US2860281A - Resonant cavity structures - Google Patents

Description

Nov. 11, 1958 I A. J. YOUNG ETAL 2,860,281

RESONANT CAVITY STRUCTURES Filed May 11. 195.4

zi w w p xmmav [0457 48- United States Patent RESONANT CAVITY STRUCTURES John Ralph Bagnall, to English Electric a British Arthur James Young, Danbury, and

Chelmsford, England, assignors Valve Company Limited, London, England, company This invention relates to resonant cavities and more specifically to resonant cavities of the kind adapted to co-operate as tuned circuits with associated electron discharge tubes for ultra high frequency working.

For the sake of brevity andclarity of description the invention will be particularly described herein as applied to resonant cavities adapted to co-operate with associated so-called klystron tubes but, as will be obvious later, the invention is not limited to this particular application but may be used to advantage in all cases in which a resonant cavity is required to be associated with an electron discharge tube.

One important use of the invention-not, by any means, the only -one-is in radar apparatus. In many marine radar installations, and in other micro-wave equipment, there is a fixed frequency magnetron oscillator in cooperation with a klystron local oscillator, which'is employed to heterodyne the oscillations from the magnetron to a predetermined intermediate or beat frequency for superheterodyne reception. So far as the user of such equipment is concerned, his requirement as respects the tuning of the klystron local oscillator is merely that he must be able to tune it over the comparatively narrow band of frequencies over which the oscillations from a given magnetron, under given operating conditions, are in practice scattered. Unfortunately, however, due to inherent manufacturing difficulties, the manufacturer of a klystron, especially of a klystron for use on the shorter wave lengths, must invariably make his tube to accommodate a much wider spread of frequencies; in fact the maximum spread of frequencies from magnetron to magnetron in any specific equipment is, in practice, only a small fraction of that which the manufacturer of a klystron must accommodate.

For this reason it is common practice to provide two tuning adjustment controls for a klystron oscillator or other device using an evacuated electron discharge tube in conjunction with a tuning resonant cavity. The first is what may be termed a manufacturers control-i. e. an adjustment which is intended to be made by the manufacturer or by a maintenance engineer--and the second is what may be termed a users controli. e. a control actuated by a knob or handle which is convenientto the user. The manufacturer uses the first control to adjust the center frequency to a value at which the second control will tune over the range required when used in the equipment in question.

In the case of a klystron oscillator the manufacturers control is exercised upon the grid spacing, variation of which, of course, produces variation of the effective capacitance of the resonant cavity associated with the tube. The grid spacing is exceedingly small and a very small change in the gap produces a large change in capacitance. To quote practical figures, in the case of a klystron operating in the X-band a change of one thousandth part of an inch in the gap produces a frequency change of the order of 100 mc./s. This form of control involves that the whole resonant system must be ice enclosed within the evacuated envelope of the tube with the result that changes in external atmospheric pressure cause consequent minute, but none the less serious, changes in the relative mechanical disposition of parts within the envelope. In some cases the manufacturers control is in the form of a capacity electrode which can be adjusted across the cavity resonator and is set to provide the desired initial frequency. This control may be regarded as a trimmer capacity control auxiliary to the main capacity which is the grid gap. In practice, with an X-band klystron, this control will vary frequency by about 30 mc./s. per thousandth part of an inch. The users control is generally a variable inductance tuner.

The present invention seeks to provide a capacity tuning adjustment for a resonant cavity which will give a relatively wide range of control, does not involve locating the cavity or the adjustment member thereof within the evacuated envelope, which can be readily adjusted by the manufacturer or by a maintenance engineer and left ad justed for a long period-normally for the life of the associated tuba-and which is simple, durable and cheap to manufacture.

According to this invention a resonant cavity structure adapted to co-operate as a tuned circuit with an electron discharge tube for ultra high frequency working comprises a first electrode forming part of said structure and positioned to be in capacity coupling relationship with an electrode of a tube inserted in its normal position in said structure, a second electrode behind said first electrode (i. e. behind when viewed from said tube electrode) and means for adjusting the relative position of said first and second electrodes to cause the second one to project to an adjustable extent from behind the first one.

Preferably the first electrode is fixed and the second electrode is slidable over the back thereof.

