A Switched-antenna Nadir-looking Interferometric Sar Altimeter for Terrain-aided Navigation

Conventional terrain-aided navigation (TAN) technique uses an altimeter to locate the position of an aerial vehicle. However, a major problem with a radar altimeter is that its beam (or pulse) footprint on the ground could be large, and therefore the nadir altitude cannot be estimated accurately. To overcome this difficulty, one may use the nadir-looking synthetic aperture radar (SAR) technique to reduce the along-track beam width, while the cross-track ambiguity is resolved with the interferometry technique. However, the cross-track resolution is still far from satisfactory, because of the limited aperture size of antennas. Therefore, the usual three-antenna array cannot resolve multiple terrain points in a same range bin, effectively. In this paper, we propose a technique that can increase the cross-track resolution using a large number of antennas, but in a switched fashion, not raising hardware cost.