US2749524A - Switching devices - Google Patents

Description

June 1956 1.. A. DEROSA ET AL 2,74%524.

SWITCHING DEVICES Filed April 1, 1952 2 Sheets-Sheet 2 INVENTORS LOUIS A DE RosA FRANCS x. BUCHER BY THEODORE u QOLDAN ATTORNEY United States Patent SWITCHING DEVICES Louis A. Derosa, Bloomfield, Francis X. Bucher, Nutley, and Theodore J. Goldan, Clifton, N. 3,, assignors to International Telephone and Telegraph Corporation, a corporation of Maryland Application April 1, 1952, Serial No. 279,872

Claims. (Cl. 333-97) This invention relates to switching devices and more particularly to a rapidly operated mechanical type of switching device for microwave energy.

In direction finding systems it is sometimes desirable to have several antennas or antenna arrays for complete coverage of 360 azimuth, each antenna being located and so designed as to cover a particular angle in azimuth, such for example as 90 where fourth such antennas are provided. Such provision of separate antennas may be required at spaced locations on board a ship or from other structure comprising the site for the direction finding system. Where such an arrangement is provided, it is important to switch or couple the antennas sequentially at a rapid rate to a receiver for continuous indication throughout the 360 scanned. Bearing in mind the switching requirements of such an antenna system, it is an object of the present invention to provide a switching device for rapidly coupling sequentially a plurality of circuit connections or connections from a plurality of antennas to a common connection with a minimum of transition time loss.

Another object is to provide a switching device having a minimum of insertion loss over a frequency bandwidth varying from D. C. to the centimeter wavelength region.

Another object of the invention is to provide switch sectors having a high degree of decoupling therebetween.

Still another object is to provide a switch having a given characteristic impedance through the transition couplings to the switch sectors and through such sectors to a common switching connection associated with such sectors.

A further object of the invention is to provide switch sectors of novel conductor arrangements.

One of the important features of the invention is the provision of a strip-line transmission sector arrangement for co-action with a rotatable contact member; and another important feature is the matching characteristic of the transition coupling between a coaxial line and the strip-line sector. The strip-line sectors are mounted in close spaced relation adjacent the surface, preferably planar, of a simulated ground conductor and in coupled relation to coaxial lines for energy propagation in substantially TEM mode. The strip lines are spaced a much smaller distance from the planar surface of the ground conductor than the spacing between the inner and outer conductors of the coaxial line. This close spacing insures a concentrated electric field, almost entirely between the opposed surfaces of strip line and ground conductor. The distribution of the field beneath the strip line is symmetrical to that of its image formed in the plane surface of the ground conductor. This form of field distribution provides for energy propagation therealong in substantially a TEM mode, other high order modes established by any physical discontinuity being rapidly attenuated in the region of such physical discontinuities. By this close spacing of the parallel conductors and, by making the strip ICC very thin, radiation losses and intersector coupling are greatly minimized.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein;

Fig. l is a view in end elevation of the switch shown connected in circuit to antennas and a receiver-indicator;

Fig. 2 is a cross-sectional view of the switch taken substantially along line 22 of Fig. 1;

Fig. 3 is a view in crosssection showing the plan of the sector arrangement taken substantially along line 3--3 of Fig. 2;

Fig. 4 is a fragmentary sectional view of a transition coupling between a coaxial line and the strip line taken substantially along line 4-4 of Fig. 3;

Fig. 5 is a fragmentary view of two adjacent strip-line sectors illustrating the field distribution at the gap between sectors;

Figs. 6 and 7 are cross-sectional views of a coaxial line showing the field distribution therein, first where the center conductor is coaxial of the outer conductor and second, where the center conductor has been displaced laterally within the outer conductor;

Fig. 8 is a cross-sectional view of the strip-line connection of a switch sector taken substantially along line 8-3 of Fig. 3; and

Figs. 9 through 12 are cross-sectional views similar to the view in Fig. 8 showing alternative forms of strip line that may be used.

Referring to Fig. 1 of the drawing, the switch of the present invention is shown in end elevation with connections indicated diagrammatically to four antennas 1, 2, 3, and 4. The antenna are coupled to the switch 5 through individual goniometers 6, 7, 3, and 9 through coaxial lines which are coupled to the switch as indicated at 10, ll, 12, and 13. The switch 5 is provided with a common output connection 14 which is coupled to a receiver and indicator unit 15. While four sectors are here shown, it will be understood that a less or greater number of sectors may be provided whichever is desired.

