Radar Cross Section Control For Antenna Over Broadband And Wide Angular Domain

With the rapid development of avionics technology,the international battlefield has become increasingly harsh.The emergence of various new types of radar,advanced detectors and accurate guidance weapons put forward higher requirements for stealth characteristics of military targets such as stealth fighters,ships and unmanned aerial vehicle(UAV).Radar cross section(RCS)is usually used to measure the stealth characteristics of the targets.Stealth technology is such an effective method that to reduce the enemy radar range fromreducing the RCS of a target.With the active jamming,passive jamming and low altitude or low altitude penetration technology,the survival rate and combat force of one's own weapon platform can be greatly improved.With the development and progress of low scattering structure and carrier,antenna,as the main device for receiving and transmitting electromagnetic wave,whose stealth performance has become the critical factor of the overall stealth characteristics.However,blind pursuit for low scattering at the cost of electrical properties of an antenna is not realistic.To deal withthe enemy radar detection from multi azimuths,radar cross section reduction(RCSR)over certain angles should also be considered.Therefore,research in broadband and wide angle domain RCSR without destroying the antenna radiation characteristics has become the main focus of the world military power nations in recent years.Traditional stealth technology of an antenna includes shape control technology,radar absorbing material technology,passive cancellation technology and active cancellation technology.Unique RCSR technique has many limitations,the exploration of broadband(including the in band and out of band)and wide angle RCSR while satisfying the radiation performance requirements is still a great challenge.The fifth generation fighter,new tactical missiles,new carrier-based aircrafts,new UAVs and other new weapons and equipment require lower RCS,and omnidirectional stealth performance.New electromagnetic metamaterial technology can control the scattering peaks deviating from the radar threat area to realize the antenna stealth within specific airspace.This thesis mainly studies the new method for antenna's RCSR,the contents include the following aspects:1.The conventional absorption bandwidth characteristics of frequency wave response of absorbing materials is not good,single-layer absorbing material is difficult to achieve broadband technology.The composite construct of matrix absorbing material layer and frequency selective surface(FSS)can broaden the bandwidth The designed absorbing material's bandwidth covers C and X bands,solving the problem that the bandwidth of absorbing material is not wide enough in the low frequency.When it is applied to the Vivaldi antenna,2-18GHz broadband range RCS R is achieved.2.Resistor-loaded multilayer miniaturized metasurface structure is introduced.The upper structure is FSS layer loaded with resistors,which has transmission characteristic to the electromagnetic(EM)wave at the antenna working frequency band.That is to say,the antenna can radiate EM wave over the in band normally,while convert the energy out of band into heat through the resistors.The lower layer is an EM band-gap(EBG)structure loading with resistive elements,which can be used to dissipate the in-band energy impinging on it.The double-layer miniaturized metasurface units are arranged around the antenna,remarkable wideband RCSR can be obtained ranging from 2 to 15.5GHz with little influence on the radiation performance of the antenna.What's more,the structure is also applied to the tightly coupled antenna array,more than 5 dB average reduction of RCS over 1-18GHz is achieved.3.Holographic Metasurface(HM)is composed of elements of different sizes of the patch,which can be utilized as the antenna cladding to control the transmission of EM wave.The incident wave can be transferred into the surface wave,so that lower backward scattering and gain enhancement of the antenna could be obtained.The partially reflecting surface(PRS)and the floor below the HM surface forms the Fabry-Perot(F-P)resonant cavity,which contributes to low RCS within the working frequency band and directivity improvement of the antenna.Using the HM surface and PRS as the cladding of the antenna,results show that the antenna gain increased by 4.1dB,obvious wideband RCSR over 9-22GHz is achieved.The method solves the contradiction between radiation performance of the high gain and low scattering characteristics.4.As a new type of electromagnetic metamaterial,polarization conversion metasurface(PCM)unit and PRS structure are combined together to form synthetic PCM-PRS unit.Most of the incident wave can be reflected into cross-polarized wave,phase difference of +90 degrees and-90 degrees are produced on the unit and the mirror unit respectively,thus the polarization of the reflected wave has been converted.The cross-polarized reflection wave phase difference between the PCM-PRS unit and its mirror unit difference is 180 degrees.Hence the backward scattering energy could be dissipated into other directions through passive cancellation.F-P resonant cavity constructed by PRS and the antenna ground can improve the gain of the antenna and decrease the in-band RCSR Simulated and experimental results show that the antenna gain is increased by 7.02 dB at center frequency,and the RCS over 8.5-20 GHz has been effectively reduced.Simultaneously,during the angular domain of-15°?15° at antenna operating band and of-33°?33° out of the operation band,the RCS are significantly reduced,with the maximum amount of RCSR is 40dB over the in band,while 37 dB over out of band.5.As an extension,frequency reconfigurable technology is introduced into the design of high gain and low RCS antenna.Adual-polarization phase tunable reflective surface is combined with PCM and PRS to realize the frequency reconfigurable antenna.Byadjusting the bias voltage of the varactor diodes,the capacitance can be tuned,and various reflective phase can be obtained,thus the working frequency of the antenna can be reconfigured.The Fabry-Perot(F-P)resonant cavity formed by PRS and the DPTRs contributes to in-band RCSR and highly directive beam.The operation frequency can be dynamically tuned from 8.75 GHz to 10 GHz,the operating frequency of the antenna shifts to lower frequency with the increase of the capacitance.And the realized gain peak shifts'to lower frequency in turn,reaching to the maximum at the center frequency.What's more,wideband RCSR over 8.3-20 GHz is obtained in both polarizations,the average reduction is greater than 7dB.In addition,the in-band RCSR bandwidth can be actively tuned with variation of the operating band.The RCS reduction of wideband antenna is equivalent to RCS reduction of multiple electronically controlled narrow band reconfigurable antennas,which provides a new method for RCS reduction of broadband antennas.