The Research On Electromagnetic Absorbers Based On Monopole Structures

As a commonly used electromagnetic(EM)shielding and stealth material,EM absorbers have great values and significance in various civil and military aspects such as antenna anechoic chamber,communication test,anti-reconnaissance,anti-interference,etc.In recent years,with the research of metasurface,EM absorbing structures have also developed rapidly.Scholars have conducted a lot of research on the working bandwidth,profile,polarization and angular stability,versatility,antenna integration,and other aspects of EM absorbers,achieving loads of results in this regard.In addition,a variety of design methods for absorbers have been proposed.Although,at present,the research on conventional EM absorbers has been very mature,the large-angle absorbing characteristic is still a bottleneck.As the incident angle increases,the absorptivity of most absorbers will deteriorate sharply,and the absorbers with wide-angle characteristics are often resonant structures with narrow bandwidth.We can hardly find EM absorbers that have both broadband and wide-angle characteristics at the same time.This thesis investigates the relevant literature of EM absorbers at home and abroad,focusing on the analysis of the design method of large-angle absorbers,and concludes the shortcomings in the existing literature.On the basis of previous works,we present some improvement and perfection,as well as an innovative method.The proposed design method has successfully broken through the current bottleneck and we design a variety of broadband electromagnetic absorbers with large angles and wide-angle domains.The main research work and innovations of this thesis are as follows:1)Based on the previously proposed EM absorber design method through antenna input impedance reciprocity,this thesis presents an improvement using the antenna radiation pattern to design the EM absorber,realizing the EM absorber with special "absorption pattern".Besides,from the perspective of the antenna array,the similarities and differences between the antenna array and the absorber array are analyzed and compared.2)Based on the proposed design method of absorbers with antenna pattern reciprocity,a wide-band electromagnetic absorber with large-angle absorbing characteristics is designed by using the large-angle radiation properties of monopole antenna.The structure is studied and analyzed in light of antennas,and a wide-angle matching layer structure is introduced,which further expands the working bandwidth,realizing a broadband EM absorber for large angles with ultra-low profile.In addition,the blind spot of antenna arrays is also studied,and it is verified that absorbers could not work at blindness.3)On the basis of the proposed monopole absorber,co-designed with a low-profile and narrow-bandwidth absorber,achieving a wide-angle-domain absorber in the narrowband range.Combining a dipole absorber with the monopole absorber,a broadband and wide-angle absorber is realized.Finally,according to the tightly coupled principle,a T-type tightly coupled absorber is designed.Its surface current is analyzed and researched,and an ultra-wideband wide-angle EM absorber is realized.