The Research On Wideband Structured Electromagnetic Absorber And Its Applications On Antennas

The electromagnetic(EM)absorber is not only served as a cover to reduce the radar cross section(RCS)of a target object,but also is usually assembled with antennas to reduce antennas' RCS.With the fast development of electronic countermeasures technologies,multi-function EM absorber is deadly demanded.However,the current research on EM absorber is constrained on wide bandwidth,low profile,multiple bands,and wide incident angles,which is just the expansion of applications of EM absorber,and does not have depth in theoretical analysis.For the applications of EM absorber in antennas,the EM absorber and antenna are basically designed separately,then simply combine them together.There are no more systematic,more scientific techniques to achieve the integrations of antennas and EM absorber to improve the performances of antennas(such as: low RCS,low cross-polarization).Based on the existing literatures,the defects of the performances of existing EM absorbers and their applications on antennas are analyzed.Then,we creatively propose a new method to design EM absorbers with wide bandwidth and multiple functions,and successfully employ them on antenna design to improve the antenna's performances.The research points are summarized as follows:1)A method to design wide bandwidth EM absorber from antenna reciprocity is proposed which transforms the design of wide bandwidth EM absorber to the design of wide bandwidth antenna.The conditions of an antenna's input impedance to achieve wide bandwidth for wide bandwidth EM absorber is deduced.2)Based on the wide bandwidth EM absorber,we propose and realize an EM absorber with a high-selectivity-edge band notch,which divides the wide absorption band into three parts,namely,low absorption band,middle full reflectance band,and high absorption band.The generalized method to extract the equivalent circuit for periodic structures is analyzed,then the equivalent circuit of the EM absorber with high-selectivity-edge band notch is constructed.The performances of the EM absorber are analyzed in detail.3)Based on the unique frequency response of EM absorber with high-selectivityedge band notch,the multi-function metal ground and absorbent radome are designed,the so-called metal ground and radome can be integrated with antennas to realize low RCS.4)For further expanding the applications of EM absorber in antennas,a polarization-discrimination frequency selective surface(PDFSS)is proposed.The so-called PDFSS can absorb EM wave in vertical polarization,while partial reflectance and transmission is obtained in horizontal polarization at the same time.By appropriately assembling the PDFSS with a source antenna,the gain and cross-polarization level of the source antenna can be improved significantly.