Natural Resonance Estimation

The complex natural resonances of an object are of considerable utility in object classification studies. For geometrically complex object shapes and other than very low frequencies, the resonances must be extracted from measurements of scattering or radiation data. The purpose of this paper is to describe the extraction of the electromagnetic complex natural resonances from scattering data measured on a compact reflectivity range housed in an anechoic chamber. The targets for this study are electroplated models (scale factors range from 1:130 to 1:200) of modern aircraft. Processing generally consists of low-pass digital filtering to smooth the data and remove, as much as possible, the clutter. The filter characteristics are selected such that the measured band-limited impulse response of the target (IFFT) is neither truncated nor distorted. Techniques and applications of the rational function fit are discussed and illustrated using the aircraft measurements.