| In this paper, broadband and multi-frequency circularly polarized microstrip antenna are studied mainly. Firstly, the basic theory of microstrip antenna and the commonly used methods of analysis are introduced. Then the circularly polarized, broadband and multi-frequency technology of microstrip antenna are summarized.Based on the theoretic analysis, a study is made on broadband circularly polarized microstrip antenna and a mode of simple structure with good antenna performance is proposed. The antenna is excited by L-shaped microstrip feed line. Wideband CP (circularly polarized) is obtained by L-shaped slot and truncating one of the corners of the antenna element. And parasitic patch is used to further enhance the bandwidth of circularly polarized. Both the simulated and measured results indicate that antenna designed have good performance and achieve the need of design on the whole. In addition, a dual-band circularly polarized annular slot antenna for wireless local area network (WLAN) application is proposed through analyzing and improving the traditional annular slot antennas, completely covering the WLAN 2.4/5.8 GHz bands.Finally, the research of the paper is summarized and some needed improved problems are proposed ulteriorly. |
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