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 TM 01 mode, and TM 10 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% (3.56 GHz-3.95 GHz). The measured 3 dB axial ratio bandwidth is 5.36% (3.63 GHz-3.83 GHz). Detailed designs and experiments are described and discussed.
K E Y W O R D Scircular polarization, dual mode, patch antenna, square-ring defected ground waveguide in 2015, and she is currently working toward the PhD degree in school of electronic and information engineering from Xi'an Jiaotong University, Xi'an, China. Her current research interests include antenna array, millimeter-wave antenna, and metasurface.PIN WEN was born in Jiangxi, China, in 1987. He received the BS degree in communication engineering and the MS degree in communication and information system from East China Jiaotong University, Nanchang, China, in 2012 and 2015, respectively. Currently, he is working toward the PhD degree at Xi'an Jiaotong University, Xi'an, China. His current research interests include antenna theory and design, tunable filters, metamaterials and superconducting filters.GUIBIN CHEN received the BS degree in communication engineering from Inner
