US2840786A - Coaxial switch - Google Patents

Description

June 24,1958

c. F. SCHUNEMANN ET AL COAXIAL SWITCH Filed Jan. 19, 1952 15-12 FE 7.1 $57 T5 Car/ 3? Sc/zzmemazzzz w a T/zeooore R. ZYzorezz nited States Patent Olhce Patented June 24, 1958 CGAXIAL SWITCH Application January '19, 1952, Serial No. 267,246

2 Claims. (Cl. 333-7) This invention relates to a coaxial switch, and, more particularly, to the coaxial switch head assembly.

it is an object of this invention to provide a coaxial switch which will exhibit excellent mechanical performance and which, at the same time, will have the required electrical performance as judged on the basis of voltage standing wave ratio, cross talk and insertion loss.

Mechanically, a switch may be requiredto satisfactorily undergo more than 10,000 actuations and may be required to operate satisfactorily .under vibration, shock, low temperatures, high temperatures, sand and dust, humidity and high altitudes.

Another object of the invention is. to provide acoaxial switch which will operate satisfactorily under the above enumerated conditions.

Still another object of the presenteinventioniis to provide novel means for adjusting the-electrical properties of a coaxial switch.

Another and further object of the present invention is to provide means for mounting an inner conductor elbow in a switch rotor.

Still another and further object of the present invention is to provide means for mounting inner conductors in the switch body. 1 7

Other and further important objects of this invention will be apparent from the disclosures in thespecification and the accompanying drawings. 1

On the drawings: a

Figure 1 is an end elevational view of a coaxial switch embodying novelfeatures of the present invention;

Figure 2 is a longitudinal sectional view taken substantially along the line IIII of Figure 1;

Figure 3 is a cross-sectional view taken substantially along the line III-III of Figure 2;

Figure 4 is a cross-sectional view taken substantially along the line IV-IV of Figure 2;- and Figure 5 is a cross-sectional view taken substantially along the line V-V of Figure 2.

As shown on the drawings:

In Figures 1 and 2,-a coaxial switch is disclosed of the single-pole type, by way of illustration. It will, of course, be understood that thevnovel principles and teachings of the present invention may also be applied, for example, to a double-pole typeyswitch. V

In the particular switch shown, an axial terminal 11 is to be selectively connected to one ,of a pair of radial terminals 12 and 13 by meansvof a switch rotor 14 which is mounted for rotation about an. axis contiguous with the axis of terminal 11.

The switch rotor 14 is driven by means of a step-bystep actuating mechanism 15 which is mounted in a cup housing 16 secured to the switch head assembly body or stator 17. The actuating mechanism, which forms no part of the present invention, includes generally a sole noid motor 18, drivingjaws 19 and a drive shaft 20 connecting with the switch rotor 14. The arm 21 cooperates with an interrupter mechanism 22 to deenergize the solenoid motor after each step thereof. The switch mechanism 23 controls the movement of the switch rotor to one of its two preselected switching positions.

As best seen in Figure 3, a detent mechanism 24 serves to center the shaft 20 for precise location of the switch rotor 14 in one of the preselected switching positions.

An end plate 26 seals the open end of the cup housing 16 and is retained therewith by means of screws 27 shown in Figure 1. The switch head body 17has a large diameter cylindrical bore for receiving a central boss 29 of the end plate 26. Transverse flanges 30 and screws 31, Figure 1, serve to connect the switch head body 17 to the end plate 26. The entire switch may be mountedby means of the radiating mounting arms 32 which are best seen in Figure 1.

For purposes of attachment of coaxial cables to the terminals of the switch head, the terminals are externally threaded as indicated at 35. The split prongs 36 of inner conductors 37, 38 and 39, are adapted for receiving the inner conductors of coaxial cables attached to the switch. The switch rotor carriesan inner conductor elbow 40 for making circuit between the axial inner conductor 39 and one of the radial inner conductors 37 and 38. For permitting rotation between the inner conductor elbow 40 and the axial inner conductor 39, the inner conductor elbow 40 is providedwith an axial pin 41 for rotation within the prongs 42 of the axial inner conductor 39. For greater contact between the radial inner conductors 37 and 38 and the inner conductor elbow 40, the inner conductors and the elbow have complementary transversely extending semi-circular notches so that the inner conductors and the elbow will overlap when registered. To accommodate rotation of the rotor 14, the generally cylindrical metallic plug 45 of the rotor 14 has a reduced diameter to correspond to the spacing between the overlapping 7 ends 46 of the radial inner conductors 37 and 38. The

switch body 17 has a reduced bore portion closely re ceiving the reduced diameter half of the switch rotor 14.

