US 3444486 A
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Description (OCR text may contain errors)
May13,1969 N. M.BANES ETAL 3,444,486
DIELECTRIC SUPPORTED POSITIONABLE INDUCTIVE TUNER FOR RESONATORS Filed Dec. 13, 1966 FIG.1.
INVENTORS NATHAN M. BANESfl/R. JOHN D. FEEHAN BY/FAYMOND M. STEPURA ATTORNEY 3,444,486 DIELECTRIC SUPPORTED POSITIONABLE INDUCTIVE TUNER FOR RESONATORS Nathan M. Banes, John D. Feehan, and Raymond M.
Stepura, Gainesville, Fla., assignors to Sperry Rand Corporation, a corporation of Delaware Filed Dec. 13, 1966, Ser. No. 601,476
Int. Cl. H01p 7/06 U.S. Cl. 33383 4 Claims ABSTRACT OF THE DISCLOSURE A turnable resonant cavity equipped with a longitudinally extensive dielectric tuning probe, one end portion of which is covered with a conductive material. The probe is variably inserted longitudinally into the resonant cavity to adjust the frequency thereof by varying the penetration of the conductive portion of the probe into the cavity magnetic field. Solely the uncovered dielectric portion of the probe slidably engages the cavity wall through which insertion is made.
The present invention generally relates to inductive tuners for cavity resonators and, more particularly, to a positionable inductive tuner requiring no sliding electrical contacts.
The use of a conductive rod or a dielectric slug for tuning cavity resonators is Well known in the art. Conductive rod tuning of a resonant cavity is accomplished by varying the penetration of the rod into the magnetic field of the cavity which in turn varies the inductance and changes the resonant frequency of the cavity. Such conductive rod tuning is not well suited for varying the resonant frequency of the cavity over a wide range. Wide range tuning involves substantial amounts of rod translation and requires the use of sliding electrical contacts in order to maintain electrical continuity between the inductive rod and the cavity walls over the full range of translation. Sliding electrical contacts are diflicult to fabricate and tend to become unreliable with extended use.
In the case of a dielectric slug, the resonant frequency of the cavity is changed by varying the penetration of the slug into the electric field of the cavity thereby presenting a variable capacitance. Although the requirement of sliding electrical contacts is eliminated when a dielectric slug is utilized, a new problem arises if vaporized metal is present in the vicinity of the dielectric slug. Such a condition exists, for example, where there is high density electron beam bombardment of grids in a reentrant cavity reflex klystron which causes vaporized metal to evolve from the grids. Vaporized metal tends to deposit on the cooler portions of the klystron interior, including the dielectric slug. The metal deposited on the dielectric slug provides a highly resistive path for the flow of current across the surface of the dielectric. This results in a lowering of the cavity Q which, in turn, lowers power output and efficiency.
Thus, the conductive rod technique is handicapped by the need for sliding electrical contacts whereas the dielectric slug scheme suffers from reduced cavity Q in the presence of vaporized metal,
One object of the present invention is to provide a wide frequency range cavity tuner requiring no sliding electrical contacts while maintaining maximum cavity Q even in the presence of vaporized metal.
Another object is to provide a wide frequency range inductive tuner for a cavity resonator requiring no sliding electrical contacts.
nited States Patent 6 ice An additional object of the invention is to provide a wide frequency range tuner for a cavity resonator having the respective advantages but not the disadvantages of conductive rod and dielectric slug tuners.
Another object is to provide a medium power, wide frequency range tuner for use above 10 gigahertz which does not have the severe mechanical tolerance problem of present designs,
These and other objects of the present invention, as will appear from a reading of the following specification, are accomplished by the provision of a longitudinally extendible dielectric tuning probe, one end portion of which is covered with a conductive material. The probe is inserted longitudinally into the resonant cavity whose frequency is to be varied so that the probe penetrates into the region where the magnetic field predominates. The conductive cladded end of the probe varies the effective volume of the cavity, as the probe is variably inserted or withdrawn, in the manner of a conventional conductive rod tuner. The uncladded portion of the probe has no effect upon the magnetic field but serves to guide and position the conductively cladded portion. The uncladded portion slidably engages the aperture in the cavity wall through which the tuning probe is inserted. The tuning probe is tapered to have a reduced cross-sectional area in the conductively cladded portion to prevent physical contact between said portion and the cavity wall.
For a more complete understanding of the present invention, reference should be had to the following specification and to the figures of which:
FIGURE 1 is a simplified cross-sectional view of the cavity tuner of the present invention utilized in a reentrant cavity reflex klystron; and
FIGURE 2 is a perspective view of the tuning probe utilized in the embodiment of FIGURE 1.
