Research On Omnidirectional Circularly Polarized Slot Antenna

In recent years,omnidirectional antennas with high-gain,low side lobe level,low cross polarization have been widely studied for replacing the directional antennas with mechanical sweep joint in the radar and satellite communication system.The circularly polarized antennas have the advantages of strong anti-interference,polarization insensitivity and reduction Faraday rotation effect.Meanwhile,the waveguide slot antennas with high efficiency,low profile,light weight,high gain and large power capacity are good candidate of practical microwave and millimeter wave systems.In this thesis,the omnidirectional circularly polarized antennas have been designed based on the traditional theory study of waveguide slot antenna.The main researches are given as follows:Firstly,the research history and research status of the circularly polarized waveguide slot antenna are systematically reviewed.Secondly,a novel omnidirectional circularly polarized parallel waveguide slot antenna loaded with corrugated ground is proposed.Based on the slant-coupled slot on the cylinder waveguide,the energy in the circular waveguide operating at TM01 mode or in the coaxial waveguide operating at TEM mode can be coupled to the parallel waveguide.Narrower beam,low side lobe level and low cross polarization can be obtained by loaded the parallel waveguide with vertical and horizontal corrugated structure.The antenna prototype operating at 10GHz is designed and fabricated.The measured impedance bandwidth and the axial ratio bandwidth of the antenna are 10%and 16%.The gain of the antenna is 3dB and the ripple in the azimuth plane is less than 1dB.Thirdly,a collinear omnidirectional high-gain circularly polarized slot antenna array for transceiver is proposed.The antenna adopts a collinear nested installation structure to ensure the isolation between the transmitting and the receiving antenna.By arranging the slot pairs equally in the azimuth plane,combining with the TM01 mode of the circular waveguide and TEM mode of the coaxial waveguide,good omnidirectional radiation pattern can be achieved.The circular polarization is realized by slot pairs placed perpendicularly.In order to increase the gain,array has been made in the axial direction.The antenna prototype operating at 10GHz is designed and fabricated.The measured results show the impedance and axial ratio bandwidth of the transmitting antenna based on the circular waveguide are 12%and 8%.The RHCP gain and the ripple in the azimuth plane of the transmitting antenna are 9.5dB and less than 0.8dB.And the impedance and axial ratio bandwidth of the receiving antenna based on the coaxial waveguide are 12%and 8%.The LHCP gain and the ripple in the azimuth plane of the receiving antenna are 10.1 dB and less than 1.2dB.