US2591696A - High-frequency electron tube structure - Google Patents

Description

April 1952 w. w. HANSEN HIGH-FREQUENCY ELECTRON TUBE STRUCTURE Original Filed Oct. 25, 1941 INVENTOR BY MQ/VSE/V ATTO RN EY WILL/14M W.

Patented Apr. 8, 1952 UNITED STATES ATENT OFFICE HIGH-FREQUENCY ELECTRON TUBE STRUCTURE tion of Delaware Original application October 23, 1941, Serial No. 416,170. Divided and this application October 30, 1946, Serial No. 706,747

6 Claims. (Cl. 250-36) The present invention relates to the art including ultra high frequency electron discharge tubes, and is more particularly concerned with such tubes of the frequency multiplier type utilizing cavity resonators. The present application is a division of application Serial No. 416,170 filed October 23, 1941, which issued as Letters Patent No. 2,425,738 on August 19, 1947.

In Patent No. 2,280,824, issued April 28, 1942, in the names of Russell H. Varian and William W. Hansen, for Radio Transmission and Reception, there is disclosed a tube of the above type used as a frequency multiplier, in which the electron beam is bunched by one cavity resonator and excites a second cavity resonator tuned to a harmonic of the energizing frequency.

It is an object of the present invention to provide an improved form of frequency multiplier tube, wherein fewer cavity resonators are used and greater and more emcient outputs may be obtained.

It is a further object of the present invention to provide an improved frequency multiplier using a single cavity resonator.

It is a further object of the present invention to provide improved forms of cavity resonators suit able for use in tubes of the above type, and which are more compact and efiicient in operation.

It is a further object of the present invention to provide improved circuits for frequency multiplier tubes.

It is another object of the present invention to provide an improved ultra high frequency filter suitable for use with tubes of the present type.

Other objects and advantages will become apparent from the specification, taken in connection with the accompanying drawings wherein the invention is embodied in concrete form.

-- In the drawings,

Fig. 1 shows a longitudinal cross-section partly in elevation of a reflex-type frequency multiplier and its output circuit.

Fig. 1a shows a somewhat modified detail of construction.

Figs. 2-8 are explanatory diagrams useful in explaining the operation of the device of Fig. 1.

Fig. 9 shows a cross-section of a modified filter device suitable for use with the device of Fig. 1.

Referring to Fig. 1, the frequency multiplier of the present invention has a single resonator H formed of a substantially spherical portion I3 and two opposed re-entrant conical portions I5, it having respective central apertures 2|, 23. A focussing cathode structure l 9 (which may be of the type shown in Figs. 5 or 6-8 of parent application Serial No. 416,170 or any other type) is aligned with openings 2 l. 23 adjacent conical portion l5. A repelling electrode structure 25 is aligned with cathode I 9 and openings 2|, 23 adjacent conical portion Hi.

In operation, battery 21 is connected between cathode l9 and the grounded resonator II. In this way, cathode I 9 in conjunction with the accelerating electrode formed by the outerv face of re-entrant conical portion I5, projects a beam of electrons through exciting gridless openings 2 I, 23 of the re-entrant portions [5, I6 of resonator ll. Openings 2|, 23 may also contain electron permeable grids 66 and 6'! therein; it will be understood that the operation of the frequency multiplier with or without permeable grids would be substantially the same. The electron beam is then reversed by repelling electrode structure 25, which is held at a potential just slightly above that of cathode l9 by a connection to battery 27, and thus serves to reverse the beam and reproject it through the resonator openings 23, 2|.

Ordinary cavity resonators have a plurality of resonant frequencies, which, however, are not integral multiples of a fundamental frequency. By the special arrangement of the present inventlon, however, the resonator H can resonate at severa1 frequencies exactly harmonically related, as will be clear from the following explanation, referring to Figs. 2-7.

Referring to Figs. 2-4, it has been found that a resonator of the present type has a magnetic field B whose component of fundamental frequency in the median plane is given by sin k1- B1 kr where i being the wavelength and 1' being the radial distance from the center I! of spherical section l3.