Heretofore, it has been felt necessary in the coaxial switch art to have the insulating sleeves mounting the inner conductors made of the same material as that mounting the inner conductor elbow. According to the present invention, however, it has been found that the utilization of different dielectric materials improves the mechanical performance of the switch as well as the electrical characteristics of the switch.

Particularly advantageous results have been obtained by the use of Polytetrafiuoroethylene resin for the insulating sleeves 50, 51 and 52 which are used to mount the inner conductors 37, 38 and 39. This material, which is commonly referred to as Teflon, is satisfactory over the temperature range involved, has a low dielectric constant (approximately 2.2) and has low power 1055. Since Teflon has a coefiicient of thermal expansion of about 10 times that of steel or brass, it can be cooled to a low temperature and dropped into the terminal bores or passages. In order to prevent rotation of the Teflon sleeve, axial grooves 54 are formed in the inner walls of the terminals into which the Teflon will be extruded upon return to room temperature, as best seen in Figure 4. Thus the sleeves are retained against rotation even when subjected to low temperatures. The adaptor inserts 53 are force fitted into the terminal openings and retain the sleeves against outward displacement axially of the terminal bores. The ends of the sleeves 50, 51 and 52 have recesses 62, 63 and 64 therein with annular shoulders 65 abutting the inserts 53. As shown in Figure 4, the grooves 54 may be four in number. In the particular switch illustrated, the grooves may be from .010 to .014

inch deep and 11/16 in length.

The rotor plug in its peripheral face has a circular recess into which may be molded a disk of insulating material indicated by the reference numeral 56. The function of this disk 56 is to prevent contact between the inner conductor which is not registered with the arcuate conductor 40 and the plug 45. The material of this plug may be any suitable insulating material which will prevent cross talk in the switch to thedesired degree.

The inner conductor 40 is mounted in the rotor plug 45 by molding the insulating material therearound. The insulating elbow 57 thus formed serves to insulate the conductor 40.

Since Teflon cannot be molded into a metal structure, advantage of its low power loss cannot be taken in the switch rotor. It has been found that advantageous results can be obtained by the use of Polytrifluorochloroethylene resin. This material, which is commonly known as Kel-F, has the desired temperature characteristis and can be molded. Furthermore, the'KelF section dielectric constant approximately 2.3 is matched with that of Teflon by proper selection of relative diameters so as to minimize the discontinuity introduced by the use of different dielectric materials in the stator and rotor.

It has been discovered that the insulating elbow 57 may be advantageously retained in place by drilling a number of holes radially into the rotor plug as indicated in Figures 2 and by the reference numeral 58. When the insulating material is molded in the rotor, it extrudes into these holes to firmly hold the insulating elbow 57 in place. It has further been discovered that by the proper selection of the location of these holes 58, the electrical characteristics of the switch can be improved, as will hereinafter be explained.

It is believed that improved electrical characteristics are obtained by the proper selection of the location of the holes 58 in the rotor plug 45. It has been previously established that certain discontinuities in the conductors of a coaxial cable may be considered as capacitance shunting a transmission line or principle-wave equivalent circuit at the discontinuity. Such discontinuities occur between the outer conductor of the stator and the outer part of the rotor if mechanical clearance is provided. Such capacitance effect is also obtained where there is a discontinuity in dielectric material. Further, where there are changes in the diameter of one of the conductors, an effect occurs equivalent to that of a capacity shunting the line. Thus, in the present switch there would be an effective capacitance shunting the line at each end of the shoulders 59, 60 and 61 representing changes in the diameter of the outer conductor and further capacitance between the stator and the rotor portions of the outer conducotrs representing the mechanical clearance therebetween. It has been found that the holes 58 in the rotor plug likewise act as capacitances across the line. If, however, this capacitance effect produced by holes 58 is located an odd multiple of quarter wave lengths from the other capacitance effects, the capacitance introduced by these holes will tend to subtract from the capacitance introduced by the shoulders 59, 60 and 61 and the capacitance produced by the mechanical clearances between the stator and rotor; and this would tend to reduce deflection along the line and thus reduce the standing wave ratio. For example, if at a particular frequency the rotor path is about one wave length, and if the holes 58 are located at one-quarter of a wave length from one end, a beneficial effect would be obtained.

