Dual-Band Quasi-Independently Tunable Reconfigurable MIMO Antenna Array with Etched Ground Decoupling

This paper presents a compact dual-band reconfigurable MIMO antenna array for frequency-agile, high-isolation operation in densely integrated wireless systems. Each element employs an air-gap-suspended patch fed by an L-shaped probe, with two sets of varactor diodes placed at different current-concentration regions to enable approximately independent continuous tuning of the low band (1.27–1.7 GHz) and the high band (2.21–2.55 GHz). Surface-current analysis shows that the low band is dominated by the fundamental patch mode, whereas the high band is excited by the U-shaped slot edge resonance; the spatial separation of the two modes supports their quasi-independent control. At the array level, U-shaped defected ground structures (DGS) are etched between adjacent elements to modify the coupling current paths and enhance inter-element isolation in both operating bands, without degrading impedance matching. Parametric studies confirm that the DGS consistently improves isolation across all tuning states. Simulation results show low envelope correlation coefficient (ECC), high diversity gain (DG), and stable radiation characteristics throughout the entire tuning range. The proposed design combines a compact structure, approximately independent dual-band continuous tuning, and stable isolation performance, offering a promising solution for space-constrained next-generation wireless communication systems.