GB2066588A

GB2066588A - Coaxial line termination

Info

Publication number: GB2066588A
Application number: GB7941040A
Authority: GB
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1979-11-28
Filing date: 1979-11-28
Publication date: 1981-07-08

Abstract

Short circuit termination of a coaxial line is provided by a shorting member (27) having inner and outer abutments (31, 29) faced and spaced apart so to engage with the inner and outer conductors (13, 11) of a connector (1) attached to the coaxial line. The abutments (31, 29) are interconnected by a resilient conductive structure (33) e.g. a diaphragm - and are disposed so that with engagement of the outer abutment (29) with the outer conductor (11), the inner abutment (31) is urged into gapless contact with the inner conductor (13) as the resilient structure (33) is stressed by axial displacement. The shorting member (27) may be in the form of a connector insert (e.g. as shown in figure 3) and held in place by a coupler (3) or it may be provided as an integral part of a coupling (3). <IMAGE>

Description

SPECIFICATION Co-axial line termination This invention concerns, in general, the termination of co-axial lines. It relates, in particular, to connectors and to connector components that provide short circuit connection between inner and outer line conductors when one connector is coupled to another.

In microwave applications, when a co-axial line is terminated by a short circuit, it is desirable that secure bridging electrical contact is made between the outer and inner conductors in a consistent and repeatable manner. It is an important consideration in the calibration or testing of microwave equipment and devices, that this shorting is provided in a well defined plane and in a manner that is not dependent on signal frequency. It is a problem meeting these requirements, particularly in the termination of coaxial lines of 7 mm diameter, or less.

According to one aspect of the present invention there is provided a short circuit connector including: coupling means, for engaging a mating connector having co-axial inner and outer conductors; and, inner and outer abutment faced structures, interconnected by a resilient conductive structure, with the abutment faced structures disposed relative to one another such that with coupling of the connectors and engagement of the outer abutment faced structure with the outer conductor, the inner abutment faced structure is urged into gapless contact with the inner conductor by axial displacement of the resilient conductive structure.

Both abutment faced structures may extend proud of the plane of the resilient structure.

Alternatively, one of the abutment faced structures may be flush with the plane of the resilient structure, depending on the geometry of the mating connector.

The inner and outer abutment faced structures and the resilient structure may be integral with the body of the short circuit connector. For example these could be formed of a plastics moulding subsequently plated with a high conductivity material. In preference, however, these structures and the resilient structure, may form part of a detachable insert member retained within the body of the short circuit connector.

Preferably the resilient conductive structure is in the form of a diaphragm.

According to another aspect of the present invention, therefore, there is provided an insert component for a short circuit connector, this component having: a body suited for insertion and retention in short circuit connector; and, inner and outer abutment faced structures interconnected by a resilient conductive structure, these structures being disposed to enable gapless and resilient contact across the inner and outer conductors of another connector.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings of which: FIGURE 1 is a cross-section drawing of a pair of mating connectors providing short circuit termination in a conventional manner, the section being taken in a plane passing through a common axis; FIGURE 2 is a cross-section view of part of a conventional modified connector showing a sprung collet retained in a recess in the inner conductor of the connector; FIGURE 3 is a cross-section drawing of a pair of mating connectors embodying features of the invention, viewed from a plane passing through their common axis; FIGURE 4 is a perspective view of a shorting female connector, one of the mating connectors shown in figure 3; FIGURE 5 is a cross-section drawing of a shorting insert for the female connector shown in figure 4; and FIGURES 6, 7 and 8 are cross-section drawings each of an aiternative pair of mating connectors, viewed from a plane passing through their common axis.

As shown in figure 1 conventional short circuit termination for a co-axial line is provided by two mating connectors 1 and 3. The first of these connectors, a standard SMA 3 mm male type connector 1, has an annular body 5 on which a captive nut 7 is retained by means of a circlip 9 held in annular recesses in both the body 5 and the nut 7. Within the body 5 there is mounted a pair of concentric conductors, one an outer conductor 11, the other an inner conductor 1 3.

These conductors are held a fixed space apart and are isolated by means of an insulating spacer 1 5.

The outer conductor 11 has at its exposed end an annular plane face 17 providing a datum plane.

The inner conductor 13 is shouldered to provide a second annular plane face 1 9 that is inset from the datum plane 1 7 by a short distance, typically 0.25 mm. Projecting from this shoulder 19, at the centre of the inner conductor 13, is a co-extensive pin 21. The second of these connectors, 3, a female shorting connector, comprises a solid annular body 23 of conductive material having a threaded portion 25. The thread is constructed to co-operate with the captive nut 7 of the other connector, and the solid body 23 is recessed to receive the exposed end portion of the outer conductor 11. The recess has a plane face 29 to provide abutment against the datum face 1 7 of this conductor 11 when the nut 7 is tightened upon the thread.The centre of the threaded body 23 is provided with a bore for receiving a splitended, radially compliant, tubular insert 26. This insert 26 is constructed to receive, and make contact with the pin 21 of the male connector 1.