Referring to Figs. 2, 3, and 4, wherein the details of the switch are shown, it will be noted that the input coaxial line coupling 13 is shown with the outer conductor 16 thereof connected to a cylindrical wall 17 which in part houses the switching elements. One end of the switch housing is formed by an end wall 18 which may be integral with the cylindrical wall 17, or may comprise a separate part suitably secured thereto. The opposite end wall 19 is removably secured to the cyiindrical wall 17 and contains therein a passageway 20 for the output coupling 14. The inner conductor 21 of the coupling 14 is provided with a brush 22 suitably shaped with respect to the dimensions of the passageway 20 to provide proper impedance match with the coaxial line of the coupling 1%. The end wall 18 is provided with a bearing 23 through which a shaft 24 projects from a motor 25. Carried by the shaft 24 is a brush support 26 of insulating material. The support 26 carries a conductive spindle 27 mounted axially of the shaft 24 and a laterally disposed conductor 28 arranged to support a brush 29 for sliding engagement with switch sectors 3% 31, 32, and 33. The brush 22 of the coaxial output 14 engages the spindle 27 whereby a conductive path from the sectors to the output coupling is provided.

The end plate i9 is provided with an annular planar surface 34- to which is clamped, as indicated at 36, a dielectric plate 35, such for example as glass, polystyrene, polyethylene, Teflon or Mycalex. T he switch sectors fill, Ill, 32, and 33 may be bonded or otherwise applied to the dielectric plate 35 by known printed circuit techniques, each sector comprising an are extending through nearly 90 and a central radial input connection as indicatcd at 3'7, Fig. 3. The length of each arcuate section, however, is preferably a small fraction of a wavelength of the highest frequency, such for example about or less. The center conductor 33 of the coaxial connection 13 has secured thereto a fiat conductive strip 39 which extends into the switch housing and is angularly disposed toward the end plate 15. The angular disposition t conductive strip 39 is such that when the end plate 19 is secured to the wall E7, the strip 39 will bear in conductive contact with the input strip 37. If desired, the strip 39 may be soldered or otherwise made integral with the couductor strip 37. The plate 19 has four curved recesses 19a which constitute transition surfaces between the outer conductor it: and the planar surface 34.

Before summarizing the operation of the switcn, attention is called to the illustrations shown in Figs. 5, 6, 7, and 8. in Fig. 6, a coaxial line is shown comprising an outer conductor 4 and an inner conductor 41. Where the inner conductor is truly coaxial of the outer conductor the electric field may be re resented by a plurality of equally spaced radial lines 42. When the inner conductor ll is moved from its coaxial position toward the outer conductor as indicated at iln, Pig. 7, the field distribution radically changed, the field being highly concentrated between the conductor surfaces most closely disposed. T is concentration is indicated at if the inner conductor is brought quite close to the outer conductor, the portion of the outer conductor furthest from the inner conductor may be cut away without materially affecting the electric field. Such a conductor arrangement is illustrated in Fig. 8 which comprises a crosssectional 'v'lfiW taken along line ti3 of Fig. 3. in this illustration, the planar surface 34 of the wall simulates the outer or ground conductor and the strip 37 the inner conductor. The two conductors are separated by dielec tric plate 35.

The transition between the coaxial line coupler l3 the sector conductor arrangement is best shown in Pig. The wall It? is provided with an opening 17a which coincides with the inner diameter of the outer conductor 1%. The plane of the surface 3 of the end plate 19 intersects the opening 17a, the curved recess 19:: of the plate providing a transition between the inner surface of the outer conductor l6 and the planar surface 34. By this transition the electric field changes from the distribution indicated in Fig. 6 to a concentrated field between the strip conductor 37 and the planar conducting surface 'By suitably proportioning the sector to which the conductor 37 is connected, the signal current received by the associated antenna is conveyed thereto and periodically conducted away by movable contact 29.

