US3599196A

US3599196A - Plural chambered, oscillator-coaxial line resonator-detector assembly for moving object detection systems

Info

Publication number: US3599196A
Application number: US733672A
Authority: US
Inventors: George Boyko
Original assignee: Pinkertons Inc
Current assignee: Pinkertons Inc
Priority date: 1968-05-31
Filing date: 1968-05-31
Publication date: 1971-08-10
Anticipated expiration: 1988-08-10

Abstract

A plural chambered assembly for electromagnetic moving object detection systems. One chamber forms the outer conducting surfaces of a cavity resonator having a centrally disposed conductor short-circuited at one end to the conducting surfaces and open at the other end. Collectively the center conductor and outer conducting surfaces define a coaxial line resonator. A rectifier and rectifier load are electrically connected to the center conductor and physically mounted within the cavity chamber. A second contiguous chamber houses a solid-state, sinusoidal, continuous wave oscillator. A radiator is capacitively coupled to the center conductor of the coaxial line resonator.

Description

gutted States Patent :72] Inventor George Boyko Fruulngham, Mass.

{21] Appl No. 733,672

[22] Filed May 31.1968

[451 Patented Aug. 10.1971

173] Assignee Pinkertons. Incorporated New York, N.Y.

{541 PLURAL CHAMBERED, OSCILLATOR-COAXIAL LINE RESONATOR-DETECTOR ASSEMBLY FOR MOVING OBJECT DETECTION SYSTEMS 5 Claims, 4 Drawing Figs.

[52] US. Cl .0 340/258,

(51 Int. Cl. ..,....G08b1 3/ 22 GOls 9/44, 1103f 3/60 [50] Field of Search ..340/258, 25

A, 25C; 343l702,900, 8-, 330/56; 331/96, 97, 101-, 334/45 [56] References Cited UNlTED STATES PATENTS 2,161,707 6/1939 Hathaway 343/900 X 2,859,434 11/1958 Auer,Jr.eta1..t. 343/8 3,162,823 12/1964 Beaty 1/101 X 3,210,752 10/1965 Bojkow 340/258 3,270,292 8/1960 Harwood 334/45 X 3,307,099 2/1967 Weller et a1. 334/45 UX 3,440,650 4/1969 Kimball l 340/258 3,470,476 9/1969 Wilson 3 1/101 X 3,246,266 4/1966 331/101 X Racy Primary Examinen-John W. Caldwell Assistant Examiner- Perry Palan Atrorney-RusselL Chittick & Pfund ABSTRACT: A plural chambered assembly for electromagnetic moving object detection systems One chamber forms the outer conducting surfaces of a cavity resonator having a centrally disposed conductor short-circuited at one end to the.

conducting surfaces and open at the other end. Collectively the center conductor and outer conducting surfaces define a coaxial line resonator. A rectifier and rectifier load are electrically connected to the center conductor and physically mounted within the cavity chamber. A second contiguous chamber houses a solid-state,'sinusoidal, continuous wave oscillator. A radiator is capacitively coupled'to the center conductor of the coaxial line resonator.

PATENTEDAUBIOBH 9599.196 I SHFETIOFZ INVENTOR.

BY GEORGE BOYKO PATENTEUMJGIOIQYI 3.599.196

SHEET 2 OF 2 5O 52 60 I 62 I 94 9+ REGULATED 6 mg INVENTOR.

GEORGE BOYKO BY PLURAL CHAMBERED,.OSCILLATOR-COAXIALLINE RESONATOR-DETECTOR ASSEMBLY FOR MOVING OBJECT DETECTION SYSTEMS CROSS REFERENCES TO RELATES APPLICATIONS The subject matter of the present application is related to the ElectromagneticMoving Object Detection System Utilizing A Coaxial Line Resonator and Alarm System described in my copending'applications Ser. No. 733,673, filed'May3l, 1968 and Ser. No. 733,671,-filed May 31, I963", respectively.

BACKGROUND OF THE INVENTION In existing'moving objectdetection systems of the type having one'or more remote antennas and a central control unit, the remote antennas are'generally'driven by acorrespondjng number of oscillators housed inthe central control unit. In some instances, two remote antennas aredriven by a single oscillator in the control unit. lfmorethan one'pair ofantennas is required to cover the desired protection area, an additional oscillator is added at the control unit for-each pair of additional antennas. The remotely located antcnnasare connected to the oscillators in the central control unit by coaxial cable. This arrangement presents a number of problems including signal attenuation along the coaxial cable, false alarms caused by motion of the cable, limitations on the separation distance between the remoteantennas; and thecentrel control unit-end the genera] expense ofinstalling thecoaxial cable.