When this insert 26 is mounted in the bore, it is often, as a consequence of manufacturing tolerance, inset from the plane face of the recess by a small distance. The inset distances between the pin shoulder 19 and datum face 17, and between the insert 26 and the recess face 29 are introduced deliberately because there is no axial compliance in the inner conductor 13 and in the insert 26. When the connectors are coupled, and the datum face 1 7 and recess face abutted, a gap 28 is left between the shoulder 19 and the insert 26. Current, passing down the co-axial line, is constrained to follow a convoluted path from the outer conductor 11 to the inner conductor 13 via the radially spring split insert 26 in the centre of the shorting connector 3.Small unwanted impedance resulting from this arrangement introduces indeterminacy in the electrical position of the plane of the short and this is moreover frequency dependent. Also it is difficult to reproduce these conditions exactly when the connectors 1 and 3 are decoupled and subsequently reconnected.

Axially compliant connectors similar to the connector shown in figure 2, are known. The inner conductor 13 of this connector is provided with a bore and this retains a compliant contact member 14. This contact member 14 is a small four pronged split ended collet. It is normally held in the bore of the inner conductor 13 by the spring action of the four prongs, so that its exposed end face is slightly proud of the ends of the conductors. When this connector is mated to a short circuit connector, the spring action of the collet 14 ensures firm and definitive contact. In 7 mm co-axial line connectors, the size of the inner conductor, typically 3.04 mm diameter, allows this arrangement. This arrangement requires high precision in manufacture and is relatively expensive.Also in miniature and subminiature connectors this arrangement becomes inconvenient because of the smaller size of the inner conductor. For example, the diameter of the inner conductor is 1.27 mm for the 3 mm SMA centre conductor and even smaller, 0.86 mm, for the 1.7 mm OSSM centre conductor.

The male connector shown in figure 3 is of the same construction as the known connector 1 already described with reference to figure 1 above, but the second of the mating connectors, the female, also shown in figure 4, is of different construction and comprises a hollow body 23' having an externally threaded front end portion 25 machined to accommodate the male connector 1.

A short circuit insert member 27 is provided and is a sliding fit in the hollow body 23'. The insert member 27, also shown in figure 5, is constructed as a hollow cylindrical cup of springy metal of high electrical conductivity (e.g. chrome copper). The base of the cup 27 is machined to provide, at its external surface, outer and inner annular abutment faces 29 and 31 standing proud of and integral with an axially compliant diaphragm 33. These abutment faces 29 and 31 are spaced to cooperate with the annular faces 1 7 and 1 9 of the co-axial outer and inner conductors 11 and 13 of the male connector 1. The abutment faces 29 and 31 are machined to a superior finish and are slightly less in radial thickness than the corresponding annularfaces 17 and 19 with which they are designed to co-operate.

As shown in figure 5, the inner annular abutment face 31 stands proud of the outer annular abutment face 29 by a distance greater than the maximum inset distance between the shoulder 19 of the inner conductor 13 and the datum face 17, which latter distance is typically -0.25 mm. The diaphragm 33 is reduced to a thickness of between 0.08 mm and 0.18 mm to allow adequate axial compliance and resilience. A hole passing through the centre of the inner annular abutment face 31 has a clearance diameter sufficient to allow the inner conductor pin 21 to protrude freely through the case of the cup 27.

When the two mating connectors 1 and 3 are coupled and the nut 7 tightened on the thread 25, axial force is applied bringing the outer conductor face 17 and outer annular abutment face 29 into electrical contact. At the same time the shoulder face 1 9 of the inner conductor 13 and the inner annular abutment face 31 of the conductive insert member 27 are abutted, urged, and maintained in gapless electrical contact by the spring action of the axially stressed diaphragm 33. This spring action substantially eliminates the small unknown impedance and renders the electrical position of the short circuit independent of frequency in a substantially repeatable manner.

For protection against corrosion and for good electrical contact the insert member 27 and the body 23 of the female connector 3 are gold-plated to about 5 ym.

It is convenient to glue the insert member 27 into the body recess. If the abutment faces 29 and 31 of the insert member 27 become damaged or scored, the insert member 27 may be removed readily from the recess by punching it out of the body 23 from the rear and the female coupler 3 may be refurbished with a replacement insert member.

The insert member 27 may also be used to provide short circuit termination of a female type connector. Thus as shown in figure 6, the insert member 27 is now retained in the body 5 of the connector 1. The inner and outer conductors 1 3 and 11 are in this case embodied in an externally threaded female, 3 mm SMA connector 3. The inner conductor 13 has at its exposed end 35 a split-ended tubular configuration, the end face 37 of which is inset axially from the datum face 1 7 of the outer conductor 11. When the two mating connectors 1 and 3 are coupled, the abutment; faces 29 and 31 of the insert member 27 make electrical contact with the datum face 1 7 and the end face 37, the abutment face 31 being resiliently held in contact position by the action of the diaphragm 33 which is axially displaced.

