US2544680A - High-frequency electron tube structure - Google Patents

Description

March 13, 1951 Filed June 28, 1945' W. W. HANSEN HIGH-FREQUENCY ELECTRON TUBE STRUCTURE 2 Sheets-Sheet 1 FREQUENCY MULT/PL/EP o o- INVENTOR 1 M VSE/v ATTORNEY March 13, 1951 w. w. HANSEN 2,544,680

HIGH-FREQUENCY ELECTRON TUBE STRUCTURE Filed June 28, 1945 2 Sheets-Sheet 2 INVENTOR Way/2M W. ,q/vaz/v ATTORN EY fiatented lVlar. 1 3,

HIGH-FREQUENCY ELECTRON TUBE STRUCTURE William W. Hansen, Garden City, N. Y., assignor to The Sperry Corporation, a corporation of Delaware 11 Claims.

The present invention relates to the art including high frequency electron discharge devices, circuits and methods and, more particularly, to such methods, circuits and devices adapted to operate at super-high frequencies of the order of loamegacycles per second or higher.

The present application is a continuation-inpart of prior copending application Serial No. 416,170, filed October 23, 1941, now Patent No. 2,425,738 granted August 19, 1947, for Tunable High Frequency Electron Tube Structure.

. In one embodiment, the invention more specifically relates to frequency multiplier devices adapted to convert lower frequencies into such super-high frequencies. The present invention is more particularly directed to devices utilizing cavity resonators in inductive relation to grouped or variable-current electron streams for the purpose of extracting such super-high frequency energy from these streams.

In prior Patent No. 2,281,935, granted May 5, 1942, in the names of R. H. Varian and W. W. Hansen, the present inventor, there is disclosed one type of frequency multiplier in which a constant-current electron stream of uniform electron velocities is varied periodically in velocity (velocity-modulated) at a fundamental frequency. The velocity-modulated stream is thereafter passed through a field-free drift space within which the uniform-current, variable-velocity electron stream is converted into a variable-density or variable-current electron stream, sometimes termed a density-modulated electron stream, by the velocity-grouping action incident to faster electrons overtaking slower electrons. This variable-current stream is then passed through an output cavity resonator in inductive relation thereto, which resonator, being tuned to a super-high harmonic frequency of the predetermined fundamental frequency, serves to extract harmonic frequency energy from the stream for use as desired. v

. One major feature ofthe present invention'resides in the modification of such a frequency multiplier permitting its use for high ratios of frequency multiplication with markedly increased emciency. According to the present invention, the magnitude of the electron current is varied periodically at the same fundamental frequency as that at which-the electron velocities are varied, before passage of the electron stream through the field-free drift space or drift tube, in distinction to the prior art devices where the electron current-magnitude was left unchanged before entering the drift space. In the present de- Application June 28, 1945, Serial No. 602,007

vice, the current variation is performed simultaneously and cophasally with the velocity modulation. It has been found that the harmonic frequency energy content of the stream after passage through the drift tube is thereby materially increased; providing increased power output from the output resonator for a given input fundamental frequency voltage amplitude or, from another point of view, permitting equivalent output with smaller input. Since in prior art devices the ratio of output-to-input' frequencies, termed the frequency multiplication ratio, is limited by the fact that for higher ratios the output is very small, the devices of the present invention permit higher ratios to be used, since the output amplitudes at such output frequencies are materially increased.

A further feature of the invention resides in the application of the fundamental frequency input voltage directly between the cathode and an.

adjacent electron-accelerating electrode, with this fundamental frequency voltage superposed upon the electron-accelerating voltage, thereby producing simultaneous and combined current variation and velocity modulation of the electronv stream, which is followed by velocity-grouping of the electrons of the stream in a field-free drift space, resulting in a type of electron grouping especially highly desirable in frequency multiplying devices and adapted to produce substantial amounts'of output power at the super-high multiplied output frequency.

' Still another feature of the present invention resides in constructional features for devices of theabove-described type, especially adapted to produce the improved results characteristic of the present invention.

I These and other features of the invention will become apparent from the following detailed 'description and the appended drawings, in which:

Fig. I-represents a schematic circuit diagram of the present improved electron discharge device and its circuit;

Fig. 2 shows a longitudinal view, partly in cross-section, of one form of the electron discharge device of the present invention;

Fig. 2A shows a fragmental cross-sectional view of the device of Fig. 2, taken along line A--A 'Referring to .the drawings, in Figs. 1 and 2 there is showna cathode ll of any suitable conventional type adapted to supply free electrons. Cathode 11 may include conventional focussing and control electrodes. Adjacent to cathode I1 is an electron-permeable grid or accelerating electrode 69. Connected between cathode I1 and grid 69 is a suitable unidirectional voltage source 68 having its negative terminal connected in a.

manner to be described below to cathode l1 and its positive terminal connected to grid 69. Cathode Il, grid 69, and potential source 68 serve to.- form the stream of electrons projected through grid 69.

