Research And Design Of K/Ka Band Monopulse Feed System

In the mobile satellite communication system or some situations,the antenna needs to get the ability to track the satellite.There are generally three tracking methods for tracking system: step tracking,conic scanning and zero signal tracking.The zero signal tracking is also named as monopulse tracking,which can track object with high-precision.For reflector antenna,the key component of getting zero signal is feed system,which includes high-order mode coupler feed and array monopulse feed.High-order mode coupler feed has superior comprehensive performance.According to the projection,this thesis studies a K/Ka band monopulse reflector antenna system applied to the ground satellite communication terminal.The purpose of this thesis is that design a multi-mode monopulse communication antenna feed system,which performance can satisfy the requirements and the structure is easily to be manufactured.The work of this thesis is as follows:(1)In this thesis,the TE21 mode coupling technique is used to extract the antenna zero signal for the system to achieve monopulse tracking.A TE21 mode coupler is designed.Eight coupling arms are used to extract TE21 mode from the main waveguide.In this thesis,the aperture parameters of each coupling arm are weighted by Bessel function and further optimized,so that the coupler has excellent coupling characteristics,but has little influence on the main mode TE11.In the design,on the premise of ensuring excellent electrical performance,the thickness of metal wall of the coupler could be increased as much as possible to reduce the influence of processing deformation on coupler performance.(2)The signals of 8 coupling arms of TE21 mode coupler are combined according to certain rules to get the necessary difference beam signals for tracking.In this thesis,two kinds of difference beamforming networks are designed: One is waveguide difference beamforming network and the other is microstrip difference beamforming network.The waveguide difference beamforming network has the advantages of low loss,but its structure is complex.In this thesis,through the reasonable design of the topology of the network,the power combiner and other components are optimized,so that the difference beamforming network has good electrical performance.At the same time,it has the feasibility and simplicity of processing.The microstrip difference beamforming network has the advantages of simple structure,low cost and light weight.(3)A corrugated horn is designed.Through optimization,it has good pattern equalization and low cross polarization performance.Its increased neck diameter can not only through the TE11 main mode but also the TE21 high-order mode.Combining with a reflector,the taper level of the horn is designed reasonably,so that the antenna has high efficiency.(4)Combining with a K/Ka-band circular polarizer,an OMT,a low-pass filter,a high-order mode coupler,a corrugated horn and a reflector,a completed monopulse antenna system is made.The simulation results of the antenna system show that the sum beam and the difference beam pattern and port characteristics are better.All components of the feed network can be made by common processing and manufacturing methods.