Study On Wideband Circularly Polarized Antennas

The performance of antenna,as an important component of the front-end in RF antenna wireless communication system,affects the performance of the whole system directly.Circularly polarized(CP)antennas can suppress rain and fog interference,resist multipath fading and slow down ionospheric Faraday rotation effect,which are widely used in satellite communication,electronic countermeasures,radio frequency identification etc.With the rapid development of multi-functional integrated RF system,there is an urgent need for a broadband antenna design compatible with multiple communication frequency bands.The CP antenna with wideband operating characteristics has been a research hotspot in the field of antenna and microwave in recent years.In this paper,combining with the development trend of modern communication,the wideband CP antenna is used as the research object,the wideband CP microstrip antenna based on multiple resonant modes and the wideband single/dipole combined omnidirectional CP antenna are studied.The author's major works are as follows:1.A Wideband microstrip CP antenna is investigated.Based on the cavity mode theory,a wideband microstrip patch antenna with multiple resonant modes is proposed.The different resonant modes of two different antennas are excited by the shorting pins.And the two microstrip antennas are effectively combined by radiating edge coupling,so that the resonant frequencies of the three modes are uniformly distributed and a multimode wideband microstrip antenna design is realized.On this basis,the proposed multimode wideband microstrip antenna is sequentially rotated and symmetrically arranged,a wideband feed network is designed based on the weak coupling mechanism,the four antennas are excited with equal amplitude and 90° phase difference,and then a wideband CP microstrip antenna is realized.In addition,the radiation performances of the CP antenna is optimized by introducing a bent metal edge wall around the radiator.The measure results show that the antenna achieves 96% impedance bandwidth and 86% 3-d B axial ratio bandwidth,with good wideband circular polarization performance.2.A wideband omnidirectional CP antenna is studied and a wideband omnidirectional CP antenna with a combined single/dipole structure is proposed.Firstly,two orthogonal polarization components are generated by monopole and dipole antennas respectively,and both of them have omnidirectional radiation characteristics.Secondly,the spatial position and feed structure of the antenna are designed by using the wave range difference of the monopole/dipole spatial radiation field,so that the orthogonal polarization components generated by both of them are effectively superimposed to form an omnidirectional radiating CP wave.Finally,the design of the wideband omnidirectional CP antenna is realized by wideband matching optimization of the monopole/dipole antenna structure.The measure results show that the antenna has 49.6% impedance bandwidth,35% 3-d B axial ratio bandwidth and good omnidirectionality performance with gain variation in horizontal plane being less than 1.8 dB.