Preferably also the second electrode is carried by a deformable member anchored to the cavity structure, means being provided to deform said member to adjust the position of the second electrode.

The invention is illustrated in the single figure of the drawing which is a part sectioned elevation of one embodiment of the invention as applied to a klystron tube and associated cavity resonator.

Referring to the drawing a klystron tube lt of the well known disc seal type is soldered into position in a cavity resonator structure 2. The klystron tube has the usual bottom and middle connector discs 3 and 4 respectively which are soldered in position in correspondingly shaped. apertures in the walls of the cavity structure. The upper fiat wall 5 of the cavity structure is provided. with a ringlike electrode 6 constituting a first capacity electrode extending partly across the cavity and in capacity coupling relationship with the inserted tube 1 to provide a fixed capacitance. This electrode 6 is, as will be seen, part of the structure of the top of the resonator structure 2. Behind the electrode 6 is a second capacity electrode or an adjustment 7 which is controllably slidable up and down (in the figure) over the back of the first capacity electrode 6 and in direct contact therewith. As it slides down its extent of projection beyond the lower edge of electrode 6 is varied. It is carried by a deformable member constituted by a ring diaphragm 8 whose outer edge is soldered to the top of the resonator or, as shown, clamped between the said top and the rest of the resonator. Means such as screws or bolts 9 with lock nuts 10 are provided to deform the diaphragm 8 and thus adjust the electrode- 7 over the back of electrode 6.

The arrangement illustrated gives a very fine adjustment and in the case of an X-band klystron a tuning rate of about 30 mc./s. per thousandth part of an inch movement of electrode 7 while a wide range of coverage is provided. In practice, adjustment is effected until the nor- U mally provided inductive tuner (not shown) covers the required band.

The invention has the advantage that it does not require the provision of any micro-wave chokes.

In manufacture the position of the electrode 6 is chosen to give an initial frequency near but a little above the top,

frequency of the intended band of use. If this is done the device will still operate satisfactorily if a given klystron tube is replaced (at the end of its life) by another of the same design and type: in other words, normal manufacturersvariations between klystron tubes of the same design are accommodated.

While we have described our invention in one of its preferred embodiments, we realize that modifications may be made, and We desire that it be understood that no limitations upon our invention are intended other than may be imposed by the scope of the appended claims.

We claim:

1. A resonant cavity structure adapted to co-operate as a tuned circuit with an ultra high frequency electron discharge tube comprising in combination with a resonant cavity structure a first capacity electrode in the form of an annulus which extends partly across the cavity, a second annular shaped capacity electrode radially behind the first capacity electrode and fitting close to the latter so that the inner surfaces of both electrodes are in sliding and good electrical contact therewith, said first and second capacity electrodes being adapted to form effectively a single capacitive electrode capacitively coupled to said discharge tube which constitutes the second capacitive electrode, and controllable means operable from outside said structure for adjusting the relative position of the first and second capacity electrodes whereby the second electrode can project to an adjustable extent from radially behind said first capacity electrode with respect to said discharge tube so as to vary the total effective area of said single capacitive electrode relative to said discharge tube.

2 A resonant cavity structure as set forth in claim 1, wherein the first capacity electrode is fixed and wherein the second capacity electrode is slidable over the back thereof relative to the discharge tube.

3. A resonant cavity structure as set forth in claim 1, which includes a deformable member carrying said second capacity electrode and anchored to the cavity structure, said controllable means including means for deforming said member to adjust the position of the second capacity electrode.

4. A resonant cavity structure for co-operating as a tuned circuit with an ultra high frequency electron discharge tube, the structure comprising a first capacity electrode of cylindrical form and encircling the tube, the first capacity electrode forming part of said structure, a second capacity electrode of cylindrical form and encircling said first capacity electrode and in good electrical contact therewith, said first and second capacity electrodes being adapted to form effectively. a single capacitive electrode coupled to said discharge tube, a, deformable ring diaphragm, the outer periphery of which is fiXed to said structure and the second capacity electrode being carried by the diaphragm at the inner periphery thereof, and means for deforming said member to adjust the extent to which said second capacity electrode projects from behind said first capacity electrode.

References Cited in the file of this patent UNITED STATES PATENTS

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