US2641658A

US2641658A - Radio-frequency generator

Info

Publication number: US2641658A
Application number: US199825A
Authority: US
Inventors: Donald H Preist
Original assignee: Eitel Mccullough Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1950-12-08
Filing date: 1950-12-08
Publication date: 1953-06-09
Anticipated expiration: 1970-06-09

Description

June 9, 1953 Filed Dec. 8, 1950 D. H. PREI$T- RADIO-FREQUENCY GENERATOR P0 WER OUTPUT 7'0 LOAD 2 Sheets-Sheet l 5; INPUT 37 38 RESONATOR Paws/2 INPUT FROM DE/VE 12.9.1

INVENTOR.

Donald H. Prel's ATTORNEY June 9, 1953 Filed Dec. 8, 1950 D. H. PREIST RADIO-FREQUENCY GENERATOR 2 Sheets-Sheet 2 INVENTOR. Dona/d H. Pre/s? BY M6247 ATTOQNEY Patented June 9, 1953 ITE STATES PATENT o FicE I v 'RADlO-FREiiiiii GENERATOR I Donald H. Preist, Mill Valley, Califi, assignor to ,Eitel-McCullough, Inc., San Bruno, Calif., a

corporation of California Application December 8, 1950, Serial No. 1'99,825

7 Claims.

My invention relates to generators of radiofrequency power using electron tubes, and more particularly to high-power generators using A still further object is to provide such a generator which'may be designated to operate either i as an amplifier or as an oscillator.

The invention possesses other objects and features of advantage, some of whichwith the foregoing, will be set-forth in the. following description of my invention. It is to be understood that Ido not limit myself to this disclosure of species ofmy invention as I may adopt variant embodiments thereof within the scope of the claims.

Referring to the drawings: Figure 1 is a vertical sectional view of theimproved R. F. generator embodying my invention;

and v I Figure 2 is a transverse sectional view taken along the plane indicated by line 2-2 of Figure 1. I, j

In terms of broad inclusion the radio frequency generator comprises a plurality of tetrodes dis-, posed in a circle about an axis and each havingan anode and screen grid and control grid and cathode; output and input resonators each comprising an annular cavity extending axially of the circle and having inner and outer conductors, the anode of each tetrode being electrically connected to the inner conductor of'the output resonator andthe cathode of each tetrode being electrically connected to the inner conductor of the input resonator; means including a condenser coupling the screen grid of each tetrode to the outer conductors .ofthe resonators; and

an .annular hollow conductor extending axially of the input resonator and encircling the inner conductor thereof. the last mentioned conductor being open at one end and electrically connected tothe control grid of each tetrode at the other end. Whenthe apparatus isoperated as an amplifier the screen grid condenser functions as an R. F. by-pass condenser and when operated as an oscillator this condenser isdesigned as a feed- 7 back device for .feeding energy from, the output resonator to the input resonator. An important feature in my apparatus is the arrangement of the control grid line or conductor within the input resonator, as this is'conveniently adaptable for a tetrode structure wherein the control grid terminal naturally'lies between the cathode and screen grid terminals;

In greater detailand referring to the drawings, my radio-frequency generator" constructed as an amplifier comprises a plurality of tetrodes I disposed in a circle about an axis, which tubes are of like constructionand have like characteristics. While five tubes are shown, it is understoodthat any desired number may be employed depending upon'the power output required. Tetrodes 1 are of conventional construction having a cathode-'2, control grid 3, screen grid 4 and anode 6, 'the anode being external andall the electrodes being preferably cylindrical and coaxial. The preferred tube used with my circuitry has coaxial terminals for the electrodes, such as the cathode terminal 1 opposite the anode and thecontrol grid terminal ring 8 and screengrid terminal ringil inter,-

posed in the envelope wall between the cathode terminal-and anode. This sequence of'terminals on the envelope is a natural and customary ter minal arrangement in tetrode type tubes. The heating structure for the cathodeis not shown but may comprise :any suitable means such asan inner filament for heating the cathode cylinder 2 by electron bombardment, in which case the filament leads preferably extend out through the tubular cathode terminal 1.

The amplifier "has an output resonator Hand an input resonator l2, which resonators comprise annular-shaped cavities that are coaxial with the tube circle and arecommon to the pluralityof tubes I. Output cavity resonator l-l is made up of an inner annular conductor comprising metal cylinders 13 joined by an end ring l4, and outer conductors comprising metal cylinders 1-6. These conductors thus form a pair of communicating annular cavity sections IL-the space joining the cavity sections being located adjacent the upper portions'of tubes 1. In a like manner the input cavity resonator is made up of an inner annular conductor comprising 'meta'l cylinders l8 joined by'an end ring IS, and outer conductors comprising metal cylinders 2! I which latter cylinders inay be integralxwith the outer cylinders I6 of 'the output resonator.v The 22, the space joining such cavity sections being located adjacent the lower portions of tubes vI.

