Range-gated field disturbance sensor with range-sensitivity compensation

DETAILED DESCRIPTION A detailed description of embodiments of the present invention is provided below with respect to the figures.
FIG.
1 is a block diagram of a range-gated field disturbance sensor with range sensitivity compensation according to the present invention.
The basic system includes a gated RF oscillator 10 which drives a transmitting antenna 11.
The gated RF oscillator 10 generates a sequence of bursts having a burst width determined by a burst width modulator 12 which is connected across line 13 to the gated RF oscillator.
The burst width modulator 12 defines a burst width in response to an input control 14 to select the range of the device.
The burst repetition rate is determined by a clock 15 which drives the burst width modulator.
Clock 15 is phase modulated by a random source 16, such as noise which may be amplified to produce a modulation signal, or may be inherent in the burst repetition rate oscillator.
Also, pseudo random modulation may be used.
The gated RF oscillator 10 is frequency modulated by an intermediate frequency source 17 connected to the gated RF oscillator 10 across line 18.
The transmitted burst 19 reflects off a target 20 and the echo is detected by a receive antenna 21.
The receive antenna 21 drives an RF mixer 22, which is also coupled to the transmitted signal, as schematically illustrated by line 34.
The output of the RF mixer 22 is coupled to an intermediate frequency amplifier 23 which is tuned to the frequency of the FM intermediate frequency source 17.
The output of the intermediate frequency amplifier 23 is coupled to a synchronous rectifier 24, which is synchronized by the FM intermediate frequency source 17.
The output of the rectifier 24 is supplied through a lowpass filter 25 and baseband amplifier 26 to a threshold detection circuit, generally 27.
The threshold detection circuit comprises a first comparator 28 having a negative input coupled to a positive threshold value 29, and a positive input coupled to the output of the baseband amplifier 26