Single-feed wideband circularly polarized patch antenna using dual mode defected ground waveguide coupling structure

A dual mode square-ring defected ground waveguide (SR-DGW) with defected square patch is first proposed to excite a single-feed dual mode circularly polarized (CP) patch antenna, which can improve the impedance bandwidth and achieve the CP radiation pattern. The defected square patch is called the perturbation element. By optimizing the size of the perturbation, the degenerate modes of the dual mode SR-DGW are split and their orthogonal modes can be excited simultaneously. Due to the dual mode of the SR-DGW, the TM01 mode, and TM10 mode of the square patch antenna are excited simultaneously, which can improve the impedance bandwidth of the antenna. Meanwhile, owing to the orthogonal modes, CP radiation pattern of the antenna is obtained. Then, for a better impedance matching, an L-shaped spurline embedded in the feedline is introduced. The simulated and measured results show a good performance of the proposed antenna. The measured -10 dB impedance bandwidth is 10.4% (3.56GHz-3.95GHz). The measured 3 dB axial ratio bandwidth is 5.36% (3.63GHz-3.83GHz). Detailed designs and experiments are described and discussed.