The fundamental component of the electric field E in the median plane is given by central cross-section of Fig. 2, the magnetic field lines are circles cutting the plane of the section perpendicularly, and the electric field lines are arcs of circles in the plane of the section. These fields E1 and B1 are plotted against radial distance r, in Figs. 3 and 4.

Similarly, a third harmonic oscillation may be set up in the same resonator, whose electric and magnetic components in the median plane are given by cos Sit-r B sin 3101* ac- 3701' which are indicated in Figs. 5-7. The major principle of the device of Fig. 1 resides in setting up both of these oscillations simultaneously.

To explain the operation of the device let it be assumed that resonator H is oscillating weakly at the fundamental frequency f. The electron beam is then velocity-modulated on passing through resonator H, and is reversed in direction by repelling electrode structure to re-enter resonator H. With the bunching distance between opening 23 and repeller 25 properly adjusted (approximately to one-fourth the length of the drift space in the conventional two-resonator velocity-modulation tube shown in U. S. Patent No. 2,242,275) the field in the resonator will extract energy from the electrons and the oscillations will build up. However, the bunched a beam also contains harmonic frequency current components, which will excite resonator l l to oscillation at the harmonic frequency also. Since this harmonic frequency field will also velocitymodulate the electrons, it too builds up in resonator ll, but to a lower level than the oscillations of fundamental frequency. Since the harmonic field is always weaker than the fundamental field, most of the energy for maintaining the harmonic field comes from the harmonic in the bunching caused by the fundamental field. In this manner the resonator i l is caused to oscillate at both fundamental and harmonic frequencies, either or both of which may be extracted therefrom for useful purposes.

It will be apparent that the apparatus of Fig. 1 may serve as a self-sustained generator producing two frequencies simultaneously, or that a fundamental frequency wave may be supplied to resonator H, whereupon the device will produce harmonics in the same resonator.

To explain how resonator i! may be tuned to both fundamental and harmonic frequencies, ref erence may be had to Fig. 8, wherein is shown a simple cylindrical resonator 28. If a tuning paddle 22 is placed at A, the inductance of the resonator is reduced, increasing the resonant frequency. Placing the paddle 22 at 0 increases the capacitance and decreases the resonant frequency. For some intermediate position B, obtainable empirically, the paddle will not alter the resonant frequency for this mode of oscillation. In a similar manner, a position can be found where another paddle will not tune the harmonic oscillation. It can be shown that each paddle will tune one mode of oscillation and not the other.

This theory is applied to the frequency multiplier of the present invention. As shown in Fig. 1, two tuning paddles 29, 3! are inserted into the resonant cavity .ii to tune it to the fundamental and harmonic frequencies, respectively, the positions of the paddles being chosen as discussed above so that each tunes only a respective frequency. As shown, cavity H is completely evacuated. Hence re-entrant insulating sections 33, 35 serve to maintain the vacuum, while permitting eifective insertion of paddles 29, 3| into the resonant cavity. Paddles 29, 31 are adapted to be rotated byknobs 3?, 39 for tuning adjustment. Scales ii, 43 and pointers 45, 41 serve to indicate the paddle settings, and thereby the frequencies.

Energy is abstracted from resonator H by a coupling loop 69 and transmission line 5!. A filter, comprising a tuned resonant chamber 53, is inserted in this line, coupling loops 55, 51 serving as input and output to the resonant chamber 53. This chamber 53 is tuned to the harmonic frequency and passes only that frequency to the utilization circuit, the fundamental being reflected backv into cavity 4 I. It thus forms a very high Q filter.

If fundamental frequency energy is also desired, other coupling loops such as loop 58 may be used, together with suitable frequency selective devices. Loop 58 may also serve as a fundamental frequency input when that type of operation is desired.

Fig. 9 shows a filter which can be used in place of the resonator 53 of Fig. 1. Here the main transmission line 5: is joined by a parallel shortcircuited stub line 59. The stub line 59 is shown as having several sections 6 i 63, with differing diameters of central conductor.

If a 3:1 multiplication ratio is considered as an illustrative example, sections 65 and E! are selected to be one-quarter-wave long at the third harmonic frequency while section 63 is selected to be three-quarters wave long at this frequency. Hence the entire stub line 59 presents a very high shunt impedance to line 51 at the third harmonic frequency, and has little effect upon transmission of harmonic energy.

