Design Of Broadband High-Gain Circularly-Polarized Antennas

Broadband high-gain Circularly-Polarized antennas are designed to solve the problems that may caused by increasingly complicated wireless telecommunication systems,They have many outstanding features including broad work bandwidth,high gain and circular polarization.Thanks for the use of this kind of antennas,many problems caused by limited work bandwidth and low gain were overcome efficiently.Besides,circularly-polarized antennas have great performances when working in the increasingly complicated electromagnetic envirnoments and nature environments because they have strong anti-interference ability.In view of the great performances mentioned above,broadband high-gain CP antennas have become a hot spot of research and have been widely used in wireless communication systems,satellite navigation,etc..A broadband high gain CP antenna working at KU band was designed in this paper.Besides,based on the theory of polarization of electromagnetic wave and Fabry-Perot cavity,a partially reflective array plate was designed,With the help of this plate,the linearly polarized wave can be converted into a circularly polarized one,and the antenna gain can be improved at the same time.The details of my work are as follows:An aperture coupled microstrip antenna working at KU band is designed,The antenna is fed by a Wilkinson power divider which has a 1/4 wave length difference between its two output stubs.The antenna can create a circularly polarized wave when fed by the power divider through two H-shaped apertures which are orthogonally etched on the metal ground.A Fabry-Perot cavity was designed for the feed antenna in order to increase the gain.A metal horn was made for the antenna innovatively so that a much higher gain can be achieved.The final experimental results show that the antenna has a-10-dB impedance-matching bandwidth of about 20.8% and a 3-dB axial ratio bandwidth of 12.8%.The peak gain of the antenna is about 16.3-dBi and the 3-dB gain bandwidth is about 19.4%.The wideband high-gain and circular-polarization performances are demonstrated.Based on the theory of electromagnetic wave polarization,a linear-to-circular polarization converter is proposed.This converter consists 81 microstrip periodic units which are cross-shaped.With the help of this converter,the linearly polarized wave provided by a slot-fed patch antenna can be converted to circularly polarized wave.At the same time,the dielectric plate which has a high permittivity can build a Fabry-Perot cavity with the metal ground of the slot-fed patch antenna,so that a higher gain can be achieved.The experimental results show that the gain can be increased by 5-dB at 11.8GHz-13.2GHz,the peak gain is 11.2-dBi.The 3-dB gain bandwidth is over 16%.An axial ratio less than 3dB can be realized at 12.55GHz-13.12 GHz.