It is accordingly ageneral object of the present invention to provide a unitary, oscillator-antenna assembly that can be used as a remote'sensor without requiring a coaxial cable-connection between the assembly and the central control unit.

It is a specific object of the present invention to provide a unitary, plural chambered, oscillator-coaxial line resonator detector assembly-for electromagnetic movingobject detection systems.

It is a feature of the invention that the twoassembly chambers are contiguous and share a common walLThis feature allows a very small lead length between the oscillator circuit housed in one chamber andthe coaxial line-cavity formed by the other chamber. In addition, itprovides a low packaging profile forthe entire assembly.

These objects and other objects and features of the present invention will best be understood from a preferred embodiment thereof, selected for purposes of illustration, and shown in theaccompanying drawings in which:

:FIG. I is an isometric view of the assembly showing'the antenna, housing and baseplate;

FIG. 2 is a partial schematic and block diagram of the electrical circuitry of the oscillator, coaxial line resonator and'detector housed'within the assembly shown in FIG. 1;

FIG. 3 is a bottom view of the assembly with the bottom plate removed and a portion oftheassembly broken away; and,

FIG. 4 is an-exploded-view in partial cross section showing the physicalv mounting and electricalcoupling of the antenna to the center conductorof the coaxial line'resonator.

Turning now to the drawings, and particularly to FIG. 1 thereof, there is shown in isometric view, a plural chambered, oscillatoncoaxial line resonator-detector assembly constructed in accordance with the present invention and indicated generally by the reference number 1. The major components of the assembly 'lflthat are visible in=FIG. l are a bottom or baseplate 12, a generally'rectangular hosing '14, an antenna.l6 and an antenna mounting insulator 18. Before discussing indetail thephysicalconstruction and mounting of the components within the housing ,as illustrated in'FIG..3, it will be helpful to briefly discuss theelcctrical circuitry of the oscillator-coaxial line resonator-detector assembly.

Looking at FIG. 2, there is shown a tunable oscillator 20 which employs asingle, grounded base NPN transistor-22 to generate the continuousysinusoidal waves that excite coaxial line resonator 24. A typical operating frequency for oscillator '20 is 400 megahertz. Of course, other frequencies generally in the UHF range can be used in moving object detection systems. RF ground for the base of transistor 22 is established bya capacitor 26 that shunts base resistor 28. The base resistor 28, together with resistor'30 forms a bias voltage divider from 8* regulated to ground. Emitter resistor 32 provides a DC feedback path for oscillator stabilization while RF feedback is prevented by a shunt capacitor 34 which places a'RF ground at the bottom ofradiofrequency choke 36. Coupling of the generated radiofrequency energy to the power supply (not shown) is prevented by a second radiofrequency choke 38 in the collector circuit.

The required in-phase RF feedback to sustain oscillation is provided by the collector-base and emitter-base capacitances. The frequency determining components of the oscillator com prise inductor 40, variable capacitor 42 and a portion of the coaxial line center conductor 44. The oscillator frequency is tuned by varying the series capacitance of the frequency determining circuit. This is accomplished by adjusting the variable capacitor 42'. I

Coaxial line resonators of the type illustrated in'FIG. 2 are now'g'enerally classified cavity resonators/Henney, Radio Engineering Handbook, 5th Edition, page 6-46. Conceptually, the coaxial line resonator 24 can be regarded as a coaxial tran'smksion line short-circuited at one end and open at the other. Terman, Electronic and Radio Engineering, 4th Edition, pages l59-l61. The coaxial line resonator is capacitively loadedand'tuned by a variable capacitor-46 located at the open end of the line. This location provides the greatest tuning effect per unit of capacitance, but other locations along the center conductor 44 can be utilizedfor thevariable capacitor 46.

Physically, the coaxial line resonator or cavity can have a true coaxial construction, i.e., inner-and outer cylindricalconductors with a common axis or a hybrid configuration. The

present invention utilizes a hybrid or trough line configuration that has a center conductor positioned within a rectangular prism cavity. The rectilinear configuration ofthe coaxial line" resonator of the'present invention is more desirable than the classic cylindrical configuration because it simplifies mechanical fabrication production line assembly and component mounting.

The term coaxial line has been selected to describe the resonator or cavity 24 because it connotes a centrally disposed conductor surrounded by one or more conducting surfaces. This is true even though thedefined cavity may have a rectangularshape of the type shown in "FIG. 3. As used herein, the

term coaxial line'resonator" shall mean a resonant cavity center conductor 44 of the resonator. The coupling should be as loose aspossible within the limits imposed by the desired detection range. The loose coupling of the oscillator to the high Q coaxial line resonator circuit effectively isolates the oscillator from motion produced impedance changes in the antenna circuit thereby maintaining the frequency stability of the-oscillator.

