Multi-Ring 4×4 UWB–X–Ku MIMO Antennas for High-Resolution Microwave Imaging: A Review
Keywords:
Ultra-wideband, multiple-input multiple-output, multi-ring antenna, microwave imaging, mutual coupling, X-band, Ku-band.Abstract
Wideband antennas for high-resolution microwave imaging must provide broad impedance matching, low mutual coupling, high efficiency, stable radiation, and sufficient spatial diversity. Multi-ring radiators integrated with 4×4 multiple-input multiple-output (MIMO) architectures are attractive because multiple resonant current paths can extend operation across conventional ultra-wideband (UWB) frequencies into the X- and Ku-bands. Lower frequencies provide greater penetration, whereas higher frequencies improve spatial discrimination. This review examines UWB imaging requirements, multi-ring resonance mechanisms, MIMO diversity, broadband isolation techniques, imaging-oriented performance metrics, and reconstruction considerations. Representative designs are compared in terms of bandwidth, isolation, diversity, and imaging relevance. Key research challenges include broadband decoupling, frequency-stable radiation, near-field calibration, realistic imaging validation, and joint optimization of antenna geometry and reconstruction. Multi-ring 4×4 MIMO arrays therefore offer a promising platform for biomedical imaging, nondestructive testing, and short-range high-resolution radar.
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