A Pattern Reconfigurable MIMO Antenna Design Using Characteristic Modes

A novel pattern-reconfigurable two-port multiple-input multiple-output (MIMO) antenna system at Wi-Fi band has been designed by resorting to characteristic modes analysis. The design method of the proposed MIMO antenna array is based on the selective excitation of three orthogonal characteristic modes. The selective excitation is achieved by integrating two pairs of capacitive coupling elements (CCEs) on the same plane with the ground. Two feeding networks related to two ports have been designed for achieving a good impedance matching and providing the feeding to the CCEs. By switching the p-i-n diodes in each feeding network, the selective excitation mode of the two ports can be varied, thus leading to the reconfigurable patterns. Three operating states can be obtained for the proposed antenna design. Simulation results demonstrate that the envelope correlation coefficients of the proposed MIMO antenna array are far less than 0.5 due to the orthogonality of radiation patterns between the characteristic modes in each of the three states. Measured S-parameters and the radiation patterns of a realized prototype are in good agreement with simulation ones confirming the reliability of the design method.