Isolation Enhancement for MIMO Patch Antennas Sharing a Common Thick Substrate: Using a Dielectric Block to Control Space-Wave Coupling to Cancel Surface-Wave Coupling

This article presents a novel and simple decoupling method to increase the isolation between two closely spaced patch antennas sharing a common thick substrate. The decoupling can be simply realized by adding a pure dielectric block (DB) above the coupled array. By means of DB to modify the space permittivity (propagation constant), the space-wave coupling can be controlled to cancel surface-wave coupling for isolation enhancement. Five benchmarks of combinations of two patch antennas with different positions or orientations are investigated to validate the decoupling concept and elaborate on the design procedure. The results show that the proposed method could provide over 20 dB isolation enhancements for patch antennas with 0.1λ
₀
or 0.027λ
₀
separation distances. Besides, wide isolation bandwidths and good radiation performances can be achieved for the DB-loaded antennas without reduction in total efficiency, front-to-back ratio (FBR), boresight gain, or polarization purity. Notably, the DB can be designed independently of the original array, making this method potential for some previously fabricated arrays without requiring modifying or replacing them with new ones.