A Compact Low-Profile Hybrid-Mode Patch Antenna With Intrinsically Combined Self-Decoupling and Filtering Properties

A new type of patch antenna with intrinsically combined self-decoupling and filtering properties is first proposed to address the mutual coupling between elements of the same bands and adjacent bands. By specially engineering the metallic patch of a conventional microstrip antenna into two tightly connected radiators, i.e., a primary patch radiator and a secondary stub-loaded inverted-F radiator, this novel hybrid-mode patch antenna under dual closely located resonances of a TM ₀₁ patch resonator mode and an inverted-F resonator mode is favorably achieved. More importantly, the stub-loaded inverted-F radiator could not only introduce two radiation nulls allocated at both the lower and upper passband edges, leading to a good filtering response with a sharp band skirt and good selectivity in the boresight gain curve, but also function as an effective isolator that suppresses its near-field coupling, endowing its intrinsic self-decoupling property. Moreover, the developed patch antenna maintains the geometrical advantages of the typical microstrip antenna, including compact size, low profile, and single-layer configuration. In particular, the unique self-decoupling and filtering properties of the developed patch antenna make it a good candidate for multiantenna systems consisting of antenna elements operating at both the same bands and adjacent bands. Prototypes of the self-decoupled filtering patch antenna alone and two types of two-element arrays operating at the same band and adjacent bands, respectively, have been designed, fabricated, and measured. The measured results, in good agreement with their simulated values, validate its low mutual coupling performance for multi-antenna applications.