Design Of Dual-band And Dual-polarized Shaped Reflector Antenna

Reflector antenna is widely used in communication,radar,radio astronomy and other fields,it is a kind of high gain antenna whose performance is very excellent.At the same time,with the rapid development of science and technology and the modernization of national defense,more demands are required on the performance of radar function.People put forward more and more requirements on the reflector antenna with shaped beam,such as cosecant square shaped beam antenna and area shaped beam antenna.In order to achieve the function of target recognition and regional coverage,the design of antenna and performance of feed need to be improved continuously.So,it is very important to study the shaped reflector antenna.This paper focuses on the research project,analysing the theoretical basis and design process of doubly curved reflector with shaped beam,the feed system of dual band dual polarized feed horn and waveguide feed device.The main contributions of this dissertation are as follows:The analysis method of the cosecant squared pattern antenna is studied.First illustrating the principle of“central-section curve”and“strip”in detail,and analyzing the general rules of the elliptic curve from the geometrical point of view,which provides a theoretical basis for the strip's equations;Then we discuss the far-field radiation characteristics of the cosecant squared pattern antenna in a way of physical optics.Because of that this antenna is different from the traditional structure of reflection symmetry plane,we put forward a specific solution.The design process of the cosecant squared pattern of the antenna are studied.Aiming at the lack of domestic and overseas literatures,the calculation process of this antenna are presented in detail,including the calculation of reflection surface parameters and three kinds of methods of strip equations,Then we discuss the matching problem of four kinds of strips equation and primary fields,which provides a theoretical reference for the researchers selecting of such bands;Because of the particularity of the dual curvature shaped reflector structure,it is difficult for general simulation software to construct model directly,so the author introduces three commonly used modeling scheme,and the detailed description of the construction process enable readers to grasp these methods easily.The dual-band and dual-polarized shaped reflector antenna is studied.First we design a dual band pillbox feed horn which works in the C and X double bands based on the geometric characteristics and principle of polishing line.The parabolic equation of different band is different and different polarization waves show different permeability through the metal grid,which provides a method to achieve the design of dual polarized feed.The result shows that the 3dB lobe broadband is stable within the range of 500MHz bandwidth in the C band and 700MHz bandwidth in the X band,of which the beam direction difference is stable in the range of 8~o?1~o;Secondly,the orthogonal model coupler is discussed,and the design of a miniaturized ortho-mode transducer is introduced.The overall size of the coupler is less than 92mm and the measured results of the isolation of two port are below-20dB.At last,the radiation characteristics of dual-band and dual-polarized reflector antenna are studied,which is good in the vertical plane from ~o8 to45~o at the lower band and the gain and maximum beam direction is satisfied.But the level of the side lobe of the horizontal plane is a little high,so we discuss some methods that how to reduce the side lobe of the double curved reflector antenna.We summary four effective measures to reduce the overall sidelobe level value to less than-30dB from a lot of experimental data.