It is found that by making the spacing between the conductor strip 37 and the planar conductor surface 3% very small compared to a wavelength of the electromagnetic energy transmitted over the coaxial line, that the electric iield is concentrated almost entirely between the opposed surfaces of the conductor strip 37 and the surface 34. By way of example, for a frequency of between 200 and 400 megacycles per second the conductive strip 357' was chosen of a width of 0.321 and a thickness of 0.002 with a spacing between the strip and the surface 34 of 0.032". These particular dimensions were chosen for an impedance match to a ohm coaxial line. These dimensions, of course, are illustrative only, it being understood that a wide selection of dimensions and proportions may be made without departing from the invention.

The strip conductor used in one preferred embodiment was Rhodium foil. Other materials which are tarnish and wear-resistant, such as platinum-iridium as well as certain alloys, may also be used. The brushes 22 and 29 are preferably of soft, resilient, tarnish-resistant matel rial, an example being a multiple wire brush of spring gold alloy known as Baker & Co. #559. The energy flow along the strip is believed to be mostly in the conductor skin nearest the ground conductor except at the point of brush contact where the energy currents how to the upper surfaces and through the brush contact.

The strip conductor may be applied by any known printed circuit technique or may comprise strip conductors prccut and cemented to the dielectric plate. Cure printed circuit technique that may readily used is where the other conductive layer is applied to a dielectric plate, coated in accordance with the conductive configuration desired, and then placed in an etching bath, whereby the uncoated conductive material is removed, leaving the desired conductive configuration.

An important feature of the invention is the decoupling between adjacent switch sectors. in Fig. 5, adjacent sectors 3t and 3 :e illustrated with the dielectric material removed to best indicate the electric field between the sectors and the conductive surface 34. By making the spacing between the sector strips and the surface 34 small compared to a quarter wavelength the electromagnetic energy, the field is confined substantially to the area di ectly underlying the sector strips 3:? and This enables close spacing of the ends of the die-cent sectors with a minimum of coupling. With the dimensions as stated above, the gap between adjacent sectors was selected as small as 0.020". With this dimension the coupling between adjacent sectors was found to be below 100:1 for frequencies ranging between 200 and 460 megacycles.

To summarize the operation of the switch, the antennas 1, 2, 3 4 may be arranged in any desired way and in one application may be disposed at right angles to each other so as to cover individually azimuth sections of the group thereby covering total of 366. The signal energy received by the antennas is coupled through goniorncters, suitably synchronized with the speed of the motor 25, to the switch sectors as, 31, 32, and 33. The brush 2? is rotated in contact with the sector strips at a high rate, whereby the field covered by the individual antennas are scanned sequentially and the signal energy conducted therefrom is applied through output coupling to the receiver-indicator unit 15. in this manner, direction finding indications for the complete 360 may be obtained. It should be understood, however, that the switch may be used in the reverse, that is the coupling IA- may comprise an input coupling whereas the couplings ill, ll, l2, and 13 may comprise output couplings for sequentially feeding a plurality of antennas or other circuitryt it should also be understood that the switch sectors may comprise a less or greater number than the four here illustrated.

In addition to the particular strip-line formation of thc conductor sectors, shown in Figs. 2 to 5 8, other forms may be used. As shown in Fig. 9, the dielectric strip may have a pedestal-like ridge 4-3 upon which the conductive strip 46 is carried and spaced with reference to a planar conductor 47. The lateral extent of the dielectric plate may be varied as desired. in Fig. 10, the planar conductor may be provided with a ridge adapted to carry a strip of dielectric material 49 on which is carried a strip conductor 56. Each of the forms shown in Figs. 9 and 10 tend to minimize any tendency for lateral spreading of the electric field.

In Fig. 11 the planar conductor 51 is provided with a groove or open channel 52 in which a dielectric 53 may be disposed for the purpose of supporting a conductor strip 54. In Fig. 12 a similar conductive arrangement may be provided wherein the channel is of the semicircular shape in cross-section as indicated at 55 and the strip may be in the form of a round wire 56 supported on dielectric '57 contained in the trough 55. The conductor 56 may be partly embedded in the dielectric if desired. In addition to these forms, other strip line coufigurations and supporting arrangemnets will be readily apparent to those skilled in the art.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made by way of example only and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.

