| Antenna is a key component for wireless radio systems. With the rapid development of wireless communication technology, there is a growing demand of variety of antennas. Among various antennas, circularly polarized antenna is widely used in radar, satellite and mobile communication systems due to its special radiation characteristics. In order to increase the system capacity and the spectrum utility efficiency, the polarization diversity technical has been proposed, and the antenna in the system is required to work in different modes and different wireless systems as needed. In this thesis, the circularly polarized slot antennas and polarization reconfigurable slot antennas for the polarization diversity systems are mainly addressed.Firstly, a wideband circularly polarized slot antenna for the wireless local area networks (WLAN) system is presented. The antenna is fed by the coplanar waveguide (CPW), working at frequencies from 2.32 to 2.57GHz. The HFSS software is used to analyze and optimize the antenna parameters. An antenna prototype based on design results is constructed and measured. Measured results indicate that good circular polarization of the proposed antenna is obtained. The antenna meets the WLAN system requirements.Secondly, a reconfigurable annular rectangular-slot antenna with switchable polarization is presented for the polarization diversity systems. Circular polarization radiation of the proposed antenna is obtained by introducing protruded strips in the annular rectangular-slot structure. Eight diodes are added to reconfigure the structure of the annular rectangular-slot. Switching between right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) is achieved by turning the pin-diodes on or off. The HFSS software is used to analyze and design the antenna. An antenna prototype is constructed, and the measured results are in good agreement with the simulated ones. The proposed antenna has simple structure and can be controlled easily.Finally, some drawbacks of these two antennas are indicated, and the problems remain to be studied further are given. |
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