An X-Band High-Isolation MIMO Antenna with a Resonant Ring Metamaterial Decoupling Structure

This paper proposes a compact broadband multiple-input multiple-output antenna array with a novel single-layer metamaterial decoupling structure. The metamaterial unit, composed of two symmetrically arranged split rings with distinct resonance characteristics, is positioned above the antenna elements to suppress mutual coupling. Measurements indicate that a -10 dB impedance bandwidth of 8.1–12.4 GHz (42.2% fractional bandwidth) covers the entire X-band. By integrating the metamaterial layer, the design achieves a minimum interport isolation of -22.7 dB (a 10.2 dB improvement) while maintaining a peak gain of 7.2 dB. Comprehensive evaluations of radiation patterns (front-to-back ratio >15 dB), envelope correlation coefficients (<0.002), and diversity gain (>9.99 dB) validate the proposed antenna’s suitability for X-band systems, particularly in phased array radars and satellite communications demanding high isolation and wideband operations.