A novel synthetic aperture radar (SAR) constellation called Constellation of Geostationary and Low Earth Orbit SAR (ConGaLSAR), including one geostationary illuminator and several low Earth orbit CubeSat transponders, was previously proposed with outstanding revisiting. The MirrorSAR technology used in transponder significantly simplifies the satellite; however, it brings complexity to the imaging geometry, resulting in failures of the traditional bistatic imaging method. The introduction of probe signals achieves accurate measurement of the additional transponding distance. In this article, a three-step imaging method is proposed to realize accurate imaging processing aiming at the transponding mechanism and wide swath observation: 1) linear time variation for range cell migration grid correction; 2) second range compression for the additional squint angle introduced in the previous step; and 3) range cell migration correction in the range-Doppler domain for nonuniform cell grid caused by bistatic SAR (BiSAR). Digital simulations and real BiSAR data experiments are conducted to verify the effectiveness and accuracy of the algorithm. Moreover, the influence of the elevation is analyzed, confirming its excellent tolerance of elevation errors under the condition of a 3-m resolution and a 40-km swath width, which conforms to the system design of ConGaLSAR.

Range and azimuth ambiguities are contradictory in SAR system, which restrict the improvements of resolution and swath in satellite platform. Multichannel needs big and complex antenna. And it is proved that orthogonal transmitting signals cannot suppress range ambiguity. Thus high resolution and wide swath system is still a challenge in SAR development. In this paper, we design a novel range ambiguity suppressing method with single channel, which transmits amplitude modulation chirp signals. Through frequency filtering, the ambiguity images can be separated. A minimum mean square error algorithm is then proposed to restore the resolution robustly. Experiment based on Radatsat-1 echo shows that the proposed method can reduce the range ambiguity by 20 dB. Using this method, single-channel system can extend the swath width twice.

It is known to all that time-domain back projection (BP) algorithm has several advantages for synthetic aperture radar (SAR) imaging[1], such as easily motion compensation for any flight track, unlimited size of the observe scene, arbitrary wide bandwidth and large integration angle. Because of the heavy computational burden of BP algorithm, many fast back projection (FBP) algorithms have proposed in recent years[2-6]. We introduce a novel fast back projection algorithm which can speed up image formation and avoid coordinates transform at the same time. This method mainly utilizes the character of subapertures' oversampling and reconstructs the bandwidth by fusing all the subbands of subapertures. It also analyses the effects and influence factors for the number of subapertures. The simulation result shows that the algorithm can efficiently reduces the computational complexity while keep the image resolution.

This paper proposes a new method to suppress azimuth ambiguities for synthetic aperture radar (SAR) images. This thought derives from sidelobes suppression in SAR images, by comparing the values of two or more versions of normalized SAR images, which are obtain after different weighting functions for the same image, we choose the minimum one as its final value, therefore the new image could have lower sidelobes. Azimuth ambiguities will be relieved after smaller azimuth processor bandwidth, but the azimuth resolution also be deteriorated, on this condition, by using the similar concept as sidelobes suppression, we can preserve the resolution of mainlobe and suppress the azimuth ambiguities at the same time.

Video-SAR combines SAR imaging and video techniques together, enabling continuous surveillance of a specific area, which is a new developing microwave detection technology. Several airborne Video-SAR achievements have been published; however, less attention has been paid to the moving targets in the Video-SAR as well as spaceborne platforms. In this paper, the continuous observation problem of spaceborne Video-SAR is solved by multi-relay-receivers mode and the geostationary transmitter can cover a large scene uninterruptedly. A sketchy describe of a spaceborne Video-SAR system performance parameters is presented. An airborne Video-SAR simulation is carried out to testify the effectiveness of this system.

For SAR-GMTI system, efficient motion parameters estimation is a key challenge for moving targets imaging and localization, especially in low SNR scenarios. By four dimension (4-D) parameters searching, the Radon FRFT can achieve motion parameters estimation even when the SNR is low. But the 4-D searching operation brings heavy computation load. Focusing on these, we propose an efficient Radon FRFT estimation method to achieve efficient motion parameters estimation. By utilizing the unexploited geometry information, the efficient Radon FRFT method can reduce the original 4-D searching into only 2-D searching, promoting the motion parameters estimation efficiency in great extent. Compared with the conventional Radon FRFT method, the efficient Radon FRFT performs much better efficiency with comparable estimation accuracy.