Design Of Dual-band And Dual-polarized Radar Antenna

Reflector antenna is widely used in the decimeter band to the millimeter band because of its simple structure,low cost,high gain and low sidelobe level.With the radar to achieve target recognition and regional coverage,there are different requirements for the shape of antenna beams,such as cosecant square shaped beams,regional shaped beams and so on.Therefore,a complete design method of shaped reflector antenna system is very important.In view of this,this paper systematically expounds the design method of narrow beams in horizontal plane and cosecant square shaped beam in vertical plane with double-curved shaped reflector,The measured results show that the shape angle and sidelobe electrical equality index parameters are good.Finally,through actual feedback,several improved feeder methods are proposed and compared with the shaping index of the original shaping reflector.The problem that the sidelobe level of the shaped pattern of the antenna is higher than that of the first sidelobe level in the range of 60 to 140 level has been solved for a long time.The sidelobe level of the improved antenna decreases about 1.5 d B in the range of the angle compared with the previous one,and is also lower than that of the first sidelobe level,The overall sidelobe level of azimuth plane also decreased by more than 1.5d B.Finally,the design method of shaped array is introduced,and the shaped pattern can be obtained by array method.The main contributions of this dissertation are as follows:Firstly,the cause of horn double beam formation is analyzed theoretically and the lobe width and direction as the feed of shaped reflector are given and the parameters of the feed horn are measured in practice.Secondly,aiming at the high side lobe of the feed in I-band,the improved method of adding a reflective baffle under the radiation aperture of the feed horn is introduced and the problem of high right first sidelobe level in I band of feed horn is solved.Finally,the effects of the presence of absence of gratings at the radiation aperture,thickening the radiation aperture's thickness and the absence of gratings at the radiation aperture and thickening the radiation aperture's thickness on the H-band with lobe width,sidelobe level and direction are modeled and simulated.It lays the foundation of the feed for the simulation to get the secondary shaped radiation pattern.Secondly,the theory of cosecant square shaped beam is introduced.Then,according to the antenna's characteristics of narrow beam in horizontal plane and cosecant square beam invertical plane,the central-section curve and strip equation of reflector antenna for realizing the beam characteristics are theoretically analyzed.The advantages and disadvantages of various strips are described in detail,and the far field of reflector is theoretically analyzed by physical optics method.Then the calculation part of shaped reflector is introduced.Firstly,the system parameters of the reflector are estimated,the focal length and the angle of the reflector are selected,and the central-section curve's equation and strip equation are calculated.Then,the shape reflector is modeled and the simulation results and measurement results of secondary shaped radiation pattern in horizontal plane and vertical plane in two frequency bands are obtained.Finally,the effects of the presence of absence of gratings at the radiation aperture,thickening the radiation aperture's thickness and the absence of gratings at the radiation aperture and thickening the radiation aperture's thickness on the H-band with Secondary radiation pattern are simulated.The author compares new radiation pattern with the original radiation pattern,and gets the conclusion.Finally,the basic knowledge of the array antenna is introduced,theoretical analysis and Simulation of the cosecant square shaped beam in vertical plane and the knowledge of phased array are presented.