Broadband And Wide-Angle RCS Reduction Techniques For Antennas

Reducing the radar cross section(RCS)of antennas on aircraft such as fighter jets is of great military significance for the realization of stealth of aircraft.At present,there are two difficulties that need to be overcome in realizing the reduction of the RCS of the antenna.The first point is the wide-band reduction of the RCS of the antenna,and the other point is the wide-angle reduction of the RCS of the same frequency antenna.In this thesis,the frequency selective absorption structure(FSR)and the polarization conversion structure(PCS)are mainly used to realize the broadband and wide-angle reduction of the antenna RCS.The main contents are as follows:First,a highly selective absorption-transmission-absorption(A-T-A)type FSR is proposed.FSR is loaded onto PCS and applied to circularly polarized(CP)slot antenna arrays to achieve ultra-wideband reduction of antenna RCS.Outside the operating frequency band(out-of-band)of the antenna,the energy of the incident electromagnetic wave(EM)is directly absorbed by the FSR,while within the operating frequency band(in-band)of the antenna,the incident electromagnetic wave penetrates the FSR and irradiates on the PCS under the FSR structure,satisfies the phase cancellation condition,and diffuses at the same time,thereby reducing the in-band RCS.Due to lower insertion loss in the passband,higher quality factor(Q value)in the transmission band,and wider absorption band,the proposed FSR can minimize the gain loss of CP slot antenna arrays(only 0.2 d B),and expands the RCS reduction bandwidth to 135.5%(5–26 GHz).Furthermore,due to the centrosymmetrical properties of the FSR and PCS structures,the CP slot antenna array exhibits single-station RCS reduction performance for both horizontally polarized(HP)and vertically polarized(VP)incident waves.Second,based on the traditional polarization conversion structure and the traditional energy band gap structure,an energy band gap polarization conversion structure is designed,and this structure is used for the metal ground of the inverted-F antenna to solve the traditional phase gap.The phase cancellation structure causes the problem of increasing the ineffective aperture of the antenna in the process of realizing the antenna RCS reduction,and incidentally solves the problem that the traditional phase cancellation structure is not suitable for the RCS reduction of the scanning antenna array.The final designed antenna has good impedance matching at3.16GHz-3.35 GHz.At 3.24 GHz,the 8×8 antenna array can scan within-50° to 50°,and the grating lobe level is lower than-10 d B.And it has 10 d B RCS reduction capability in the whole working frequency band of the antenna.Third,the traditional phase-cancelling surface arrangement is improved based on genetic algorithm,so that the single-station RCS peak value of the coded antenna array is smaller than that of the checkerboard antenna array without affecting the scanning performance of the antenna array.