The purpose of this paper is to design a new type of decoupling structure for Ka band and to analyze the decoupling effect of this structure. The equivalent circuit model of the “d-shaped” Uniplanar Compact Electromagnetic Band Gap(UC-EBG) structure is established, and its band-stop filter characteristics are obtained through simplified analysis. The distribution parameters of the decoupling structure are calculated based on the conformal transformation and elliptic integral calculation. The simulation results of the equivalent circuit are consistent with the simulation of the decoupling structure. Applying this decoupling structure to the array antenna improves the isolation between array elements and reduces the mutual coupling effect of array elements.