U.S. patent number 3,801,978 [Application Number 05/273,596] was granted by the patent office on 1974-04-02 for ultrasonic-microwave doppler intrusion alarm system.
This patent grant is currently assigned to E-Systems Incorporated. Invention is credited to David N. Gershberg, Alex Y. Lee.
United States Patent |
3,801,978 |
Gershberg , et al. |
April 2, 1974 |
ULTRASONIC-MICROWAVE DOPPLER INTRUSION ALARM SYSTEM
Abstract
Motion within a large specified volume is detected by multiple
ultrasonic transducer assemblies with a redundant microwave antenna
to reduce false alarms. Each of the ultrasonic transducer
assemblies contains a plurality of highly directive transmitting
radiating elements and/or a plurality of highly directive receiving
elements. Combining networks interconnect the various radiating
elements in parallel to a frequency source. The microwave
transducer includes a transmit/receive antenna coupled to a
microstrip oscillator through a microstrip balanced mixer. Signals
from the ultrasonic transducers are processed by means of time
integration to provide an alarm signal. Similarly, signals received
at the microwave antenna are processed by means of time integration
to provide an alarm signal. Alarm signals from both the ultrasonic
subsystem and the microwave subsystem are combined in logic that
responds to generate a system alarm only upon the simultaneous
existence of alarm signals from both sources. Also coupled to the
ultrasonic subsystem and the microwave subsystem is an automatic
self-testing and tamper determining system. When either transducer
source indicates a fault condition, an alarm signal is generated by
combining logic networks.
Inventors: |
Gershberg; David N. (Rockville,
MD), Lee; Alex Y. (Arlington, VA) |
Assignee: |
E-Systems Incorporated (Dallas,
TX)
|
Family
ID: |
23044624 |
Appl.
No.: |
05/273,596 |
Filed: |
July 20, 1972 |
Current U.S.
Class: |
340/516; 340/554;
367/94; 340/522; 342/28; 342/52 |
Current CPC
Class: |
G08B
13/2494 (20130101); G08B 13/1645 (20130101); G01S
13/56 (20130101); G01S 13/862 (20130101) |
Current International
Class: |
G08B
13/24 (20060101); G01S 13/86 (20060101); G01S
13/56 (20060101); G01S 13/00 (20060101); G08B
13/16 (20060101); G08b 013/16 (); G08b
029/00 () |
Field of
Search: |
;340/258C,258D,258A,258R,409,411 ;343/7ED,7A,5PD,17.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Curtis; Marshall M.
Attorney, Agent or Firm: Richards, Harris & Medlock
Claims
What is claimed is:
1. An ultrasonic-microwave intrusion system including an alarm for
producing an indication of movement within a specified area, the
combination comprising:
an ultrasonic detector responsive to movement within the specified
area and providing an output signal varying with such movement,
a microwave detector responsive to movement within the specified
area and providing an output signal varying with such movement,
combining circuit means connected to said ultrasonic detector and
said microwave detector for generating a signal to the alarm when
the output of said detectors simultaneously exists at a level
indicating movement within the specified area, and
a test circuit connected to said ultrasonic detector and microwave
detector and responsive to fault conditions in said detectors to
generate a fault indication signal to the alarm.
2. An ultrasonic-microwave intrusion system as set forth in claim 1
wherein said ultrasonic detector includes:
a transmitting transducer for radiating into the specified area
radio frequency energy,
receiving elements responsive to the radiated energy reflected from
a moving body within the specified area and generating a doppler
frequency signal,
circuit means actuated by the doppler frequency signal to generate
the sensor output reflecting movement with the specified area,
a frequency generator connected to said transmitting transducer
means, and
a fault responsive circuit providing a fault indication signal upon
a failure in the transmitting elements.
3. An ultrasonic-microwave intrusion system as set forth in claim 2
wherein said transmitting transducer includes:
a plurality of bandpass filters having one of a plurality of
radiating elements as a part thereof for emitting radiation into
the specified area,
a plurality of resistive elements individually in series with one
of the plurality of bandpass filters, and
circuit means for connecting said plurality of bandpass filters and
series resistive elements in parallel to said frequency
generator.
4. An ultrasonic-microwave intrusion system as set forth in claim 2
wherein said frequency generator includes an R.C. driven
operational amplifier, and a radiating element coupled to one
terminal of the operational amplifier to lock the frequency output
of said generator to the frequency-temperature characteristics of
said radiating element, said radiating element is also employed as
a transmitting element in the overall system.
5. An ultrasonic-microwave intrusion system as set forth in claim 4
wherein said frequency generator further includes a complimentary
symmetry power output switch coupled to the output of said
operational amplifier.
6. An ultrasonic-microwave intrusion system as set forth in claim 1
wherein said microwave detector includes:
a monostatic radiating element emitting microwave energy into the
specified area and responsive to reflected energy from a moving
body,
an oscillator for providing a carrier frequency signal,
a balanced mixer connected to said radiating element and said
oscillator for demodulating a reflected signal received by said
radiating element with the output of said oscillator,
doppler amplifier means receiving a signal from the balanced mixer
for amplification thereof,
integrator means connected to the output of said doppler amplifier
and integrating the output thereof with respect to time, and
a level detector receiving the signal from said integrator and
producing an alarm signal when the integrator output exceeds a
preset level.
7. An ultrasonic-microwave intrusion system as set forth in claim 6
wherein said balanced mixer includes:
an RF impedance inverter having one end tied to said radiating
element and the other end to the output of said oscillator,
a first peak voltage detector at the radiating element end of said
RF impedance inverter for sampling the RF voltage magnitude at the
radiating element,
a second peak voltage detector at the oscillator end of said RF
impedance inverter for sampling RF voltage magnitude at said
oscillator, and
means for combining the energy sampled by each of the peak voltage
detectors into a balanced mixer output signal for applying to an
input of said doppler amplifier.
