Microwave sensing

Claim 1

Micowave sensing apparatus comprising, microwave transceiving means for radiating microwave energy and receiving energy reflected from items to be sensed to provide a signal indicating the presence of the sensed items, said microwave transceiving means including driver/detector means for cyclically enabling said transceiving means only during a predetermined initial portion of a cycle that is less than 1% of the duration of said cycle, means for monitoring said transceiving means during said initial portion of the cycle and providing a monitor signal representative of the result of said monitoring, means for amplifying said monitor signal, threshold detecting means for providing a threshold signal when the magnitude of the amplifier monitor signal exceeds a predetermined value, hold-off delay means for providing an output pulse in response to only those threshold signals that occur outside the duration of an output pulse provided by said hold-off means, and output signal conditioning means responsive to said output pulses for providing utilization signals useful in the industrial environment representative of items sensed by said apparatus, said microwave transceiving means comprising a cavity-controlled Gunn oscillator means for generating and receiving microwave energy operating at a predetermined microwave frequency and pulsed at a predetermined audio-frequency rate at a duty cycle significantly less than 1% and having a Gunn diode, and said means for monitoring including means for sampling the current drawn by said Gunn diode during each pulse, changes in the reflected energy received by said Gunn oscillator means resulting in a change in said current.