Surrounding the path of the electron stream beyond grid 69 is a drift tube 1.5 providinga fieldfree drift space therewithin. Drift. tube 15 is conductively connected to and supports grid 69. Grid 69 and tube 15 are preferably grounded as. at 61. The far end of drift tube T supports a similar grid 66 which is adjacent to a corresponding grid 65, thereby providing a narrow output gap between grids 66 and 6,5. The electron stream after passing through grids 66 and 65 is. collected on the conducting end wall of the device, such as at Si, or by any other conventional electron-collecting means.

The grids 66 and 65 form portions of the walls. of an output cavity resonator 89. As shown in Fig. 2, resonator 89may be formedwith a flexible. wall 88 so that its resonant frequency may be adjusted by suitable tuning screws 93 controlling the separation between grids or, output electrodes: 66 and 65. Any other. type of. tuning means may be used for resonator 89, or it may be manufactured as fixed-tuned at the desired output frequency.

Resonator 89, collector wall 91, drift tube 15, and wall 81 connected thereto preferably: form part of the evacuated enclosure or envelope for the electron discharge device. Cathode" issuitably supported in insulated fashion within this envelope as by a glass or insulating end bell 0rseal 18 completing the envelope.

In operation, the fundamental frequency voltage to be frequency-multiplied is superposed on the, voltage of source 68impressed between cathode H and grid 69, so that the cathode-grid voltage is a unidirectional voltage pulsating at the fundamental frequency. One manner of applying this fundamental frequency. voltage between electrodes H and 69 is, shown in Fig- 1, although other methods may be used, asin 2, and, 3, described below, Thus, a. parallel-resonant lumpedroo'nstant circuit comprisingparallel cona nected inductance H and capacitance, 13.18. con-- nected betweenthe negative terminal, of source 68 and cathode 11. Source fiflmaybesuitablybypassed with respect. to alternating currents, if desiredas by a conventional by -pass. condenser 80 connected thereacross. the secondary of a radio frequency transformer whose primary winding 83 is inductively coupled. Primary winding 83- is; supplied.

to winding H. with the fundamentalv frequency to be multiplied, in any convenient manner. An; illustrative source of fundamental frequency mightrbe a; low radio frequency source l2feeding-afrequency multiplier 14 of conventional type,- the-frequency" of source I2 and the multiplication ratio; of multiplier 14 being selected to; provide'the: desired fundamental frequency 1. For. example, source 127 might be a crystal-controlled oscillator to-..pro-..

vide frequency-stabilized operation.

Although the series fed resonator H; 13"shown in Fig. l differs from the unitycoupled feedstruc Inductance H forms,

' from cathode 11' to grid 69:

ture shown in Fig. 2, it will be understood that the two circuits are equivalent. As shown in Fig. 2, inductance H comprises a single loop of hollow tubular conductor having one end grounded by connection to drift tube 15 and the other end capacitively coupled to cathode 11 by a suitable bypass condenser 19. The. loads 81 for the unidirectional or low. frequency potentials necessary to operate cathode 11, such as the heater voltage leads and the accelerating voltage supply lead from. source 68, are brought in at the grounded end of hollow conductor H and extend therein to the heater and cathode. In this way it is unnecessary to insulate these leads 8! with respect toradio frequency voltages, since the tubular conductor H acts as a shield, and the entrance point into-conductor H is made adjacent the point of lowest radio frequency potential. Primary winding 83 is formed of a single loop of wire in inductive relation to conductive loop H, and is coupled to. the fundamental frequency source; such as 14, 12, in any suitable.- manner.