8. An ultrasonic-microwave intrusion system as set forth in claim 7
including an RF choke coupled to said transmission line at the
radiating element end thereof.
9. An ultrasonic-microwave intrusion system as set forth in claim 8
wherein said balanced mixer further includes a D.C. level sampling
connection for generating a fault condition signal to said test
circuit means.
10. An ultrasonic-microwave intrusion system including an alarm for
producing an indication of movement within a specified area, the
combination comprising:
transmitting transducers for radiating into the specified area
ultrasonic energy,
receiving transducers responsive to the radiated energy reflected
from a moving body within the specified area and generating a
doppler frequency signal,
circuit means actuated by the doppler frequency signal to generate
a signal reflecting movement within the specified area,
a frequency generator connected to said transmitting
transducers,
a fault responsive circuit providing a fault indication signal upon
a failure in the transmitting transducers,
a monostatic radiating element emitting microwave energy into the
specified area and receiving reflections from the moving body
within the area and providing an output signal varying with such
movement,
an oscillator,
a balanced mixer connected to said radiating element and said
oscillator for combining a signal from said radiating element with
the output of said oscillator,
doppler amplifier means receiving a signal from said balanced mixer
for amplification thereof,
integrator means connected to the output of said doppler amplifier
means for integrating the output thereof,
a level detector receiving the signal from said integrator and
providing an alarm signal when the integrator output exceeds a
present level,
combining means connected to said circuit means and said level
detector for generating a signal to the system alarm when the
output of said circuit means and said detector simultaneously
exists at a level indicating movement within the specified area,
and
test circuit means connected to said frequency generator and said
balanced mixer and responsive to fault conditions therein to
generate a fault indication signal to the system alarm.
11. An ultrasonic-microwave intrusion system as set forth in claim
10 wherein said transmitting transducers include:
a plurality of bandpass filters having one of a plurality of
radiating elements as a part thereof for emitting radiation into
the specified area,
a plurality of resistive elements individually in series with one
of the plurality of bandpass filters, and
circuit means for connecting said plurality of bandpass filters and
series resistive elements in parallel to said frequency
generator.
12. An ultrasonic-microwave intrusion system as set forth in claim
11 wherein said fault responsive circuit includes:
a peak voltage detector having a diode connected to the common
connection of said resistive elements, and
an output capacitor interconnected to one electrode of said diode
and the output of said frequency generator.
13. An ultrasonic-microwave intrusion system as set forth in claim
11 wherein said frequency generator includes an R.C. driven
operational amplifier, and a radiating element coupled to one
terminal of the operational amplifier to lock the frequency output
of said frequency generator to the frequency-temperature
characteristics of said radiating element.
14. An ultrasonic-microwave intrusion system as set forth in claim
10 wherein said balanced mixer includes:
an RF impedance inverter having one end tied to said monostatic
radiating element and the other end to the output of said
oscillator,
a first peak voltage detector at the radiating element end of said
impedance inverter for sampling the energy at the radiating
element,
a second peak voltage detector at the oscillator end of said
impedance inverter responsive to energy at said oscillator, and
means for combining the energy sampled by each of the peak voltage
detectors into a balanced mixer output signal.
15. An ultrasonic-microwave intrusion system as set forth in claim
14 including an R.F. choke coupled to the radiating element end of
said transmission line.
16. An ultrasonic-microwave intrusion system as set forth in claim
15 wherein said balanced mixer further includes a D.C. level
sampling connection for generating a fault condition signal to said
test circuit means.
17. In an intrusion alarm system wherein an ultrasonic detector and
a microwave detector each generate a signal varying with movement
within a specified area, said detector signals combined in circuit
means for providing an alarm when the detector signals
simultaneously exists at a level indicating movement within the
specified area, wherein the microwave detector comprises in
combination:
a monostatic radiating element for emitting microwave frequency
energy into the specified area and responsive to such energy
reflected from a moving body within such area,
an oscillator for generating the frequency signals radiated by said
radiating element,
a balanced mixer connected to said radiating element and the output
of said oscillator for combining a signal from said element with
the output of said oscillator,
doppler amplifier means receiving a frequency signal from said
balanced mixer for amplification thereform,
integrator means connected to the output of said doppler amplifier
means and integrating the output thereof with respect to time,
and
level detector means receiving the signal from said integrator and
producing an alarm when the integrator output exceeds a preset
level.
18. In an intrusion alarm system as set forth in claim 17 wherein
said balanced mixer includes:
an RF impedance inverter having one end tied to said radiating
element and the other end to the output of said oscillator,
a first peak voltage detector at the radiating element end of said
impedance inverter for sampling the energy at the radiating
element,
a second peak voltage detector at the oscillator end of said
impedance inverter responsive to energy at said oscillator, and
means for combining the energy sampled by each of the peak voltage
detectors into a balanced mixer output signal.
19. In an intrusion alarm system as set forth in claim 18 wherein
said balanced mixer further includes an RF choke coupled to the
radiating element end of said transmission line.
20. In an intrusion alarm system as set forth in claim 19 wherein
said balanced mixer further includes a D.C. level sampling
connection for generating a fault condition signal to a test
circuit.
21. In an intrusion alarm system wherein an ultrasonic detector and
a microwave detector each generate a signal varying with movement
within a specified area, said detector signals combined in circuit
means for providing an alarm when the detector signals
simultaneously exist at a level indicating movement within the
specified area, wherein said ultrasonic detector comprises in
combination:
transmitting transducer elements for radiating into the specified
area ultrasonic energy,
receiving transducer elements responsive to the radiated energy
reflected from a moving body within the specified area and
generating a doppler frequency signal,
circuit means actuated by the doppler frequency signal to generate
the sensor output signal reflecting movement within the specified
area,
a frequency generator connected to said transmitting transducer
elements, and
a fault responsive circuit providing a fault indication signal upon
a failure in the transmitting antenna.
