With appropriate geometry configurations, bistatic Synthetic Aperture Radar (SAR) can break through the limitations of monostatic SAR for forward-looking imaging. Thanks to such a capability, bistatic forward-looking SAR (BFSAR) has extensive potential applications. This paper develops a frequency-domain imaging algorithm for translational invariant BFSAR. The algorithm uses the method of Lengendre polynomials expansion to compute the two dimensional point target reference spectrum, and this spectrum is used to perform the range cell migration correction (RCMC), secondary range compression and azimuth compression. In particular, the Doppler-centroid and bistatic-range dependent interpolation for residual RCMC is presented in detail. In addition, a method that combines the ambiguity and resolution theories to determine the forward-looking imaging swath is also presented in this paper.

Bistatic synthetic aperture radar (BSAR) with one fixed station (OF-BSAR) can be used in wide area surveillance, ground moving target indication etc. This paper analyzes the spatial variance of OF-BSAR. Analytical expressions of the spatial invariance region in the data space are given. Using these results, we can determine the spatial invariance region in the data set and the imaging area. After that, we give a data blocking scheme for raw data focusing. Numerical simulation verifies the results of this paper.

For Doppler parameter estimation of forward-looking SAR, the third-order Doppler parameter can not be neglected. In this paper, the azimuth signal of the transmitter fixed bistatic forward-looking SAR is modeled as a cubic polynomial phase signal (CPPS) and multiple time-overlapped CPPSs, and the modified cubic phase function is presented to estimate the third-order Doppler parameter. By combining the cubic phase function (CPF) with Radon transform, the method can give an accurate estimation of the third-order Doppler parameter. Simulations validate the effectiveness of the algorithm.

An effective operation mode and a space-time synchronization technique for the spaceborne/airborne hybrid bistatic synthetic aperture radar (SA-BSAR) using sources of opportunity are presented. Our motivation lies in the fact that the existing approaches in the literature, where the transmitter antenna must be steered, can only be used in the hybrid bistatic SAR systems with cooperative transmitter. The presented mode is to widen the receiving beam for the purpose to increase the scene extension in azimuth. The inspiration comes from the much shorter receiving distance as compared to the one in mono-static spaceborne SAR. This means that the receiving gain can be significantly reduced to provide the same signal-to-noise ratio (SNR) with respect to the mono-static case. The feasibility of the wide-beam mode is first preliminarily verified by a quantitative analysis of SNR and a demonstration that the pulse repetition frequency (PRF) used in the spaceborne illuminator can easily satisfy the PRF constraints of the SA-BSAR. The influence on the azimuth ambiguity to signal ratio (AASR) is also discussed and the corresponding broadening factor of the maximum allowable for receiver beamwidth is subsequently derived. Afterwards, the formulae for calculating the overlap time, the scene extension and the azimuth resolution are deduced. As there are no grating lobes in satellite antenna pattern since the non-cooperative illuminator normally operates in the side-looking mode, an existing technique for the space-time synchronization in cooperative hybrid systems can not be directly applied. The modification performed and its underlying principle are presented in detail. The simulation results demonstrate the effectiveness of the wide-beam mode, and show that in most cases a useful scene extension (on the order of at least 1 km) can be achieved with a roughly equivalent azimuth resolution as compared to the one in mono-static spaceborne SAR. In some cases, explicit measures to suppress the azimuth ambiguity must be taken to achieve the expected scene extension.