A further important discovery has been made, namely, that advantageous mechanical and electrical results are obtained by spacing the inner conductor sleeves 50, 51 and 52 from the insulating elbow 57 by means of annular shoulders 59, 60 and 61. These shoulders not only limit the axially inward expansion of the sleeves 50, 51 and 52, which might occur due to temperature changes, and provide the necessary clearance spaces 66, 67 and 68 between the rotor and the sleeves 50, 51 and 52, but the shoulders have also been found to improve the electrical performance of the switch when the dimensions of the shoulders are properly selected. In particular, it is believed that the spaces 66, 67 and 68 comprise air match sections for minimizing undesired electrical effects such as reflection due to the change in dielectric and due to the necessary clearance between the stator insulating sleeves 50, 51 and 52 and the rotor insulation sleeve 57. In the embodiment disclosed, the air match is achieved-by dimensioning the air sections provided by the shoulders 59, 60 and 61 to have characteristic impedances closely approximating those of the adjacent matched dielectric filled sections of the switch. 7

There is thus provided according to the present invention a rotary coaxial switch in which the superior electrical characteristics of Teflon are utilized as the stator insulation whilethe slightly difierent, but moldable, Kel- F is used in the rotor. 7

It will, of course, be understood that various details of construction may be varied through a wide range, depending upon the conditions, without departing from the principles of this invention, and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claims.

We claim as our invention:

1. In a coaxial switch having a stator including an outer conductor and a generally solid plug-type rotor having a passage therein whose wall provides an outer conductor and wherein the clearance between said stator outer conductor and said rotor outer conductor introduces a capacitance effect at a given frequency, the improvement which comprises said rotor having a hole opening into said rotor passage approximately an odd multiple of quarter wave lengths from the clearance between said stator outer conductor and rotor outer'conductor to provide a capacitance effect opposing the capacitance efiect introduced at the clearance.

2. A coaxial switch for operation with signals of a predetermined wave length comprising a stator having a rotor mounted therein, a plurality of coaxial lines extending into said stator and terminating in proximity to said rotor, said rotor having an interior surface defining an outer conductor passage extending between exterior surface portion of said rotor, an inner conductor extending within said outer conductor passage of said rotor, and a body of dielectric material supporting said inner conductor Within said outer conductor passage, said interior surface having a cylindrical bore communicating with said outer conductor passage intermediate the ends of said passage and extending to an exterior surface portion of said rotor, and dielectric material integral with said body of dielectric material and extending within said cylindrical bore, said cylindrical bore intersecting said outer conductor passage substantially an odd multiple of a quarter wave length from one end of said outer conductor passage to provide a capacitance effect opposing the capacitance effect introduced at the discontinuity between said one end of said outer conductor passage and the outer conductors in s'aid'stator cooperating therewith.

' (References on following page) 6 References Cited in the file of this patent published at Wilmington, Delaware by the Polychemicals Dept., E. I. du Pont de Nemours & Co., 174/ 110.6. 2 066 802 UNITED STATIIES PATENTS 5 Product Engineering Bulletin, No. 52, 1954, page 2, RfWntree at a 1937 published at Wilmington, Delaware by the Polychemicals 2,358,499 Fledler SePt- 1944 5 Dept., E. I. du Pont de Nemours & 00., 174/110.6. gjg g gspley "*"f June 92 Cold Treating Practice with Deepfreeze, Motor 2 1 3 i fi'a g 3 Products Corp., copyright 1946, pages 23-28. 6976 2; t A- 1951 Modern Plastics, June, 1946, pages 134 and 13s. 2565643 B dd 6 a P 1951 (Copy in Scientific Library and Div. 37.

i a 1 10 KEL-F Technical Bulletin 2-1-49, published Jan- OTHER REFERENCES uary 194 9, by M. W. Kellogg Co. (Copy in Div. 50.)

Plastics Bulletin, vol. 12, No. 46, 1950, page 185,

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