22. In an intrusion alarm system as set forth in claim 21 wherein
said frequency generator includes an R.C. driven operational
amplifier, and a radiating element coupled to one terminal of the
operational amplifier to lock the frequency output of said
generator to the frequency-temperature characteristics of said
radiating element.
23. In an intrusion alarm system as set forth in claim 21 wherein
said transmitting transducer elements include:
a plurality of bandpass filters having one of a plurality of
radiating elements as a part thereof for emitting radiation into
the specified area,
a plurality of resistive elements individually in series with one
of the plurality of bandpass filters, and
circuit means for connecting said plurality of bandpass filters in
series with said resistive elements in parallel to said frequency
generator.
24. In an intrusion alarm system as set forth in claim 23 wherein
said fault responsive circuit includes:
a peak voltage detector having a diode connected to the common
connection of said resistive elements, and
an output capacitor interconnected to one electrode of said diode
and the output of the frequency generator.
Description
The present invention relates to motion detection systems operating
on the doppler principle, and more particularly, to a combination
of ultrasonic and microwave doppler motion detection systems for
reliable movement evaluation.
One class of motion detector systems employs a sensitive receiver
in conjunction with a transmitter to receive and measure an
electric field. If an intruder or foreign object disturbs the
electric field there results a variation in the field strength
which is detected by the receiver and used to trigger an indicator
or alarm system. Another class of motion detector systems in the
space alarm system characterized by the transmitting of energy into
a specified space to be protected, or the space surrounding an
object to be protected, and subsequently receiving that portion of
the transmitted energy that is reflected by the surroundings. An
alarm is triggered upon detection of a disturbance, i.e., frequency
change, in the reflected energy caused by an intruder within the
area. Any frequency change of the reflected energy, as compared to
the transmitted energy, will indicate an object is moving within
the area being monitored. This is the principle of operation of the
well known "doppler" effect. This type of system detects a doppler
frequency shift in radiation reflected by moving objects within a
specified area.
The present invention pertains to a space alarm system of the
doppler type, and more particularly, to a doppler system in which
the energy radiated is ultrasonic energy from one set of
transducers and microwave electromagnetic radiation from a
monostatic antenna.
The basic parameter in the optimization of any motion detection
system is the attaining of the highest probability of detection of
motion, with the lowest probability of false aarm. Although
numerous systems have been devised to reliably extract a doppler
signal from a received wave, false alarms continue to exist. Since
an intruder moves a much slower rate than do the transmitted
radiations, the doppler effect of the moving intruder causes a very
small percentage variation in the frequency of the received
radiation. For example, if energy having a frequency of 20 KHz is
reflected from an intruder moving at one foot per second, the
doppler effect of the motion of the intruder will cause the
received frequency to differ from the transmitted by only 37 Hz.
This is a very small shift to reliably detect. An optimized
detector will, however, reliably detect the doppler effect while
rejecting extraneous signals which can be confused with a motion
generated doppler signal.
A motion detection system in accordance with the present invention
has a lower false alarm rate than existing systems of comparable
complexity by combining an alarm signal from a microwave subsystem
with the alarm signal from an ultrasonic subsystem. Only if an
output signal exists from both subsystems simultaneously will a
system alarn be sounded indicating motion within a specified
space.
In many applications, motion detection systems are called upon to
protect an extended area. In protecting such areas, certain
problems are encountered. For example, an antenna unit of an alarm
system which is sensitive to intruders at great distances from the
antenna usually has an excessively high probability of responding
to extraneous disturbances which originate near the antenna. On the
other hand, a unit designed to have a more uniform sensitivity both
near and far from an antenna is more likely to respond to
disturbances originating beyond the confines of the area being
protected. Therefore, for the uniform coverage of an extended area,
it is generally desirable to employ a plurality of units
distributed about the area to be protected. A drawback of many
microwave doppler types of intrusion detectors is the need for
expensive and complex systems utilizing separate transmit and
receive antennas for protection of extended areas or, if a single
antenna is used, expensive duplexer networks are used to protect
the receiver from damage by the high power signal being
transmitted. An advantage of the system of the present invention is
the utilization of multiple ultrasonic transducers for coverage of
large specified volumes wherein the sensors are interconnected in
parallel by inexpensive bandpass filtering networks. Further, a
microwave subsystem, for improving system reliability, utilizes a
single omnidirectional transmit/receive (monostatic) antenna in
conjunction with miniaturized RF circuitry to provide balanced
doppler mixing without complex radio frequency devices.
One area of intrusion alarm systems which has heretofore received
little investigation is the problem of fault detection within the
system. More presently available intruder systems may be simply
disenabled by an intruder prior to his entry into a protected area.
In addition, a failure of one or more of the transducer assemblies
may render the complete system ineffective in a manner not
detectable by an operator. With the present invention, both the
ultrasonic and microwave portions of the system are provided with
automatic self-test and tamper monitoring and external self-testing
circuits. The ultrasonic automatic self-testing and tampering
circuitry employs techniques wherein the monitoring signal is
transmitted on the same two wire cable that carries the ultrasonic
power to the ultrasonic transmitting elements. The microwave
portion of the system provides an automatic self-testing capability
by use of a D.C. level sampling connection in a balanced mixer
circuit having an output that supplies the automatic self-testing
and tamper capability.
Both the ultrasonic and microwave subsystems feed the automatic
self-testing and tampering signals through an automatic
self-testing and tampering logic network. These signals, as derived
from the ultrasonic oscillator and the microwave transmission
oscillator, will vanish if: (1) the microwave power fails, (2) the
ultrasonic power fails, or (3) if the lines supplying ultrasonic
power to the ultrasonic transmitting elements are cut or shorted.
The automatic self-testing and tampering combining logic network
alarms if any one of the tamper signals vanishes.
