Design For A Vehicle Shaped Reflector Antenna With An Elliptical Beam

With the rapid development of economic science and technology,the mobile satellite communication,as a new mode of communication,has been used widely in recent years.The vehicle mobile satellite communication which is a part of the mobile satellite communication plays an important role in the fields of earthquake disaster,firefighting,public security and so on.As the part of the vehicle mobile satellite communication station,the antenna which determines the performance of the communication system is crucial.The vehicle antenna with the large longitudinal dimension has an unsteady gravity,meanwhile,it causes the vehicle can't pass the short culvert.The reflector antenna with an elliptical beam whose dimension of azimuth plane is large but dimension of horizon plane is small can improve the gain of the antenna and improve the mobility of the vehicle.More importantly,to ensure expedite data transmission in the communication system,the antenna's attitude needs to be adjusted in real time by the antenna servo control system,so that the electromagnetic beam of the antenna can be always pointed to the satellite when the vehicle moves.When the reflector antenna characterized by the elliptical beam which is narrow in azimuth plane but wide in horizon plane is used for tracking satellite,only tracking and searching in the azimuth plane is necessary for the satellite,which speeds up the beam scanning for the servo control system.The classical offset dual-reflector with elliptical beam has an asymmetric structure that leads to the increase of longitudinal and transverse dimensions,which reduces the mobility of vehicle antennas.This type of antennas is not suitable for the vehicle mobile satellite communication with limited installation space,it also cannot meet the requirement of fast tracking scan for the station.When the axis ratio of elliptical beam is large,there is still a problem about regional overlap on reflector surface for varifocal ring-focus antenna with symmetric structure,this antenna cannot realize the shaped beam for its radiated electromagnetic waves,so it cannot increase the antenna's gain and reduce its side-lobe level.With supported by the Joint Research Fund in Astronomy(U1631115)under cooperative agreement between the National Natural Science Foundation of China(NSFC)and Chinese Academy of Sciences(CAS),A shaped elliptical beam reflector antenna with large axis ratio was designed and fabricated for one actual project,its far-field radiation pattern was simulated and measured? The main work and innovation of this paper can be summed up as follows:(1)Two kinds of corrugated horn feeds(the primary illuminator for reflector antennas)of the reflector antenna were designed.The near-field radiation pattern calculated by the finite element method was analyzed.Then a mutant straight slot corrugated conical horn was chosen as the feed for the reflector antenna of this project.(2)Combining the Snell's law,the equivalent ray path condition and the law of conservation of energy,the plane curve of the long axis of the reflector was firstly designed.When the axis ratio of the reflector is large,a new constraint condition proposed in design and equivalent ray path condition were used to avoid the upheaval on its surface.With the plane curves of the long axis and the short axis,the shape of other regions is derived by using the transition function.(3)The calculation process of far-field radiation pattern was derived on the basis of the mirror surface current method and a ray tracing method.Then the three far-field radiation patterns of this reflector antenna corresponding to three transition functions were calculated,these results were analyzed.Finally,the measured results and simulated results of this fabricated antenna were compared and analyzed.