Mitigation of Phase Noise in Bistatic SAR Systems with Extremely Large Synthetic Apertures

Abstract:
A major problem of airborne bistatic SAR is the severe degradation of oscillator phase noise characteristics due to aircraft motion and vibrations, particularly for large synthetic aperture times. It is well demonstrated that an oscillator’s nominal frequency f0 reacts sensitively to accelerations in proportion to its ‘g-sensitivity’. Oscillators with small f0 suffer more from this deficiency because of their increased physical size compared to higher frequency oscillators. In contrast, lower frequency oscillators commonly possess a much better (lower) close-in phase noise characteristic, which is essential to form large synthetic apertures. This paper investigates, theoretically and experimentally, the impact of aircraft motion and vibration-induced oscillator phase noise on bistatic SAR imagery. An experimental set-up to discipline the oscillators to a three-axis set of accelerometers is presented.