In accordance with the present invention, an ultrasonic-microwave
intrusion system including an alarm for producing an indication of
movement within a specified area includes an ultrasonic sensor
responsive to movement within the specified area and providing an
output signal varying with such movement. A microwave sensor also
responds to movement within the specified area and provides an
output signal varying therewith. Connected to the ultrasonic sensor
and the microwave sensor is a combining circuit that generates a
signal to the system alarm when the output of both sensors exists
simultaneously at a level indicating movement within the area of
interest. Test circuitry also connects to the ultrasonic sensor and
microwave sensor and responds to fault conditions within the system
to generate a fault indication signal to the system alarm.
A more complete understanding of the invention and its advantages
will be apparent from the specification and claims and from the
accompanying drawings illustrative of the invention.
Referring to the drawings:
FIG. 1 is a physical layout of an ultrasonic-microwave intruder
alarm system using three ultrasonic assemblies and a single
microwave antenna;
FIG. 2 is a block diagram of the intrusion alarm system of the
present invention wherein signals from an ultrasonic sensor and a
microwave sensor are combined to produce a system alarm signal;
FIG. 3 is a block diagram of the microwave sensor portion of the
system utilizing a microstrip oscillator connected to a balanced
mixer;
FIG. 4 is a schematic of a microstrip oscillator coupled to a H
microstrip balanced mixer;
FIG. 5 is an equivalent circuit of the microwave portion of the
system illustrating that a matched antenna presents a resistive
load with no target present;
FIG. 6 is a block diagram of the ultrasonic sensor portion of the
system of FIG. 2 employing a plurality of transmitting radiating
elements and a plurality of receiving elements;
FIG. 7A and 7B are schematics showing circuitry for combining the
receiving elements and the transmitting elements, respectively;
FIG. 8 is a schematic of an oscillator, distribution and tampering
monitoring circuitry for the ultrasonic transmitting elements;
FIG. 9 is a plot of frequency in KHz as a function of temperature
for a typical ultrasonic radiating element;
FIG. 10 is a schematic of a radiating element controlled oscillator
and driver circuitry; and
FIG. 11 is a schematic of a test modulator and mixer circuitry for
the ultrasonic sensor portion of the system of FIG. 2.
Referring to FIG. 1, there is shown an intrusion alarm system for
protecting a specified area, for example, a room 100 feet by 50
feet, employing a central detector unit 10 and outboard transducer
units 12 and 14 all mounted approximately 9 feet above floor level
by means of pipe brackets 16 which also serve as cable conduits.
The central detector unit 10 includes four ultrasonic receiving
elements 18 (only two shown) and a microwave antenna 20 which
functions in both the transmit and receive modes, as will be
explained. In each of the outboard transducer units 12 and 14,
there are ultrasonic transmitting elements 22 (only two shown). For
some small areas to be protected, one or more ultrasonic
transmitting elements 22 and the ultrasonic receiving elements 18
may all be incorporated into a central detector unit eliminating
the need for the outboard transducer units. The present embodiment
actually incorporates one ultrasonic transmitting element (not
shown) in the central detector unit. This transmitting element
controls an oscillator frequency, as to be described.
Operationally, when using outboard transducer units or a composite
central detector unit, the system functions in the manner to be
described.
Signals to and from the central detector 10 and the outboard
transducer units 12 and 14 are provided from a central controller
24 containing system electronics. A master control switch 26
controls operation of the system to provide intrusion protection
when required and to disenable the system for alarm free movement
within the specified area to be protected. Alarm signals from the
central controller 24 are supplied to a monitoring console 28,
which as shown includes four rows of alarm annunciators of any
commercially available type. Since more than one specified area may
be monitored from the same console 28, a plurality of central
controllers 24 will connect to the console 28, one for each of the
annunciator positions if full utilization of the console is
anticipated.
Referring to FIG. 2, there is shown a block diagram of the doppler
intrusion alarm system of FIG. 1 including the ultrasonic subsystem
30 that incorporates both the transmitting elements 22 and the
receiving elements 18 along with the microwave subsystem 32 that
comprises the microwave antenna 20. Each of the subsystems 30 and
32 are complete doppler intrusion alarm systems within themselves
and will be subsequently described.
An output alarm signal from each of the subsystems 30 and 32 is
applied to inputs of a detector combining logic 34 within the
central controller 24 for supplying an alarm signal on a line 36 to
the monitoring console 28. Typically, outputs of the subsystems 30
and 32 may be logic level signals varying between an upper and
lower state and applied to a NAND gate within the combining logic
34 for producing a logic varying signal on line 36. In accordance
with standard logic network operation, an alarm signal appears on a
line 36 whenever both inputs to the detector combining logic 34
from the subsystems 30 and 32 are at the same logic level. Thus,
the detector combining logic 34 triggers only when both subsystems
30 and 32 alarm simultaneously indicating motion within the
specified area to be protected. Hence, redundancy is provided to
reduce the false alarm rate as often inherent in previous intrusion
alarm systems.
Both the ultrasonic and microwave subsystems are continuously
monitored for proper operation and in addition to tampering by
someone attempting to bypass the system, self-test signals are
applied to the subsystems 30 and 32 over a line 38 from the central
controller 24. Both the ultrasonic and microwave subsystems provide
self-testing and tampering signals to an automatic self-testing and
tamper testing combining logic 40. These signals are derived from
the ultrasonic and microwave transmission oscillator outputs and
will vanish if the microwave power fails, the ultrasonic power
fails or if the line supplying power to the ultrasonic transmitting
transducers is cut or shorted. The automatic self-test and tamper
testing combining logic 40 provides an alarm signal through the
monitoring console 28 on a line 42 if any one of the tamper signals
or self-testing signals vanishes. The automatic self-testing and
tamper testing combining logic 40 may comprise an arrangement of
NAND gates or OR gates as required to produce an alarm signal on
line 42 whenever any of the self-test and tamper signals
vanishes.