55 Thus the annular cavities of the output and input resonators are concentric with the axis of the tube circle, each cavity being of U-shape in cross-section and common to the plurality of tubes I. It will also be noted that the main sections l1 and 22 of the output and input cavities extend axially of the tube circle so that the principal propagation in these cavities is axial rather than radial of the tubes.

It will thus be noted that each resonator comprises two cavity sections, each section being constituted by the space between a pair of concentric cylinders. The length of each section, measured axially of the circle of tube units, is substantially greater than the width of the section, measured radially of the circle of tube units, i. e., the difference in radius of the concentric cylinders which define the section (ignoring the thickness of the cylinders). An annulus having a greater axial than radial dimension, measured as described is defined hereinafter as an axially extending annulus.

Anodes 6 of the tetrodes I are electrically connected for radio-frequency current to the inner conductor of the output resonator, in the device illustrated this being a direct connection to the end ring 14 which is apertured so that the anodes project upwardly into the hollow inner conductor. Suitable means for cooling the anodesmay thus be provided in the open space of the hollow con-' ductor. In a similar manner cathodes 2 of the tetrodes are electrically connected for radiofrequency current to the inner conductor of the input resonator, this being a direct connection to the cathode terminals 1 which project downwardly through the end ring IQ of the hollow conductor. Suitable leads for the cathode heater means of the several tubes may thus extend out through the hollow conductor.

Any suitable metal such as brass may be used for the various conductors described which make up the boundary walls of the cavities. For purposes of mechanical support the inner conductor of the output resonator is factened to upper rings 23 of insulating material interposed between the cylinders l3 and 16. Likewise the inner conductor of the input resonator is 'held in position by lower rings 24 of insulating material interposed between the cylinders I8 and 2|.

Screen grids 4 of the tetrodes are electrically coupled for radio-frequency current to outer conductors of the resonators. In order toisolate the D. C. screen grid voltage, the coupling includes an R. F. bypass condenser comprising a transverse metal plate 26. connected to the outermost conductors I6 and 2| and a second metal plate or ring 21 connected to screen grid terminal rings 9. These plates are spaced by a suitable insulating layer 28, the capacitance of this bypass condenser in the amplifier being large enough to prevent any appreciable amount of feedback of energy from the output to the input resonator. Member 26 which forms the lower plate of the condenser also comprises the dividing wall between the cavity resonators, it being a metal disk extending transversely across the unit and fastened at the periphery to the outermost conductors l6 and 2| which constitute the shell of the generator. As illustrated, this plate member is apertured to receive the tubes so that the later project partially into the upper cavity and partially' intothe lower cavity;

From the above structure it will be seen that an output cavity circuit is provided between the anodes and screen grids of the tetrodes, and that an input cavity circuit is provided between of the cavity sections.

the cathodes and screen grids. In order to establish the third desired circuit for applying the required R. F. voltage between the control grids and cathodes, I provide an annular open ended transmission line within th input resonator. This is conveniently adaptable for tetrode structures wherein the control grid terminals 8 naturally lie between the cathode and screen grid terminals. As shown, the control grids 3 are connected to the closed end of an open ended hollow metal conductor extending axially of the input resonator and encircling the inner conductor thereof. This grid conductor comprises a pair of cylindrical walls 29 joined by an end ring.3| connected to the control grid terminal rings 9, the end ring 3! being apertured to receive the tubes. For purposes of adjusting the axial length of the grid line the side walls of the hollow conductor preferably have slideable sections 32 at the open end. For optimum operation the length of the hollow grid conductor is preferably made equal to an integral number of half wave lengths electrically at the operating frequency.

Adjustable means are provided for tuning the output and input resonators to the desired operating frequency. For this purpose a pair of annular metal plates 33 are provided in sections ll of the output resonator, on opposite sides of the inner conductor, so as to form the upper end walls These plates are slideably mounted on the cylindrical walls I3 of the inner conductor, and axial adjustments is achieved by means of plunger rods 34 of insulating material projecting through supports 23. Rods 34 may be connected externally to insure that plates 33 are adjusted in unison. Plates 33 are connected to the inner conductor only and have cylindrical flanges 36 closely spaced to the wall conductors It so that the devic also functions as a choke to confinethe R. F. and isolate the D. C. anode voltage. For this purpose the flanges 36 of the choke are made effectively a quarter wave long at the operating frequency, telescoping sleeves (not shown) being provided on the flanges if desired to adjust their length. Positive anode potential may thus be applied by direct connection with the inner conductor as indicated at 31. Tuning the output resonator is accomplished by adjusting the end plates 33 to make the cavity sections ll the'desired length for a selected operating frequency, as will be readily understood.

