Parmeko Limited

Other

John D McCann

James H Stephen

Michael A Flemming

A surveillance system transmits a microwave carrier signal through a surveillance zone (14). Two low frequency energy fields are also established in the zone being produced by respective pairs of closely spaced apart low frequency signals radiated from opposite sides of the zone. A receptor reradiator in the zones receives these signals and reradiates a reply signal to a receiver the reply signal consisting of the microwave carrier signal amplitude modulated in accordance with the instantaneous value of the low frequency fields at the location of the receptor reradiator. The receiver separates out preselected intermodulation products and activates an alarm only when the preselected intermodulation products are present.

Surveillance systems

A system for monitoring the position of a receptor reradiator in a surveillance zone having a first means for transmitting a first signal through the zone, and a receptor reradiator operable in response to reception of said signal to radiate at least one reply signal which is a function of the first signal and of the position of said receptor reradiator in the zone. There is also a receiver for receiving the reply signal, means controlled by the receiver, dependent upon the reply signal to indicate the position of the receptor reradiator in the zone, and an alarm triggerable by the receiver responsive to the latter for receiving the reply signals.

Detection system

This invention is directed to a receptor reradiator for use in a system for detecting the position of the receptor reradiator in a surveillance zone. It comprises a first aerial means for receiving the first signal, second aerial means for radiating said reply signal and a non-linear element coupling the first and second aerial means.

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Abingdon, United Kingdom

John D McCann