Bandwidth Enhancement of H-Plane MIMO Patch Antennas in Integrated Sensing and Communication Applications

In this paper, a low-cost compact decoupled bandwidth enhancement technique is proposed to address the high mutual coupling issue between wideband closely-spaced multiple-input and multiple-out (MIMO) patch antennas. The wideband decoupling property is realized by combining two decoupling circuits introduced by defected ground structure (DGS) and coplanar decoupling structure, respectively. An equivalent circuit is given to clarify the decoupling mechanism and provide physical insight. To validate the feasibility of the proposed design scheme, two prototypes of decoupled wideband patch arrays based on coplanar-fed and probe-fed schemes are simulated, fabricated, and measured in the 5.8 GHz ISM band, respectively. Experimental results show that for both of the two kinds of prototypes, the poor isolation can be improved from 10 dB to better than 20 dB within a wide-matched bandwidth of 10% under an extremely close edge-to-edge distance of
$0.038 \lambda _{0}$
. In addition, systematic validation for radar sensing performance has been discussed by integrating the proposed antenna with the custom-designed radio frequency system. Moreover, the performance metrics of MIMO parameters and verification of extending to
$1\times 4$
antenna arrays are also discussed for both two basic feeding schemes. Compared with the two-element patch arrays, multi-element patch arrays maintain decent performance for isolation enhancement and wideband isolation bandwidth larger than 10%, indicating the proposed decoupling technique is promising for large-scale wideband MIMO systems in integrated sensing and communication applications (ISAC).