Publications

The comparative performances of switching top and bottom transponder antennas versus the bottom antenna alone, in target detection by ARTS III and by PCD, were investigated in order to determine which of the two antenna configurations is preferable. A variety of military aircraft participated, performing climbouts, orbits, straight and level segments, and descents, in order to expose a wide range of aspect angles to the interrogator. Data were collected at Washington, D.C., utilizing the ATCBI at Andrews Air Force Base, and at NAFEC, utilizing the Elwood site. The frequency of occurrence of lost targets, particularly of consecutive lost targets, was found to vary considerably from one aircraft type to another. Analysis of the reduced data provides a reasonable basis, however, for concluding that, to maximize average probability of detection, the bottom antenna is better in the terminal area but switching antennas are better for En Route application. To minimize long sequences of misses which cause track loss on turns, the switching antenna appears more favorable in both flight regimes. The data also suggest that a higher probability of detection can be obtained in both environments, without incurring serious penalties, by reducing the leading edge detection thresholds.