Isolation Enhancement for MIMO Patch Antennas Using Near-Field Resonators as Coupling-Mode Transducers

In this paper, a novel decoupling technique for closely packed patch antennas using near-field resonator (NFR) above each antenna element is proposed. The decoupling mechanism is illustrated by investigating the electric-field (E-field) and magnetic-field (H-field) distributions. The E-field distributions indicate that the NFRs above the patches serve as coupling-mode transducers to produce an orthogonal coupling mode at the desired resonance, leading to high port isolation between the patches. The H-field distributions demonstrate that the H-fields in the substrate are confined within the excited element, leading to the effective suppression of antenna mutual coupling. The NFR can be easily applied to multiple-input multiple-output (MIMO) antennas having multiple patch elements. Three practical decoupling examples are demonstrated and the simulation and measurement results show that impedance matching for each antenna port and isolation of better than 20 dB are achieved for all these examples using the NFRs. Moreover, for the H-plane and E-plane decoupling of wideband two-port MIMO antennas, wide decoupled impedance bandwidths of 6.1% and 5.8% are obtained, respectively. More results of radiation patterns reveal that good radiation performance is reserved with no reduction in realized gain or front-to-back ratio.