| Tropospheric scatter communication has the characteristics of long transmission distance,high speed,high security and strong anti-interference ability.Therefore,it is particularly important to design a reflector antenna with multiple beams and low sidelobe levels.According to the requirements of engineering application,this paper not only systematically studies the C-band multi-beam angular diversity reflector antenna but designed dielectric rod feed and an orthomode transducer(OMT).Subsequently,the reflector antenna shaping technology was applied to engineering,and a dual-beam angle diversity reflector antenna was successfully developed,on this basis,another multi-beam angle diversity reflector antenna was developed.The two reflector antennas can realize dual-beam and multi-beam angular diversity transmission respectively.The work of this paper can be summarized as:1.Design of the feed.According to the requirements of the multi-beam angle diversity reflector antenna,a dielectric rod feed was developed.The feed adopts 6 sections of three sections(mode conversion section,impedance matching section and curve conversion section).The feed has a fixed phase center,features of rotationally symmetric far-field pattern,high gain and low sidelobe level.The system's requirements for feeds are achieved.2.Design of the orthomode transducer(OMT).A pin-type OMT has been developed.Its common end adopts a hexagonal to rectangular transition to suppress the generation of higher-order modes.The polarized isolator can realize the transmission and reception isolation of the dielectric rod feed.It has the advantages of low voltage standing wave ratio,low transmission loss,and high port isolation.Subsequently,the dielectric rod feed and the OMT were combined to conduct joint simulation and physical processing tests.The test results are basically consistent with the simulation results.The port isolation and voltage standing wave ratio are good,which can meet the requirements of engineering applications.3.Design of shaped reflective surface.Based on the reflector antenna shaping theory,GRASP is used as the platform to shape the secondary reflector of the dual-beam reflector antenna and the primary and secondary reflectors of the multi-beam reflector antenna,achieving a single secondary reflector to achieve dual beams.The purpose of multi-beam transmission.Finally,the above-mentioned feed source and the OMT are placed in an offset-focus form,and the overall performance of the shaped main and auxiliary reflecting surfaces is analyzed.The gain of each beam of the two angular diversity reflector antennas is greater than 44 d Bi,the first sidelobe electrical average is less than-15 d Bc,the beam angle between adjacent beams is 0.9 times the beam width,and the VSWR of each port is below 1.3.It has high application value in tropospheric scatter communication. |
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