US2973485A - Electrical switching systems - Google Patents

Description

Feb. 28, 1961 s. M. HAMBERGER 2,973,485

ELECTRICAL SWITCHING SYSTEMS Filed March 24, 1959 3 Sheets-Sheet 1 44 69 52 45 5 I J, 62 H 70 45 0 U r m 2 2 l 1 29 1 74 I F 31 22 Fig.1 v

69 7o 65 l 73 51 7O 1961 s. M. HAMBERGER 2,973,485

ELECTRICAL SWITCHING SYSTEMS Filed March 24, 1959 5 Sheets-Sheet 2 INVEN'TOK SYDNEY xwsu. MFW'BFRQR Feb. 28, 1961 s, M. HAMBER}GER' I 2,973,485

ELECTRICAL SWITCHING SYSTEMS Filed March 24, 1959 3 Sheets-Sheet 3 40 -19\ 1 23 6 1 i J 6 25 14 I Q 3 9 i 22 5 26 26 i i 7 1511 8 Fig. 3

INVEN'NK ELECTRICAL SWITCHING SYSTEMS Sydney Maxwell to The General Electric Company Limited, London, England Filed Mar. 24, 1959, der. No. 801,560

Claims priority, application Great Britain Mar. 31, 1953 6 Claims. (Cl. 333-7) This invention relates to electrical switching systems.

It is an object of the invention to provide an electrical switching system which is adapted to connect a first coaxial conductor transmission line to any one of a plurality of other coaxial conductor transmission lines.

According to the invention, an electrical switching system includes a first coaxial conductor tranmission line, a plurality of further coaxial conductor transmission lines each having its outer conductor connected to the outer conductor of the first line, and an electric discharge device having a gas filled envelope, the device having its interior formed so as to provide a plurality of discrete regions in each of which a gas discharge plasma may be established and being provided with means to inhibit movement of a gas discharge plasma from any one of said regions to any other of said regions, the device being mounted so that said regions are respectively disposed between an end of the inner conductor of the first line and ends or" the inner conductors of the further lines, and the arrangement being such that upon setting up a gas discharge plasma in a selected one of said regions, the first line is effectively connected for the transmission of a signal to that one of the further lines whose inner conductor is associated with said selected one of said regions.

By a gas discharge plasma is meant a region in a gaseous electrical discharge where there is substantially no net electric charge, the number of positive ions and electrons being substantially equal.

One arrangement in accordance with the invention will now be described by way of example with reterence'to the accompanying drawings, in which:

Figure 1 is a plan view, shown with parts broken away, of a switching system designed to connect a first coaxial line to any one of four further coaxial lines and designed to operate at the so-called S band of frequencies;

: Figure 2 is a part sectional elevation of the system shown in Figure 1, the section being taken along the line Il1l of Figure 1; and

Figure 3 is a sectional elevation of an electric discharge device incorporated in the switching system.

Referring to the drawings, the switching system includes an electric discharge device having a glass envelope 1 filled with krypton at a pressure of about 4 millimetres of mercury. The envelope 1 includes a central tubular portion 2 which is closed at both ends, the portion 2 being of uniform circular cross-section and having an outside diameter of about 2 centimetres and a length of about 4.5 centimetres. The envelope 1 also includes four further tubular side portions 3 which project perpendicularly from, and open into, the central portion 2, the side portions 3 being spaced at equal angular intervals around the central portion 2 and being dis osed adjacent one end of the central portion 2 with their axes coplanar. Each side portion 3 has an overall length of about 3 centimetres, and the major part of each side portion 3 has an outside diameter of about 1 centimetre; that end of each side portion 3 remote from Hamberger, Chilton, England, assignor.

tts a o ice the central portion 2 is closed and is formed by an end portion 4, WhlCll has a slightly smaller diameter than the remainder of the portion 3.

Referring now particularly to Figure 3 of the drawings, the discharge device includes a circular cylindrical metal tube 5 which is sealed through the end of the central portion 2 remote from the side portion 3, the tube 5 having an outside diameter of 0.8 centimetre and a length of 5.8 centimetres, and being made of an alloy designed to match the thermal expansion of the envelope 1. The tube 5 is coaxial with, and extends through nearly the whole length of, the central portion 2. Four circular apertures 6, each of diameter 0.4 centimetre, are formed in the tube 5, so as to be respectively disposed opposite the four side portions 3 with the axes of the side portions 3 passing respectively through the centres of the apertures 6.

