Ultrasonic intrusion alarm

Claim 2

An ultrasonic intrusion alarm system comprising: means for transmitting an ultrasonic signal into a zone under surveillance; means for receiving signals returned from said zone; detection means operative in response to said received signals to provide either a first or a second output signal in the presence of a valid moving target and in accordance with the sense of target motion, and to provide both first and second output signals in the presence of interfering phenomena; and means for processing said output signals to provide an alarm indication only in the presence of either of said first or second output signals.

Claim 3

A system according to claim 1 wherein said detection means is operative in response to a received signal, the spectrum of which is unbalanced with respect to the transmitted signal to provide said first or second output signals.

Claim 4

A system according to claim 1 wherein said detection means is operative in response to a received signal, the spectrum of which is unbalanced with respect to the transmitted signal to provide either said first or second output signals, and operative in response to a received signal, the spectrum of which is balanced with respect to the transmitted signal to simultaneously provide said first and second output signals.

Claim 5

A system according to claim 1 wherein said detection means includes: a sideband splitter having first and second outputs and operative to provide an upper sideband or a lower sideband signal on only one of said first and second outputs in the presence of a moving target and to provide both upper and lOwer sideband signals on respective ones of said first and second outputs in the presence of interfering phenomena.

Claim 6

A system according to claim 4 wherein said detection means further includes: first filter means coupled to said first output for receiving said first output signal; second filter means coupled to said second output for receiving said second output signal; first detector means coupled to said first filter means; second detector means coupled to said second filter means; and means for combining the output signals from said first and second detector means and operative to provide an output signal only in the presence of either a signal from said first detector means or said second detector means.

Claim 7

A system according to claim 1 wherein said detection means includes: a pair of quadrature mixers operative to receive said return signals from said zone and to provide a pair of quadrature output signals; means for providing a reference signal derived from said transmitted signal to said pair of quadrature mixers; and means operative in response to said quadrature output signals to provide said first or second output signal.

Claim 8

A system according to claim 3 wherein said receiving means includes a variable gain amplifier; and further including: means for providing a reference signal of predetermined threshold level; and means for comparing the amplitude of said first and second output signals with that of said reference signal and for providing an error signal in response to such comparison when the amplitude of said first or said second output signal exceeds said threshold level; and an integrator operative in response to said error signal to provide a control signal to said variable gain amplifier to vary the gain thereof to provide maximum contrast between the energy in respective sidebands of said received signal and to maintain a predetermined low false alarm rate under varying levels of interfering phenomena.

Claim 9

A system according to claim 3 wherein said alarm indicating means includes: means operative in response to either said first or said second output signal to provide an alarm indication only after a target is detected for a predetermined duration of time.

Claim 10

A system according to claim 8 wherein said alarm operating means includes: a limiter for receiving either said first or said second output signal; and integrator means operative in response to the output signal of said limiter and having a threshold level the exceedance of which causes an alarm indication.

Claim 11

A system according to claim 6 wherein said reference signal providing means includes: frequency offsetting means operative in response to a signal from said transmitter to provide a first local oscillator signal to one of said mixers above the transmitter frequency and a second local oscillator signal to the other of said mixer below said transmitter frequency; and filter means for receiving said quadrature signals and for respectively providing upper and lower sideband signal components thereof.

Claim 12

A system according to claim 1 wherein said detection means includes: a pair of mixers operative to receive said return signals; a phase shift network coupled to said transmitter and operative to provide quadrature mixing signals to said pair of mixers whereby said mixers provide a pair of quadrature output signals; a quadrature phase difference network operative in response to said quadrature output signals to provide a pair of sinusoidal quadrature phased signals; means for summing the signals from said phase difference network to provide a first output signal; and means for subtracting the signals from said phase difference network to provide a second output signal.

Claim 13

A system according to claim 1 wherein said transmitter comprises: a pair of serially connected integrators; a feedback network connecting the output of one integrator To the input of the other integrator to provide feedback oscillation; a power amplifier coupled to the output of one of said integrators for providing energy for transmission in said zone; and means coupled to the output of said first and second integrators to provide quadrature signals.

Claim 14

A system according to claim 1 wherein said receiving means includes a broadband amplifier; said detection means includes: a pair of narrowband filters operative to detect frequencies in the upper and lower sidebands of said received signals, respectively; and control means for adjusting the frequency of said transmitting means to a value at the center of the filter band of said narrowband filter.

Claim 15

A system according to claim 1 wherein said detection means includes: a pair of quadrature mixers operative to receive a return signal from said zone and to produce a pair of quadrature output signals; a pair of bandpass filters operative to respectively receive said quadrature output signals; a pair of comparators each operative to receive a signal from respective ones of said bandpass filters and to produce a signal upon exceedance of a received signal above a predetermined reference level; detector means for providing signals representative of noise clutter level; and digital means operative in response to signals from said comparators and from said detector means to provide an output signal representative of an alarm indication.