Radar presence detection at preselected range

Claim 2

Radar apparatus for detecting the presence of a target at a preselected range, said apparatus comprisIng: means for transmitting and receiving pulsed oscillatory energy, said means being responsive to the presence of a reflective target at a range which is variable by a control signal applied to said means, said means providing a target signal having an amplitude which is reduced in response to the presence of a target at the then extant sensitive range; switching means for periodically switching said control signal between two levels, one level corresponding to said preselected range the other corresponding to a different range, said switch-ing means also providing a reference signal which varies in synchronism with the switching; and means for combining said target signal and said reference signal in phase opposition to provide a net signal having a minimum constituent at the periodic switching frequency when a target is present at said preselected range.

Claim 3

Radar apparatus for detecting the presence of a target at a preselected range, said apparatus comprising: a super-regenerative oscillator having a nominal squeg period which varies as a function of a bias signal applied thereto; means for providing a bias signal to said oscillator and periodically switching the bias signal between two levels, each level providing a nominal squeg period corresponding to a respective predetermined range, said means also providing a reference signal which varies in synchronism with said switching; detector means interconnected with said oscillator for providing a noise envelope signal having an amplitude which varies as a function of the extent of random variation in said squeg period; and means for combining said noise envelope signal and said reference signal to provide a net signal having a minimum constituent at the periodic switching frequency when a target is present at a preselected one of said ranges.

Claim 4

Radar apparatus for detecting the presence of a target at a preselected range, said apparatus comprising: a super-regenerative oscillator having a nominal squeg period which varies as a function of a bias signal applied thereto; means for providing a bias signal to said oscillator and periodically switching the bias signal between two levels, each level providing a nominal squeg period corresponding to a respective predetermined range, said means also providing a reference signal which varies in synchronism with said switching; detector means interconnected with said oscillator for providing a noise envelope signal having an amplitude which varies as a function of the extent of random variation in said squeg period; and means for combining said noise envelope signal and said reference signal to provide a net signal having a minimum constituent at the periodic switching frequency when a target is present at a preselected one of said ranges.

Claim 5

Radar apparatus as set forth in claim 2 wherein said bias signal-providing means comprises a free-running multivibrator.

Claim 6

Radar apparatus as set forth in claim 2 wherein said super-regenerative oscillator is interconnected with a mono-stable multivibrator, the multivibrator being triggered into its astable state by an initial burst of oscillation by said oscillator and being operative, after return to the stable state, to modify the biasing of said oscillator to produce a squeg period which is relatively long in relation to either said predetermined or said different range.

Claim 7

Radar apparatus for detecting the presence of a target at a preselected range, said apparatus comprising: a super-regenerative oscillator having a nominal squeg period which varies as a function of a bias signal applied thereto; a free-running multivibrator circuit for providing two different bias signal levels in periodic alternation corresponding to said preselected range and a different range, respectively, said free-running multivibrator also providing a reference signal which varies in synchronism with said alternation; a mono-stable multivibrator circuit for controlling the application of said bias signal levels to said oscillator, said mono-stable multivibrator circuit having a first state in which said oscillator is biased into super-regenerative oscillation at a squeg rate having a period which corresponds to the return time of a signal reflected from a target at said preselected range, said switching circuit being operative to switch automatically from a second state to said first state afer a substantially predetermined time interval in said second state, said time interval being substantially longer than said return time, said switching circuit being responsive, after a predetermined delay following switching from said second state to said first state, to triggering signals applied thereto for switching from said first state to said second state; detector means interconnected with said oscillator for providing a noise envelope signal having an amplitude which varies as a function of the extent of random variation in the proportion oF time said mono-stable multivibrator remains in said first state; means for combining said noise envelope signal and said reference signal to provide a net signal having a minimum constituent at the periodic switching frequency when a target is present at a preselected one of said ranges; and means for providing a target present indication when the net signal constituent at the periodic switching frequency falls below a predetermined threshold.

Claim 8

Radar apparatus for detecting the presence of a target at a preselected range, said apparatus comprising: a super-regenerative oscillator having a nominal squeg period which varies as a function of a bias signal applied thereto; a free-running multivibrator circuit for providing two different bias signal levels in periodic alternation corresponding to said preselected range and a different range, respectively, said free-running multivibrator also providing a reference signal which varies in synchronism with said alternation; a mono-stable multivibrator circuit for controlling the application of said bias signal levels to said oscillator, said mono-stable multivibrator circuit having a first state in which said oscillator is biased into super-regenerative oscillation at a squeg rate having a period which corresponds to the return time of a signal reflected from a target at said preselected range, said switching circuit being operative to switch automatically from a second state to said first state afer a substantially predetermined time interval in said second state, said time interval being substantially longer than said return time, said switching circuit being responsive, after a predetermined delay following switching from said second state to said first state, to triggering signals applied thereto for switching from said first state to said second state; detector means interconnected with said oscillator for providing a noise envelope signal having an amplitude which varies as a function of the extent of random variation in the proportion oF time said mono-stable multivibrator remains in said first state; means for combining said noise envelope signal and said reference signal to provide a net signal having a minimum constituent at the periodic switching frequency when a target is present at a preselected one of said ranges; and means for providing a target present indication when the net signal constituent at the periodic switching frequency falls below a predetermined threshold.

Claim 9

Radar apparatus as set forth in claim 3 wherein said reference signal is square-wave and wherein said system includes means for producing a square-wave signal from the a.c. component of said noise envelope signal, said square-wave signals being combined in phase opposition when the noise signal is modulated by the presence of a target at said preselected range.