Study on isolation improvement between closely packed patch antenna arrays based on fractal metamaterial electromagnetic bandgap structures

A decoupling metamaterial (MTM) configuration based on fractal electromagnetic bandgap (EMBG) structure is shown to significantly enhance isolation between transmitting and receiving antenna elements in a closely packed patch antenna array. The MTM-EMBG structure is cross-shaped assembly with fractal slots etched in each arm of the cross. The fractals are composed of four interconnected ‘Y-shaped’ slots that are separated with an inverted ‘T-shaped’ slot. MTM-EMBG structure is placed between the individual patch antennas in a 2×2 antenna array. Measured results show the average inter-element isolation improvement in the complete band of interest is 17 dB, 37 dB and 17 dB between radiation elements #1 & #2, #1 & #3, and #1 & #4, respectively. With the proposed method there is no need for metallic via-holes. The proposed array covers the frequency range of 8- 9.25 GHz for X-band applications, which corresponds to a fractional bandwidth of 14.5%. With the proposed method the edge-to-edge gap between the antenna can be reduced to 0.5λ0 with no degradation in the antenna’s radiation patterns. The gain of the antenna array varies between 4 dBi and 7 dBi. The proposed method is applicable for implementation of closely packed patch antenna arrays, e.g. multiple-input-multiple-output (MIMO) systems, and synthetic aperture radars (SAR)