The discharge device also includes a thermionic cathode 7 in the form of a circular cylindrical metal cup 8, having an outer diameter of 0.5 centimetre, which is provided with an electron emissive coating on its outer surface. The cup 8 is secured coaxially inside the tube 5 opposite the apertures 6 so that the whole of each aperture 6 is backed by an electron-emissive surface. The cup 8 is located inside the tube 5 by means of three metal struts 10 (only two of which are seen in the drawings) and by means of a stud 11; the struts 10 secure the open end of the cup 8 to one end of a metal sleeve 12 tightly fitted inside the tube 5, and the stud 11 secures the base of the cup 8 to a metal cap 13 which serves to close the inner end of the tube 5. A heater filament 14 is disposed inside the cup 8, one end of the filament 14 being secured to the cup 8 and the other end of the filament 14 being connected to a relatively thick lead wire 15 via a connecting wire 16; the lead wire 15 is sealed through aglass dome 17 which is sealed to the periphery of the narrower end of a tapering sleeve 18 the wider end of which is secured inside the outer end of the tube 5. The wire 16 is located by virtue of passing through an apertured glass disc 19 sealed inside the open-end of the cup 8 and through an apertured ceramic disc 20 secured inside the sleeve 12, and that part of the wire 16 disposed between the disc 20 and the wire 15 is provided with an electrically insulatingsleeve 21.

Four metal caps 22 are respectively sealed over the tubular end portions 4, and four metal rods 23 are respectively sealed through the closed ends of the portions 4, the rods 23 being in electrical contact with the caps 22 and projecting coaxially inside the portions 4; those ends of the rods 23 inside the envelope 1 are each disposed 2.6 centimetres from the tube 5. Three of the rods 23 are solid, while the remaining rod is in the form of a copper pumping stem 23' (see Figure 1); the pumping stem 23' enables the envelope 1 to be evacuated and filled with gas during manufacture, the stem 23 being sealed oil when the desired pressure of gas inside the envelope 1 is obtained.

A glass screen 24 is mounted inside the envelope 1, the screen 24 including a main tubular portion 25 of circular cross-section, which fits inside the portion 2 of the envelope 1 with one end sealed to the end of the portion 2 adjacent the side portions 3. The screen 24 also includes four tapering tubular portions 26 of circular cross-section which project inwardly from the main tubular portion 25; the wider ends of the portions 26 have diameters corresponding approximately to the diameters of, and are approximately respectively in register with, the side portions 3. The free ends of the portions 26 effectively abut against the tube 5 and respectively surround the four apertures 6. Thus, the interior of the discharge device includes four discrete regions which are respectively defined by the portions 26 of the screen 24 in combination with the associated side the envelope 1.

Referring now to Figures 1 and 2 of the drawings which illustrate the complete switching system, the discharge device is mounted so that the tube 5 efie'ctively constitutes one end of the inner conductor 27 of the first coaxial line, while each cap 22 and associated rod 23 efiectively constitute'one end of the inner conductor 28 of one of the further coaxial lines. For this purpose the inner conductor 27 is provided with a series of spring fingers 29 which fit tightly around the tube 5 so as to connect electrically the rest of the inner conductor 27 to the tube 5, and similarly each inner conductor 28 is provided with a series of spring fingers 29 which fit tightly around the relevant cap 22 so as to connect electrically the rest of the inner conductor 28 to the cap 22 and the associated rod 23. v

Each inner conductor 27 or 28 includes a tubular portion 30 contiguous with the relevant spring fingers 29, and that end of the tubular portion 30 remote from the discharge device fits over one end of a rod 31 (see Figure 2) which also forms part of the relevant inner conductor 27 or 28. Each rod 31 is secured by means of a nylon screw 32 to an apertured partition 33 extending across the relevant tubular portion 30; each tubular portion 36 is electrically insulated from the relevant rod 31 with respect to direct current by means of an electrically insulating washer 34 which is trapped between the rod 31 and the relevant partition 33 and by means of an electrically insulating sleeve 35 which is trapped between the rod 31 and the surrounding part of the tubular portion 30. p

The outer conductors 36 of the further coaxial lines are contiguous with the outer conductor 37 of the first coaxial line so that the outer conductors 36 and 37 are all electrically connected together. The outer conductors 36 are linked to the outer conductor 37 by means of a central member which consists essentially of a generally circular cylindrical block 38 and a tubular member 39. The block 38 has formed in it four elongated recesses 74 of circular cross-section which are respectively arranged to accommodate the side portions 3 of the envelope 1 with the axes of the portions 3 respectively coincident with the axes of the recessesM. The block 38 is formed by two separate parts 40 and 41 to enable the discharge device to be removed from the switching system. (Half of the part 43 is shown broken away in'Figure 1 for the sake of clarity.) The parts 40 and 41 are normally secured together by means of a number of screws 42 the heads of which engage in the part 40 and the shanks of which screw into threaded holes 43 formed in the part 41; two locating pins 44 project from the part 41 and respectively fit inside two holes 45 formed in the part The part 46 is provided with a circular aperture 46 which accommodates part of the centralportion 5: of the envelope 1.