Referring to FIG. 3, there is shown a block diagram of the
microwave subsystem 32 including the transmit/receive antenna 20
coupled to a transmit/receive balanced mixer 44, the latter also
coupled to a microwave frequency oscillator 46. A doppler frequency
signal from the balanced mixer 44 is applied to a doppler
filter-preamplifier 48 that builds up the signal strength from the
mixer and defines the doppler frequency pass-band. The doppler
frequency passband rolls off at about 12 db per octave on the lower
end and 36 db per octave on the upper end. This rapid upper end
roll off improves rejection at 120 Hz, which is the frequency
associated with false alarms due to the plasma generated by
florescent lamps.
The doppler filter preamplifier 48 is provided with a resistive
attenuator 50 for injecting an external test signal in accordance
with a command on the line 38 from the central controller 24. This
signal simulates the doppler frequency effect from the balanced
mixer 44 as produced by a moving intruder and causes a normally
functioning system to alarm while the test signal on line 38 is
being applied to the attenuator 50.
Signals from the filter preamplifier 48 are applied to a
filter-postamplifier 52 for further amplification of the doppler
frequency signals. An output from the postamplifier 52 is applied
to a rectifier/integrator 54 that renders the doppler signals
unidirectional by means of a standard full wave rectifier and then
couples this unidirectional signal to an integrator circuit. The
unidirectional signal is integrated with respect to time and when
the doppler signal has existed for a sufficient length of time for
the integrator to have integrated to an established level, a signal
applied to an alarm level detector 56 triggers the detector to
produce an alarm signal on a line 58 to the detector combining
logic 34.
Returning to the microwave subsystem "front end" including the
balanced mixer 44 and the oscillator 46, there is shown in FIG. 4
these components fabricated using microstrip techniques. The
balanced mixer 44 employs a symbolic H microstrip structure to
miniaturize the assembly, reduce false alarms, improve reliability
and provide greater economy. A mixer as illustrated provides
balanced doppler mixing with a single transmit/receive "monostatic"
antenna 20 without utilizing conventional circuitry involving
circulators, hybrids, power amplifiers and additional circuit
complicating components.
Considering first the microstrip oscillator 46, a transistor 60 has
a grounded collector electrode, an emitter electrode coupled to an
inductance coil 62 and a base electrode tied to a microstrip line
64. Also coupled to the microstrip line 64 is a resistor 66 and
adjustable capacitors 68 and 70. The adjustable capacitor 68
provides a means for tuning the frequency of oscillation of the
oscillator 46 and the capacitor 70 provides maximum power coupling
between the oscillator 46 and the mixer 44. Also included as part
of the oscillator 46 is a resistor 72 conected to the inductance
coil 62 and a line capacitance 74 at a terminal 76 for roviding a
D.C. voltage to the oscillator.
Microwave transmission frequencies from the oscillator 46 are
applied to the H microstrip line 78 through the capacitor 70. Tied
to the output end of the microstrip line 78 is the transmit/receive
antenna 20 and an inductance coil 80. Coupled to the junction of
line stubs in the main transmission line of the H microstrip line
78 are peak detector diodes 82 and 84. Peak detector diode 82 mixes
to pass doppler frequency signals to a resistor capacitor network
including a resistor 86 and a capacitor 88. This is the so-called
doppler frequency produced by movement within the specified
protected area. The peak detector diode 84 mixes to pass a
phase-inverted doppler frequency signal to a resistance capacitance
network including a resistor 90 and a capacitor 92. Resistors 86
and 90 are interconnected to an output terminal 94 that provides an
interconnection to the filter-preamplifier 48. A line capacitor 96
is associated with the line interconnecting the resistors 86 and
90.
In operation of the oscillator 46 and the balanced mixer 44,
relatively low operating frequency (e.g., 915 MHz) is established
by the oscillator 46. By employing a relatively low operating
frequency the effective frequency reflective cross section of a
target within the specified area is small when the target
dimensions are small with respect to the operating wavelength of
the oscillator 46. Hence, for short wavelengths at X-band
frequencies false alarm could occur from small targets such as cats
and mice; whereas, at the longer wavelengths corresponding to 900
MHz false alarms from small targets of this type are lowered. A
second advantage of operating the oscillator 46 at a relatively low
frequency is economical in that it may be generated by a simple
transistorized oscillator fabricated in microstrip. To obtain
equivalent power at X-band, it is usual to employ a cavity-diode
oscillator. Also, diodes and other circuit components of the mixer
44 at the relatively low operating frequencies are more economical
than in equivalent X-band mixers. A third advantage of a relatively
low operating frequency from the oscillator 46 is that indoor
microwave systems respond to the 120 Hz plasma produced by
florescent lighting tubes. Consequently, it is advantageous to
provide a microwave frequency which places 120 Hz outside the
doppler frequency passband for target speeds of interest.
The transmission frequency from the oscillator 46 is applied to the
input terminal of the balanced mixer 44 which may best be
understood in operation by treating a moving target within a
specified area in terms of a time-varying impedance reflected
thereby back into the antenna 20. Such an approach is considered
valid so long as the target speed is negligible with respect to the
velocity of wave propagation. For intrusion alarm systems, this is
hardly a problem. Physically, a target creates a weak spatial VSWR
pattern which is dragged along as it moves. This pattern couples
into the microwave antenna 20 as a time-varying impedance.
With reference to the equivalent circuit of FIG. 5, the microwave
antenna 20 presents a resistive load 20a (Z.sub.o) with no target
present. If the antenna terminal voltage of the transmitted wave is
represented by E and the antenna terminal voltage of a target
return wave given by V, the microwave range equation is as
follows:
V = EG.lambda..sqroot..sigma./(4.pi.).sup.3/2 x.sup.2 e .sup.-
.sup.j4.sup..pi. x/.sup..lambda. (1)
where x = distance between the antenna 20 and a target 98,
.sigma. = microwave cross section of the target 98,
.lambda. = operating wavelength of the system, and
G = the gain of the antenna 20.
