Isolation Enhancement for $1\times3$ Closely Spaced E-Plane Patch Antenna Array Using Defect Ground Structure and Metal-Vias

This paper introduces an effective solution for improving isolation in linear antenna array. The array is composed of three-element E-plane single feed patch antennas (the overall size is $0.59\,\,\lambda _{0}\,\,\times1.02\,\,\lambda _{0}$ ), which are closely placed with approximately $0.037~\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength at 4 GHz. The decoupling structure consists of T-shaped and rectangular ring shaped defect ground structure (DGS) with six metal-vias. The decoupling mechanism is illustrated by investigating the current vector on the ground plane. The current distribution indicates that the decoupling structure along the outer edge of the radiation patch sever as coupling current converter to produce reverse current opposite to the direction of the ground coupling current, which transmits along the outer edge of the radiation edge. The measured results show that the enhancement in the isolation at 4 GHz is 10.8 dB for $\vert \text{S}21\vert $ , 17.5 dB for $\vert \text{S}23\vert $ and 16.6 dB for $\vert \text{S}31\vert $ . After applying the decoupling structure, the 10-dB impedance bandwidth (3.95 - 4.04 GHz) of antenna 1 remains unchanged. Meanwhile, the 10-dB impedance bandwidth of the antenna, which is located in the middle of the three-element antenna array, increases by 86 MHz (from 114 MHz to 200 MHz). When the decoupling structure is loaded, the maximum gain only decreases by 0.12 dB (from 3.94 to 3.82 dB). The decoupling structure has the advantages of simple structure, easy processing, and independent design of the array, so it can be applied to multielement patch array, such as massive multiple-input multiple-output (M-MIMO) system.