Intrusion detection radar system with amplitude and frequency carrier modulation to eliminate targets at short and long ranges
First Claim
1. A method of reliably detecting intruding targets in a protected region, said method comprising the steps of:
- (a) operating a transmitter to produce a microwave signal having successive, repetitive first and second portions of first and second frequencies, respectively, and radiating said microwave signal from an antenna into said protected region;
(b) operating a receiver to detect a resulting return signal received by said antenna from a target to produce first and second doppler signals corresponding to said first and second frequency portions of said microwave signal, respectively;
(c) operating the receiver to produce a gating signal and using the gating signal to gate said first and second doppler signals during first and second predetermined intervals onto first and second conductors, respectively, to reject any portion of said first and second doppler signals due to targets beyond a predetermined cutoff range;
(d) subtracting one of said gated first and second doppler signals from the other to produce a suppressed doppler signal the amplitude of which is approximately proportional to the range of the reflecting target; and
(e) producing an alarm signal in response to said suppressed doppler signal if said suppressed doppler signal exceeds a predetermined magnitude for at least a predetermined interval, to reject any portions of said first and second doppler signals which are due to small, close in targets such as rain on or vibration of a radome enclosing said antenna.
1 Assignment
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Accused Products
Abstract
An outdoor microwave transceiver area intrusion detection system includes circuitry for both amplitude and frequency modulation of the microwave carrier signal pulses, which are transmitted at approximately a 50% duty cycle pulses, from a radar antenna to a target. The return signal is mixed with a portion of the transmitted signal to produce first and second doppler frequency signals which are amplified and sampled during a narrow gating pulse. The two resulting sampled doppler frequency signals are alternately switched, in synchronization with the amplitude and frequency modulation signals, into first and second sample/hold circuits to reconstruct the first and second doppler frequency signals. The reconstructed signals are coupled to a differential amplifier to obtain a "range signal" which is proportional to the phase difference between the first and second doppler signals. The range signal is amplified and used to set an alarm circuit if its amplitude exceeds a certain threshold level for a certain interval of time. Signals from "close in" targets, due to rain on the radome surface and the like, are eliminated by the low value of the range signal. Signals from distant targets are cut off by the narrow gating pulse.
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Citations
24 Claims
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1. A method of reliably detecting intruding targets in a protected region, said method comprising the steps of:
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(a) operating a transmitter to produce a microwave signal having successive, repetitive first and second portions of first and second frequencies, respectively, and radiating said microwave signal from an antenna into said protected region; (b) operating a receiver to detect a resulting return signal received by said antenna from a target to produce first and second doppler signals corresponding to said first and second frequency portions of said microwave signal, respectively; (c) operating the receiver to produce a gating signal and using the gating signal to gate said first and second doppler signals during first and second predetermined intervals onto first and second conductors, respectively, to reject any portion of said first and second doppler signals due to targets beyond a predetermined cutoff range; (d) subtracting one of said gated first and second doppler signals from the other to produce a suppressed doppler signal the amplitude of which is approximately proportional to the range of the reflecting target; and (e) producing an alarm signal in response to said suppressed doppler signal if said suppressed doppler signal exceeds a predetermined magnitude for at least a predetermined interval, to reject any portions of said first and second doppler signals which are due to small, close in targets such as rain on or vibration of a radome enclosing said antenna. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 19, 20, 21)
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10. A system of reliably detecting intruding targets in a protected region, comprising in combination:
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(a) transmitter means for producing a microwave signal having successive, repetitive first and second portions of first and second frequencies, respectively, and radiating said microwave signal from an antenna into said protected region; (b) receiver means for detecting a resulting return signal received by said antenna from a target to produce first and second doppler signals corresponding to said first and second frequency portions of said microwave signal, respectively; (c) means in said receiver means for producing a gating signal and utilizing said gating signal to gate said first and second doppler signals during first and second predetermined intervals onto first and second conductors, respectively, to reject any portions of said first and second doppler signals due to targets beyond a predetermined cutoff range; (d) means in said receiver means for subtracting one of said first and second doppler signals from the other, to produce a suppressed doppler signal the amplitude of which is approximately proportional to the range of the reflecting target; and (e) means for producing an alarm signal in response to said suppressed doppler signal if said suppressed doppler signal exceeds a predetermined magnitude for at least a predetermined interval, to reject any portions of said first and second doppler signals which are due to small, close in targets such as rain on or vibration of a radome enclosing said antenna. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 22, 23, 24)
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Specification