that effectively suppresses the mutual coupling and improves the isolation between two closely spaced microstrip antennas. The H-wall consists of an H-shaped copper strip etched on a substrate, and a row of periodic vias through which the strip is connected to a ground. The H-wall is inserted between two microstrip antennas, and surrounds one-half of the peripheral edge of each antenna. The important advantage of the proposed H-wall is that it does not significantly degrade the antenna bandwidth, gain, and front-to-back (FB) ratio unlike other isolation structures based on resonator or defected ground structure (DGS). A prototype has been fabricated and measured to confirm the validity of the proposed design, as shown in Fig. 1. Two microstrip patch antennas operating at 5.2 GHz are faced to each other with a small gap of 3mm (0.052λ
0
). The patch size is 16.4 × 16mm
²
(0.284λ
0
× 0.277λ
0
). The H-wall consists of a 2-mm width copper strip and 0.5-mm diameter ground vias. They are etched on a 1.57mm thick substrate (ε
r
= 2.5, tan δ = 0.0015). The measured return loss and isolation are shown in Fig. 2. The prototype is well matched at 5.2 GHz and has a high isolation of 51 dB at this frequency. The measured 10-dB return loss bandwidth is 3.2%, which is wide enough considering the patch size. In an anechoic chamber measurement, a high forward gain of 4.9 dBi with an excellent FB ratio of 24 dB is obtained at 5.2 GHz. The proposed mutual coupling reduction method can be used in various antenna array applications.