Electromagnetic intrusion sensor

Claim 2

An electromagnetic intrusion sensor for use in remote locations for extended periods of time, comprising: means for transmitting an electromagnetic signal having a carrier frequency modulated in amplitude at a modulation frequency; means for receiving said electromagnetic signal upon reflection from objects moving before said means for transmitting; a mixer circuit electrically coupled in common with said means for transmitting and said means for receiving, for producing a third signal by mixing said reflected electromagnetic signal with said transmitted electromagnetic signal; a filter electrically coupled to said mixer circuit for filtering said third signal by attenuating the carrier frequency components in said third signal; a detection stage for providing an output signal in dependence upon the envelope of said filtered third signal and, means for detecting variation in amplitude of successive peaks of said output signal components wherein a variation in amplitude thereof represents an intrusion into a standing wave pattern between said transmitted electromagnetic signal and said reflected electromagnetic signal.

Claim 3

The electromagnetic intrusion sensor of claim 1 wherein said electromagnetic signal is a continuous wave signal.

Claim 4

The electromagnetic intrusion sensor of claim 1 comprising means for pulsing the operation of said means for transmitting, said detection stage, and said means for detecting, by periodically generating pulses whereby the power consumption of the sensor is reduced.

Claim 5

The electromagnetic intrusion sensor of claim 1 wherein said variation in amplitude of said standing wave pattern results from a change in phase between said electromagnetic signal and said reflected electromagnetic signal when at least one of said objects is in motion.

Claim 6

The electromagnetic intrusion sensor of claim 4 wherein said electromagnetic signal is a continuous wave signal.

Claim 7

The electromagnetic intrusion sensor of claim 3 wherein said means for pulsing comprises a device for periodically interrupting the transmission of a continuous wave signal which produces a standing wave pattern.

Claim 8

The intrusion sensor of claim 3 wherein said detection stage comprises a box car detector whereby said output signal varies in dependence upon the difference between the amplitude of the modulation frequency of said electromagnetic signal and the amplitude of the modulation frequency of the reflected said electromagnetic signal.

Claim 9

The intrusion sensor set forth in claim 3 wherein said output signal comprises a step pulse and said detection stage comprises: a bipolar common emitter amplifier adapted to receive said filtered third signal from said filter; first low-pass filter means coupled to the collector terminal of said common emitter amplifier for separating modulation frequency components of said third signal from lower frequency components of said third signal; and, a sample-hold circuit for providing in response to reception of each of said pulses a step pulse having a magnitude dependent upon the peak amplitude of the last occurring of said lower frequency components of the third signal.

Claim 10

The intrusion sensor set forth in claim 8 wherein said common emitter amplifier is biased in the OFF state.

Claim 11

The intrusion sensor set forth in claim 8 wherein said sample-hold circuit comprises: an emitter follower having a base terminal adapted to receive said lower frequency components from said low-pass filter; a charging capacitor coupled to the emitter terminal of said emitter follower; a dumping transistor having a collector-emitter circuit coupled in parallel with said charging capacitor and a base terminal adapted to receive said pulses.

Claim 12

The intrusion sensor set forth in claim 10 further comprising: second low-pass filter means having a cut-off frequency below the frequency of said periodic pulses, adapted to receive said step pulse provided by said sample-hold stage.

Claim 13

The intrusion sensor set forth in claim 11 wherein said means for detecting comprises: a Doppler amplifier adapted to receive each filtered step pulse from said second low-pass filter means; a comparator having an input threshold, for generating a logical ONE output state in response to reception of each filtered step pulse from said Doppler amplifier having an amplitude in excess of the threshold; and, a digital counter for initiating an alarm upon the occurence of a predetermined number of said logical ONE output states.

Claim 14

The intrusion sensor set forth in claim 12 further comprised of: said digital counter included a reset circuit; and, timing means sensitive to generation of logical ONE output states by said voltage comparator, for gauging passage of time and for triggering said reset circuit upon expiration of a selected period; whereby, upon generation of a first of said logical ONE output states said timing means commences gauging passage of time.

Claim 15

The intrusion sensor of claim 1 further comprising: an antenna circuit having an electrical length equal to one quarter of the wavelength of said modulation frequency, coupled in common with said means for transmitting and said means for receiving.

Claim 16

The intrusion sensor of claim 14 further comprising said antenna circuit having a single radiating element.

Claim 17

An electromagnetic intrusion sensor, comprising: means for generating an electromagnetic signal having a carrier frequency modulated in amplitude at a modulation frequency; an antenna circuit having an electrical length equal to one quarter of the wavelength of said modulation frequency, for propagating said electromagnetic signals and for receiving echoes thereof; a first stage having an input terminal coupled in common with said means for generating and said antenna circuit, for producing an intermediate signal by mixing the components of said electromagnetic signal and said echoes; a low pass filter having a cut off frequency less than said carrier frequency, coupled to receive said intermediate signal from said first stage; and, a second stage for producing an output signal varying in dependence upon the envelope of said intermediate signal passed by said low pass filter.

Claim 18

An electromagnetic intrusion sensor, comprising: means for generating an electromagnetic signal having a carrier frequency modulated in amplitude at a modulation frequency; an antenna circuit having an electrical length equal to one quarter of the wavelength of said modulation frequency, for propagating said electromagnetic signals and for receiving echoes thereof; a first stage having an input terminal coupled in common with said means for generating and said antenna circuit, for producing an intermediate signal by mixing the components of said electromagnetic signal and said echoes; a low pass filter having a cut off frequency less than said carrier frequency, coupled to receive said intermediate signal from said first stage; and, a second stage for producing an output signal varying in dependence upon the envelope of said intermediate signal passed by said low pass filter.

