Reduction of Mutual Coupling and Realization of Circular Polarization of Dual-Port MIMO Antenna With Negative Edge-to-Edge Distance

A simple and efficient solution to suppress the mutual coupling (MC) between dual microstrip patches with close and even negative edge-to-edge distance is proposed and applied to realize the circularly-polarized (CP) radiation without extra decoupling circuits in this communication. The TM_1.5,1 mode is excited and adjusted to achieve the MC reduction by only loading shorting pins and etching slots. Furthermore, by asymmetrically adding four stubs between the etched slots, the high-order mode can be improved to generate dual orthogonal electric fields with 90° phase difference for circular polarization. Two prototypes are simulated, fabricated and measured. Measured results indicate that the proposed decoupling method can efficiently enhance the isolation while having little impact on the reflection bandwidth. The proposed designs have the potential for linearly-polarized (LP) and CP multi-input multi-output (MIMO) communication systems with compact size and limited spaces.