A novel defected ground structure for high-isolation circularly polarized MIMO patch antenna

This paper introduces a method to reduce mutual coupling in a two-element multiple-input multiple-output (MIMO) antenna, which is a significant challenge due to the need for high isolation over a wide frequency range with close element spacing. Previous works typically achieved high isolation within a narrow bandwidth. The paper presents a novel defected ground structure (DGS) with a modified I-shaped slot, which effectively minimizes mutual coupling in a dual-sense MIMO circularly polarized (CP) antenna over a broader bandwidth than the previous approaches. The fabricated 2-element prototype with an overall size of 0.98λ × 0.71λ × 0.05λ and an edge-to-edge spacing of 0.08λ at the center operating frequency has a measured bandwidth of 2.5% (5.2–5.33 GHz). Across this band, the isolation is always better than 35 dB and the gain is higher than 4.8 dBi. The MIMO parameters are also investigated, which proves the good diversity performance of the proposed design.