Research On Wideband Circularly Polarized Waveguide Slot Antenna

Wideband wireless communication technology is an important issue for the communication systems because of it providing large communication capacity and good security. Circularly polarized antennas have advantages of the strong anti-interference property and the capability of receiving any forms of linear polarized wave or circular polarized wave with same rotation sense. Meanwhile, waveguide slot antennas have advantages of high gain, high efficiency and compact structure. Therefore, wideband circularly polarized waveguide slot antennas are deeply researched in this thesis. Two types of broadband circularly polarized antennas are proposed and designed. The studies have been conducted as follows.Firstly, a circularly polarized cavity-backed H type wide slot array fed by slotted waveguide is proposed. On the basis of the longitudinal slot of the feed waveguide, the antenna is loaded with square metal cavity of 45 degree rotation, and an H-type wide slot is formed by adding rectangular metal perturbations on the upper surface of metal cavity. The cavity-backed square slots perform wideband circular polarized radiation. Then a 1-by-8 circularly polarized array has been designed. Simulated impedance bandwidth of 4%, axial ratio (AR) bandwidth of 6.4%, a gain of 17dB and a sidelobe level of 17dB have been obtained at 12.5GHz.Secondly, in order to reduce the antenna profile, the cavity is optimized for normal placement on the basis of the first design and H type wide slot is changed to a square wide slot with a pair of square perturbations in the diagonal direction. Optimized antenna height is reduced by 25%.A 1-by-8 circularly polarized array has been developed with an measured impedance bandwidth of 6.9%, AR bandwidth 7.6%, a gain of 15.4dB and aperture efficiency of 53.7%.Thirdly, a novel type of circularly polarized waveguide slot array with double layer patch is designed. The overall antenna profile is low with height of half a free space wavelength.The stacked patch structure can generate two close resonant points, thus widening the AR bandwidth. Then a 1-by-10 circularly polarized array has been designed. Simulated impedance bandwidth of 5.4%, AR bandwidth of 15.2% and a gain of 17dB have been obtained at 10.5GHz.