,At the fundamental frequency, however, sections 6! and 65 will be one-twelfth wave long, and. section 63 will be three-twelfths wave long. In adding the impedances of these sections, however, the effect of change in diameter of the central section, which causes a different characteristic impedance to exist there, must be considered. The enlarging of the central portion 63 has the effect of adding capacitance to the line. Hence the electrical length of the line will be greater than the physical length, which is /12 wavelength, and, by suitable choice of conductor dimensions may be made substantially exactly one-half-wavelength. Hence stub line 59 will present a short-circuit to wave energy of fundamental frequency, and prevent its transmission to the utilization device.

It is clear, of course, that similar principles may be used for any multiplication ratio, to permit passage of any desired harmonic while suppressing fundamental nd other harmonic frequencies.

While the present device has con illustratively described as producing a third harmonic, it will be understood that the invention is not so limited, since a wide range of harmonic frequencies can be obtained.

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:

1, High frequency apparatus comprising a cavity resonator, means for passing an electron stream through said resonator and for reflecting the same back thereinto for causing said resonator to resonate both at a fundamental and at a harmonic frequency, and means comprising tuning means difierently located within said resonator and selectively operated for tuning said resonator to one of said frequencies independently of the other.

2. High frequency apparatus comprising a cavity resonator, means for effecting recurrent passages of an electron stream through said resonator, one passage of said stream efiecting changes in velocity of the electrons of the stream resulting in electron bunching, and a second passage of said bunched stream through said resonator effecting the driving of said resonator, whereby the same oscillates at a natural frequency and at a harmonic thereof, tuning means comprising an adjustable conducting member projecting a desired distance into said resonator for varying the fundamental frequency of said resonator and independent tuning means comprising a second adjustable conducting member projecting a different distance into said resonator for varying the harmonic frequency thereof.

3. High frequency apparatus comprising an evacuated cavity resonator having a pair of opposed frusto-conical walls with aligned openings in their opposed inner smaller ends and also having a spherical segment wall connecting the enlarged ends of said frusto-conical walls, means including a cathode and repeller electrodes, said electrodes having concavefocussin surfaces for efiecting recurrent passages of an electron stream through and exteriorly of said resonator by way of said aligned openings, one passage of said stream producing changes in the velocity of the electrons of said stream resulting in electron bunching exteriorly of said resonator and the return passage of said bunched stream through said resonator effecting the driving of said resonator, whereby the same oscillates at a natural frequency and at a harmonic thereof.

4. High frequency tube structure as in claim 3 further including means comprising conduit and filter circuit means for selectively extracting en,-

'frusto-conical walls, means including a, cathode and repeller electrode for effecting recurrent passage of an electron stream through and exteriorly of said resonator by way of said permeable walls,

one passage of said stream producing changes in the velocity of the electrons of said stream resulting in electron bunching exteriorly of said resonator and the return passage of said bunched stream through said resonator effecting the driving of said resonator, whereby the same oscillates at a natural frequency and at a harmonic thereof, tuning members for independently tuning either of said frequencies of said resonator and means for selectively extracting energy at either one of said frequencies.

'6. Apparatus as in claim 5 wherein the smaller ends of said frusto-conical walls support electron permeable grids forming a gap acrosswhich an electron beam may be projected said extracting means including a conduit and a filter circuit connected therein.

WILLIAM W. HANSEN.

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

UNITED STATES PATENTS Number Name Date 2,114,114 Van Roberts Apr. 12, 1938 2,220,922 Trevor Nov. 12, 1940 2,222,899 Fraenckel Nov. 26, 1940 2,239,905 Trevor Apr. 29, 1941 2,253,503 Bowen Aug. 26, 1941 2,253,589 Southworth Aug. 26, 1941 2,280,824 Hansen et a] Apr. 28, 1942 2,289,220 Smith July '7, 1942 2,305,883 Litton Dec. 22, 1942 2,350,907 Kroger June 6, 1944 2,397,411 Dow Mar. 26, 1946

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