Three-Dimensional Sar With Fixed Transmitter and Its Scattering Explanation

Abstract

Abstract-During the experimental data processing, we find that corner reflectors cannot be focused properly using 3-D SAR with a moving transmitter due to the phase reversal phenomenon based on the phase history analysis, i.e., the phases at different observation angles might shift rad, and the echoes cancel, rather than accumulate, to each other. To overcome this defect, 3-D SAR with fixed transmitter is designed. Since the geometry of the transmitter and targets remains unchanged during the observation session, the coherence of echoes is well preserved. The mechanism of 3-D SAR with fixed transmitter can accurately be explained using the Stratton-Chu equation. For perfect conductor, the 3-D image is related to the electric current density. For general dielectric medium, the 3-D image is related to the electric current density, magnetic current density and directional vector of scatterer. Experimental results show that one can focus corner reflectors and cavity-shaped objects by fixing the transmitter, which might fail for the traditional 3-D SAR because of the phase reversal phenomenon.

3-D Sar Imaging Based RCS Measurement Technique With Fixed Transmitter

“…where, η represents the system deviation of 3-D imaging system caused by the magnetic current density, when the aperture angle is smaller than 20 degree, η > 0.98, which can be ignored in practice [10]. For perfect conductor, the (complex) values of the 3-D image is only estimationJ a (p ) of the − → J :…”

“…In stage two, denoting the polarization direction of the receiver antenna asâ and the position of receiver in the receiver array as p, the received voltage at p is the scattering of the induced electric/magnetic currents projected toâ, which can be expressed as [10]:…”

“…According to [10], the (complex) values of the 3-D image is estimationX a (p ) of the superposition of the − → J and the outer product of − → M and the unit vector from the virtual array center to the pixelp ,p indicates the directional vectors from the receiver p to the target at p ,…”

“…According to the results in [10], for synthetic aperture technique, the spatial variation of scattering characteristic will cause acquired data non-coherent and deteriorate the SAR image quality greatly when the aperture angle is rather large. To eliminate the variation, the transmitter needs to be fixed.…”

“…To overcome these defects, many imaging based RCS measurement techniques are developed. The most practical and mature ones are based on synthetic aperture radar (SAR) imaging to model the target's scattering, such as inverse SAR imaging based RCS measurement [5][6][7][8] and linear array SAR imaging based RCS measurement [9][10][11].…”