The time-varying terminal impedance Z(t) of the antenna 20 may be
derived from the equation:
Z(t) = Z.sub.o (1 + .GAMMA.)/(1 - .GAMMA.) (2)
where
.GAMMA.= V/E = G.lambda..sqroot..sigma./(4.pi.).sup.3/2 x.sup.2 e
.sup.-.sup.j4.sup..pi.
If the target 98 moves at a speed S then:
x = St (4)
and
e .sup.- .sup.j4.sup..pi. x/.sup..lambda. = e
.sup.-.sup.j2.sup..pi. (2S/.sup..lambda. )t (5)
where the term 2S/.lambda. is the expression for doppler
frequency.
Returning to the general case of time-varying impedances, the net
radio frequency voltage B across the terminal impedance Z(t), see
FIG. 5, is given by the equation:
B = 2EZ(t)/[Z.sub.o +
Solving this equation for the present impedance Z(t) results
in:
B = E [1 + G.lambda..sqroot..pi./(4.pi.).sup.3/2 S.sup.2 t.sup.2
e.sup.-.sup.j.sup..omega.t ] (7)
connected providing
where .omega. = 2.pi. times the doppler frequency.
From the equation (7), a doppler output frequency is obtained from
the peak detector diode 82 which produces a voltage proportional to
the absolute magnitude of the radio frequency voltage B. At the
diode 82 an output is produced as given by the expression:
.vertline.B.vertline. .alpha. E [1 +
G.lambda..sqroot..sigma./(4.pi.).sup.3/2 S.sup.2 t.sup.2 cos
.omega.t] (8)
This expression contains a D.C. level signal with a weak amplitude
modulation at the doppler frequency imposed thereon. The modulation
intensity is inversely proportional to S.sup.2 t.sup.2, which is
the normal range attenuation for microwave signals.
In most intrusion alarm systems of the doppler frequency type, the
doppler signal must be amplified on the order of 90 db to bring it
to usuable level. Since the D.C. level of the peak detector 82 can
be several volts, capacitive coupling is employed between the
detector 82 and the doppler amplifier chain including the
preamplifier 48. This prevents D.C. saturation of the amplifier
chain, however, it does not isolate amplifiers 48 and 52 from a
time variation of the D.C. voltage level. Such a variation arises
from amplitude modulation and noise on the oscillator 46 and can
produce false alarms from the radar subsystem 32.
To minimize the effects of D.C. level variation, the peak detector
diode 84 is connected to the microstrip network 78 and
interconnected with the peak detector diode 82. This cancels out
the D.C. voltage at the terminal 94 to provide balanced mixing. It
follows, that the doppler frequency signals will also cancel out
unless the doppler output of the diode detector 84 is phase
inverted with respect to the output of the diode detector 82. In
the balanced mixer of FIG. 4, this is accomplished by connecting
the detector diode 84 across the transformed radio frequency
impedance Z'(t) in accordance with the equation:
Z'(t) = Z.sub.o.sup.2 /Z(t) (9)
This transformation is performed by a four terminal radio frequency
network known as an impedance inverter.
A further advantage of the H structured mixer 44 of FIG. 4 is that
it may be considered a pseudo-lumped LC impedance inverter network.
The detector diodes 82 and 84 at the output and input of the
network, respectively, operate as high impedance peak detectors and
draw very little radio frequency current. Thus, their effect on the
radio frequency impedance may be neglected. Since the antenna
terminal impedance Z(t) and the transformed radio frequency
impedance Z'(t) reduces to the open circuit impedance Z.sub.o with
no target 98 present, the radio frequency voltage magnitude is the
same for both diode detectors 82 and 84, resulting in equal D.C.
voltage level out of both detectors. Considering the diode polarity
and the interconnections thereof with the load resistors 86 and 90
a zero D.C. output voltage at the terminal 94 appears with no
target 98 present.
Two additional important features of the mixer 44 are the RF
inductance coil 80 at the output terminal to ground and a D.C.
voltage level sampling connection at the anode of the diode
detector 82. This sampling connection includes a resistor 99 and a
line capacitor 100. This circuit supplies an automatic self-testing
and tamper testing output from the "front end" of the microwave
subsystem 32. Thus, the automatic self-testing and tamper testing
output provides a continuous check on the microwave "front end,"
while the externl test signal provided to the attenuator 50
provides periodic checks of the remaining system components. The RF
inductance coil 80 acts as a D.C. return for the diode detectors 82
and 84 and as a ground shunt for low frequency (60 Hz) disturbances
that might couple to the stub 78a from the system environment.
Considering now the utrasonic subsystem 30, FIG. 7 is a block
diagram of a complete ultrasonic doppler intrusion alarm system
generating an alarm signal on line 102 to the detector combining
logic 34. The four ultrasonic receiving transducers 18 are coupled
to a transducer combining circuit 104 having an output applied to a
filter-preamplifier 106. The ultrasonic transmitting transducers 22
of the outboard detector 12 are coupled to a transducer combining
circuit 108 receiving transmission energy and sending test signals
over a line 110 connected to a monitor circuit 112. Similarly, the
ultrasonic transmitting transducers 22 of the outboard detector 14
are coupled to a transducer combining circuit 114 receiving
transmission energy and sending test signals over a line 116 to the
monitor circuit 112. An important feature of the ultrasonic
subsystem 30 is the circuitry for sending ultrasonic power and
automatic self-testing and tamper testing signals over the same two
wires cables 110 and 116 to the combining circuits 108 and 114,
respectively.
An amplified signal from the filter-preamplifier 106 is mixed with
a modulation frequency generated by an oscillator 118 in a mixer
circuit 120. Modulated signals from the mixer 120 are amplified in
a filter-amplifier 122 where they are raised to a suitable level.