Thecoaxial line resonator 24 is constructed with the center conductor 44 having a physical length that is less than /4 l\ at the operating frequency. The electricallength of the line is ad justed by varying capacitor 46. The output from the coaxial line resonator iscapacitivelycoupled through capacitor 50 to radiator .16. The radiatonwhich has a'length between /4 It and /2 A, is voltage fed to achieve maximum detection sensitivity. lt can beam from FIG. 2, that the output from the coaxial line resonator is taken at a point52 that is very close to the .point ofmaximum voltage on the center conductor 44.

Changes in the impedance of the antenna circuit produced by motion of an object within the radiated field pattern of the alarm system are sensed by a rectifier $4. The rectifier is connected to the centerline 44 of the coaxial line resonator at a point 56 located slightly below the output tap 52 for the amen na. The connection point for the rectifier is a compromise between achieving maximum voltage output and minimum effect upon the Q of the coaxial line resonator. A load for the rectifier 54 is provided by resistor 58.

The detected motion signals from rectifier 54 are capacitively coupled through capacitor 60 to a high gain, low frequency amplifier 62. After amplification, the motion or alarm" signal is used to activate a suitable, electrical, visual and/or audible alarm means 64. A range control, illustrated representationally by adjustable knob 66, is provided in the amplifier circuit to preset the range within which motion of an object will trigger the alarm system.

With the exception of the coupling capacitor 60, amplifier 62 including the range control 66 and the alarm 64, all of the previously discussed electrical components are mounted within or on the assembly housing 14. If desired, the rectifier 54 and rectifier load resistor 58 can be mounted outside of the chamber 82. The components are identified in FIG. 3 by the same reference numerals that were used in the partial schematic and block diagram of FIG. 2. The basic structure of the housing 14 is illustrated in the isometric and bottom view: of FIGS. 1 and 3, respectively. The rectilinear housing is formed from two end walls 68 and 70, two

sidewalls

12 and 74, a top plate 76 and the removable bottom or baseplate 13. The walls and top plate are constructed from an electrically conductive material, such as, cadmium plated steel or aluminum, and are joined together, as by soldering, to form a plurality of continuous electrically conductive surfaces. The bottom plate 12 is also made of an electrically conductive material and, when removably secured to the housing by screws 78, completes the shielding of the components within housing 14.

Looking specifically at FIG. 3, a longitudinal, electrically conductive center wall 80 divides the interior of the housing 14 into two generally

rectangular chambers

82 and 84. It can be seen that when the bottom plate 12 is screwed to the housing 14, the continuous electrically conducting surfaces of the end walls 68 and 70, top and

bottom plates

76 and 12. and center wall 80 will produce the cavity" portion of the coaxial line resonator 24. Thiscavity or chamber 82 together with the center conductor 44 electrically comprise the coaxial line resonator 24.

The center conductor 44 is physically mounted on and electrically short-circuited to one of the conducting surfaces that form the resonant cavity, in this case, end wall 68, The other end of the conductor is open and capacitively loaded by variable capacitor 46. The center conductor is current fed from oscillator at tap point 48. Physically, the oscillator tuning variable capacitor 42 is located partially in cavity chamber 82 and partially in the oscillator circuit chamber I4. An aperture 86 in the center wall 80 provides mounting room for the variable capacitor. Access to the variable capacitor trimmer screw 88 is provided by an aperture 90 in the housing end wall 68, as shown in FIG. 1.

The physical dimensions of the in general, and the coaxial line resonator in particular, will vary depending upon the operating frequency of the oscillator 20. 'At a nominal frequency of 400 megahertz, the cavity or chamber ll of the coaxial line resonator is approximately 3 96 inches long and has a square end profile of VIXVB inches. The center conductor 44 is formed from a l/l6-inch strip of the same or similar electrically conductive material and has a length of approximately 3 inches. The dimensions of chamber 84 are not critical because the chamber functions only as a mounting area and electromagnetic shield for the oscillator components. However, for ease of assembly and fabrication. the opcillator chamber 84 is made approximately the same size as the resonator chamber 82.

