Study of flight route effects on aircraft RCS signature at VHF frequencies by means of wire grid models

A perspective in future radar systems is to perform target recognition to better control air traffic. In a military context, new technologies lead to the development of stealth targets, especially in conventional radar bands, which are additional difficulties for recognition. The use of the low frequency band, particularly near the resonance range for the considered targets, is a promising way to fight against radar cross section (RCS) reduction because stealth techniques are then difficult to implement. Indeed, the backscattered field induced by the target is the result of interactions between its different parts and it is less directive at lower frequency. It can then be assumed that the RCS signature of a given target is less sensitive to small aspect angle changes. Nevertheless, observations made with the monostatic multifrequency and multipolarization HF-VHF radar MOSAR show that small changes in aircraft flight route sometimes result in important RCS signature changes. The aim of this paper is to evaluate the influence of flight route on the RCS signature of commercial aircraft at low frequencies by means of computational models. First of all, the modeling of several aircraft is described and the accuracy of the modeling is discussed. Then, the models are used to evaluate the flight route effects in the low frequency band by studying different cases which take into account the flying height and spatial position of the aircraft. It is shown that an accurate knowledge of the aircraft flight route is required for aircraft identification.