Reduction of Radar Glint for Complex Targets by Use of Frequency Agility

Abstract

A result of Morinaga et al. [6] for the autocorrelation function of phase rate of narrowband Gaussian noise when averaged over accompanying wideband Gaussian noise is used to derive the power specturm of inherent glint and, thereby, its variance for a frequency-agile radar assuming Gaussian random angular motion of a complex target. The zero-frequency spectral density of inherent glint is shown to be -9.8 dB relative to that for a fixed-frequency radar under similar conditions. This result is not sensitive to the product of the agility bandwidth and the radial target extent, provided this product is adquate (as is normally ensured by current design practice for given target types). The associated glint variance with adequate agility bandwidth is shown to be 0.142 ϒ20, where ϒo is the relevant radius of gyration of the collection of radar scatterers comprising the target. A theoretical relation due to Durrani and Greated [8], derived in another context, indicates that the wideband echo spectrum resulting from frequency agility needs, in fact, to have a bandwidth of the order of 103 times that of the narrowband echo spectrum associated with target angular motion to achieve the above 9.8-dB improvement factor. For the lesser bandwidth ratios of 102 and 10, the indicated improvement factors fall to 9.4 dB and 6.5 dB, respectively.