The Study Of Absorptive Frequency Selective Surface And Its Application In Antenna Stealth

To improve the viability and penetration ability of the future weapon system, radar stealth technology attracts more and more interest. The antenna system is often one of the primary scattering sources. How to reduce the radar cross section(RCS) of antenna without disturbing its radiation performance appears to be more important. In recent decades, frequency selective surface(FSS) with bandpass property has been studied to be applied in stealthy radome, which permits the transmission of electromagnetic signal at a particular operation frequency, and meanwhile reflect waves at any other frequencies to the direction away from the incoming wave. However, when confronted with bi-static/multi-static detection, the reflected waves to other direction still can be received, then this approach would fail to protect the antenna to be invisible.In this paper, the theory and design of an absorptive frequency selective surface(AFSS) have been researched, which is characterized by a transmissive/absorptive property, namely it possesses a high in-band transmission within the operation band and a wide out-of-band absorption simultaneously. AFSS has been applied as novel stealthy radome, which absorbs, instead of reflecting, the out-of-band wave, and the bistatic RCS of antenna could be reduced.Firstly, an AFSS structure with property of transmission at low frequency and absorption over high band has been designed. The insertion loss at transmission band of 1GHz is lower than 0.8d B, and the absorption over wideband from 3GHz to 9GHz is at least 10 d B. Then it is applied as a planar stealthy radome for a microstrip antenna. The influence on the radiation performance of the antenna has been investigated and optimized. Both numerical analysis and experimental measurement have been carried out to verify the bistatic RCS reduction of the radome. However, due to its large periodicity, backward grating lobe might appear in the absorption band, which will cause undesirable increase of mono-static RCS. AFSS with miniaturized elements is proved to be efficient to eliminate the grating lobe problem. A miniaturized AFSS(MAFSS) with the similar transmissive/absorptive property has been designed. Numerical and experimental results have been presented to validate its efficiency on elimination of grating lobe.Finally, the theory of AFSS with property of transmission at high frequency and absorption over low band has been researched. Two feasible methods have been presented(i.e. ?/4 shorted choke loaded and parallel LC loaded). Two AFSS structure by these methods were designed to be transmissive at X band and absorptive over low band. A prototype of the former method has been fabricated and its transmissive/ absorptive property was measured.