Research On Multifunctional Stealth Radome Based On Frequency Selective Surface

With the application of various high technologies and detection technique in the military,it becomes particularly urgent to reduce the probability of weapons and equipment being discovered and improve their survivability in modern battlefield.Stealth technology,known as low observable technology,can change or minimize the detectable information of a target and thus reducing its probability of being discovered by enemy detection systems.Generally speaking,radar stealth is the main stealth technology because of the radar antenna on the weapon or aircraft is the main electromagnetic scattering source.Therefore,it is of great strategic significance to design radome with both transmission and stealth functions to reduce the Radar Cross Section(RCS)of the target and enhancing their survivability.For radomes used for aircraft stealth,ideally,it should be transparent to the radar within the working band of the radar antenna,while out of the operating band,it could reflect the potential incoming waves to other directions or absorb them completely.Compared with traditional radomes,the frequency selective surface(FSS)with band-pass property can greatly improve the stealth effect of radar system by selectively transmitting electromagnetic waves and reflecting the out-of–band incident waves to other directions.However,the stealth method of reflecting out-of-band incoming waves by FSSs can only take effect on monostatic RCS reduction.When there are multiple radar stations,the electromagnetic waves reflected in all directions by FSS are easily picked up by the detection stations in other locations,and thus exposing the target's position.At this point,the radome composed of integrated absorptive/transmissive metamaterial can basically absorb all incoming waves outside the working band of the antenna,making it unable for radar detection stations at all positions to receive the response of the detected waves.This is of great significance for reducing multi-station RCS and improving the stealth performance of weapons and equipment.This dissertation introduces the design process and analysis method of various multifunctional radomes based on FSS,including frequency reconfigurable FSS and integrated absorptive/transmissive metamaterials.For the integrated absorptive/transmissive metamaterials,we study and design the frequency selective rasorber(FSR)of2D structure,and on this basis,we propose a new type of ultra wideband absorber based on2D and 3D hybrid structure and several FSRs with different absorption/transmission performances.The main works of this dissertation are summarized as follows:1.First of all,two 2D integrated absorptive/transmissive metamaterials have been designed based on the principles of circuit analog absorbers(CAA).It includes a low-frequency-transmission/high-frequency-absorption radome and a low-frequency-absorption/high-frequency-transmission radome with broadband transparent window.The two radomes are designed with smaller cell period and thinner thickness,which are more convenient for practical applications.2.On the basis of 2D integrated absorptive/transmissive metamaterial,an FSR with low-frequency-transmission/high-frequency-absorption performance based on 2D and 3D hybrid structure was designed.The FSR of the proposed new structure consists of a 3D lossy layer on the top and a 2D band-pass FSS below,the overall size of the FSR is only0.11?₀×0.11?₀×0.071?₀(?₀ is the free space wavelength corresponding to the central frequency of the transmission band),so it has good angular stability.At the same time,the equivalent circuit method is used to analyze the working principle of the hybrid-structured FSR and the effectiveness of the equivalent circuit is proved.In addition,we have designed a band-pass FSS that can be tuned over a wide band.By applying different bias voltages to the varactors loaded on the FSS,the central frequency of the passband can be varied from C band to Ku band.Finally,we combine the 3D lossy layer of the low-frequency-transmission/high-frequency-absorption FSR with the frequency reconfigurable FSS to synthesis an FSR with a tunable transmission band.The integrated absorptive/transmissive metamaterial designed with the function of transmission band reconfigurable can be better applied in the complex and changeable electromagnetic environments.3.A compact absorber CUWA(Compact Ultra Wideband Absorber)with ultra-wide absorption band has been designed based on the previously proposed 2D and 3D hybrid structure combined with multi-resonance units.The CUWA has a 144%absorption bandwidth with the compact size of 0.10?_L×0.10?_L×0.11?_L(?_L is the free space wavelength corresponding to the lowest absorption frequency),which meets the actual demands for thinner absorber thickness and wider absorption bandwidth.At the same time,the causes of the resonance points in the ultra-wide absorption band of CUWA are analyzed in detail,which provides theoretical guidance for designing the same type of the ultra-wide band absorber.4.By inserting split resonant ring(SRR)into the high-frequency resonance unit and combining the low-frequency resonance unit to form a multi-resonance structure,a compact FSR with ultra-wide absorption band and internal passband is designed,namely compact ultra wideband frequency selective rasorber(CUWFSR).In order to further improve the transmission performance,we design a short-circuit branch with 1/4 high-frequency wavelength to inhibit the absorption of the low-frequency resonance unit at the high frequency,and thus reducing the insertion loss of the CUWFSR at the transmission band.The bandwidth for S11 less than-10d B of the improved CUWFSR is about 137.3%and the minimum insertion loss of its transmission window is only 0.59d B which is 1.2d B lower than the previous one.Besides,the absorption rate on the both sides of the passband is basically above 90%.The improved CUWFSR combines two methods of generating transmission window in the absorption band which provides a new idea for the design of ultra-wideband FSR with low insertion loss and multi-resonance structures.