A Self-Decoupling Circularly Polarized MIMO Microstrip Patch Antenna Array

A self-decoupling circularly polarized (CP) multi-input multi-output (MIMO) microstrip patch antenna (MPA) array is proposed. The array comprises two identical square microstrip patch antennas (MPAs) and each patch is excited by a coaxial cable through an L-shaped microstrip line. Moreover, two corners are etched on the patch for CP radiation. It has been found that by appropriately selecting the length of the L-shaped microstrip line, CP radiation can be generated in the active MPA, and linearly polarized (LP) radiation can be obtained in the passive MPA, thus realizing polarization mismatch. On the other hand, a null-field region can be obtained in the coupled MPA. By placing the feeding probe of the coupled MPA in the null-field region, no energy can reach the port. Therefore, a high port isolation of more than 47 dB can be realized between the driven antenna and passive antenna, without requiring additional decoupling structure.