Research On Ka-band Antenna And Tracking Technology Of Mobile Satellite Communication Earth Station

Developing along with satellite communication technology,satellite communication mobile earth stations is not only an important component of satellite communication,but also an indispensable part of achieving information transmission among nodes in satellite communication network.Satellite communication mobile earth stations have grown from the previous large stationary stations to the present varieties of light and small stations.In recent years,owing to the limited bandwidth resources of satellite communications,research direction has been shifted toward Ka-band,and tracking performance is also required to be improved.In this study,some novel antenna design methods and tracking and alignment algorithms are proposed.By reasonable design of satellite communication antennas,antenna conical scanning mechanical structure,novel tracking algorithms and novel sensor applications,the purpose is to enable satellite communications mobile earth station tracking more accurate,faster and more cost-effective.In this study,a design for Ka-band satellite communication antenna in mobile earth station is introduced.This kind of antenna uses splash-plate feed based on ring-focus antenna.This thesis discusses how to form subreflector and dielectric.Due to ring-focus paraboloid as main reflector and no shelter of strut and feed,this antenna has high gain,low sidelobes and small VSWR.In this study,the design theory of the novel splash-plate feed antenna is described,and the relative equations are derived.The measured results of the splash-plate feed antenna VSWR and patterns are highly consistent with the simulation,which indicates that the antenna performs well and the design methods are effrective.The common tracking of two-axis mobile satellite communication portable stations generally adopts gradual alignment method,and this thesis presents an improved method.Taking a two-axis tracking system in mobile satellite communication station as an example,the influences of roll axis on system performances are discussed.The three-axis compensation methods of space alignment are derived.The methods can search quickly even if antenna has no azimuth sensor.Then the tracking errors are analyzed in the simulation.In the case of roll angle ? ±30°,with roll compensation,the system can find the satellite when azimuth angle rotates once,which verifies the correctness of the compensation algorithm.It also shows that roll compensation can greatly improve the efficiency of the initial searching.The conical scanning and tracking of rotational main surface has large rotational inertia,slow scanning and tracking speed.In this study,the rotational focus excursion sub-surface is adopted in conical scanning,measuring and tracking.This method has advantages of no hollow motor,small rotational inertia,low cost and compact manner.In this study,the influences of antenna sub-reflector focus excursion technology on the pattern are analyzed theoretically,and the relevant formulas are derived.On the basis,a kind of antenna sub-reflector excursion structure is designed,and the specific engineering realization is introduced.Performances test results indicates that the conical scanning technology of sub-reflector has high speed and stable performances.If the existing mobile earth stations need precise and accurate tracking,they usually use expensive strapdown inertial navigation systems which can independently seek north.In order to reduce the cost,most mobile earth stations use MEMS strapdown inertial navigation systems.However,the existing MEMS strapdown inertial navigation systems cannot independently seek north.Therefore,in general,mobile earth stations have an ambiguous problem about one-dimensional space searching.In view of the development of MEMS technology in recent two years,this thesis proposes a strapdown inertial navigation system based on low-cost MEMS gyroscope.This thesis proposes index comparison and conducts simulations mainly aiming at the three-dimensional pointing output of strapdown inertial navigation systems.The simulation results indicate that the strapdown inertial navigation system based on low cost IMU has the output error of the pointing north angle within 9o.If the mobile earth station uses this low-cost inertial navigation system,it can greatly shorten the time of searching for the satellite and reduce tracking error,thereby improving the tracking performance.