US2854532A

US2854532A - robson

Info

Publication number: US2854532A
Authority: US
Publication date: 1958-09-30
Anticipated expiration: 1975-09-30

Description

Sept. 30,1958 T. s. ROBSON TUNABLE CIRCUITS FOR HIGH FREQUENCIES 2 Sheets-Sheet 1 Filed Jan. 23, 1956 F1603 ll'Z/l) 1 5120276022,

Sept. 30, 1958 'r. $.'ROBSON- TUNABLE cmcuns FOR HIGH FREQUENCIES 2 Sheets-Sheet 2 Filed Jan. 23, 1956 men/2291 276.1530 bqjolz/ United States Patent TUNABLE CIRCUITS FDR HIGH FREQUENCIES Application January 23, 1956, Serial No. 560,844

Claims priority, application Great Britain January 27, 1955 6 Claims. (Cl. 179-171) This invention relates to tunable circuits for high frequencies and especially, though not exclusively to such circuits as used with disc seal valves.

When it is desired to amplify electrical signals of ultrahigh frequency so-called disc seal valves are often employed, the valves having input and output circuit in the form of co-axial line circuits. In order that a valve in such an arrangement can be replaced quickly it is usual to arrange that the anode circuit is folded back over the input circuit as described in U. S. patent specification No. 2,235,414. A disadvantage of this arrangement is that the input circuit is inaccessible and it is difficult to couple to the input circuit without increasing its length and making it operate with an electrical length containing more quarter wavelengths than would otherwise be necessary. In the event of the input circuit being operated as an open circuited line it is diificult to bring out the cathode and filament leads.

To maintain the advantage of the folded anode line circuit whilst rendering the input circuit more accessible it has been proposed to construct the anode circuit of two co-axial tubes both of considerably greater diameter than the outer tube of the input circuit. By this expedient, space is left between the two circuits for any coupling probes which are necessary. When the anode circuit is constructed in this way it will be appreciated that the anode circuit is in the form of a folded cavity resonator having, when considered in cross-section, two parts which though adapted to resonate as a single cavity are at right angles to each other, one being an annular part formed by the two co-axial tubes and the other being an inner part formed by discs which connect the inner ends of these tubes respectively to the control electrode and to the anode. It is usual to tune the anode circuit of a disc seal valve by means of a short circuiting ring which is disposed between the two conductors and can be moved along the axis of the conductors and so vary the electrical length of the resonator line formed thereby. However when both limbs of a folded anode circuit are of appreciable length, such tuning means introduce the disadvantage that the frequency range is limited by the inability of the short circuiting ring to come closer to the valve than the end of the two co-axial tubes. Therefore the highest frequency which it should be possible to reach with a given construction is not attainable,

The object of the present invention is to reduce this last-mentioned disadvantage and according to the present invention there is provided a tunable electrical circuit comprising a cavity resonator which is formed in at least two parts adapted to resonate as a single cavity and disposed at an angle to each other, and means for virtually varying a dimension of each of said parts to tune said resonator.

In one form of the invention, the resonator compnses an annular part and an inner part extending towards the axis of the annular part from one end thereof, and in this form of the invention the means for varying a d1- ICC 2 mension of each part of the resonator may comprise tuning means movable in an axial direction in said annular part and other tuning means movable in a radial direction in said inner part.

In order that the invention may be clearly understood and readily carried into elfect, the invention will be described with reference to the accompanying drawings, in which:

Figure 1 is a sectional elevation of an ultra-high frequency thermionic valve circuit employing a tuned circuit according to the present invention. 7

Figure 2 is a plan view of Figure 1 with the top cover of the anode circuit removed, and

Figure 3 illustrates a modification of Figure 1.

Referring to Figure 1, reference 1 represents a disc seal thermionic valve having an anode 2, control electrode 3 and a cathode 4. The input circuit of the valve is formed of two co-axial conductors 5 and 6 which are connected, .for high frequency currents, to the control electrode and cathode respectively of the valve 1. The signals to be amplified in the valve are injected into the input circuit by a coupling probe 7. The anode circuit of the valve comprises two concentric tubes 8 and 9 both of considerably greater diameter than the outer tube 5 of the input circuit so that a space is left between the two circuits for the coupling probe 7. The upper ends (in the drawing) of the tubes 8 and 9' are connected for high frequency currents to the control electrode and anode respectively of the valve 1. The connections are efiected by