Claim 19

An intrusion sensor set forth in claim 16 further comprising second filter means for separating modulation frequency components of said output signal from lower frequency components of said output signal.

Claim 20

An intrusion sensor set forth in claim 16 further comprising said antenna circuit having a single radiating element.

Claim 21

An electromagnetic intrusion sensor, comprising: means for generating an electromagnetic signal having a carrier frequency modulated in amplitude at a modulation frequency means for pulsing the operation of said means for generating; an antenna circuit having an electrical length equal to one quarter of the wavelength of said modulation frequency, for propagating said electromagnetic signal and receiving echoes thereof; a first stage having an input terminal coupled in common with said means for generating and said antenna circuit, for producing an intermediate signal by mixing said electromagnetic signal and said echoes; filter means for providing paths of differing impedance to said electromagnetic signal and said echoes and to said intermediate signal; and, a second stage coupled to receive said intermediate signal from said filter means, for producing an output signal varying in dependence upon said intermediate signal.

Claim 22

An electromagnetic intrusion sensor, comprising: means for generating an electromagnetic signal having a carrier frequency modulated in amplitude at a modulation frequency means for pulsing the operation of said means for generating; an antenna circuit having an electrical length equal to one quarter of the wavelength of said modulation frequency, for propagating said electromagnetic signal and receiving echoes thereof; a first stage having an input terminal coupled in common with said means for generating and said antenna circuit, for producing an intermediate signal by mixing said electromagnetic signal and said echoes; filter means for providing paths of differing impedance to said electromagnetic signal and said echoes and to said intermediate signal; and, a second stage coupled to receive said intermediate signal from said filter means, for producing an output signal varying in dependence upon said intermediate signal.

Claim 23

An intrusion sensor set forth in claim 19 wherein said second stage comprises a box car detector whereby said output signal varies in dependence upon the difference between the amplitude of the modulation frequency of said electromagnetic signal and the amplitude of the modulation frequency of said echoes.

Claim 24

An intrusion sensor set forth in claim 19 wherein said means for pulsing provides pulses, further comprising: second filter means for separating modulation frequency components of said output signal from lower frequency components of said output signal; and, a sample-hold circuit for providing in response to each of said pulses a step pulse having a magnitude dependent upon the peak amplitude of the last said lower frequency components of the output signal.

Claim 25

An intrusion sensor as set forth in claim 21 wherein said means for pulsing provides regular periodic pulses of uniform length.

Claim 26

An intrusion sensor as set forth in claim 22 further comprising: a low-pass filter having a cut-off frequency below the frequency of said periodic pulses coupled to the output terminal of said sample-hold circuit.

Claim 27

An intrusion sensor as set forth in claim 23 further comprised of said antenna circuit having a single radiating element.

Claim 28

In an electromagnetic sensor of the type including: a pulse circuit for providing regular periodic pulses of uniform length; a transmitter for generating during said pulses a carrier frequency signal modulated in amplitude at a modulation frequency; and, an antenna circuit for propagating the modulated carrier frequency signal and for receiving echoes thereof; a network for detecting the presence of Doppler signals, comprising: a first mixed circuit reactively coupled in common with said transmitter for providing an intermediate signal by mixing the modulated carrier frequency signal and said echoes; a first low-pass filter having a cut-off frequency below said carrier frequency for separating said carrier frequency from said intermediate signal; a second stage coupled to receive said intermediate signal from said first low-pass filter, for providing an output signal in dependence upon the envelope of said intermediate signal; a second low-pass filter having a cut-off frequency below said modulation frequency for separating modulation frequency components of said output signal; and, a sample-hold circuit for providing in response to reception of each of said pulses a step pulse having an amplitude dependent upon the peak amplitude of the output signal during each said pulse.

Claim 29

In an electromagnetic sensor of the type including: a pulse circuit for providing regular periodic pulses of uniform length; a transmitter for generating during said pulses a carrier frequency signal modulated in amplitude at a modulation frequency; and, an antenna circuit for propagating the modulated carrier frequency signal and for receiving echoes thereof; a network for detecting the presence of Doppler signals, comprising: a first mixed circuit reactively coupled in common with said transmitter for providing an intermediate signal by mixing the modulated carrier frequency signal and said echoes; a first low-pass filter having a cut-off frequency below said carrier frequency for separating said carrier frequency from said intermediate signal; a second stage coupled to receive said intermediate signal from said first low-pass filter, for providing an output signal in dependence upon the envelope of said intermediate signal; a second low-pass filter having a cut-off frequency below said modulation frequency for separating modulation frequency components of said output signal; and, a sample-hold circuit for providing in response to reception of each of said pulses a step pulse having an amplitude dependent upon the peak amplitude of the output signal during each said pulse.

Claim 30

A network of the type set forth in claim 25 further comprising: a third low-pass filter having a cut-off frequency below the frequency of said periodic pulses coupled to the output terminal of said sample-hold circuit.

Claim 31

A network of the type set forth in claim 26 further comprising: a Doppler amplifier adapted to receive each filtered said step pulse from said third low-pass filter; a voltage comparator having an input threshold, for generating a logical ONE output state in response to reception of each filtered said step pulse from said Doppler amplifier having an amplitude in excess of the threshold; and, a digital counter for initiating an alarm upon the occurrence of a predetermined number of said logical ONE output states.

Claim 32

A network of the type set forth in claim 27 wherein said first mixer circuit comprises: a junction field-effect-transistor having a drain terminal capacitively coupled to receive the modulated said carrier frequency signal and said echoes.

Claim 33

A network of the type set forth in claim 28 wherein said second stage comprises: a bipolar PNP type transistor common-emitter amplifier biased in an OFF state; whereby said output signal is provided only upon reception of an intermediate signal having an envelope amplitude in excess of a threshold value.