One end of the tubular member 39 is in the form of a relatively thin-walled portion 47 which fits into a circular recess 48 formed in the outer main 'face of the part 46, and the member 39 is secured to the block 38 by means of screws 69 the headset which engage with an outwardly projecting circumferential flange 50 formed on the member 39.

The outer conductors 36 respectively include four main tubular portions 5 and the adjacent ends of the tubular portions 51 respectively fit in four shallow recesses 52 formed in the block 38; the arrangement is such that the inner surfaces of the portions 51 are respectively in register with the relevant recesses 74. The tubular portions 51 are respectively secured to the block 38 by means of four clamping members 53 which respectively engage with four outwardly projecting circumferential flanges 5% formed on the tubular portions '51. Each clamping member 53 includes an externally threaded portion 55 which screws into the block 38; and the relevant flange 54 is trapped between the free end of portions 3 of d the threaded portion 55 and a circumferential shoulder 56 formed in the block 38.

Similarly, the outer conductor 37 includes a main tubular portion 57, and that end'of the tubular portion 57 adjacent the outer conductors 36 fits into a shallow recess 58 formed in the tubular member 39, the arrangement being such that the inner surface of the tubular portion 57 is in register with the inner surface of part of the tubular member 39. The tubular member 57 is secured to the tubular member 39 by means of a clamping member 59 which screws into the tubular portion 39 and holds an outwardly projecting circumferential flange 60 formed on the tubular portion 59 against a shoulder 61 formed in the tubular member 39.

The tubular portion 59 is provided with a coupling 62 to enable the portion 59 to be connected to a further section of the outer conductor 37, and the tubular portions 51 are provided with similar couplings (not shown).

Electrical connections for applying operating voltages to the electrodes of the discharge device are provided as follows. A small circular hollow projection 63 having an internal screw thread is formed on each tubular portion 30, and a metal tube 64 of circular cross-section is secured to the projection 63 by means of a hollow bolt 65, the tube 64 having an outer diameter corresponding to that of the relevant projection 63; the shank of the bolt 65 passes through, and is a sliding fit within, the tube 64, and the end of the bolt 65 screws into the relevant projection 63. The tube 64 extends through a circular aperture 66 formed in the relevant tubular portion 51 or 57, and a tubular stub 67 of circular cross-section surrounds each tube 64, the stub 67 projecting away from the relevant tubular portion 51 or 57 and one end of the stub 67 being sealed to the periphery of the relevant aperture 66. (It should be appreciated that, in Figures 1 and 2, one of the stubs 67 associated with the outer conductors 36 is shown broken away.) The other end of each stub 67 is provided with an outwardly projecting peripheral flange 68, and a metal disc 69 is secured to the flange 63 by means of nylon screws 70, the periphery of the disc 69 being in register with that of the flange 68. An annular sheet 71 of polythene is trapped between the disc 69 and the flange 68 so as to insulate electrically the disc 69 from the relevant stub 67. An aperture 72 is centrally formed in each disc 69, and that port of the disc 69 bounding the aperture 72 is trapped between the head of the relevant bolt 65 and the adjacent end of the relevant tube 64. Thus, it will be appreciated that besides a providing an electrical connection between the relevant disc 69 and tubular portion 30, each bolt 65 and its associated tube 64 serve to support and accurately locate the relevant tubular portion 30 inside the associated outer conductor 36 or 37. The length of each stub 67 is so chosen that the relevant disc 69 is spaced from the associated tubular portion 30 by a distance equal to a quarter of the wavelength corresponding to the mean frequency at which the switching system is designed to operate; it should be appreciated that the suse of such an arrangement enables an electrical connection with respect to direct current to be made to each inner conductor 27 or 28 without any significant impedance discontinuity with respect to microwave energy appearing in operation in the relevant transmission line. A pin 73 is secured to each disc 69 to provide an electrical contact; it will be appreciated that a voltage applied to a pin 73 will be applied either to one of the rods 23 or to the tube 5 and cathode 7. In operation, the outer conductors 36 and 37 of the coaxial lines are connected to earth.

The lead wire 15 of the discharge device projects from that bolt 65 associated with the outer conductor 37, the wire 15 being provided with an electrically insulating sleeve 75 so as to insulate electrically the wire 15 from the relevant bolt 65.

