US 3618135 A
Description (OCR text may contain errors)
ilnited Statea Patent  Inventor Carroll 1E. Weller Cincinnati, Ohio ] App]. No. 9,220  Filed Feb. 6, 1970  Patented Nov. 2, 19711  Assignee Avco Corporation Cincinnati, Ohio  VARIABLE CAPACITOR 011* THE LOCKING TYPE 3 Claims, 7 Drawing Figs.
 11.8. CI 333/83 1R, 333/98 R, 151/31, 85/84  Int.Cl 111101p7/06, F16b 39/06, F16b 39/284  Field otsearch 333/97,98; 151/31; 85/84  References Cited UNITED STATES PATENTS 1,279,919 9/1918 Scusa 151/31 Primary Examiner- Herman Karl Saallbach Assistant Examinerwm. H. Punter Attorney-Charles M. Hogan ABSTRACT: The invention here disclosed is a variably positioned capacitance or susceptance element ofparticular utility in tuning striplines and cavities excited in the TEM mode. It is characterized by a bushing having an expansible segmented fore portion which projects through an aperture in the wall of the device being tuned, together with a locking screw arranged to force the segments into the edges of said aperture, thereby to assure favorable electrical characteristics and a secure lock of the setting of capacitance or susceptance.
PATENTEU rem/2 I971 .R mE (L TL NE V W WE L L O R R A C ATTORNEY.
VARIAIIIILIE IIAIPA'CI'IGR (IF THE LOCKING TIIIPIE BACKGROUND OF THE INVENTION AND OBJECTS One purpose of the invention is to provide a capacitor hav ing negligible series resistance and parasitic inductance. Correlatively, another object of the invention is to provide a capacitor having high values of Q and self-resonant frequency.
A further objective is to accomplish firm and secure mechanical locking without disturbing any one of many possible capacitance or susceptance settings.
The low loss capacitor in accordance with the invention is useful in ultra high frequencies and microwave frequencies. In one form it is used as a variable susceptance in the tuning of a wave guide.
DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following description of the accompanying drawings, in which:
FIG. I is a perspective view of a variably positioned capacitance element in accordance with the invention;
FIG. 2 is a sectional view through the end wall ofa coaxial cavity showing a longitudinal section of the FIG. 1 capacitance element as installed in place, and in association with an inductor;
FIG. 3 is an end view of the wave guide wall showing the location of wrench receiving apertures in the FIG. I capacitor;
FIG. I is a form of wrench suitable for use in adjusting the capacitor;
FIGS. 3 and 6 are longitudinal sectional views of modified forms of capacitance element in accordance with the invention;
FIG. 7 is an elevational sectional view of a preferred form of variable susceptance device in accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION Referring first specifically to FIG. 2, there is shown a section of the end wall ofa coaxial cavity II) in which is mounted an inductive element II (pictorially shown). The invention is useful in any tunable structure having distributed parameters. The coaxial cavity is tuned to resonance by means ofa cylindrical piece of metal which is variably positioned with respect to the inductive element II. In accordance with the invention, there is provided a structural tuning means in the form of a variably positioned tuning element I2 which is adapted to be fitted into an aperture in the tunable structure It) and to be variably projected into the resonant structure so as to tune it. The aperture I3 is circular in form as it opens out into the interior of the cavity. The rear portion of the aperture I3 is enlarged and provided with threads 14.
The variably positioned bushing I2 is hollow and its fore portion is multiply split as illustrated by slot IE to provide four or more arcuate segments such as 16 and I7. The rear portion of bushing I2 is enlarged or flanged and is formed with threads 18, complementary to threads Id, so that the bushing may be advanced or retracted into the aperture I3 and variably positioned as desired.
It is important that, when the capacitance parameter is predetermined by a selected positioning of the bushing 12, the bushing then be locked in place in such a manner as not to upset the capacitance parameter of the tuned cavity. For that purpose the bushing I2 is formed interiorly, near its front, with a' generally conical ball-containing compartment, converging towards the front and providing thrust surfaces I9. Locking means adapted to bear against said thrust surface 19 is provided in the subcombination of a setscrew 20 and a ball 21, confined within said conical chamber, said ball being generally the equivalent of a blunt nose on the setscrew in that the ball is advanced against the thrust surfaces, the ball being seated in a concave seat 22 on the front of the setscrew.
Referring now to FIG. I, there is shown a wrench, comprising a wafer 23 from which project four prongs, such as 26, 23 and 26, adapted to be seated in complementary depressions such as 26, 29 and 30, for example, formed on the rear face of bushing I2. The wafer 23 is manually turned to advance or retract bushing I2, as required. TI-Ie depressions are shown in FIG. 3.