In figures 7 and 8, alternative short circuit insert members 27' and 27", each suited to N-type mating connectors 1 and 3 which are of different conductor geometry, are shown.

In figure 7, the outer conductor 11 extends as part of the body 5 of the connector 1, a male connector. The inner conductor 1 3 of this connector 1 has at its exposed end a pin projection 21, but the shoulder face 1 9, at the base of this projection 21, is set well back from the datum face 1 7 at the end of the outer conductor 11. To suit this different geometry, the inner abutment face 31 of the insert member 27' is provided at the end of a tubular extension 39 extending from the diaphragm 33. This tubular extension 39 has an internal diameter appreciably greater than the diameter of the pin projection 21 so that when the tubular extension 39 is in located position it fits loosely around the pin projection 21 without impediment to the resilience of contact made between the abutment face 31 and the shoulder face 19.

In figure 8, the outer conductor 11 is part of the body 23' of the connector 3, a female connector.

The inner conductor 13 extends axially beyond the datum face 1 7 which is formed here at the base of a recess in the body 23'. The exposed end 35 of conductor 13 is of split-ended tubular construction. To suit this different geometry, the outer abutment face 29 of the insert member 27" is provided at the end of a tubular extension 41 extending from the periphery of the diaphragm 33.

At the centre of the diaphragm there is a locating pin 43. This pin 43 is a loose fit inside the end 35 of the inner conductor 13 so that there is no impediment to the resilient contact made between the end face of the inner conductor 11 and the inner abutment face 31 of the insert member 27".

This inner abutment face 31 may be flush with the surface of the diaphragm 33, as shown in the figure 8, or it may stand proud of this surface. In either case, the axial separation of the inner and outer abutment faces 29 and 31 is such that when the mating connectors 1 and 3 are coupled, the diaphragm 33 is axially displaced so urging contact between the inner abutment face 31 of the insert member 27" and the end face of the inner conductor 13.

Whilst in the above examples, short circuit termination is provided by a detachable insert member it will be understood that the abutment faced structures and the diaphragm 33 could also be provided as an integral part of a mating connector.

It will also be understood that the abutment faced structures may be interconnected by means of resilient conductive radial fingers in place of a diaphragm. The inner abutment faced structure, supported in this way, may be split into as many portions as there are fingers.

Claims

1. A short circuit connector including: coupling means, for engaging a mating connector having co-axial inner and outer conductors; and, inner and outer abutment faced structures, interconnected by a resilient conductive structure, with the abutment faced structures disposed relative to one another such that with coupling of the connectors and engagement of the outer abutment faced structure with the outer conductor, the inner abutment faced structure is urged into gapless contact with the inner conductor by axial displacement of the resilient conductive structure.

2. A connector as claimed in Claim 1 wherein both abutment faced structures extend proud of the surface of the resilient structure.

3. A connector as claimed in Claim 1 wherein one only of the abutment faced structures is flush with the surface of the resilient structure.

4. A connector as claimed in any one of the preceding Claims 1 to 3 wherein the abutment faced structures and the resilient structure are integral with the body of the short circuit connector.

5. A connector as claimed in the preceding Claim 4 wherein the body, the abutment faced structures and the resilient structure are formed of plastics moulding plated with a high conductivity material.

6. A connector as claimed in any one of the preceding Claims 1 to 3 wherein the abutment faced structures and the resilient structure are part of a detachable insert member that is retained within the body of the short circuit connector.

7. A connector as claimed in Claim 6 wherein the resilient structure is a diaphragm.

8. A short circuit connector constructed, adapted and arranged to operate substantially as hereinbefore described with reference to and as shown in any one of the accompanying drawings figure 3 and figures 6 to 8.

9. A short circuit connector as claimed in any one of the preceding Claims 1 to 8 and a mating connector coupled in engagement therewith.

10. An insert component for a short circuit connector, this component having: a body suited for insertion and retention in the body of the short circuit connector; and, inner and outer abutment faced structures interconnected by a resilient conductive structure, these structures being disposed to enable gapless and resilient contact across the inner and outer conductors of another mating connector.

11. An insert component as claimed in the preceding Claim 10 wherein the body of this component is tubular and provides at one end thereof an outer abutment face for engaging the outer conductor of the other mating connector.

12. An insert component as claimed in the preceding Claim 11 wherein the resilient structure is a diaphragm inset within and integral with the tubular body.

1 3. An insert component for a short circuit connector constructed, adapted and arranged to operate substantially as hereinbefore described with reference to and as shown in any one of the accompanying drawings figures 3 to 8.