What Is Synthetic Aperture Radar?

Synthetic Aperture Radar (SAR) is an imaging radar that exploits antenna motion to create a virtual aperture that is larger than the physical antenna. SAR is used on airborne or spaceborne systems to create high-resolution images of terrain or objects on the ground.

SAR systems require relative motion in the measurement scenario: either the radar or the target should be moving. Inverse SAR (ISAR) technology exploits target movement while the radar is stationary. ISAR is used to recognize airborne objects or ships at sea.

In SAR, the radar pulse width determines the illumination in the range direction, and the antenna beam width determines the illumination in the cross-range direction (see figure). When the antenna arrives at position 1 and partially illuminates the object, the returned signal is obtained and stored. This collection process is repeated as the radar moves to position 2, position 3, and so on as shown in the figure.

Thus, a synthetic aperture is constructed from multiple observations as the radar travels past the target region. Because of the change in relative position between the emitter and target for each observation, a corresponding phase shift occurs in the returned signal. SAR systems must compensate for the effects of this phase shift to improve image resolution.

Using MATLAB and Simulink, SAR or ISAR engineers can:

• Estimate SAR link budget with the radar range equation
• Simulate and test image formation algorithms for spotlight and stripmap modes
• Model antenna, environment, weather, platform, and signal processing gains and losses
• Evaluate scene geometry and hardware constraints on pulse repetition frequency, swath length, area coverage rate, and antenna aperture
• Compare ideal and effective resolution of synthetic antenna
  
• Model rain reflectivity for linearly and circularly polarized systems
• Model ground reflectivity as a function of surface roughness, operating frequency, polarization, and grazing angle

For more details, see Radar Toolbox, Phased Array System Toolbox™, Antenna Toolbox™, RF Toolbox™, RF Blockset™