In a like manner a pair of annular plates 38 are provided in the input resonator, adjustable by means of plunger rods 39 for tuning to the desired operating frequency. Here the end plates are in the nature of shorting bars having slideable contact with both the inner conductor walls I8 and the outer conductor walls 2|. In the apparatus illustrated the cathodes are operated at ground potential, the positive anode potential being applied by direct connection to the anodes as already mentioned. The control grid bias voltage is supplied from a suitable source, as through a resistor 4!, and is connected to grid line 29 by a wire 42 entering the resonator through a suitable R. F. choke 43. In a like manner the screen grid voltage is supplied from a suitable source, as through a resistor 44, and is connected to screen grid ring 21 by a wire 45 enteringthe resonator through a suitable R. F. choke 46.

R. F. driving power may be fed into the input resonator from a suitable source of drive by any suitable means, as by a. loop or probe. The pre-. ferred structure however, as illustrated, comprises a centrally located transmission. line 41 coupled to the resonator through a slot. Transmission line 41 is made-up of an inner conductor 48 terminating at the transverse dividing wall 26 between the resonators, and an outer conductor 49 which is a continuation of the innermost conductor 2i of the input resonator. Energy coupling means between the input line and resonator comprises a circular slot 50 formed by spa'cingthe inner end of conductor 2| from the. transverse wall 26. The circular arrangement of. this coupling slot is desirable because it provides uniform coupling of energy from the transmission line to the annular cavity 22.

Output power from the amplifier is preferably transferred from the output resonator to a suitable load by means of a transmission line 5| coaxial with the input line, and having an inner conductor 52 terminating at the transverse wall 26 and an outer conductor 56 formed as a continuation of the innermost conductor I6 of the output resonator. A circular slot 51 serves to couple energy from the output resonator to the transmission line 5|.

In adjusting the amplifier the output cavity resonator II between the anode and screen grid is tuned to resonance at the operating frequency, the plates 33 being adjusted so. that the axial length of each cavity section I1 is an odd number of quarter wave lengths electrically. The input cavity resonator l2 between the cathode and screen grid is adjusted by plates 38 so that the length of each cavity section 22 is roughly an integral number of half wave lengths electrically at the operating frequency. As already mentioned the length of the open end grid line 29- -32 within the input resonator is also set at approximately an integral number of half wave lengths electrically. By this arrangement, and by'the proper adjustment of. the lengths of the grid line 29-32 and the input resonator 12, it is possible to achieve the desired amplitude and phases of the R. F. voltages between the cathodes, screen grids and control grids of the tetrodes.

An important feature of my annular cavity type of generator employing a plurality of tubes is thata large amount of, R. F. power can be prosustain oscillation. Thus, in the: oscillator case; the condenser associated with the screen grid would function as. a feedback condenser rather than a bypass condenser. In other respects the structure of the R. F. generator would remain unchanged.

For purposes of illustration 1 have shown the output resonator arranged. end-to-end with the input resonator. If. it were desirable to have a more compact construction the output cavity greater than the radial dimension thereof, the

anode of. each tetrode being electrically con- F nected tol the inner conductor. of the output resonator and the cathode of each tetrode being electrically connected to the inner conductor of the :input :resonator,.nreans coupling the screen grid. of each. tetrode to the outer conductors of.

1 the resonators, and anannular hollow conductor extending axially of the input resonatorand encircling the inner conductor thereof, said hollow conductor being open at one end and electrically connected to the control grid of each tetrode at the other end.

2. A: radio-frequency generator comprising a. plurality of tetrodes disposed in a. circle about 1 an axis and each having an anode and screen.

duced at the higher frequencies without undue v circuit losses. In my improved apparatus the power amplification is obtained with no greater total power output, as measured at the load, fora generator having n number of tubes is substantially n times that obtainable from a single tube in an efiicient single tube amplifier.

Another important feature of my invention is that the above mentioned advantage of high power generation is attained with tetrode type tubes, so that the other advantages inherent in a tetrode, such as increased power gain, are also had.

