Simultaneous Enhancing Decoupling Bandwidth and Impedance Bandwidth of Stacked Microstrip Patch Antennas by Achieving the Mutual Coupling Nulls

This paper presents an effective decoupling method aimed at simultaneously enhancing both decoupling bandwidth and impedance bandwidth through independently controlling multiple mutual coupling nulls. This innovative approach addresses the broadband decoupling requirements of stacked microstrip patch antennas (S-MPAs) in multiple-input multiple-output (MIMO) systems. A novel integration of laminated resonators (LR), defected ground structures (DGS), and cosine-curve-shaped coupled line resonators (CLR) is employed to construct and regulate multiple mutual coupling nulls. Using this methodology, we proposed a low-profile two-element S-MPA array and experimentally confirmed the simultaneous enhancement of decoupling bandwidth and impedance bandwidth. The mutual coupling levels at the low-frequency (5.6 GHz) and high-frequency (5.8 GHz) nulls are -56.89 dB and -53.93 dB, respectively. Additionally, the effectiveness of this method is extended and validated in three-element arrays, where measured results indicate mutual coupling levels between adjacent and non-adjacent antenna units remaining below -30.93 dB. This confirms the scalability and mutual coupling nulls tunability of the proposed methodology for multi-coupling path suppression for stacked antenna arrays.