Radar ground-clutter shields

Metal shields (or fences) are useful in reducing the ground clutter received by a radar. The design of a clutter shield for an L-band monopulse radar employing a 60-ft parabolic reflector with Cassegrainian geometry is verified by scale-model measurements at Ka-band. It is shown that a 100-ft fence, at a distance 500 ft from the radar, will give a nominal one-way clutter reduction of 20 dB. Tracking is expected to be virtually unaffected down to about 7.8° in elevation, but the low limit on useful performance is about 4.8°. More than 10 dB additional clutter reduction can be achieved by cutting rectangular slots in the top edge of the fence. However, polarization dependence and antenna geometry yield an average clutter suppression of 5 dB. In addition, the slots as other periodic structures are subject to "grating lobes." These place a restriction on the fence geometry. This is investigated experimentally on the scale model and explained by a mathematical analysis. A nonperiodic edge treatment is expected to be free of this troublesome effect.