Design of MIMO Antenna Isolation Structure Based on a Hybrid Topology Optimization Method

A hybrid topology optimization (HTO) method is utilized to optimize the isolation structure of a multiple-input multiple-output (MIMO) antenna. The HTO method, in which the scalar isotropic material with penalization (SIMP) and the level set method (LSM) are integrated, is based on the gradient optimization method with fast convergence speed. It combines the advantages of strong topology-searching ability of SIMP and smooth structure boundary of LSM. The proposed HTO method is adopted to optimize the isolation structure for good impedance matching, high isolation and high polarization purity of the MIMO antenna simultaneously. By setting the optimization structure as a symmetric one, the number of optimization variables is reduced by half. The optimization is validated by the full-wave simulation and the measurement. At the expected frequency of 5.8 GHz, the measured mutual coupling between the MIMO antenna elements with a center-to-center distance of 0.25λ₀ is reduced by more than 24 dB, and the cross-polarization ratio reaches more than 27 dB. Furthermore, the reason for the isolation improvement is analyzed as well.