Research On RCS Reduction Technology Of Vivaldi Antenna And Vivaldi Array

Antenna is a key component of transmitting and receiving information in combat systems,and it's one of the most obvious scattering sources that contribute to the Radar Cross Section(RCS)of the system.Therefore,the RCS reduction technology of the antenna is very important.The Vivaldi array is widely used in airborne fire control radar of the aircraft because of its high gain and wide bandwidth.In order to improve the stealth performance of the aircraft,the research on RCS reduction technology of the Vivaldi antenna and array is of great demand.Based on the application background of the Vivaldi antenna,this thesis analyzes the working principle,studies the RCS reduction methods and reduces the RCS of the Vivaldi antenna and array.The main contributions of this thesis can be summarized as follows:1.In order to reduce the RCS of the Vivaldi antenna without wasting its radiation characteristics,a low RCS Vivaldi antenna based on slotting technology is proposed.In this thesis,a traditional Vivaldi antenna operated in X-band is designed as the reference antenna.Slots are etched in the area where the surface current distribution is weak in the radiation state to avoid the negative effect on the radiation characteristics.Three cosine expressions are used to control the length of the slots in three different regions,respectively.The most effective RCS reduction is achieved by adjusting these three cosine expressions.When the low RCS antenna is illuminated by a y-polarized incident wave facing the main radiation direction of the antenna,the 6d B reduction bandwidth can cover the X-band,the maximum and minimum reduction value is 16.39 d B and 6.78 d B,respectively.Compared with the reference antenna,the gain of the proposed antenna is improved,with a maximum increase of 3.14 d B.2.In this thesis,an absorber with a multi-layered structure of metal-substrate-air-metal is proposed firstly.The absorber expands the absorption bandwidth by loading resistors on the metal patch layer.It also adopts the center-symmetric structure to ensure polarization insensitivity.The simulated results show that the absorber unit can maintain a higher absorptivity than 80% with normal incident wave in X-band.Increasing the angle of the incident wave,the absorptivity decreases,but it can't go below 70% until the angle of the incident wave reaches 45.In order to further improve the absorptivity of the absorber unit,some holes are punched around the dielectric substrate to change the equivalent electromagnetic parameters of the absorber so that the equivalent relative permittivity is closer to the equivalent relative permeability.In this way,a better impedance matching between the absorber and the free space is realized and the absorptivity is improved.The simulated results show that the final absorber unit can maintain a higher absorptivity than 90% with normal incident wave.The absorptivity can't go below 80% until the angle of the incident wave reaches 50.3.In order to achieve the RCS reduction of the Vivaldi array,a low RCS Vivaldi array based on loading the absorbing layer is proposed.Firstly,the proposed low RCS Vivaldi antenna is used as the array element.A metallic reflective plate is placed behind the array considering the application background of Vivaldi antenna.The RCS of the reference array will increase a lot because of the specular scattering of the reflection plate.In order to reduce the specular scattering brought by the metallic reflective plate,the proposed absorber units are periodically arranged on a two-dimensional plane to form an absorbing layer in place of the reflective plate in the reference array.The RCS reduction is effectively achieved by the absorbing characteristics of the absorber.The simulated results show that the maximum and minimum in-band reduction under x-polarized incident wave is 18.82 d B and 9.38 d B,respectively,and the average reduction is 13.43 d B.While the proposed array is illuminated by a y-polarized incident wave,the maximum and minimum in-band reduction is 23.51 d B and 7.7d B,respectively,and the average reduction is 13.74 d B.