Investigation of Alternatives for the Calibration of Reflector-Antenna SAR Systems with Multiple Azimuth Channels

Abstract

Reflector antennas with a multichannel feed are a well-known trend for the implementation of new High-Resolution Wide-Swath (HRWS) imaging methods. Advantages include a larger antenna aperture, which combined with other digital tools enables missions such as the Tandem-L mission, which now can image the whole of the Earth's surface faster than the Tandem-X mission. The use of multiple channels in azimuth is a promising advancement for these systems. These advanced methods require the usage of beamforming techniques, which require a precise knowledge of the antenna patterns used. During the radar flight, phase and magnitude imbalances between the channels might arise, due to, for example, different temperature, gravity, and displacements influencing the feed and the reflector’s geometry. The objective of calibration methods in azimuth is to suppress these imbalances, yielding a better performance for applications and finally an improved image quality. Most calibration methods in azimuth have a well-known behavior and efficiency proven for planar antenna based Synthetic Aperture Radars. However, for the rather new reflector case, as known calibration techniques cannot be applied directly due to different channel properties, a gap needs to be filled. Alternatives exploring analogies between planar antennas and reflector antennas were investigated throughout this thesis. Specifically, one approach which extends the Digital Channel Balancing (Ender, 1996), suitable for correcting residual calibration errors, is analyzed.