Influence of Antenna Pattern on Synthetic Aperture Radar Image Sidelobe Level in NDE Applications

The influence of the antenna gain pattern on synthetic aperture radar (SAR) image sidelobe level is analyzed in this article. The traditionally used antenna with wide beamwidth results in relatively constant and large sidelobe level in SAR image. The presence of these sidelobes can mask adjacent weak indications, which often necessitate windowing or implementation of other signal processing techniques in order to help reduce the effect of image sidelobes associated with strong target indications. Alternatively, using an antenna with a relatively narrow beamwidth provides for an inherent weighting function applied to the target spectrum, which is calculated within the SAR algorithm, along the cross-range direction, and this weighting function is directly related to the scanning antenna gain pattern properties. Consequently, an antenna with a relatively narrow beamwidth produces a lower SAR image sidelobe level along the cross-range direction. Corroborating results from numerical simulations and measurements are provided to illustrate the impact of antenna gain pattern on SAR image sidelobe level.