| In modern warfare,radar technology is the main method for target detection,and radar stealth technology plays an important role in improving the survivability of aircraft and other targets on the battlefield.How to efficiently design and optimize Radar Absorbing Material（RAM）and achieve broadband absorbing performance is an urgent problem.However,the practical application requires not only the stealth material to absorb the incident waves in the stealth band,but also the carrier antenna need to radiate electromagnetic energy with low loss in its operating band,so it is significant to study the design method of Absorptive/Transmissive structure.In addition,due to the Rozanov Limit,which limit absorbers’profile,so the thickness of traditional RAM in the low frequency of microwave is large,especially in the P-band（0.23GHz～1GHz）.In view of the requirements of absorbing/transmission materials for"wide-band","low-profile"and"light-weight",it is of great significance to carry out research on ultra-wideband and low-profile technology.The main research and contents of this paper are as follows:Firstly,an equivalent circuit model（ECM）of a novel circuit analog absorber（CAA）with multi-layered structure is proposed based on the impedance matching principle,and the relationship between ECM and physical structure is derived.Then,the performance with single-band,dual-band and broadband absorption of the absorber structure is realized by different number of lossy-layers so as to verify the reliability of this ECM.An ultra-wideband absorber with a quadruple-layered structure is designed and tested with a resistive thin-film process,which achieved more than 90%absorption in the frequency band of 2.1 GHz to 37.5GHz,and the maximum oblique incidence angle supported is 30°.In order to achieve carrier conformal,the ultra-wideband absorber were carried out at the column surface carrier,which get the circle center angle of 30°and 60°,the measured results showed that the absorber can still meet the absorption rate with 90%.On the other hand,while the absorbing band is extended to higher frequencies,which leads to an electrically small size and the inevitable generation of higher resonant frequencies,so there will be an error between ECM and the physical model.In order to solve this problem,a space mapping（SM）for optimizing absorber structure is proposed,which achieved an ultra-wideband absorber covering the frequency band from 3 GHz to 94 GHz.Secondly,in order to meet the requirement of efficient absorption of out-of-band electromagnetic waves while ensuring normal in-band signal transmission,the design method of Absorptive/Transmissive Frequency Selective Structure（ATFSS）is investigated.A method of designing HIS cells with bandpass characteristics by connecting a spiral inductor is proposed,which is connected in series on a square-loop frequency selective surface（FSS）.A bandpass FSS（BPFSS）based on a complementary structure is designed by equivalent circuit model analysis,and an integrated ATFSS with dual-band absorption and medium-frequency transmission is realized by combining the HIS and BPFSS.In addition,a quasi-F-P resonant cavity antenna composed of ATFSS and Dielectric Resonator Antenna（DRA）is proposed and tested.The results indicate that the ATFSS loaded DRA antenna can significantly improve the realized gain and reduce the radar cross section（RCS）of the carrier platform.Finally,the mechanism and solution of impedance mismatch of absorbers in low frequency band are investigated for the inherent bottleneck that the current absorbers structure is limited by Rozanov Limit,which leads to absorbers’high profile.Based on the above ATFSS design,an ultra-thin and ultra-wideband ATFSS design scheme loaded with Non-Foster devices is proposed,the simulation results indicate that the absorbing rate above90%is achieved in dual-band of 80MHz～5GHz and 13.7GHz～14.5GHz,and the 1d B transmission loss band is achieved from 8.1GHz to 12GHz.The overall thickness is 20mm which corresponds to the relative profile of only 0.0053λmax. |
PDF Full Text Request