Research And Design Of Tri-Band Highly Performing Transmitting And Receiving Antenna Feeds

Modern satellite communication service requires antennas to be multi-band enabled, movable and tracking enabled. With the development of Ka and higher bands, multi-band antennas combining the conventional operating bands can fully utilize the spectrum resources and reduce the cost of earth stations. Also, in the service of mobile satellite communications, compact tracking antennas are becoming the heated research area. Meanwhile, Multi-band and self-tracking antenna feeds are usually the key towards satisfying these requirments. From this perspective, a Ku band linearly polarized compact monopulse feed, with a Ku/K dual-band monopulse feed and an X/Ku/Ka tri-band receiving and transmitting feed is designed and simulated in this thesis.Firstly, in order to reduce the formidable length of linearly polarized monopulse tracking feed, a compact half-length TE21 mode coupler based on coaxial waveguide is designed. The coupler abbreviates the length to half of the conventional circular waveguide counterpart while maintains the approxiamate coupling rate of TE21 mode and rejection of other modes. The coaxial waveguide TE21 mode and the inner circular waveguide dominant mode are used repectively to transmit difference mode and sum mode. With the design of choke rings and dielectric rod, the Ku band linearly polarized monopulse feed is composed to obtian difference and sum patterns and also transmitting pattern. The feed structure is compact because of the half-length TE21 mode coupler. The sum receiving and transmitting patterns of this feed are axially symmetric, and monopulse tracking can be realized combined with the difference pattern.Besides, a Ku/K dual-band monopulse feed is designed to realize self-tracking in multiple bands. TE11 and TE21 modes of coaxial waveguide are combined to form dual-mode monopulse mechanism in Ku band linearly polarized situation, while TE11 and TM01 modes of circular waveguide are combined to form dual-mode monpulse mechanism in K band circularly polarized one. The feed has equivalent sum patterns and difference patterns with null at the axial direction in Ku and K bands. As a consequence, it has the capability of measuring the error between the pointing direction of antenna and the position of satellite simultaneously in the both operating bands.Finally, an X/Ku/Ka tri-band receiving and transmitting feed is proposed. The Rx and Tx dual circular polarizations of X band are shaped in square waveguide metal board circular polarizer, and then fed to shared X/Ku coaxial waveguide by four rectangular arms. The Rx and Tx dual linear polarizations of Ku band are fed to a smaller coaxial waveguide, and then into the shared X/Ku through a step convertor. The Rx and Tx dual circular polarizations of Ka band in inner circular waveguide are fed by ortho-mode transducer and dual-band screw circular polarizer. The patterns of X and Ku bands are obtained by axially corrugated horn, and the patterns of Ka band are obtained by dielectric rod. The tri-band feed is simulated to have stable taper levels and thus is capable for antennas to expand band capacity.