Massive MIMO Array Design with High Isolation by Using Decoupling Cavity

—This letter proposes an isolation enhancement method for massive multiple-input multiple-output arrays using decoupling cavities (DC). The proposed DC is made of a pure Polypropylene (PP) board, and an air cavity is engraved on it. The DC has high transmission in the normal direction and a high insertion loss in the tangential direction of the arrays, respectively. The DC operates with a broadband response due to the low dielectric constant of the substrate. An example of a 4×4 array with an inter-element distance around half wavelength is designed to verify the proposed isolation enhancement method. The triple-layers stacked DC are employed seamlessly above the array. The isolation of the array was enhanced to 24 dB within the bandwidth of 4.21-4.79 GHz. At the same time, the radiation characteristics of the arrays before and after loading the DC basically keep consistent.