Research On Wide Axial-ratio Beamwidth Circularly Polarized And Pattern Diversity Antennas

With the development of wireless communication,users' demand for communication quality is also increasing.As an important component in communication system,the performance of antenna affects the quality of the whole communication.Therefore,it is important to improve the performance of the antenna.Circularly polarized antennas have been widely studied due to their advantages such as anti-polarization mismatch and strong anti-interference ability.In order to enable the circular polarization antenna to achieve signal coverage in a wider space,and to ensure the normal mobile communication,the antenna is required to maintain good circular polarization characteristics in a wider range,that is,the receiving antenna is required to have the characteristics with a wide axial-ratio beamwidth.Moreover,in order to solve the problem of multipath fading caused by the surrounding environment,antenna diversity is usually adopted.The directional graph diversity antenna can have the performance of two or more antennas,which increases the transmission and reception capacity of the wireless channel,thus can alleviate the fading effect and improve the utilization of spectrum resources.In particular,microstrip antenna is suitable for modern wireless communication due to its advantages of low production cost and small appearance.In this paper,several microstrip antennas with wide beam-ratio and pattern diversity are designed,as follows:1.Two dual-bandwidth circular ratio beam circularly polarized antennas are designed.The directional radiation antenna achieves its dual-frequency characteristics through a coupling structure and operates in the GPSL1 and L2 bands.The antenna achieves circular polarization performance through four split ring slots on the patch.By increasing the slits on the antenna floor,the axial ratio characteristic of the antenna is improved,and the axial ratio beam width of the antenna is widened.The axial ratio beamwidth of the antenna reaches 140° and 180° at two frequencies,respectively.Furthermore,a dual-frequency dual circularly polarized omnidirectional antenna was designed,and slits were added at an appropriate position on the floor to improve the axial ratio of the antenna.The 3-d B axial ratio of the omnidirectional antenna covers all horizontal planes at two frequencies,and reaches 240° and 280° in the vertical plane,respectively.2.A circularly polarized antenna with pattern diversity for GPS application(L1 band)is designed.The antenna is fed by coaxial probes.The antenna can give broadside and omnidirectional conical radiation patterns when it is respectively excited at the two ports.With the introducing of the slots on the patch,the antenna achieves circular polarization for both broadside and conical patterns.The two pattern modes work in the same frequency band.This design has good port isolation and achieves good performance with pattern diversity.3.A low profile broadband pattern diversity microstrip antenna is designed.The antenna has two ports,which generate signals in the same direction and in different direction respectively through the feed network,and stimulate the same radiator to produce directional beam and dualbeam radiation characteristics.The gain performance of the antenna is improved by introducing slits in the radiator.The coincidence bandwidth of the two radiation patterns reaches 19.8%(3.22GHz-3.93GHz),and good isolation between the two ports is obtained.The antenna has a low-profile structure.