PASSIVE SECONDARY SURVEILLANCE RADAR USING SIGNALS OF REMOTE SSR AND MULTIPLE ANTENNAS SWITCHED IN SYNCHRONISM WITH ROTATION OF SSR BEAM

摘要

The range from which transponder replies can bereceived at a virtual secondary surveillance radar of thetype described in U.S. Pat. No. 4,115,771 is extended byreplacing the omnidirectional antenna previously utilized toreceive replies from transponders within the range of theSSR with a stationary array of a plurality of directiveantennas arranged in a circle and having radiation patternspointing in different directions from the center of andcovering a respective sector of the circle, and sequentiallyswitching on the antenna of the array covering the sector inwhich the rotating beam of the associated SSR is thenpointing. In an arrangement in which the SSR and PSSR areso widely separated that in certain pointing directions theSSR beam overlies more than one sector of the antenna array,the antennas are sequentially switched on at calculatedswitching times determined from the pointing direction ofthe SSR beam and the times it takes in the geometricalarrangement between the SSR beam and the radiation patternsof the antennas of the array, for a given SSR interrogatingpulse to propagate, from launch, along the beam until itreaches the line separating the first encountered sectorfrom the next adjacent sector, between second and thirdsectors, and so on, such that a high gain directive antennais always pointing in the proper direction to receive replysignals from a transponder intercepted by the scanning beamof the SSR.