co-axial discs

10 and 11, which have flanges 14 and 15 at their inner ends. These flanges are conductively connected to the anode 2 and control electrode 3 so that polarising potentials can be applied to the electrodes, but the flanges are insulated from the

discs

10 and 11 for direct current by insulating rings as indi cated. The anode circuit is therefore in the form of a cavity resonator comprising an annular part and an inner part extending towards the axis of the annular part from one end thereof, the inner part of the resonator being apertured so that a valve can be fitted to the resonator with electrodes of the valve electrically coupled to the Walls of the inner part of the resonator. The anode circuit is tunable by a sort circuiting ring 12 which is movable in known manner in an axial direction along the annular part of the resonator formed by the tubes 8 and 9, so as to vary the electrical length thereof. However the anode circuit has further tuning means in the form of short circuiting bars 13 which are disposed in the inner part of the resonator, namely between the

discs

10 and 11 at angularly spaced positions about the axis of the valve 1, these bars being movable in a direction perpendicular to the axis of the tubes 8 and 9 towards or away from the valve. In the present example the bars 13 are movable in the radial direction. The number of short circuiting bars 13 is not critical, three or four being for example suitable. In the present case four short circuiting bars are employed, as can be seen in Figure 2. The bars are curved in the present example but may alternatively be straight and when in their in ner most positions they may either form a closed ring, a closed square or some other configuration, close to and around the valve.

When tuning the anode circuit, for the range of frequencies covered by the short circuiting ring 12, the bars 13 are retained in their extreme outer positions as shown in Figure 1. When the short circuiting ring 12 is in the position nearest to the valve, namely the position indicated by dotted lines in Figure 1, the anode circuit can be tuned to a still higher frequency by moving the bars 13 towards the valve. Th highest frequency to which the circuit can be tuned is therefore, by virtue of the 3 invention, limited only by the size of the valve and its physical constants.

In the modification shown in Figure 3, the co-axial tubes 8 and 9 of the anode circuit are disposed above the valve so that the anode circuit is now in effect folded upwardly. The diameter of the inner tube 8 in this case has to be large enough for the valve to be replaced through it. This arrangement leaves the input circuit even more accessible than in the arrangement shown in Figure l.

The tuning mechanism for the circuit may include mechanical and electrical interlocking means for indi' cating which of the two tuning means should be employed, and to prevent the wrong one being used.

In one practical form of the invention, the valve 2 was an American type valve 4X150G. The short circuiting ring 12 enabled the resonant frequency and the anode circuit to be varied from 250 to 700 mc./s., with the resonator operating in the fundamental or lambda/ 4 mode. The short circuiting bars 13 then enabled the frequency to be varied from 700 mc./s. to 960 mc./s., the combined lengths of the two parts of the resonator being one foot long in-this example. Therefore by virtue of the invention it was possible to tune over a frequency range from 250 to 960 mc./s. with a comparatively compact circuit, operating as aforesaid in the fundamental mode.

What I claim is:

l. A tunable electrical circuit comprising a cavity resonator having an annular part and an inner part extending towards the axis of the annular part from one end thereof, said parts being adapted to resonate as a single cavity, tuning means movable in an axial direction in said annular part and other tuning means movable in said inner part in a direction towards and away from the axis of the annular part.

2. A circuit according to claim 1 wherein said inner part is formed with an aperture and a thermionic valve is fitted in said aperture with electrodes of the valve electrically coupled to the walls of said inner part.

3. A circuit according to claim 2 comprising a further cavity resonator electrically coupled to electrodes of said valve and disposed at least partly within the annular part of said first resonator, being spaced from the inner wall of said annular part, one of said resonators forming an input circuit for said valve and the other resonator forming an output circuit from said valve.

4. A circuit according to claim 2 comprising a further cavity resonator electrically coupled to electrodes of said valve and projecting to the opposite side of the inner part of the first resonator from the annular part thereof, one of said resonators forming an input circuit for said valve and the other resonator forming an output circuit from said valve.

5. A circuit according to claim 2 comprising a further cavity resonator electrically coupled to electrodes of said valves and disposed co-axially with the annular part of said first cavity resonator, said further cavity resonator being spaced from said annular part, one of said resonators forming an input circuit for said valve and the other resonator forming an output circuit from said valve.

6. A circuit according to claim 1 each of said tuning means comprising short circuiting means movable within the respective parts.

References Cited in the tile of this patent UNITED STATES PATENTS 2,525,452 Gurewitsch Oct. 10, 1950 2,554,501 Preist May 29, 1951 2,641,657 Preist June 9, 1953