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A frequency tracking loop based on triangle function frequency discriminator and adaptive loop bandwidth adjustment is proposed to track the Doppler frequency of weak direct‐sequence spread spectrum (DSSS) signal. The proposed structure first provides a frequency discrimination with wide pull‐in range to lock the large residual frequency offset after acquisition. Then, the adaptive loop bandwidth adjustment is employed to improve the accuracy of frequency estimation. Compared with the conventional tracking loop, the proposed structure has wider pull‐in range and higher sensitivity. Simulation results verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]

A fast super‐resolution method for joint Doppler frequency, direction of departure and direction of arrival estimation in bistatic MIMO radar is presented. First, the 3D echo signal model of bistatic MIMO radar with uniform linear transmit and uniform linear receive array is established. Then, the Kronecker compressive sensing (KCS) is introduced to improve the 3D parameters estimation performance. Moreover, a novel fast orthogonal matching pursuit (OMP) algorithm utilising 3D fast Fourier transformation is also presented to reduce the computation burden of KCS. Finally, the effectiveness of the method is validated by the simulation. [ABSTRACT FROM AUTHOR]

In the inverse synthetic aperture radar imaging, the autofocus is a required step for generating high‐quality images. However, due to many factors, the aperture data may be sparse so that the classical motion compensation approaches and imaging algorithms are not proper. On the basis of the compressed sensing technique and two optimisation methods (the gradient projection method and the conjugate gradient method), a novel autofocus algorithm, which can be used in sparse aperture imaging, is proposed in this Letter. The phase errors induced by the translational Doppler frequency are estimated and the focused image is reconstructed simultaneously by dual iterative computation. This approach is verified by real data processing. [ABSTRACT FROM AUTHOR]

The Doppler rate of geosynchronous synthetic aperture radar (GEO SAR) is zero at some orbital positions due to their high altitude. Also, the Doppler frequency varies along the range direction in the squint mode which is widely used in GEO SAR. The above‐mentioned Doppler characteristics have serious effects on the calculation of geo‐location error, which are not considered in the conventional model. To solve the problem, an accurate model of the geo‐location error is derived based on the range‐Doppler equations and the geometry of the squint GEO SAR. The proposed model perfectly matches the simulation results, and can be widely used in both the broadside mode and the squint mode of the spaceborne SAR. Furthermore, the sensitivity of the geo‐location error to error sources is analysed based on the simulation for GEO SAR. It is found that the satellite velocity error is the main error source of the geo‐location error in GEO SAR. [ABSTRACT FROM AUTHOR]