Extrapolation of near-field RCS measurements to the far zone

Abstract

Abstruct-An algorithmic procedure for extrapolating near-field radar cross section (RCS) measurements to the far zone has been evolved, coded, and experimentally validated. The derivation of the extrapolation algorithm uses the optical model to estimate the surface currents induced on the scattering body by the incident field and a specially weighted version of the Fourier transform to calculate the near-field scattering amplitudes associated with such surface currents. The extrapolation algorithm entails three steps. First, near-field measurements of the scattered electric and/or magnetic field are used to infer the monostatic vector potential A,,,. Next, the inverse Fourier transform of the inferred vector potential is multiplied by a special weighting function to estimate an equivalent obliquity factor 0.. Finally, the far-field scattering pattern is estimated by taking the Fourier transform of the reweighted obliquity factor. We have validated our extrapolation procedure with anechoic chamber data taken on a right-circular aluminum cylinder 25 X high and 2.5 X in radius at near-field range of 19 percent of 2D*/X, where D is the nominal target diameter and h the radiation wavelength. In particular, we have compared the extrapolated RCS pattern for this target with an analytical estimate of its far-zone pattern and noted good amplitude and phase agreement over a 20" cone of scattering angles.

Verification of Shadow Region Effect on Radar Cross Section of Targets Using Physical Optics Method

“…This is owing to having only one stationary point and the shadow region has no seeming effect on the scattering waves as a result of the lack in the vicinity of concave-convex inflection points. This proves that illuminating and scattered waves are subject to wavefront curvature [25].…”

Overview of RCS Extrapolation Techniques to Aircraft Targets

“…Similarly, the every point of imaging can be regarded as reradiating source, thus the new Green function is derived as G(k, R 0 ) = e −j2k|R 0 −r | /(4π|R 0 − r |) 2 . The scattering field collected by radar in near-field can be expressed as following…”

“…Generally it needs huge testing field or complex expensive compact range system [1,2]. However, an outside test field site or a compact range system is very expensive.…”

Near-field to far-field transformation for RCS measurement including ground bounce

“…If the target were measured in the free space environment, the far-field RCS will be successfully predicted from measured electric field:Es(φ,θ) in the Fresnel region [3]- [5].…”

“…Meanwhile the RCS measurement of the large actual target in the far-field region is very difficult. The application of near-field to far-field RCS transformation method [3]- [5] is desired. However the non-uniformity of the illuminated electric field on the target causes some errors in the far-field RCS prediction.…”