Radar antenna architectures and sampling strategies for space based moving target recognition

Abstract

Ground moving target indication (GMTI) by a space based radar system demands special antenna and data acquisition concepts to overcome the problem of discriminating the target signal from the clutter returns, which - because of the high speed of the satellite - comprise a broad mixture of radial velocities within the antenna beam leading to a large Doppler spread. These concepts - realised by different kinds of phase centre diversity - offer the capability for techniques like ATI (along track interferometry), DPCA (displaced phase centre antenna), or STAP (space time adaptive processing). For a space based system, the number of receiver channels connected to subapertures is limited to a few (normally two or three) because of their weight and volume and the high data rates. The classical ATI architecture with the antenna split into two halves admits only suboptimum GMTI performance. Nevertheless, since phased array antennas offer the possibility to switch the phases and amplitudes of the T/R modules from pulse to pulse, more degrees of freedom can be introduced increasing the perfor- mance considerably. As a low-priced alternative to phased array systems, analogue multi-port antennas, e.g. multi-feed reflector antennas, can be used to generate multi-dimensional data bearing information on radial motion of targets. In this paper different concepts of spatial-temporal diversity are discussed and analysed for realistic system parameters with respect to ambiguities and detection performance for moving targets.