S.E. Grigas, D.Ts. Litovchenko, A.A. Skorynin

Possibilities of the modern spaceborne radars to detect low-RCS moving targets are limited by receiver thermal noise and background clutter. To overcome thermal noise high power transmitters, large antennas and low-noise amplifiers are used. Background clutter can be suppressed by improving spatial resolution using synthetic aperture radars (SAR). Aerial low-RCS targets detection using SAR systems has some distinctive features. High signal-to-noise ratio requires high spatial resolution which leads to long coherent integration time. However if the target is fast enough it spreads over multiple resolution elements at the SAR image which results in low signal-to-noise ratio and low detection probability. Optimal integration duration is the maximum time interval during which moving target stays within the single resolution element. Since the integration duration for the moving target is less than for the stationary target, signal-to-noise ratio decreases. Therefore high sensitivity SAR is required for low-RCS moving target indication. Moreover the resulting SAR image has low spatial resolution which results in the high clutter level. The main lobe clutter spectrum width depends on the spacecraft velocity and the length of the SAR antenna. If the target speed is high enough Doppler frequency of the radar signal reflected from the target could lie outside the main lobe clutter spectrum. In this case radar signals reflected from the underlying surface enter the radar through the antenna-s side lobes, which leads in the clutter suppression. The obtained results allow us to formulate requirements for the future spaceborne SAR capable of surveying high speed aerial targets down to 1m2 RCS at the background of highly reflective underlying surface.