Design Of Multiband Feed

With the rapid development of satellite communication technology,as well as the increase of communication services,limited spectrum resources have become one of the bottlenecks of satellite communication.In order to expand the capacity of communication system,multi-frequency community antenna becomes a trend of development.The reflector antenna,as a common form of satellite communication of ground station,naturally becomes an active area of research.And the feed,as a core component of reflector antenna,almost determine the performance of reflector antenna system.Therefore,the research of multiband feed has become the key point.According to the demands of research,relevant analysis method and geometric characteristics of reflector antenna have been discussed firstly in this paper.Furthermore,on the basis of related performance indexes of reflector antenna system,the scheme of multiband feed system,operating in quad-band of Ku/Ka,has been designed in this paper.The multiband feed system consists of multiband feed horn and antenna feed parts.Of which,the design of multiband feed horn is the key point of this study.The multiband feed horn is required to operate in Ku/Ka band and its operating bandwidth reaches 2.5 times.For the reason of being applied to 0.5m offset parabolic antenna,it is requested that the multiband feed horn remains basically same beam width and shares nearly same phase center to improve the energy utilization efficiency of reflector antenna system.Aimed at the application of multiband feed horn,a large-angle corrugated horn with ring-loaded slots is designed.And it is composed of four-section ring-loaded slots and corrugations.In order to reduce the fabricating cost and ensure preferable electrical properties of the large-angle corrugated horn with ring-loaded slots,the loaded depth and width of the four ring-loaded slots are the same,and the depth and width of the four corrugations also keep same.Because the designed multiband feed horn is a large angle corrugated horn,for the convenience of fabricating,the four-section ring loaded slots and corrugations are all perpendicular to the inner surface of the horn.The calculation results demonstrate that the designed large-angle corrugated horn with ring loaded slots almost possesses same beam width and same phase center in quad-band,and achieves fine performance indexes.The antenna feed parts of the multiband feed system consist of ortho-mode transducer,circular polarizer and filter.Among them,the ortho-mode transducer is applied to separate the orthogonally polarized electromagnetic waves which are linearly polarized.Considering the factors of electrical properties and fabricating cost,the step gradient waveguide type is adopted for the ortho-mode transducer.The calculation results show that the designed ortho-mode transducer possesses fine characteristics of impedance matching and isolation in operating band.The transformation between the linearly polarized wave and the circularly polarized wave is implemented by circular polarizer.Taking performance indexes and fabricating accuracy in count,a metal diaphragm type structure is adopted for circular polarizer.Through calculation,fine characteristics of phase shift and impedance matching in working band have been obtained by the designed circular polarizer.For the purpose of improving the isolation between the transmitting port and receiving port,a filter is connected to the receiving port of ortho-mode transducer.Comprehensively considering design indexes and engineering requirements,the structure of coupled cavities and resonant windows is applied to the design of filter.Moreover,for the convenience of fabricating,a plane structure in one of the inner surfaces of filter cavity is adopted for filter.The computation results illustrate that the designed filter has excellent impedance matching characteristic in the passband,and possesses fine attenuation characteristic in the stopband.Finally,the multiband feed horn and 0.5m offset parabolic antenna are jointly simulated.The computation results demonstrate that the reflector antenna system achieves fine performance indexes in the quad-band in Ku/Ka with its operating bandwidth reaching 2.5 times.Besides,according to the demands of research,circularly polarized feed system,which operates in Ka-band,is designed and jointly simulated with 0.5m offset parabolic antenna.The calculation results illustrate that the reflector antenna system achieves fine performance indexes and the target of research is reached.