In operation, resonant circuit H, I3. is tuned: substantially to the input fundamental frequency; and resonator 89 is tuned substantially tov a. de:- sired harmonic. frequency output. The electrons. emitted by cathode l!- are. then subjected to: a unidirectional: accelerating electric fieldv provided; by source. 68, upon. which issuperposed a fundaa mental frequency field produced by. the voltage across tuned circuit ll, 13. During the positive portions of the fundamental frequency cycle when grid 69 is most positive withrespect tocathode. 11,. a relatively large number; of electrons will flow Also, these elecetrons will have greater-than-average' velocity. At the instantswhen.the fundamental frequency componentoftthe voltage between grid= and cathode 1.1 is zero, an average number of electrons with average velocity will enter the drift tube I5. During the negative portionsof the fundamental. frequency cycle; when grid 69' is: least positive with respect to cathode 1 1, a mini-- mum number of: electronshaving lowest velocitywill enter the drift. tube I51 Accordingly; the electron stream is simultaneously subjected to velocity-variation or modulationand'current'vaniation. or densitymodulation, and in fixed cophasal relation, since minimum current magni---- tude and minimumvelocity-are produced simul-- taneous y In frequency multipliers of the velocity-modulation type, such-asdiscl'osed in theabove-mentionedPatent No. 2,281,935, it has been discovered that the lowest velocity electronsare adrawback in obtaining optimum harmonic-frequency energy content in the electron stream, since'these mini mum-velocity electrons prevent the electronbunching action from producing an optimum shape of electron bunch forthe purpose or producing' harmonic frequency energy; Also; the" maximum-velocity electrons are most useful in producing harmonic frequency output. By the present invention the number of these harmful minimum-velocity electrons is reduced, since'theelectron current is a minimum simultaneously with minimum electron velocity.- In this way the action of minimum-velocity electronsin impair ing the eificiency of the electron-bunching-phe nomenon is greatly reduced; since fewer of'thes'e minimum-velocity electrons are produced than in prior art devices. 0n the other hand; the average and maximum-velocity electrons arein creased in number relative to. the minimum-- velocityelectrons, so that their useful contribution to the electron-bunching process is enhanced. For these reasons greater efficiency and output is experienced by use of the present invention over prior frequency multipliers in which pure velocity modulation was utilized without any simultaneous or prior current variation.

The devices shown in Figs. 1 and 2 incorporate a lumped-constant type tuned input circuit 1 I, 13. This type of circuit is advantageous where the fundamental frequency is of the order of magnitude of 200 megacycles per second or less, and permits the use of fundamental frequency sources of conventional and well-understood type which may be multiplied in frequency by factors of from ten to thirty by the device of the present invention. However, where the fundamental frequency becomes higher than approximately 200 megacycles per second, the radiation inherently experienced adds a troublesome dissipative factor to the input circuit. In addition, the dimensions of the inductance and capacitance elements become impracticable.

The present invention is not restricted to the use of lumped-constant input circuits, as shown in Fig. 2, but may also utilize a cavity resonator for the input circuit where such higher fundamental frequencies are utilized. Such a device is shown in Fig. 3, where identical elements are given the same reference numeral, and corresponding elements are given corresponding but primed reference characters. As will be seen, the only difference between the devices of Figs. 2 and 3 is in the input circuit and manner in which the fundamental frequency electric field is superimposed upon the unidirectional electron-accelerating electric field between the cathode and the accelerating grid.

In Fig. 3, the cathode TI is shown illustratively as formed by an emissive button or disc supported within a supporting conductive cylinder 4| within which is positioned the cathode heater shown schematically at 42 and supplied with heating energy from a suitable source such as a battery 43. Cathode 11 is connected to one of the heater terminals by a connecting link shown at 44, and is thereby directly connected to the negative terminal of the accelerating voltage source 68 whose positive terminal is grounded at 61 as in Fig. 1.

Surrounding cathode TI is an input cavity resonator 46 formed by an outer cylindrical wall 47, an inner cylindrical wall 48, a first connecting end wall 49 connecting walls 41 and 48, and a second end Wall 5| connecting wall 41 to the grid 69 and drift tube 75. Inner wall 48 is insulated from the cathode supporting cylinder 4| as by the insulating seal 18' which also serves to complete the vacuum envelope of which resonator 46 now forms a part.

In order to reduce the physical size of the resonator 4B for its given fundamental resonant frequency, a flange member 52 is supported on the inner wall 48 opposite the end wall 5|, and, if desired, also opposite the outer cylindrical wall 41, as shown at I52. This flange 52 provides an effective lumped capacitance which permits the use of practicable sizes of resonator 46 even for relatively low fundamental frequencies. No tuning means is shown for resonator 4'6, but it is to be understood that any conventional type of tuning means permitting adjustment of the resonant frequency of this resonator may be utilized.

