Study On Radar Cross-section Control Based On Frequency-selective Surface

The radar cross-section of a target is a key parameter that determines the process and result of radar detection.In the modern military system,there are often two scenarios.One is that when facing the enemy's reconnaissance,radar stealth technology can be used to reduce the RCS so that the radar echo of the target cannot be detected by the enemy's reconnaissance radar.The other is to conduct anti-reconnaissance against the enemy or when the target needs to be tracked,the enhanced backward radar scattering helps to provide a stable echo signal within the predetermined frequency and angle range or to expand the distance that the target can be detected.Therefore,studying on the control of radar cross section is of great significance.In this paper,the reduction and enhancement of radar cross section are studied based on frequency selective surface.In terms of radar-cross section reduction,bandpass frequency selective surface with unique filtering characteristics can be used as a radome,but due to the strong reflection outside the passband,which means the lager radar cross section,thus reducing the reflection outside the passband of FSS and reduce the radar cross section of the radome is important.As a combination of frequency selective surface and rasorber,FSR has the performance of electromagnetic wave transmission and absorption,which can effectively suppress the reflection outside the passband.However,the FSR that suppresses the reflection outside the passband reported in the literature mostly achieved relies on the absorption of lossy material or lumped resistive element.Based on the finite large FSS and passive phase cancellation principle,a frequency selective structure which can reduce the reflection outside the passband and maintain the passband band without using lossy material and the resistive component is realized in this paper.The frequency range observed is 5 GHz to 15 GHz,and the working frequency of the passband is 10 GHz.The design goal of this paper is to reduce the reflection outside the passband at the frequency below the passband through the phase cancellation principle and expand the cancellation band range.The main work for this design is as follows:First,a simple square slot is adopted as the basic unit cell to design a traditional bandpass frequency selective surface with a working frequency at 10 GHz.In order to characterize the reflection and transmission coefficients of finite large arrays,a method of extracting the reflection and transmission coefficients of finite large period structures based on scattering electric fields is analyzed.In order to reduce the strong reflection outside the passband by the concept of passive phase cancellation,different types of unit cells are constructed by means of double-layer cascade and changing the cascade spacing on the basis of single layer square slot,these unit cells meet the objective conditions that required for passive phase cancellation design principles.Therefore,the proposed multi-layer frequency selective structure with checkerboard pattern is obtained by combining these unit cells into a certain number to form supercells and further combining appropriate number of supercells Due to the phase cancellation principle,the proposed design can generate interference cancellation in the direction of the incident wave,so as to reduce the reflection amplitude at low frequency of the passband,which is beneficial to the reduction of RCS.Simulation and experimental results show that compared with the one-dimensional checkerboard structure,the two-dimensional checkerboard structure has better cancellation performance and angular stability for electromagnetic waves,as well as better passband transmission performance.In addition,for the proposed frequency selective structure,two main parameters that influence the bandwidth of phase cancellation had discussed in this paper.One is the overall lateral size of the structure,the results show that at the normal incidence in TM polarization,from 6 ×6 unit to 12×12 unit of one-dimensional chessboard double-layer structure,the relative bandwidth of reflection coefficient |R|?-10 dB can be increased by 11.19%;The second is the number of layers of the structure,the results show that when the number of layers increases to four,the low-frequency end of the band with reflection coefficient less than-10 dB can be extended to below 5 GHz.In terms of radar cross-section enhancement,the local outer surfaces of many radar targets usually intersect each other at a certain angle,thereby inadvertently forming a obtuse dihedral structure on a complex target surface such as a boat or a vehicle and caused low radar cross section.In order to enhance the backward radar cross section of the obtuse dihedral corner structure under near-grazing incidence,this paper proposes a circular FSS unit with dual polarization control characteristics,and forms an effective design of phase gradient super surface loading.The loading area and reflection phase gradient of the metasurface were determined through analyzing angles of incidence and reflection for two illuminated inner surfaces of the obtuse dihedral corner structure.Dimensions of unit cells of the metasurface were obtained according to the calculated reflection phase distribution.Full-wave simulation results indicate that backscattering cross-section at the operating frequency of 10 GHz can be augmented by 16.5 dB and 13.3 dB for the phi-polarized and theta-polarized incident electromagnetic waves,respectively,by virtue of the obtuse corner structure loaded with two metasurfaces for its both inner surfaces.Moreover,the analysis of bistatic scattering patterns demonstrates that effective manipulation of reflection direction of the obtuse dihedral corner structure through metasurface loading serves as the key basis of the backscattering cross-section enhancement.