US 2855543 A
Description (OCR text may contain errors)
7', 1958 w. 0. WHITE MICROWAVE BEAM TRANSMITTER Filed April 30, 1953 Inventor: William C.Whit,e,
by His Attorney.
MICROWAVE BEAM TRANSMITTER William C. White, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 30, 1953, Serial No. 352,085 51Claims. (Cl. 315-34 My invention relates to microwave beam transmitters. Beamed sources of microwave energy are finding increasing numbers of applications, especially in industry where they may be employed in detection and control systems. In such applications, however, the use of laboratory type of equipment is becoming increasingly inconvenient and impractical since such equipment requires special skills in operation and maintenance. It is further desirable that this type of apparatus, which includes discharge devices, resonators, and antennas, be incorporated in unitary assemblies which are compact and sturdy and meet the usual requirements of low cost and trouble-free construction.
It is therefore a primary'object of my invention to provide an improved and simplified microwave beam transmitter construction.
It is another object of my invention to provide a microwave beam transmitter suitable for industrial applications. i
In accordance with my invention the electrodes of a discharge device, an oscillator resonator system, and
an antenna are positioned within a parabolic reflector,
the face plate for the reflector being sealed thereto to complete the vacuum chamber for all the components of a microwave beam transmitter including the discharge device electrodes. Since the components are all within one vacuum enclosure, no insulating seals for the microwave-energy conductors are required, the only seals being those for the discharge device cathode and for the anode leads.' In a preferred embodiment the electrode leads-also serve to support the oscillator assembly and to thus position the antenna near the focus of the parabolic reflector. Only direct current and heater current connections need be made to the terminals of the unitary assembly thus provided so that a minimum of training and skill is required for the operation and maintenance of the transmitter;
' The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure is a view, partly in section, of a microwave transmitter embodying my invention.
Referring now to the drawing a microwave beam transmitter is positioned within a parabolic reflector 1 suitably made of a glass bowl having a parabolic curve with an inner metalized coating 2 to provide a reflecting surface forelectromagnetic waves. A glass face plate 3 sealed to the rim of the bowl encloses the reflector and provides a vacuum envelope for an oscillator 4 and antenna 5 contained therein. A cylindrical glass neck 6 .is fused between the base and the reflector bowl 1 to facilitateclamping it to a mechanical support 7. In order that the transmitter may be either held or stationed as desired, the support member 7 suitably includes metal straps 8 which are tightened around the cylindrical base' portion 6 and fastened together by a bolt 9 so that the clamp can be readily loosened to permit the removal of the transmitter and insertion of a replacement unit.
Within the reflector bowl the oscillator 4 includes a triode discharge device designed for operation in a high vacuum and having respectively a cathode 10, a control grid electrode 11-and an anode 12, the operating surfaces of these electrodes being disk-shaped and arranged in parallel planes. Each electrode is provided with suitable cylindrical conductive terminals and insulating spacers are positioned between the electrodes to hold them in the desired relationship.
In the particular discharge device construction illustrated in the drawing the cathode 10 is made in the form of a cylinder or eyelet having a closed end constituting the active cathode surface and having a flange at the other end. One end of an internal heater element shaped to define an annular recess or grid-anode cavity resonator between it and the grid washer 11. The portion of the anode flange 17 adjacent the grid washer is spaced therefrom by an insulating washer 18, suitably made of a ceramic material. The anode is apertured to facilitate evacuation of the interelectrode spaces.
To complete the oscillator assembly an annular flanged metallic resonator member 19 is provided, the outer flange being slipped over the periphery of the anode flange 17 and the inner flange being positioned around the flange of the cathode 10. An insulating spacer, suitably provided by a band of a ceramic or mica 20, is positioned between the member 19 and the cathode between them. The grid-cathode cavity resonator is thus defined by the resonator member 19, the cathode 10 and the grid 11, the grid-cathode spacer 15 being a dielectric and hence in itself comprising part of the resonator. In a vacuum tube, the insulating ceramic spacing disks must be continuous and vacuum tight but for the assembly described here, Where the whole enclosure is evacuated, this is not necessary and spoked-wheel design of spacer disks'can be employed. Thus lowered dielectric losses are obtainable as less ceramic material is in the highfrequency electric fields. When the cathode is heated to emit electrons and a positive voltage is applied to the anode the oscillator will operate at the frequency established by the resonators.
In this case, the grid-anode resonator, being the physically smaller of the two, establishes the operating frequency and the space enclosed by the grid-cathode resonator is adjusted by sliding the annular resonator member 19 over the anode flange so that a harmonic of the grid-cathode resonator frequency corresponds to either the fundamental or a harmonic frequency of the grid-anode resonator. Coupling between the two resonators is provided by both the interelectrode capacitances and also by the path between the resonators through the spacing insulator 17. In the particular resonator construction shown the operating frequency is designed to be of the order of 5000 megacycles, the Wave length at this frequency beingsufliciently small so that a reflector of relatively small dimensions, such as suitable for portable use, will operate efiectively to beam the high frequency energy.
