Research On Switchable Frequency Selective Surface For Antenna Stealth

In recent years,the perceptive detection capabilities of military radar detection systems have been continuously improved,which has brought huge challenges to the offense and defense of stealth aircraft.The antenna is one of the main sources of scattering in the aircraft,and it is easy to be exposed to the detection system,so that the stealth performance of aircraft is greatly reduced.Frequency selective rasorber(FSR)has both wave absorption and transmission characteristics,which can absorb detecting electromagnetic waves outside the working frequency band,without affecting the antenna’s radiation performance.Therefore,a new idea for the stealth radome is provided.In the future battlefield environment,it is required that radome can transmit the in-band wave to better reduce its influence on the radiation performance of antenna,realize the absorbing effect in the non-working band on both sides of the transmission band,and reduce the invalid transition band between the transmission band and the absorption band as much as possible.Furthermore,when the antenna is silent,it is required that the radome can absorb the wave in the working band,so that the antenna has the characteristics of in-band stealth.Aiming at the above stealth requirements,this dissertation makes some optimization and innovation on the traditional frequency selective surface(FSS),and designed three kinds of FSR with different structures.The main content of this dissertation can be summarized as the following:1.Research on the FSR whose passband is located inside the absorption band.In view of the problems of separation of the absorption and transmission band,and high insertion loss of the transmission band in the existing frequency selective rasorbers,a FSR that can efficiently absorb waves on both sides of the transmission window is proposed.Different frequencies wave absorption outside the working frequency band is realized by loading chip resistors at different positions of the upper lossy FSS unit.A complementary double-layer structure is adopted on the lower bandpass FSS,and two Jerusalem crosses of similar size are staggered to reduce the in-band insertion loss and expand the bandwidth of the transmission window.The simulation results show that the proposed FSR has a 3d B transmission window in1.09GHz-1.3GHz,the bandwidth is 210 MHz,and the minimum insertion loss in the transmission window is 0.71 d B.On both sides of the transmission window,the low frequency absorption band is 0.6-0.83 GHz,the high frequency absorption band is 1.32-2.52 GHz,where the absorption rate exceeds 80%.At the same time,the proposed structure has good angle stability and polarization stability.2.Design and research on the FSR whose state can be electric switched.There are certain limitations in terms of antenna stealth and poor flexibility in the passive FSR.In response to this problem,an electric adjustable FSR that can realize in-band stealth of antennas is proposed.The in-band transmission/absorption mode switch is realized by loading four varactor diodes in the lossy layer and two PIN tubes in the bandpass layer.In the transmission mode,the minimum insertion loss of the transmission window(2.65GHz)is only 0.39 d B,and the transmission efficiency is 91%.There are two absorption bands with absorbing efficiency over 80% on both sides of the transmission window,which are 1.64-2.39 GHz and2.99-5.97 GHz respectively.In the absorption mode,the transmission window becomes a new absorbing band and the full frequency wave absorption is realized.The absorbing efficiency can reach more than 80% in 1.75-6.1GHz.3.Research on the three-dimensional FSR.The characteristics of wave absorption is achieved by loading a large number of lumped resistors in tradition two-dimensional FSR,and it is not easy to produce multiple resonance points by metal resonance in a plane structure.Aiming at solving the above problems,a FSR of the three-dimensional structure is designed and researched,where a two-dimensional band-pass FSS and the parallel plate waveguide is combined.The dielectric loss and resistance loss are both used to absorb the incident electromagnetic wave,so as to reduce the number of lumped elements and extend the absorption bandwidth.In addition,a metal hole is introduced on the waveguide plate to reduce the insertion loss of the transmission band,and some metal branches are adopted to adjust the transmission and absorption resonance points.A low insertion loss of 0.24 d B is achieved at 3.5GHz,and the absorption band still covers both sides of the passband.The absorption efficiency is greater than 80% in 1.05-2.75 GHz and 3.95-6.20 GHz.