Stealth Design And Beam Controlling Characteristics Of Antenna Based On Metamaterials

In modern wars,radar detection capability is usually the basis for acquiring information and building defense.The first radar emerged in the 1930s.Since then,the radar has been developing continuously.Various radar detection methods have been constantly updated,and radar detection capability has been greatly improved.The rapid development of radar detection technique poses increasing challenges to the survivability of the weapon platforms.How to improve the stealth performance of the target has become a research focus.Radar stealth technology has been developed rapidly.Various stealth technologies have effectively reduced the detection probability of targets.However,in the face of various detection methods and various detection technologies,stealth technology still needs to be studied in depth.As an important part of the weapon platform,the antenna is a strong scattering source.The stealth design for antennas is an important research focus.Scholars have put modification,loading lumped element,emitting jamming signal and many other means to control the antenna Radar Cross Section(RCS).However,in the face of increasingly developed radar detection technology,the antenna RCS reduction is still a research focus that needs to be further studied.In recent years,the concept of metamaterial has been proposed,which provides a new research direction for radar stealth technology.Metamaterials are rich in variety and has unique characteristics to control electromagnetic(EM)waves.After reasonable design,metamaterials can be used in radome,absorber and antenna coating structure to reduce antenna RCS,control antenna beam and improve antenna gain,etc.It has greatly promoted the development of radar stealth technology.However,in the face of increasingly complex EM environment,people's requirements for EM waves control increase continually.In order to improve the practicability of the metamaterials,many multifunctional and complex structures have been widely studied.Metamaterials are developing rapidly in the direction of broadband,miniaturization,reconfigurability,high angular stability and so on.Based on the working theory of metamaterials,this dissertation takes the aircraft as the application platform to study wideband metamaterials with high angular stability and analyzes their application on antenna RCS reduction.The main contents include:1.Based on the analysis of equivalent circuit theory,a tri-band Active Frequency Selective surface(AFSS)and a wideband AFSS is proposed,which are designed by loading PIN diode in the structures.The tri-band AFSS can control the beam of the omnidirectional monopole antenna.The working frequency band of wideband AFSS structure covers the X-band,which can replace the traditional band-pass FSS to be used in stealth radome to realize the in-band stealth characteristics in the time domain.2.Based on the working theory of metamaterials in controlling the phase of incident waves,a reconfigurable Phase Gradient Metasurface(PGM)is designed by loading PIN diode.Operating with a suitable microstrip antenna,the reconfigurable PGM can tilt,aggregate and scatter the beam of the antenna.In the case of tilting the antenna beam,the beam direction of the antenna can be controlled by adjusting the phase gradient of the PGM.In the state of beam aggregation,the PGM can aggregate radiated energy of antenna and improve the gain.In the beam scattering state,the PGM can disperse the incident energy and reduce antenna RCS.3.Based on the dispersion characteristic of Spoof Surface Plasmon Polariton(SSPP),a wideband absorber with high angular stability is designed.The SSPP structure can excite the EM waves in the microwave frequency band to form evanescent waves on the surface of the structure,which makes the structure obtain the ability of absorbing the incident EM waves.Unlike from the absorber designed by traditional two-dimensional FSS,the SSPP absorber has higher angular stability and better polarization insensitivity.Under the premise of ensuring the normal operation of a Vivaldi antenna,the SSPP absorber can work as reflection ground of the antenna to reduce its bistation RCS,which is verified by simulation and experiment.4.Based on the operation principle of FSS and SSPP structures,a frequency selective rabsorber(FSR)with a high transmittance window between two wide absorption bands is presented.Based on the equivalent circuit model,a double-layer absorber designed by FSS is proposed,which can absorb the incident waves in lower frequency band and transmit ones in upper frequency band.On the other hand,an SSPP-based absorber is designed.It absorbs the incident waves in upper frequency band,while it is permeable for the waves in lower frequency band.The proposed FSR is obtained by combining the FSS-based and the SSPP-based absorbers,which has a pass band covering the entire X-band and two absorbing bands covering L-,C-,Ku-and K-bands.The proposed FSR can replace traditional bandpass FSS structure to be used in the design of stealth radome,which can reduce bistatic RCS in the out-of-band EM waves.It further enhances the stealth characteristic of the radome.