Signals out of the filter-amplifer 122 are applied to a
rectifier-integrator 124 wherein a full wave rectifier converts the
doppler signals into unidirectional signals and applies them to a
conventional integrator circuit. The integrator integrates the
unidirectional signal with respect to time, and at a predetermined
level triggers an alarm detector 126 for generating an alarm signal
on the line 102 to the combining logic 34.
External self-testing and tamper testing of the ultrasonic
subsystem 30 is provided by a test modulator 128 coupled to the
oscillator 118. A self-test control signal on a line 130 triggers
the test modulator 128 to provide a test signal on line 132 to the
filter-preamplifier 106. The external self-test control signal on
line 130 cannot be coupled directly to the ultrasonic doppler
filter-amplifier 122 to provide a reliable test of the ultrasonic
subsystem 30. Such a test would bypass the preamplifier 106 and
balanced mixer 120 completely, giving a "good" system indication
even if one or both of these components were in a fault condition.
Consequently, the ultrasonic signal modulated at a frequency within
the doppler passband is coupled into the ultrasonic preamplifier
106 in order to test the complete system chain.
The test signal on line 130 is a square wave from the central
controller 24 and the test modulator 128 comprises a simple switch
producing bursts of ultrasonic signals at a test signal rate. These
bursts, as generated on line 132, are suitably attenuated for a
proper test of the ultrasonic preamplifier and then coupled to the
amplifier 106 input. The amplified test bursts from the
preamplifier 106 are applied to the balanced mixer 120, which
periodically becomes unbalanced to produce an output signal to the
amplifier 122. An important consideration is that the ultrasonic
test bursts on line 132 and the ultrasonic mixer drive signal from
the oscillator 118 not be in phase quadrature otherwise very little
mixer unbalance and output signal will be produced.
Considering now the transducer combining circuits 104, 108 and 114,
the combining circuit 104 is shown in FIG. 7A and the combining
circuits 108 and 114 are shown in FIG. 7B. The simplest approach
for combining multiple transducers would be a parallel connection;
unfortunately, parallel-connected transducers seldom give balanced
performance because their resonant frequencies and impedances are
seldom matched in a practical situation. For example, if the
parallel transducers are driven as a transmitter, the transducer or
transducers having series resonant frequencies the closest to the
drive frequency will consume a large portion of the power because
the remaining transducers exhibit higher impedances. Thus, some
type of isolation/broad banding circuit is required for successful
multiple-transducer large volume intrusion alarm operation.
The receiving transducer elements 18 are combined by using the
circuit of FIG. 7A, which is derived from a basic filter circuit,
and wherein each of the transducers 18 is coupled into a resonant
circuit with a resonant inductor 134. Thus, the transducers 18 are
incorporated in bandpass filters and these filters are isolated
from one another by resistive elements 136. Impedance ratios are
chosen such that the resistive elements 136 have only slight effect
on system efficiency.
The transmitting transducer elements 22 are combined in the system
of FIG. 7B wherein each of the transducers 22 is in series with a
resonant inductor 138 to form a basic filter circuit which again
incorporates the transducers into a bandpass filter with the
filters isolated from one another by a resistive element 140. The
ultrasonic power source shown in FIG. 7B comprises the oscillator
118 of FIG. 6.
Referring to FIG. 8, each of the outboard transducer units 12 and
14 are coupled to the monitor circuit 112 which in turn receives a
frequency signal on a line 142 from the oscillator 118. The monitor
circuit 112 distributes ultrasonic power to the transmitting
outboard units 12 and 14 and receives automatic self-testing and
tamper testing information from the outboard units by means of the
two wire cables 114 and 146. The inductors 138 and the resistive
elements 140 in series with each of the transducers 22 constitute
the isolation/broad banding network discussed previously.
The ultrasonic generator 118 is coupled to the cable 114 through a
capacitor 148. Similarly, the oscillator 118 couples to the cable
146 through a capacitor 150. Coupled to the transducer side of the
capacitor 148 is a fault indicating circuit including resistors 152
and 154, the latter in parallel with a capacitor 156. A fault
indication signal on line 158 is coupled to the combining logic 40
of FIG. 2. Tied to the transducer end of the capacitor 150 is a
fault circuit including resistors 160 and 162, the latter in
parallel with a capacitor 164. A fault indication signal appears on
the line 166 and is also applied to the combining logic 40 of FIG.
2.
Tied to the interconnection of the resistive elements 140 in each
of the transducer units 12 and 14 is a diode 168. Since there is no
D.C. path to ground from the transducer side of the capacitors 148
and 150 except through the fault circuit resistors 152, 154 or 160,
162, the diodes 168 in each outboard unit clamps its respective
cable to a D.C. level. This level approaches the peak swing of the
ultrasonic oscillator 118 resulting in the condition that the
diodes 168 have little effect on operation of the transmitting
transducers 22.
Each of the fault indicating circuits may be considered as a peak
detector with a remotely located diode 168. Disconnecting of the
diode 168 from either of the fault circuits, such as by a break in
the cables 144, 146 opening the housing tamper switches 502 or
shorting of the cables causes the D.C. detector output voltage to
vanish. It should also be noted, that a failure of the ultrasonic
oscillator 118 will produce the same result.
Considering the outboard transducer unit 12, the capacitor 148
constitutes the output capacitor of the peak detector for that
portion of the system with the series resistance of the resistors
152 and 154 constituting the detector load resistor. The
interconnection of the capacitor 156 across the resistor 154
filters out the ultrasonic frequency components. When the D.C.
level at the junction of the resistors 152 and 154 vanishes, this
constitutes a fault condition signal on the line 158 to the
combining logic 40. Similarly, for the outboard transducer unit 14,
the capacitor 150 constitutes the output capacitor of the peak
detector circuit with the resistors 160 and 162 in series making up
the detector load resistor. The capacitor 164 also functions to
filter out the ultrasonic frequency component. When a D.C. signal
at the junction of the resistors 160 and 162 vanishes, this
constitutes a fault indication signal on line 166 as connected to
the combining logic 40.
