A Study Of Satellite Communication Circularly Polarized Microstrip Antennas

With the rapid development of wireless communication systems, microstrip antennas draw wide attention owing to their advantages of compact structure, low profile, easy integration and manufacture. Circularly polarized waves have several characteristics including combating multi-path reflections, reducing the Faraday rotation effect, restraining the interference of mist and so on. Therefore, circularly polarized antennas have been widely used in satellite communications, navigations and other fields. The thesis mainly focuses on circularly polarized antennas for transmitting and receiving with the advantages of high isolation and broadband circularly polarization. The major contributions are summarized as follows:1. A circularly polarized antennas for transmitting and receiving with high isolation have been studied. First of all, a single feed circular polarization microstrip antenna element with low profile is designed. Both transmitting and receiving antennas are using the square patch with additional truncated corners and a U-shaped slot, in the reception band 1f±15MHz and transmission band 2f ±15MHz respectively, to achieve a left-handed circular polarization. In order to effectively improve the axial ratio bandwidth and the gain of the antenna, the array antenna is consist of two orthogonally disposed elements. Using the methods of defects and branches decoupling thechnology effectively improves the transceiver isolation between the two ports. Then, a transceiver integrated circular polarized microstrip antenna is obtained. The array antenna is fabricated and measured, and the measured results are in good agreement with the simulated results. Secondly, in order to further improve the isolation of the receiving antenna, a elliptic function filter is designed. The simulated results show that the attenuation in the stop-band within 2f±15MHz is over 25 d B. Finally, with the filter cascading to the input port of the receiving antenna, the isolation of the receiving port improved 20 d B. Then we get the high isolation transceiver antenna.2. A broadband circularly polarized microstrip antenna has been studied. Firstly, a multi-layer circular polarization microstrip patch antenna element is designed. Using a probe feeding on the diagonal rectangular ring, the left-handed circular polarization is obtained. At the same time, a parasitic patch is added above the rectangle ring, and the air layer is introduced between the upper and lower patches, which effectively broadening the operating bandwidth of the antenna elements. Simulated results show that in the working frequency band, the |S11| of the antenna element is less than-10 d B, the axial ratio less than 3d B, and the gain more than 7.5d Bi. Secondly, in order to obtain a wider antenna axial ratio bandwidth and higher gain, the method of sequential rotation technology is adopted. Wilkinson power divider is adopted to accomplish the design of the feeding network, and the simulated results show that the performance of the feeding network basically meets the requirements of the antenna. Finally, the above-described feeding network can feed the 2×2 circularly polarized array antenna which can realize the wide band and high gain performances. Simulated results show that the antenna has good impedance matching(|S11| <-20 d B), axial ratio less than 2 d B, and gain more than 12.5d Bi in the operating band. The array antenna is fabricated and measured, and the measured results are in good agreement with the simulated results.