Design Of Multiband Feed

According to the need of research and application,this paper first introduces the basic geometry structure,analysis method and basic knowledge of feeding network devices of reflector antenna,then studies and designs an offset-feed reflector antenna working in Ku/Ka-dual band.The antenna consists of three parts: the main reflector,the primary feed and the feed network.According to the requirement,the antenna operates in Ku/Ka four-band with a band span ratio of 2.53:1.Therefore,a wide flare angle corrugated horn is designed as the primary feed.It has good standing wave characteristics and rotationally symmetrical pattern in four frequency bands,which ensures the high efficiency of the reflector antenna system.Then the feed network of multi-band feed system is designed.The Ka band feed network consists of circular polarizer,orthogonal mode coupler and filter,and the Ku band feed network consists of orthomode junction and power combining network.Among them,the Ka band Ortho-Mode Transducer uses conical branch OMT,which has good impedance matching and high isolation.In order to realize the conversion between linear polarization and circular polarization,a broadband circular polarizer is designed.The circular polarizer is in the form of Quad-Ridge with an axial ratio of less than 0.35 d B over the operating bandwidth.In order to improve the isolation of receiving and transmitting ports of the antenna system,Ku and Ka band low-pass filters are designed respectively.The simulation results show that the low-pass filters have good impedance matching characteristics in the passband and attenuation in the stopband is less than-68 d B.In order to separate the Ku-band signals,a cone-varying waveguide orthomode junction and a power synthesis network are designed.The orthomode junction consists of a splitter header and four low-pass filters,and the low-pass filter uses a block mode filter to suppress higher order modes.Then,the Ku-band feed network and the Ka-band feed network are jointly simulated,then the whole network is co-simulated together,and processing of physical samples.The results show that the standing wave of each port of the feeder network is better than 1.33,the isolation of the receiving and sending ports is greater than 77 d B,and the circular polarization axis ratio of the feed is less than 1.15 d B.Then,the electromagnetic simulation software FEKO is used to jointly simulate the whole antenna model and the 0.5m offset-feed reflector.The results show that the efficiency of reflector antenna is more than 65% and relative side lobe level is less than-22 d B in the working frequency band.Finally,the direction diagram of the feed network is tested,and the test results are basically consistent with the simulation results.