Ultrasonic elements for both the receiving transducers 18 and the
transmitting transducers 22, have a frequency temperature
characteristic shown by the curve 168 of FIG. 9. Since this curve
represents the ideal transmitting frequency for the ultrasonic
subsystem 30, maximum system sensitivity over a wide temperature
range requires that the frequency signal from the oscillator 118
track this same curve, that is, for an increase in temperature the
output frequency of the oscillator 118 should decrease along the
curve 168.
Referring to FIG. 10, there is shown a schematic of the oscillator
118 wherein an additional ultrasonic transducer element 170,
mounted in the central detector unit 10, connects to one input of
an amplifier 172 through a resistor 174 to control the frequency
output of the oscillator 118 as appearing at the terminal 176. In
addition to its frequency control function, transducer 170 radiates
sufficient ultrasonic power from detector unit 10 to render
outboard units 12 and 14 unnecessary when relatively small areas
are to be protected.
Also coupled to the noninverting input of the amplifier 172 is a
resistor network including resistors 178, 180 and 182. A positive
feedback path across the amplifier 172 includes a resistor 184
connected from the amplifier output to the non-inverting input
thereof. For the inverting input of the amplifier 172, the drive
circuit includes a resistor 186 in series with a capacitor 188 with
a feedback path including a resistor 190 and a capacitor 192.
The output of the amplifier 172 drives a complimentary symmetry
power output switch made up of transistors 194 and 196 through a
coupling capacitor 198. Transistors 194 and 196 have a common
collector connection to the output terminal 176 through a capacitor
200. An emitter electrode of the transistor 194 connects to ground
and the emitter electrode of the transistor 196 connects to a D.C.
supply source at a terminal 202. Base current for the transistor
194 is provided by the resistors 204 and 206 and a base current for
the transistor 196 is established by resistors 208 and 210.
The oscillator 118 is an R.C. relaxation type, except that the
transducer 170 shunts the noninverting amplifier input to ground
through the resistor 174. The oscillator thus locks to the parallel
resonant mode of the ultrasonic transducer 170, since the shunting
effect on the positive feedback is least at this frequency. A
feature of the oscillator 118 of FIG. 10 is that the ultrasonic
power signal is a twelve volt peak-to-peak square wave, rather than
a sine wave. Measurements indicate that radiated ultrasonic power
from the transducers 22 is somewhat greater than when the twelve
volt peak-to-peak sine wave signal drives the system.
Referring to FIG. 11, there is shown the test modulator 128 coupled
to the preamplifier 106 having an output to the balance mixer 120.
A frequency signal from the source 118, as connected to the
terminal 212, is applied to both the mixer 120 and the test
modulator 128. For the latter, the oscillator frequency signal is
connected to a resistor 214 in series with a capacitor 216.
Capacitor 216 connects to a junction 218 which also has
interconnected thereto resistors 220 and 222 and the anode of a
diode 224. Resistor 220 ties to a D.C. supply source set at a
preestablished value. Resistor 222 connects to a test signal input
terminal 226 and receives the self-test control signal over the
line 130. Also connected to the resistor 222 is a resistor 228 in
parallel with a capacitor 230.
When a test signal is applied to the terminal 226, the diode 224
conducts applying an input to the preamplifier 106 by means of a
resistor 232 in series with a capacitor 234. A resistor 236
completes a divider network with the resistor 232. Also coupled to
the input of the preamplifier 106 is a sensitivity control circuit
including a variable resistor 238 in series with a resistor 240 to
ground. The sensitivity control circuit receives signals from the
combining circuit 104 on a terminal 242. The resistor 240 is
connected in series with the sensitivity control variable resistor
238 so that the test circuit will still function with the control
set for minimum sensitivity.
An output from the amplifier 106 is applied to the center tap
terminal of a split secondary winding 244 of a mixer transformer
246 including a primary winding 248 connected to the terminal 212
through a resistor 250. Connected to the end terminals of the
secondary winding 244 are diodes 252 and 254. These diodes are
interconnected by resistors 256 and 258 with a path to ground
through capacitors 260 and 262. The output of the amplifier 106 is
also connected through a resistor 264 to ground. An output signal
from the mixer 120 appears at a terminal 266 and is applied to the
filter amplifier 122.
Operation of the test modulator is as follows: resistors 220, 222
and 228 form a D.C. voltage divider which back biases the diode 224
so long as no test signal is applied to the terminal 226. Resistor
214 and capacitor 216 and the resistor 222 constitute an ultrasonic
frequency voltage divider/phase shifter which applies an ultrasonic
voltage to the anode of the diode 224. However, the ultrasonic
voltage magnitude is insufficient to overcome the D.C. back bias,
and no current flows through the diode 224 to produce an output
across load resistor 236. Application of a test signal across the
resistor 228 periodically brings the diode 224 into conduction and
applies bursts of ultrasonic signals across the resistor 236. These
bursts are coupled to the input of the preamplifier 106 through the
resistor 232 and capacitor 234. Resistor 232 is chosen to provide
suitable attenuation in conjunction with the other circuit
impedances.
Another important feature of the present invention, the ultrasonic
transmitting and receiving transducers are selected to have a high
directivity. This makes it possible to favor certain critical
portions of the selected area to be protected. For example, a
transmit/receive transducer pair is aimed directly at a cash
register, window or other specific item, to give extra sensitivity
to these regions. Conversely, it is possible to aim the transducers
away from trouble spots such as space heaters, air conditioning
outlets and other such sources of false signals.
While only one embodiment of the invention, together with
modifications thereof, has been described in detail herein and
shown in the accompanying drawings, it will be evident that various
further modifications are possible without departing from the scope
of the invention.
* * * * *