A Low-Profile Hybrid Decoupling Method for Ultra-Compact Planar Antenna Arrays

Abstract

This paper presents a novel and compact decoupling methodology for ultra-compact planar antenna arrays with center-to-center spacing smaller than 0.3 λ. In such densely packed configurations, strong multidirectional mutual coupling significantly degrades the array performance. To address this challenge, a comprehensive decoupling strategy is proposed for a 2 × 2 array operating in the 5.8-6 GHz band. The approach integrates three coordinated mechanisms: I-shaped metallic strips for coupling-path cancellation, a dumbbell-shaped defected ground structure (DGS) for ground-current suppression, and dielectric perturbation for reducing substrate-mediated coupling. The proposed structure achieves effective two-dimensional decoupling while maintaining a low-profile and easy-to-fabricate configuration. By performing a systematic parametric study and Genetic Algorithm (GA) the structure is optimized in the multidimensional design space. Both simulated and measured results demonstrate that the proposed method successfully reduces the transmission coefficients between array elements to below -20 dB across the target frequency band, satisfying the critical design requirement. The achieved isolation enhancement does not degrade the impedance matching, and the measured radiation patterns further demonstrate that the proposed decoupling structure improves the realized gain by 2.85 dB and 4.34 dB at the lower and upper edges of the operating frequency band, respectively.