It has already been mentioned that the antenna 16 is capacitively coupled to the center conductor 44 through capacitor 50. Electrically, the coupling capacitor 50 can be considered as a separate circuit component. However, from a physical standpoint, the coupling capacitor is not a separate component, but instead is formed by the mounting components for the antenna. The antenna mounting system is shown in partial cross section in FIG. 4. The antenna 16 is screwed onto a threaded stud 92 that extends through, but is electrically insulated from the top plate 76 and the center conductor 44 of the coaxial line resonator 24. The threaded stud is insulatively secured to the center conductor 44 by an insulative nut 94 and shoulder washer 96. A metal nut 98 completes the assembly with respect to the center conductor. Capacitive coupling occurs between the center conductor 44 and stud 92 and nut 98 with the insulative shoulder washer 96 acting as the dielectric material.

The stud 92 is fixed with respect to and insulated from the top plate by the following components viewed from bottom to top in FIG. 4: nut 100, insulative washer 102, antenna insulator insert 104, insulative washers, e.g.,

cork

106 and 108, antenna insulator l8, insulative washer 110, metal flat washer 112 and nut 114. It will be appreciated'that this construction provides the necessary electrical coupling between the coaxial line resonator and antenna while at the same time producing a mechanically secure and rigid assembly of the antenna and resonator components.

A number of variations in the design of the plural chambered assembly 10 are possible. For instance, the size of the baseplate 12 is not critical as long as it is large enough to completely cover both of the

chambers

82 and 84. Preferably the baseplate is made large enough to accommodate a housing (not shown) for the circuit components that comprise amplifier 62. If desired, the amplifier housing and the oscillator-coaxial line resonator-detector assembly can be provided with a common cover (not shown) to produce a unitary, visually pleasing remote sensor unit. It will be appreciated that since the oscillator, coaxial line resonator, antenna and detector comprise a single sensor unit, no coaxial cable is required between the sensor unit and the central control unit. Furthermore, ordinary wiring can be used for the power and alarm circuits between each remote sensor unit and the control or alarm unit.

Having described in detail a preferred embodiment of the plural chambered, oscillator-coaxial line resonator-detector assembly for moving object detection systems, it will now be apparent to those skilled in the art that numerous modifications can be made thereto without departing from the scope of the present invention,

What I claim and desire to secure by United States Letters Patent is:

l. A plural chambered, oscillator-coaxial line resonator-detector assembly for electromagnetic moving object detection systems comprising:

housing means for providing two chambers one of which has a plurality of conducting surfaces defining a rectangular resonant cavity;

a centrally disposed, substantially planar strip conductor mounted within said cavity, said conductor being short-circuited at one end of one of the conducting surfaces and open at the other end; electromagnetic oscillator means mounted within the other chamber of said housing and loosely coupled to said cavity conductor;

an antenna insulatively mounted on said housing means and having an electrically conductive extension member that extends through an aperture in said strip conductor and is separated therefrom by a solid dielectric material, said strip conductor, dielectric material and extension member forming a coupling capacitor between said conductor and said antenna; and,

detector means connected to said cavity conductor.

2. The assembly of claim 1 wherein said housing means comprises:

first and second end and sidewalls and a top plate secured together to form a plurality of continuous, electrically conductive surfaces; an electrically conductive center wall secured to said end walls and said top plate, said center wall defining two chambers one of which forms a rectangular cavity resonator; and

i an electrically conductive bottom plate removably secured to said side, end and center walls to close and electrically shield said chambers.

Claims

1. A plural chambered, oscillator-coaxial line resonatordetector assembly for electromagnetic moving object detection systems comprising: housing means for providing two chambers one of which has a plurality of conducting surfaces defining a rectangular resonant cavity; a centrally disposed, substantially planar strip conductor mounted within said cavity, said conductor being short-circuited at one end of one of the conducting surfaces and open at the other end; electromagnetic oscillator means mounted within the other chamber of said housing and loosely coupled to said cavity conductor; an antenna insulatively mounted on said housing means and having an electrically conductive extension member that extends through an aperture in said strip conductor and is separated therefrom by a solid dielectric material, said strip conductor, dielectric material and extension member forming a coupling capacitor between said conductor and said antenna; and, detector means connected to said cavity conductor.

2. The assembly of claim 1 wherein said housing means comprises: first and second end and sidewalls and a top plate secured together to form a plurality of continuous, electrically conductive surfaces; an electrically conductive center wall secured to said end walls and said top plate, said center wall defining two chambers one of which forms a rectangular cavity resonator; and an electrically conductive bottom plate removably secured to said side, end and center walls to close and electrically shield said chambers.

3. The assembly of claim 1 further characterized by tuning means connected to said cavity conductor.

4. The assembly of claim 3 wherein said tuning means comprises a variable capacitor connected between the open end of said cavity conductor and one of said conducting surfaces.

5. The assembly of claim 1 wherein said detector means comprise a rectifier and a rectifier load resistor mounted within said cavity.