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Isolation and Circular Polarization Diversity in 2×1 MIMO Microstrip Patch Array Using Closed Metallic Loop

Year: 2026
Type: article
Abstract: This article presents a decoupling method to improve isolation and circular polarization in a two-element multiple-input–multiple-output (MIMO) microstrip patch antenna (MPA) array in the H-plane. The proposed approach utilizes a simple, closed metallic loop (rectangular geometry) connected to the MPA’s rear edges, allowing for ultra-compact spacing without compromising isolation and polarization diversity. The loop serves two purposes: suppressing mutual coupling by converting the coupled TM01 mode to TM11 mode and generating circular polarization by exciting orthogonal modes. Additionaly, the circular polarization is further enhanced by grounding the loop using a pair of annular vias. Characteristic Mode Analysis (CMA) is conducted to reveal the orthogonal mode pairs responsible for circular polarization and their dependence on the loop geometry. A prototype was fabricated and measured, achieving an impedance bandwidth of 4.8% (5.65–5.93 GHz) with an isolation level of 48 dB, maintaining ultra-compact edge-to-edge spacing of $0.02\lambda $ and an overlapping 3 dB axial ratio bandwidth of 1.3% (5.749–5.84 GHz). A circular polarized (CP) gain of 5.8 dBic is achieved in the broadside direction, whereas cross-polarization levels are −27 dB and −20 dB in the $\phi =0^{\circ } $ and $\phi =90^{\circ } $ planes, respectively. Furthermore, the design exhibits polarization diversity. Owing to its dual-purpose closed-loop configuration, which allows both isolation and circular polarization within a very compact footprint, the proposed array presents a simple yet effective solution for space-limited MIMO applications at 5.8 GHz wireless systems.
Source: IEEE Access
DOI: 10.1109/access.2026.3661731
Language: English
Open Access status: gold
Estimated APC paid: $2,075
OpenAlex ID: W7128316303
FWCI: 6.584
Cites: 46
Cited by: 5
Related to: 10