Synthetic Aperture Radar

Synthetic Aperture Radar (SAR) and Inverse Synthetic Aperture Radar (ISAR) are powerful sensing technologies that give the potential for imaging and azimuth/ cross-range resolution refinement, revolutionising trhe way we perceive the environment, be it be automotive, maritime or space.

SAR utilises the motion of the radar platform or the targets to synthesize a long aperture. Therefore, a high resolution two-dimensional image of the scene and targets can be generated, providing detailed information about its features such as shape and size.

SAR and ISAR are particularly valuable for automotive applications, enabling enhanced situational awareness, object detection, and obstacle avoidance in autonomous vehicles. In maritime scenarios, SAR can be utilised to detect and monitor marine targets such as swimmers, oil spills, flotsam, jetsam, and is especially useful for docking applications. SAR processing also plays a vital role in space sensing, facilitating Earth observation, planetary exploration, and monitoring of natural disasters from the spaceborne platforms.

At MISL, we are developing novel algorithms for SAR and ISAR processing, combined with back projection, range-migration compensation, motion compensation, sidelobe reduction, auto-focus techniques to enhance the radar imagery,
300 GHz sensor suite developed at MISL
SAR Imagery of trolley at 79 GHz and 300 GHz.

We have also developed a holistic simulation tool for electromagnetic simulations of a radar scene response at mm-wave and sub-THz frequencies. Using the tool, we are capable to model various types of environments and test the performance of the algorithms in controlled setting.

Simulated sea surface and processed SAR imagery
Modelled SAR Images of a satellite target at 77 GHz and 300 GHz.

Doppler beam sharpening

One SAR based technique developed and patented by the researchers in MISL is Doppler beam sharpening (DBS), a form of unfocussed SAR, straightforwardly implemented on a range-Doppler map. DBS maps the measured Doppler frequency of a target to its angular position; thus, a wide real azimuth beam is sub-divided into smaller sub-beams – Figure 1.
DBS has been successfully implemented in automotive and maritime environments using commercially available mm-wave automotive MIMO sensors and a sub-THz sensor suite developed at MISL.Three images illustrating a floating pallet formed through the application of DBSCaption: Image of floating pallet formed through the application of DBS (0.5 s integration time), with 14 overlaid coherently processed DBS images. 150 GHz radar platform moving along a Jetty at Coniston Water in the Lake District.

By combining DBS with a traditional MIMO beamformer, high sidelobes due to equivalent one-way propagation effect of the MIMO beamformer have been significantly suppressed whilst improving the cross-range resolution. Additionally, the full structure of targets is also visible that is otherwise not identifiable with MIMO imagery.

Three diagrams illustrating MIMO synthetic aperture radar (SAR) technology

Caption: Image of boat and buoys formed through the application of MIMO and MIMO-DBS (128 ms integration time). 77 GHz forward-looking radar platform moving at 9m/s at Coniston Water in the Lake District.

MIMO-DBS beamforming when combined with accurate estimates of platform dynamics (position, velocity, heading) is useful to locate and track targets in world coordinates. This will be particularly useful for scene reconstruction and path planning and is the current focus of this work.