Compact range ISAR emulations of moving SAR targets: theory and experiment

Abstract

Absfmef-This paper dseusss emulati moving targeb on compad radar ranges We show that Ul6 d e ranges used today are limited to emulating target & of 4 ds, and can not produce &ta with the range bin migralion effecis that ( E " when targets are traveling at realistic Speeas. We prupose a Y64* ?e systcm capable of emulating higher target speeds. I d e x rems-. Compact Range, Moving Target, Range Bin Migration L INTRODUCTIONCompact radar ranges (CRRs) are used to collect scaled radar cross section data to circumvent the high cost of obtaining the data'using airborne synthetic aperture radar (SAR) and full-sale targets. CRRs use a fixed radar Transmitter and Receiver with a scaled target on a rotating platform. The rotation of the platform synthesizes an extended coherent aperture for cross-range resolution.For range resolution. CRRs use N E coherent-time gated sinusoidal pulsed signals with wave numbers k. = 21r J . and uniform stepping interval Ak , k, = k, + ( P I -( Nr -1)/2) At,for n = 0.1 ,..., N ' -1. (1) Continuous wave (CW) signals are transmitted for a time interval Tp , with Tp 2 1/Ak . After coherent demodulation to an intermediate frequency. the scattered pulses are all individually simpled at a rate A, commensurate with the Nyquist sampling requirements and digitized. commonly used to effectively extract the scattering density. The fmt, which we call tomographic deconvolution [ 1.2, 31, solves for the scattering density by taking the discrete Fourier transformof the spatially sampled data This approach is usually.limited to applications where the illuminating fields can be treated as plane waves. The second approach uses phase shift focusing in lieu of time delay focusing to focus the coherent scattered signals captured over a sampled spatial apemue. The image in the second approach is defined as the square mapirude of the coherent sum of the focused signals. For cases where the targets are effectively in the far field of the spatial synthetic aperture, both these approaches produce the same results. Both approaches contain various approximations and specific choices of pixel parameters to expedite the processing. The mathematical development of the second .-* ?his work was supported in pan by the NSF under grant -.There are two signal-processing methods that are I CCR-0208830 approach follows in a smightfomard logical fashion. Moreover it is particularly effective for treating imaging scenarios involving both non-uniform illuminating fields and moving targets. Accordingly, the mathematical development featured herein will follow this second approach. II. S C A~O S O U m O N T O W A V E WLJATIONCRRs are operated at small bistatic angles, with the distances from the feed horn to the image maps very large compared to the wavelength and dimensions of antennas [6]. In this regime the radiation signals are described by 'outgoing spherical waves with axial envelopes dictated by the diffraction pattern of the transmining physical antenna. In the case of the indoor CRR, the transmit receive (TR) coherent apertur...