Research On Shaping-stealth Technology Of Microstrip Antenna Based On Characteristic Mode Theory

Good radiation and stealth performance are required for the antenna on the low-scattering platform.To realize the broadband and dual-linear Radar cross section reduction(RCSR),while keeping the radiation well,is an urgent problem to be sloved.Shape modification can reduce RCS without increasing the dimension of the antenna.However,traditional shape modification lacks clear theoritical guidance and the optimization spends too much time with unsatisfactary result,Characteristic mode theory(CMT)can analyze the characteristic modes acuurately and distinguish the scattering modes and radiating modes effictively.By adding slots to suppress the scattering modes and keep the radiating modes work propoerly,the antenna RCS can be reduced.CMT provides theoritical guidance to antenna shape modification design.Firstly,using the fundamental theory of CMT and RCS,the scattering-field formula is derived.The scattering-fie Id formula and modal weighting coefficient(MWC)are used to select the dominant modes.Taking the aperture-coupled antenna as an example,the antenna RCS analysis and reduction based on CMT are studied,and the analysis and design procedure are summarized.On the basis of the procedure,the antenna RCSR is further reduced.At a 60' incident angle,the avarage RCSR is 5.0dB and the peak RCSR is 25dB fi-om 3.2GHz to 8GHz.Secondly,the ultra-wideband cross-polarization RCSR design is studied.Taking the ring-shaped microstrip antenna as an example,the RCS and scattering modes are analyzed at normal incident wave.The dominant scattering modes are chosen by the MWCs and calculated at the RCS peak point.By analyzing the current distribution of the dominant scattering modes and radiating modes,three pairs of slots are introduced into the antenna to cutoff the scattering modal currents and keep the radiating modal currents well,which suppresses the MWCs of the dominant scattering modes.The low RCS antenna is achieved,fabricated and measured.The radiation and scattering measurement are performed,Compared with the reference antenna,the low RCS antenna achieves 6 dB RCSR on average over the frequency band of 0.5 GHz-5 GHz(163.64%)for cross-polarization.The peak reduction at 3,0 GHz is up to 23 dB.Meanwhile,the radiation performance keeps well.Finnaly,the broadband dual-linear polarization RCSR design is studied.According to the procedure,the dominant scattering MWCs are studied for dual-linear polarization and the difference between the scattering and radiating modal currents is identified.Two methods are proposed to reduce the co-polarization MWCs by introducing two pairs of slots and a square-ring slot on the ground plane.Two pairs of slots are loaded on the parasitic patch and ground plane to reduce the cross-polarization MWCs.Compared with the reference antenna,the-1OdB reflection coefficient band keeps well.The gain is decreased by 0.8dB.The proposed antenna achieves 3.5dB and 5.0dB RCSRs on average for co-polarization and cross-polarization over the frequency band of 0.5GHz-2.7GHz(137.5%).The peak reductions are up to 13dB and 13.2dB for co-polarization and cross-polarization respectively.In conclusion,the low-RCS antenna design and prototype validate the theoretical formula and the design method.The research results provide new ideas and new method for the low-RCS antenna design.