While I have described my apparatus as an amplifier, it is understood that the generator may be operated as an oscillator, and that the term generator is employed herein, as is common usage, in the generic sense. In the latter case the input transmission line 41 would be omitted and the capacitance of the condenser 26-2'l-28 decreased so as to provide sufficient feedback of energy from the output resonator II to the input or excitation resonator I2 to grid and control grid and. cathode, output and input resonators each comprising an annular cavity extendingzaxially of. said circle and having inner and outer conductors, the axial dimension; of said resonator being substantially greater. than the radial dimension thereof, the anode of each tetrode being. electrically connected. to the inner conductor of the output resonator. andthe oathode of. each tetrode being. electrically connected to the inner conductor of the input resonator, means coupling the screen grid of each tetrode tothe outer conductorsof the-resonators, and an annular hollow conductor extending axially. oiv the input. resonator and encircling the inner conductor thereof, said hollow conductor being open at one end and electrically connected tothecontrol; grid of each-tetrode at the. other end, the last mentioned conductor comprising telescoping: sections for adjusting the length. thereof.

3. A radio-frequency generator comprising a plurality of tetrodes disposed in a circle about an. axis and each having an anode and screen grid and control grid and cathode, output and input resonators each comprising an annular cavity extending axially of said circle and having inner and outer conductors, the axial dimension of said resonator being substantially greater than the radial dimension thereof, the anode of each tetrode being electrically connected to the inner annularhollow conductor extending axially of p the input resonator and encircling the inner conductor thereof, said hollow conductor being open at one end and electrically connected to the control grid of each tetrode at the other end, and tuning means in the output and input resonators for adjusting the axial length of said resonators.

4. A radio-frequency generator comprising a plurality of tetrodes disposed in a circle about an axis and each having an anode and screen grid and control grid and cathode, output and input resonators each comprising an annular cavity extending axially of said circle and having inner and outer conductors, the axial dimension of said resonator being substantially greater than the radial dimension thereof, the anode of each tetrode being electrically connected to the inner conductor of the output resonator and the cathode of each tetrode being electrically connected to the inner conductor of the input resonator, means coupling the screen grid of each tetrode to the outer conductors of the resonators, said coupling means including a condenser, and an annular hollow conductor extending axially of the input resonator and encircling the inner c-onductor thereof, said hollow conductor being open at one end and electrically connected to the control grid of'each tetrode at the other end. i

5. A radio-frequency generator comprising a plurality of tetrodes disposed in a circle about an axis and each having ananode and screen grid and control grid and cathode, output and input resonators each comprising an annular cavity extending axially of said circle and having inner and outer conductors, the axial dimension of said resonator being substantially greater than the radial dimension thereof, the anode of each tetrode being electrically connected to the inner conductor of the output resonator and the cathode of each tetrode being electrically connected to the inner conductor of the input resonator, means coupling the screen grid of each tetrode to the outer conductors of the resonators, said coupling means including a condenser plate connected to the outer conductors of the resonators and a second condenser plate spaced from the first plate and connected to a screen grid of each tetrode, and an annular hollow conductor extending axially of the input resonator and encircling the inner conductor thereof, said hollow conductor being open at one end and electrically connected to the control grid of each tetrode at the other end.

,6. A radio-frequency generator comprising a plurality of tetrodes disposed in a circle about an axis and each having an anode and screen grid and control grid and cathode, output and input resonators each comprising an annular cavity extending axially of said circle and hav-.

ing inner and outer conductors, the axial dimension of said resonator being substantially greater than the radial dimension thereof, the anode of each tetrode being electrically connected to the inner conductor of the output resonator and the cathode of each tetrode being electrically connected to the inner conductor of the input resonator, means coupling the screen grid of each tetrode to the outer conductors of the resonators, an annular hollow conductor extending axially of the input resonator and encircling the inner conductor thereof, said hollow conductor being open at one end and electrically connected to the control grid of each tetrode at the other end, an output transmission line extending axially of said circle, and energy coupling means comprising a circular slot communicating between said output line and output resonator.

'7. A radio-frequency generator comprising a plurality of tetrodes disposed in a circle about an axis and each having an anode and screen grid and control grid and cathode, output and input resonators each comprising an annular cavity extending axially of said circle and having inner and outer conductors, the axial dimension of said resonator being substantially greater than the radial dimension thereof, the anode of each tetrode being electrically connected to the inner conductor of the output resonator and the cathode of each tetrode being electrically connected to the inner conductor of the input resonator, means coupling the screen grid of each tetrode to the outer conductors of the resonators, an annular hollow conductor extending axially of the input resonator and encircling .the inner conductor thereof, said hollow conductor being open at one end and electrically connected to the control grid of each tetrode at the other end, an output transmission line extending axially of said circle, energy coupling means comprising a circular slot communicating between said output line and output resonator, an input transmission line extending axially of said circle, and energy coupling means comprising a circular slot communicating between said input line and input resonator.

DONALD H. PREIST.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,173,908 Kolster Sept. 26, 1939 2,284,405 McArthur' May 26, 1942 1 2,363,641 Carlson Nov. 28, 1944 2,404,261 Whinnery July 16, 1946