Referring again to FIG. 2, the bushing is longitudinally threaded as shown at BI and the setscrew is threaded in complementary fashion. A slot 32, formed in the end of the setscrew permits its adjustment as a conventional screw.
When the coaxial cavity has been tuned to the desired frequency by positioning bushing I2, setscrew 20 is then ad vanced so as to push ball 21 against the thrust surfaces I9, thereby forcing the segments, such as I6 and I7, radially outwardly and into firm positive contact with the sidewalls of the aperture in the cavity. The expansion of the segments into contact with the sidewall is accompanied by negligible change in the capacitance between the elements II and I2. The positive metal contact between the segments and sidewalls of the aperture provides solid grounding and reduces the series resistance and the parasitic inductance of the capacitor.
A modified form of variably positioned tuning element is illustrated in FIG. 5. In this form the ball 211 is omitted and the wedging action for causing the segments of the bushing to expand is provided by forming the nose of the setscrew with a conical surface 33. Additionally, an integral nut formation 34 is formed at the rear of the bushing to provide for adjustment ofthe bushing, here numbered I2.
In FIG. 6, there is illustrated still another modified form in which the wedging action is obtained! by shaping the front of the locking screw in blunt-nosed bulletlike fashion, as indicated at 35. The exterior threads III of this bushing, extend substantially throughout its length. It will be understood that this bushing is adapted to be fitted into a threaded aperture of uniform diameter in the wave guide, thus simplifying machining operations for forming the aperture. Adjustment of the position of the FIG. 6 bushing I2" is accomplished by the use ofa nut formation 34'.
Referring now specifically to FIG. 7, the structural tuning means, here shown, comprises a. generally cylindrical susceptance element 36 together with the cooperating bushing element 63. The susceptance element 36 has three or more slots, having uniform angular displacement, cut as shown at 611. The slots cut into susceptance element 36 make it capable of bulging or expansion at its interface with wall It). The bushing element 43 is formed in accordance with the teaching of the FIGS. 2 and 6 embodiments, having a ball 2I of FIG. 2 and the continuous threads 18 of the FIG. 6 embodiment. The expression structural tuning means" as applied to FIG. 7 includes both the susceptance element 36 and the bushing 63. The last element is split to provide expansible segments, so that both elements have expansible portions.
In the FIG. 7 embodiment, the forward end of the susceptance element 36 is projected into the wave guide 10 a significant distance.
The susceptance element 36 is exteriorly threaded as shown at 38 and is formed at its trailing end with an integral nut 62, so that the susceptance element can be adjustably threaded into the threaded aperture 46 formed in wave guide 16', also into the threads 39 of collar 45.
Secured to the exterior of the wave guide It) is the metallic collar I5, formed with screw threads 39 in alignment with screw threads III.
The bushing 43 of FIG. 7 is exteriorly threaded to complement the interior threads 3'7.
In preparing for operation, the susceptance element 36 is first positioned as desired. Then the bushing 43 is advanced so that it projects slightly into the wave guide. Finally, setscrew 20 is advanced to cause expansion of the fore portions of the bushing 43 and the wall of susceptance element 36 to lock all of the parts in secure position.
When the wave guide is pressurized, a flanged cap 46 is screwed on to collar 45 and sealing is provided by a suitable gasket 47.
In the FIG. 2 embodiment, the expansible portions of the element 12 participate in the performance of the functions of tuning, locking and providing a secured ground. Similarly, in the embodiment of FIG. 7, the expansible portions of the susceptance element 36 participate in the functions of tuning, grounding and locking.
While there have been shown and described what are presently understood to be the preferred embodiments of the invention, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined in the appended claims.
1. For use in a tunable structure of the type having distributed parameters and formed with a receiving opening having a wall, the combination of:
structural tuning means adapted to be adjustably projected into said structure,
said structural tuning means comprising a variably positioned susceptance element adapted to be fitted into said opening and a bushing member adapted to project into said susceptance member,
said susceptance element and said bushing member being split to provide expansible portions, and
means for forcing said expansible portions outwardly against the wall of said opening to lock said structural tuning means in the desired position.
2. The combination in accordance with claim 1 in which the bushing is formed interiorly with thrust surfaces and in which the locking means wedges against said thrust surfaces.
3. The combination in accordance with claim 2 in which the susceptance element is exteriorly threaded adjustably to fit into the tunable structure,
the bushing is exteriorly threaded adjustably to fit into the susceptance element and the locking means includes a setscrew exteriorly threaded to fit into the bushing.
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