6 in a coupling loop 54, thus exciting resonator 46 in a conventional manner. Because of the capacitive coupling between inner cylindrical wall 48 and the cathode supporting cylinder 4|, the excitation of resonator 46 at fundamental frequency produces a substantially uniform fundamental fre-.

The fundamental frequency voltage f derived from the source 14 is coupled to the input resonator 46 by a suitable sealed coaxial line terminal arrangement 53 terminating within resonator 46 quency alternating electric field between cathode TI and grid '69. In addition, the battery 68 produces a substantially uniform unidirectional and constant electron-accelerating electric field between cathode 1'! and grid 69. Accordingly, the electrons emitted from cathode 11' under the influence of the heat produced by heater 42 are pro-. jected through the grid 69 as in Figs. 1 and 2, and experience the same changes in current and velocity as discussed with respect to Figs. 1 and 2. Accordingly the apparatus of Fig. 3 will operate in exactly the same manner as that of Figs. 1 and 2 and will produce the same advantages discussed above.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A frequency multiplier electron discharge tube comprising a source of electrons, means for forming said electrons into a stream and including an accelerating electrode aligned with the path of said stream, means coupled to said source and electrode and comprising apparatus tuned to and adapted to be excited at a predetermined frequency for causing said electrons to form recurrent bunches, and means along the path of said stream and comprising a cavity resonator tuned to a harmonic of said predetermined frequency for extracting energy from said bunched electrons.

2. High frequency electron discharge tube apparatus comprising an electron-accelerating electrode and a high potential cathode, means for applying a high frequency voltage between said electrode and said cathode, said means including a coupling loop having one end connected directly to said grounded electrode and its other end capacitively coupled to said cathode,- said loop being a hollow tubular conductor, and potential supply leads for said cathode disposed within said tubular conductor, whereby said leads are shielded from high frequency fields.

3. The combination as claimed in claim 2, wherein said leads enter said tubular conductor near the low alternating potential point thereof, whereby high frequency pick-up in said leads is minimized.

4. A frequency multiplier apparatus, comprising a source of electrons, means for projecting electrons from said source in the form of a stream and including a grid aligned with the path. of said stream, a tuned circuit connected between said source and said grid, and a cavity resonator along said stream path and coupled to the stream passing through said grid, said resonator having a resonant frequency which is a harmonic of the resonant frequency of said tuned circuit.

5. High frequency apparatus comprising means including a cathode and an accelerating electrode for producing a stream of electrons, a resonant circuit intercoupling said cathode and accelerating electrode for simultaneously varying the magnitude of said stream and the velocities of 7. the electrons of said stream at. a fundamental frequency, means along'the. path of said. varied stream for causing said varied stream to becomevelocity-grouped, and means along said stream path for extracting energy from said velocitygrouped. stream at a harmonic of said fundamental frequency.

6. High frequency apparatus comprising means including a cathode and an accelerating electrode for producing a stream of electrons, a resonant circuit intercoupling said cathode and accelerating electrode for varying both the magnitude of said stream and the velocities of the electrons of said stream at the same fundamental frequency, and means along said stream path for extracting energy from said varied streamat a harmonic of said fundamental frequency.

7. High frequency apparatus comprising a cathode, a grid adjacent said cathode, a source of potential connected between said cathode and said. grid to form an electron stream flowing through said grid, tuned circuit means coupled between said cathode and grid and tuned to a fundamental frequency for varying both the current magnitude and the velocities of the electrons of said stream at a fundamental frequency, a drift tube surrounding the path of. said stream beyond said grid, and an output resonator positioned along the path of said stream beyond said drift tube and tuned to a harmonic of said fundamental frequency for extracting harmonic frequency' energy from said stream.

8. Apparatus as in claim '7, wherein said tuned circuit means comprises an inductance and capacitance connected in parallel and coupled between said cathode and grid.

8 9; Apparatus as in claim 7, wherein said tuned circuit means comprises a cavity resonator tuned to said fundamental frequency. l0. High-frequency apparatus comprising means including a cathode and an accelerating electrode for producing a stream of electrons, a tuned input circuit coupled to said cathode and electrode, a pair of output electrodes aligned with the path of said stream and spaced from said accelerating electrode, and an output circuit coupled to said output electrodes, said out put circuit being tuned substantially to a har monic of the resonant frequency of said input circuit.

11. Apparatus as in claim 10 further including a drift tube member surrounding said stream" path and conductively connected between saidaccelerating electrode and one of said outputelectrodes.

WILLIAM W. HANSEN.

REFERENCES CITED The following references are of record inthe file of this patent:

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