A novel hybrid resonant structure is proposed to decouple a dual-band microstrip antenna array. The decoupling structure is composed of two H-shaped strips, and the lower and upper ones respectively collaborate with an X-shaped slot to reduce mutual coupling at 4.5 GHz and 5.5 GHz. Two sub-patches of different sizes share a connection feeding line to construct the dual-band array element, which is arranged along H-plane with the edge-to-edge spacing 0.15 λl and 0.24λh (λl and λh are the free-space wavelengths of 4.5 GHz and 5.5 GHz, respectively). Simulated and measured results indicate that through loading the hybrid resonant structure, 31.6dB and 24.0dB reductions of mutual coupling at two frequencies are obtained, while the levels of coupling coefficients are both below -30 dB in two operating bands. Moreover, the modified radiation patterns, improved diversity metrics and weakened coupled current distributions further verify its superior decoupling capability. The proposed decoupling structure reveals its promise in being employed in communication system and multielement linearly antenna arrays.
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