Abstract
Because of the large range of cell migration (RCM) and nonstationary Doppler frequency modulation (DFM) produced by non-cooperative targets with rapid spinning motions, it is difficult to efficiently generate a well-focused bistatic inverse synthetic aperture radar (ISAR) by use of the conventional imaging algorithms. Utilizing the property of the inherent azimuth spatial invariance in strip-map synthetic aperture radar (SAR) imaging mode, in this work, an efficient bistatic ISAR imaging approach based on circular shift operation in the range-Doppler (RD) domain is proposed. First, echoes of rapidly spinning targets are transformed into the RD domain, whose exact analytical is derived on the basis of the principle of stationary phase (POSP). Second, the RCM is corrected by using an efficient circular shift operation in the RD domain. By doing so, the energies of a scatterer that span multiple range cells are concentrated into the same range cell, and the time-varying DFM can also be compensated along the rotating radius direction. Compared with existing methods, the proposed method has advantages in its computational complexity, avoiding the interpolation and multi-dimensional search operation, and in its satisfactory imaging performance under low signal to noise ratio (SNR) conditions thanks to the two-dimensional coherent integration gain utilized. Finally, several numerical simulations are conducted to show the validity of the proposed algorithm.
Highlights
The inverse synthetic aperture radar (ISAR) plays a crucial role in the detection, recognition or identification of rapidly spinning targets [1,2,3], because electromagnetic images of non-cooperative targets with rapidly rotating motions can be obtained
While detecting and utilizing a monostatic radar configuration, the electromagnetic energy is reflected by the stealthy targets in the direction other than that of the receiver line of sight (LOS), which yields a decrease in the signal to noise ratio (SNR) for a received radar echo signal [4,5,6]
By utilizing an efficient circular shifting operation in the range-Doppler domain, the large range of cell migration (RCM) is corrected, and the time-varying Doppler frequency modulation (DFM) can be compensated along the rotating radius direction
Summary
The inverse synthetic aperture radar (ISAR) plays a crucial role in the detection, recognition or identification of rapidly spinning targets [1,2,3], because electromagnetic images of non-cooperative targets with rapidly rotating motions can be obtained. In [13], a method is presented to achieve bistatic ISAR image distortion correction by using the coefficients of polynomial phase signal in the range bin that contains a prominent scatterer. This method is seriously dependent on the prominent scatterer, which restricts its application in a real situation. In [15], the Doppler migration caused by the geometric distortion of the bistatic configuration and the target motion is compensated by constructing the phase shift function with the estimated shift factor. ISAR imaging must use signal processing methods to characterize signals of interest [21,22]
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