We claim:

1. A switching device for coupling high frequency electromagnetic energy sequentially between a given one and the others of a plurality of coaxial connectors, comprising a conductor body having an extended surface connected to the outer conductors of said coaxial connectors, a plurality of sector conductors, means disposing said sector conductors in close spaced substantially parallel relation to said surface, the spacing of said sector conductors with respect to said surface being a fraction of the radial spacing of the inner and outer conductors of said coaxial connectors, means coupling each of said sector conductors to the inner conductor of one of said coaxial connectors and a movable conductor coupled to the inner conductor of said given connector for movement in coupled relation to said sector conductors to electrically couple said sector conductors sequentially to said given connector.

2. A switching device according to claim 1, wherein the means for disposing said sector conductors in spaced relation to said surface comprises a thin layer of dielectric material.

3. A switching device according to claim 2, wherein said conductor body is provided with sector ridges underlying said sector conductors.

4. A switching device according to claim 2, wherein said sector conductors comprise flat strips of conductive material.

5. A switching device according to claim 2, wherein said sector conductors comprise wire at least partially imbedded in said dielectric.

6. A switching device according to claim 1, wherein said conductor body is provided with a channel in the extended surface thereof and the means for disposing said sector conductors includes dielectric material disposed in said channel.

7. A switching device according to claim 1, wherein said sectors are spaced from the surface of said conductor and the ends of adjacent sectors are spaced apart by distances equal to a small fraction of a quarter wavelength.

8. A switching device according to claim 1, wherein the means coupling said movable conductor to the inner conductor of said given connector includes a conductive spindle disposed axially of a circle defined by said sectors, means conductively connecting said movable conductor to said spindle, and the inner conductor of said given connector haivng sliding contact with said spindle.

9. A switching device according to claim 1, wherein said sector conductors comprise tarnishand wear-resistant material and said contact means comprises wires of relatively soft, resilient, tarnish-resistant material.

10. A switching device according to claim 9, wherein said sector conductors comprise strips of Rhodium foil.

11.. A switching device according to claim 10, wherein said wires are of spring gold alloy.

12. In a device of the character described, a coaxial line coupler having a given dimension between the inner and outer conductors thereof, a planar conductor having a planar surface thereof disposed substantially parallel to the axis of said line but in intersecting relation to the outer conductor thereof, a line conductor, means disposing said line conductor in close spaced substantially parallel relation to said planar surface, the spacing therebetween being smaller than said given dimension, means connecting said line conductor to said center conductor and means including a portion of said planar conductor inclined to said planar surface connecting said planar surface to the inner surface of said outer conductor, said line coupler being terminated in an arcuate sector and a rotatably supported conductor is provided for movement in coupling relation along said arcuate sector.

13. A switching device comprising a housing containing a switching chamber therein, coaxial coupler connections disposed in aligned spaced relation in side walls of said housing, said housing having an end wall the inner side of which contains a planar surface, a coaxial coupler connection in said end wall, arcuate sector conductors, a layer of dielectric material supporting said sector conductors in close parallel spaced relation to said planar surface, means coupling the inner conductors of each of the side wall coaxial couplers to a corresponding sector conductor, a member rotatably and electrically coupled to the inner conductor of the end wall coaxial coupler and means for rotating said member for sequential coupling relation with respect to said sector conductors.

14. A switching device according to claim 13, wherein the means for coupling the inner conductors of each of said side wall coaxial couplers includes a conductor extending into said chamber and angled toward said end Wall, said sector conductors having extensions and said end wall being removably secured to said side walls with the angled conductors engaging said extensions.

15. In a microwave switch, a conductor body having an extended planar surface, a plurality of flat strip-like terminal sectors, means disposing said sectors in spaced series relation and in overlying close spaced substantially parallel relation to said surface, an electric coupling element disposed for movement along said series of sectors, the spacing of said sectors with respect to said surface being a small fraction of a quarter wavelength to insure confinement of the electric field to substantially the region underlying each of said sectors, and the spacing between adjacent edges of said sectors also being a small fraction of a quarter wavelength for mechanical minimum transfer time between adjacent sectors, the spacing between adjacent sectors being greater than the spacing between said sectors and said surface to minimize intercoupling between adjacent sectors.

References Cited in the file of this patent UNITED STATES PATENTS 2,409,449 Sanders et al. Oct. 15, 1946 2,411,034 Gluyas, Jr. et al. Nov. 12, 1946 2,412,159 Leeds Dec. 3, 1946 2,453,759 Robinson Nov. 16, 1948 2,611,822 Bliss Sept. 23, 1952 2,654,842 Engelmann Oct. 6, 1953

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