Synthetic Aperture Radar (SAR)

Signal Chain Walkthrough

Synthetic Aperture Radar creates high-resolution 2D images of terrain by exploiting the motion of the radar platform (aircraft or satellite). The forward motion synthesizes a virtual antenna aperture much larger than the physical antenna, achieving fine azimuth resolution independent of range.

Chirp Pulse Compression

SAR transmits long frequency-modulated (chirp) pulses for high average power, then compresses them in the receiver using a matched filter. This achieves the range resolution of a short pulse with the energy of a long pulse. Range resolution = c/(2·BW), where BW is the chirp bandwidth.

Range Compression

Correlation of the received signal with the transmitted chirp waveform compresses each pulse return into a narrow range cell. A 500 MHz chirp gives 30 cm range resolution.

Azimuth Compression

As the platform moves, each ground scatterer is illuminated across many pulses. The azimuth processor coherently combines these returns (analogous to a phased array synthesis), achieving along-track resolution equal to D/2, where D is the physical antenna length. Remarkably, this is independent of range.

Motion Compensation (MOCO)

Platform motion errors (vibration, wind gusts, flight path deviations) must be compensated using IMU and GPS data. Uncompensated motion blurs the SAR image.