Use of resonance parameters of air-intakes for the identification of aircrafts

Since the development of radar systems, extensive researches have been conducted on the detection and the identification of radar targets. In military context, these targets are often stealthy to assure their security. This can be provided by using composite materials, absorbing electromagnetic waves in usual radar frequency bands. Consequently, studies are involved in lower frequencies. These frequency bands correspond to the resonance region for object dimensions of the same order as electromagnetic wavelengths. Therefore, the fluctuation of the energy scattered by the target is significant and resonance phenomena clearly appear in this region. In this paper, we propose to show, with the example of a perfectly conducting (PC) rectangular cavity, how resonances of a target depend on its dimensions and that these resonances have two origins: external resonances corresponding to creeping waves on the surface of the target and internal resonances corresponding to possible cavity waves. Internal resonances are usually stronger than external resonances, then we propose to use internal resonance parameters of air-intakes for the identification of aircrafts.