Referring to FIGURE 1, an electron beam represented by the dashed arrows 1 is generated by a conventional electron gun (not shown) and is directed into reentrant resonant cavity 2. The resonant frequency of cavity 2 is determined by the distance between grids 3 and 4 and by the extent of insertion of composite tuning probe 5 through an aperture 6 in the walls 7 of the cavity. Only the reentrant cavity portion of the klystron is depicted in the simplified drawing for the sake of simplicity and clarity of exposition. The detailed structure of a conventional reflex klystron is described in U.S. Patent No. 2,966,611, for Ruggedized Klystron Tuner, issued Dec. 27, 1960, in the name of L. H. Sandstrom and assigned to the present assignee.
The composite tuning probe 5 of FIGURES 1 and 2 comprises a rod of dielectric material which is conductively clad at tapered end region 8. A ceramic material 9 such as, for example, A1 0 is suitable for use as the dielectric material of probe 5. The dielectric material is metalized at portion 8 by conventional plating processes, for example, by first nickel plating and then copper plating in order to provide a highly conductive surface on the probe end region. The reduced diameter of the tapered end 8 of probe 5 prevents physical contact between the conductive surface of the probe and the cavity wall 7. Wall 7 slidably engages soley the larger diameter portion 9 of probe 5 which is unclad dielectric material.
Probe 5 may be variably inserted or withdrawn from cavity 2 upon the longitudinal translation of screw 10 in a manner now to 'be described. Screw 10 engages the inner threads 14 of hollow screw 11 whose outer threads 12 engage threaded end member 13. End member 13, after assembly, is held in place by means of set screws 15 and 16. Collar 17 threadably engages screw 10 and maintains heldical spring 18 in compression against end member 13. Collar 17 serves as a mechanical stop to limit the maximum insertion of probe upon contact with ring 19 which is fixed to cup 20. Bellows 21, which is attached at one end to the bottom of cup 20', and at the other end to screw 10, allows for the longitudinal translation of screw upon the rotation of screw 11. Screw 10 is rigidly attached to probe 5.
The pitches of inner threads 14 and outer threads 12 of screw 11 are difierentially related so that a given rotation of screw 11 causes a small amount of longitudinal translation of screw 10 whereby the insertion of probe 5 within cavity 2 may be closely controlled. The adjusted longitudinal position of screw 10 and probe 5 is held fixed by crimping the shoulder portion 23 of collar 17.
In operation, probe 5 is is inserted in cavity 2 in the region where the magnetic field predominates. The conductively cladded portion (end region 8) of probe 5 reduces the eifective volume of cavity 2 available to the magnetic field thereby increasing the resonant frequency of cavity 2 in the manner of a conventional all-conductive probe. Conversely, the resonant frequency of cavity 2 decreases as the probe is withdrawn from the cavity in a. direction away from the gap between grids 3 and 4. The uncladded dielectric portion of probe 5 serves to support the conductively cladded end region 8 at an adjustable position within cavity 2 to permit the adjustment of the cavity resonant frequency. The tapering of the end region 8 prevents physical contact with the cavity wall 7 and eliminates the requirement of sliding conductive contacts between probe 5 and cavity wall 7. Such physical contact is restricted to the uncladded dielectric portion of probe 5 in the manner of conventional all-dielectric probe tuners. Thus, the composite conductive and dielectric tuning probe of the present invention is characterized by the respective advantages of prior art inductive and dielectric tuners without suffering the disadvantages thereof.
While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and the changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.
What is claimed is:
1. A tunable resonant cavity having a passage extending through a wall thereof and communicating through an aperture with the interior of said cavity through which a longitudinally extendible probe is inserted,
the resonant frequency of said cavity being determined by the amount of penetration of said probe in said cavity, said probe comprising a longitudinally extending member slidably fitted within said passage in sliding contact with the walls thereof to be guided and positioned thereby,
the surface of one end portion of said member being dielectric material and the surface of the other end portion of said member being electrically conductive material, and
means for variably inserting said probe through said aperture and into said cavity so that only said dielectric material contacts the cavity wall surrounding said aperture and so that varying amounts of said other end portion of said member pentrates into the region of said cavity where the magnetic field predominates.
2. A cavity as defined in claim 1 wherein said probe comprises a dielectric material and the surface of said other end portion is covered with an electrically conductive material.
3. A cavity as defined in claim 1 wherein said other end portion of said probe is shaped so as to avoid physical contact with the walls of said cavity.
4. A cavity as defined in claim 1 wherein said other end portion of said probe is tapered to have a reduced cross-section relative to that of said one end portion.
References Cited UNITED STATES PATENTS 3,013,230 12/1961 Simkovich 33-83 3,308,402 3/1967 Grande 33-83 FOREIGN PATENTS 307,494 8/ 1955 Switzerland.
HERMAN K. SAALBACH, Primary Examiner.
L. ALLAHUT, Assistant Examiner.
US. Cl. X.R. 315-5 .53