75 current is passed through the filament 14, and a positive voltage is applied to the rod 23 corresponding to that one of the further coaxial lines which it is desired to connect to the first coaxial line, a switching mechanism (not shown) being provided so that this voltage can be applied to any preselected one of the rods 23. The applied volage is in the form of short pulses, a few microseconds in duration and spaced apart by intervals of the order of a hundred microseconds; the amplitude of the pulses is such that a current of a few amperes will flow between the cathode 7 and that rod 23 associated with the selected further coaxial line.

' A gas discharge plasma is thus set up and maintained I between the cathode 7 and the selected rod 23, the voltage applied to the selected rod 23 being such that the gas discharge plasma is sufiiciently dense to enable a radio frequency signal to be transmitted between the first coaxial line and the selected further coaxial line with little attenuation of this signal.

It should be appreciated that a gas discharge plasma is continuously maintained in the desired region of the device by virtue of the fact that such plasma remains for a short period (of the order of a few hundreds of microseconds) after each current pulse has terminated; by using short pulses of current instead of a continuous current the noise generated by this discharge is considerably reduced.

It should be appreciated that the presence of the glass screen 24 in the envelope 1 prevents the gas discharge plasma from moving into the regions of the gaps between the cathode 7 and the other rods 23, such movement being liable to cause poor transmission between the first coaxial line and the selected further coaxial line. It should be understood that the diameters of the outer conductors 36 and 37 of the coaxial lines are sufliciently small to ensure that the cut-oif frequency of the outer conductors 36 and 37, as regards propagation in a wave-guide mode, is higher than the highest frequency at which the switch is designed to be used. Thus, in the absence of any gas discharge plasma, any radio frequency signal passing between the first coaxial line and any one of the further coaxial lines will be greatly attenuated. It will be appreciated that the gaps between the inner conductor 27 and the inner conductors 28 should be sufficiently large to provide the required attenuation in the absence of any gas discharge plasma.

It should be understood that, in alternative arrangements to that described above by way of example, it may be possible for the electrical switching system to employ a cold cathode electrical discharge device and also it may be possible for the side electrodes to act as cathodes and for the electrode disposed in said central tubular portion of the envelope to act as the anode of the device. Furthermore, whereas in the arrangement described above, the gas discharge plasma is produced by what is in efiect a direct current discharge, it should be understood that it may be possible to produce a gas discharge plasma by means of an electrodeless discharge, for example by applying a suitable radio frequency field across that part of the device wherein it is desired to produce the discharge.

It is to be noted that the electric discharge device described above forms the subject of copending British patent application No. 10,322/58.

I claim:

1. An electrical switching system comprising: a first coaxial conductor transmission line having an inner conductor and an outer conductor; a plurality of further coaxial conductor transmission lines each having an inner conductor and an outer conductor, the outer conductor of each of said further lines being connected to the outer conductor of said first line; and an electric discharge device having a gas-filled envelope, the device having its interior formed so as to provide a plurality of discrete regions in each of which a gas discharge plasma may be established and being provided withmeans to inhibit movement of a gas discharge plasma from any one of said regions to any other of said regions, the device being mounted so that said regions are respectively disposed between an end of the inner conductor of said first line and ends of the inner conductors of said further lines.

2. An electrical switching system according to claim. 1, in which said ends of the inner conductors of the first and further lines are eifectively constituted at least partly by electrodes disposed within the envelope of the discharge device.

3. An electrical switching system according to claim 2, in which the envelope of the discharge device includes a first straight tubular portion and a plurality of further straight tubular portions, the axes of the tubular portions all meeting at substantially the same point, that electrode of the discharge device which is associated with the first line being constituted by a metallic structure extending along the length of said first tubular portion, one end of the metallic structure being disposed adjacent said point, and those electrodes of the discharge device which are associated with the further lines being respectively disposed in said further tubular portions.

4. An electrical switching system according to claim 3, in which said metallic structure includes a thermionic cathode disposed at the end of the structure adjacent said point.

5. An electrical switching system as set forth in claim 3, including a screen of electrically insulating material disposed inside the envelope, the screen including a plurality of tubular portions respectively associated with said further tubular portions of the envelope, one end of each tubular portion of the screen effectively forming a continuation of the relevant tubular portion of the envelope, and the other end of each tubular portion of the screen effectively abutting against said metallic structure.

6. An electrical switching system as set forth in claim 5, in which said metallic structure includes a tubular member inside which is disposed a thermionic cathode, a

number of holes being formed in the wall of said tubular member to permit electrons to flow in operation from the cathode to any one of those electrodes associated with the further lines to which a suitable potential has been applied, and that end of each tubular portion of the screen adjacent said tubular member surrounding at least part of at least one of said holes.

References Cited in the file of this patent UNITED STATES PATENTS 2,557,961 Goldstein June 26, 1951

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