A Sequentially Rotated, Circularly Polarized Microstrip Antenna Array with Reduced Mutual Coupling

A circularly polarized microstrip patch antenna array with sequential rotation and reduced mutual coupling between its elements is proposed. A microstrip patch modified to suppress surface waves is used as the array element. The modifications include the addition of shorting pins and inclusion of a slot and edge truncations to produce a circularly polarized array element that does not excite surface waves. The designed element has higher gain and a more directional radiation pattern than a similar conventional microstrip patch antenna. In order to improve circular polarization bandwidth, sequential rotation techniques using the proposed microstrip antenna were investigated. Surface wave supersession of a 2 x 2 sequentially rotated array using the proposed design was achieved throughout the entire axial ratio bandwidth. One-layer directly fed array and two-layer aperture coupled array were investigated. The two-layer design achieved better impedance and axial ratio bandwidths than the single layer design. The design procedure, simulation results, and experimental measurements are presented.