Apparatus for determining the speed of motion of slowly moving objects

Abstract

A Gunn microwave transmitter/receiver is coupled to an antenna to transmit microwave signals perpendicularly to a surface of a motionless or a slow moving object and to receive waves reflected from the object. The frequency of the oscillator of the Gunn transmitter is controlled by the output of a sawtooth wave generator. Accordingly, the output of the transmitter is cyclically and linearly varied from a first transmitted frequency to a second transmitted frequency. An accurate timer cyclically resets the both the sawtooth generator and digital processing circuitry. The wave reflected from the object and the signal transmitted at the time of arrival of the reflected wave are processed to detect the difference between the reflected wave and the transmitted wave, or the first negative to positive zero crossing that occurs after reset. This event initiates a time window which is terminated at the end of the cycle in which the relationship is detected. During the time window, output signals from a relatively high frequency pulse source are accumulated in a counter and subsequently stored in the memory of a processor. Motion of the subject object in defined units e.g., inches is directly related to the difference in counts accumulated in the counter in successive cycles and speed is determined by relating the measured change to the time over which the change occurred. The distance to the motionless object is calculated from the frequency difference between the reflected and the transmitted waves, and/or from the phase relationship between these two signals.