Abstract

An improved receptor-reradiator, for use in a surveillance system employing a carrier frequency of UHF or higher in combination with a low frequency electrostatic field signal to be modulated on the carrier signal by the reradiator, is provided by an antenna frame wherein the metallic foil of which it is made is divided into three parts. The first part is U-shape of substantially one width and joins to a central portion of substantially reduced width which is predominantly inductive at the carrier frequency. A semiconductor diode, preferably a Schottky barrier diode or PIN switching diode, is connected in said central portion in series therewith. The opposite end of the central portion joins to an enlarged rectangular portion. At the low frequency the component has effectively two capacitive arms, one on each side of the diode, of different surface area to ensure bias signal for the diode. However, at the carrier frequency, the central portion has a high inductive reactance which, in conjunction with the inductive reactance of the U-shape portion, tunes to resonance the total capacitance of the component including that of the diode. The parts are proportioned such that the diode sees at the carrier frequency an inductance on one side and a capacitance on the other side.