Analysis And Design Of Frequency Selective Surface Rasorbers

For weapon platforms such as aircraft,the strong scattering of the radar antenna system is the main contributor to the overall radar cross section（RCS）.The FSS radome technology based on the rasorber can make the antenna communicate normally in the working frequency band,and can effectively reduce the out-of-band bi-static RCS of the antenna,and can realize the stealth of the antenna in all directions.In this thesis,how to realize the design of rasorber was investigated,and the composite of rasorber as FSS radome and antenna was designed.Firstly,according to the transmission line theory,the equivalent circuit models of the rasorber with low frequency transmission and high frequency absorption and the rasorber with low frequency absorption and high frequency transmission are respectively proposed.Its transmission reflection coefficient is calculated to analyze the accuracy of the construction of the equivalent circuit model.Thus,according to the equivalent circuit analysis,the rasorber with low frequency transmission and high frequency absorption and the rasorber with low frequency absorption and high frequency transmission were designed by HFSS.Furthermore,the analysis of the ADS equivalent circuit model fitting curve is in agreement well with the HFSS simulation results.Then,based on the proposed equivalent circuit model of the double-side absorbing rasorber,a three-legged loaded unit is used to design a double-side rasorber with transmission characteristics in the C-band and absorption characteristics in the S-band and X-band.The experimental results were basically consistent with the simulation results.Under oblique incidence of 30°,the performance under TE polarization remains stable,the transmission performance under TM polarization remains stable,and the absorbing performance decreases.Thirdly,according to the design of the the rasorber with low frequency transmission and high frequency absorption,another single-band absorbing layer is added to the single-layer double-side absorbing rasorber to broaden the absorbing bandwidth of the high frequency band,and the design of a multi-layer rasorber was realized.The simulation results show that the rasorber with transmission coefficient S₂₁ above-1 dB is satisfied in the C-band 6.2⁶.6 GHz bandwidth and reflection coefficient S₁₁ below-10 dB is satisfied in the 2.4¹4.5 GHz bandwidth.The experimental results were basically consistent with the simulation results.Finally,the radiation characteristics and scattering characteristics of the rasorber as the FSS radome combined with antenna are extensively analyzed.It is concluded that the planar FSS radomes do not affect the radiation performance of the antenna after being combined with the antenna at a certain larger distance interval.The finite large-plane FSS radome can effectively reduce the out-of-band bi-static RCS of the array antenna.After the cylindrical FSS radome and the dipole antenna are combined,the E-plane pattern of the antenna is not affected,and the H-plane pattern has a slight varation,but it does not affect the transmission of the antenna in general.The scattering characteristics of the cylindrical FSS radome maintain a good mono-static RCS reduction at the low frequency,and the increase of the RCS relative to the metal cylinder is due to the appearance of the grating lobes at the high frequency band.