Energy from theresonator is suitably coupled to the antenna 5 positioned near the focus of the parabolic wave of the reflector 1. A dipole antenna is conveniently made from a length of copper wire having oppositely extending quarter wavelength end portions and parallel center portions with the center loop 22 extending into the grid-cathode resonator for coupling to the high frequency energy thereof. An aperture in a portion of the resonator facing the base of the reflector holds an insulating grommet 23 having parallel bores through which the wire ends comprising the antenna are inserted before the end portions are bent over. A shield 24 comprising a metallic disk is fixed on the antenna grommet to prevent direct outward radiation from the antenna, the energy radiated being directed towards the parabolically curved walls of the reflector. As is well known in the parabolic reflectors, the energy emanating from the focal point thereof or a point nearby is reflected along paths substantially parallel to the parabolic axis, thus concentrating the reflected energy in a beam. Since the dimensions of the parabola are not large with respect to the Wavelength of the reflected energy, the parabola should be designed so that the distance from the focus to the reflector is one-fourth wavelength or on odd multiple thereof at the desired frequency.
The entire resonator and antenna assembly is preferably supported with respect to the reflector 1 by the electrode leads required for application of direct current and heater potentials to the discharge device elements. As shown in the drawing three conductive rods or electrode leads positioned parallel to the parabolic axis are employed, lead 25 being welded to the anode, lead 26 to the cathode flange, and lead 27 to the heater terminal. The leads extend through the bottom of the reflector 1 and the neck 6, the exposed outerends of the leads serving as base pins which are engaged by a socket 28 connected by a cable 29 to the heater and anode voltage sources represented as batteries 30 and 31 respectively. As will be noted, no high frequency leads need be sealed through the reflector, thus eleminating seal problems usually occurring where high frequency insulating seals are required.
By virtue of the unitary assembly thus provided, with the oscillator and antenna enclosed in the common vacuum envelope defined by the parabolic reflector, the transmitter is adapted for installations and hand-held operation with a minimum of skill required for operation and replacement. Any adjustments are made before the face-plate 3 is sealed and the reflector evacuated, thus removing any possibility of tampering with the transmitter.
The whole assembly may be evacuated by heating the glass envelope in an oven and later heating the electrodes by bombardment or high-frequency induction heating while the envelope is being pumped through the tubulation 32, after which the envelope is sealed off from the system at 33. These procedures are well known in connection with the manufacture of vacuum tubes. While a particular type of discharge device has been described in connection with the illustrated embodiment of my invention, it will be understood, of course, other discharge device types may be substituted.
While the present invention has been described by reference to a particular embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.
What I claim as new and desire to secure by Letters Patent of the United States is:
l. A microwave discharge device beam transmitter having an hermetic envelope, said envelope comprising a parabolic electromagnetic reflector and a dielectric face-plate sealed thereto, an oscillator structure positioned therein having electron discharge device cathode, grid, and anode electrodes, means for applying voltages to said electrodes, said means for applying said voltages being insulatingly sealed through said envelope, and an antenna coupled to said oscillator positioned near the parabolic focus of said reflector.
2. A microwave discharge device beam transmitter having an hermetic envelope, said envelope comprising a parabolic electromagnetic reflector and a dielectric face-plate sealed thereto, an oscillator structure positioned therein having electron discharge device cathode, grid, and anode electrodes, means for supporting said oscillator structure and for applying voltages to said electrodes comprising stiff conductive members insulatingly sealed through said envelope, and an antenna coupled to sa d oscillator positioned near the parabolic focus of said reflector.
3. An ultra-high frequency beam transmitter comprising a parabolic electromagnetic reflector, discharge device electrodes including a cathode, a grid, and an anode positioned within the region described by said reflector, a first resonator coupled to said cathode and said grid, a second resonator coupled to said grid and said anode, feed-back coupling conducting means between said resonators, means for applying external potentials to said electrodes, said conducting means being insulatingly sealed through said reflector near the center thereof, an antenna coupled to one of said resonators, said antenna being positioned near the focal point of said reflector, and a gas impervious insulating face-plate hermetically secured to said reflector to enclose said discharge device, electrodes, resonators, and antenna and complete a vacuum envelope therefor.
4. An ultra high frequency apparatus comprising a parabolic electromagnetic reflector, electron discharge device electrodes positioned within the region described by said reflector including a planar cathode, a grid, and an anode, a first resonator coupled to said cathode and said grid, a second resonator coupled to said grid and said anode, feed-back coupling means between said resonators, conducting means for applying external potentials to said electrodes, said conducting means being insulatingly sealed through said reflector, an antenna coupled to one of said resonators, said antenna being positioned near the focal point of said reflector, and a gas impervious insulating face plate hermetically secured to said reflector to enclose said discharge device electrodes, resonators, and antenna to complete a vacuum envelope therefor.
5. A microwave beam transmitter comprising a parabolic electromagnetic reflector, electron discharge device electrodes positioned within the region described by said reflector including a planar cathode, a grid, and an anode, conducting means for supporting said device and for applying external potentials to said electrodes, said conducting means being insulatingly sealed through said reflector, a resonator system comprising a grid-cathode resonator and a grid-anode resonator with feed-back coupling means therebetween coupled to said respective electrodes, an antenna coupled to one of said resonators positioned near the focal point of said reflector, and a glass face plate hermetically secured to the reflector rim to enclose said discharge device electrodes, said resonator system, and said antenna to define a vacuum envelope therefor.
References Cited in the file of this patent UNITED STATES PATENTS 1,958,591 Roberts May 15, 1934 52,339 Dallenbach Aug, 25, 1936 2,404,261 Whinnery July 16, 1946 35,804 Spooner Feb. 10, 1948 76,725 Gurewitsch July 19, 1949 76,971 Fremlin et a1 July 26, 1949 0,603 Dorgelo Nov. 21, 1950