GB2064234A

GB2064234A - Improved centre conductor element for female microwave coaxial connector

Info

Publication number: GB2064234A
Application number: GB8030400A
Authority: GB
Original assignee: Krytar Inc
Current assignee: Krytar Inc
Priority date: 1979-11-26
Filing date: 1980-09-19
Publication date: 1981-06-10
Also published as: GB2064234B

Abstract

A centre conductor element for a miniature female, air dielectric, coaxial connector has two concentric tubes, one of which is an inner and shorter tube 34 and the other is an outer and longer tube 46. The inner shorter tube engages the end of a male pin 26 and provides for centering of the mating male pin, and the longer outer tube is slotted to form fingers which are resiliently biassed inwards to make contact, at their ends, with the male pin. <IMAGE>

Description

SPECIFICATION Improved centre conductor element for female microwave coaxial connector This invention relates to a new improved centre conductor female element for a miniature coaxial connector.

Present day requirements in microwave systems and components are leading to the continually increasing use of higher and higher frequencies for coaxial microwave systems and components. In order to provide mode free performance at these higher frequencies, it has been necessary to make connectors physically smaller. The commonly used SMA connector is an example of a miniature coaxial connector that can be used at higher microwave frequencies. The SMA is a sexed connector that is usable to 26 GHz.

Recently, a new high performance 3.5 mm sexed coaxial connector, commonly known as the APC-3.5 and manufactured by the Amphenol Division of Bunker Ramo, has been introduced that gives mode free performance to 34 GHz, see S. F.

Adam, G. R. Kirkpatrick, N. J. Sladek, S. T. Bruno, "A High Performance 3.5 mm Connector to 34 GHz," Microwave Journal, Vol. 19, No. 7, July 1976. The APC-3.5 is a coaxial connector pair comprising a male and female connector, each element of which is compatible with standard type SMA connector now commonly used. Unlike the SMA, the APC-3.5 is an air dielectric connector.

That is, in the vicinity of the male-female centre conductor connection, air is the dielectric in the region between the centre conductor and outer conductor.

The APC-3.5 was designed to provide improved electrical performance, mechanical ruggedness, and reliability to the type SMA. It does provide improved electrical performance.

However, the female connector has been found to have an unacceptably high failure rate with repeated usage. This is caused by both mechanical distortion and failure of the centre conductor female element. The APC-3.5 female element is slotted to provide four fingers that are resiliently biased toward each other so that, when the male pin of the mating connector is inserted, positive contact is made at the ends of the fingers. When failure occurs, the cause is usually found to be that at least one of the female element fingers is not making contact, at its end, with the male pin. This causes undesirable electrical reflections which typically become severe, or resonate, at frequencies above 10 GHz.

The failure mechanism can be explained as follows: Due to nominal design clearances and dimensional tolerances, there can be quite a bit of play of "slop" in the mating of APC-3.5 and SMA connectors. This play allows the SMA or APC-3.5 male connector pin to engage either off centre or at an angle with respect to the APC-3.5 female element. The APC-3.5 connector has outer and inner conductor diameters of.1 38 inch (3.5 mm) and .060 inch respectively which make the female element fingers too fragile (approx. .011 inch thick) to forcibly centre the mating male pin.Either of the situations is illustrated in Figures 1 and 2 of the drawing herein and can cause one or more of the female element fingers to be deflected as shown, and not make contact at their ends with the male pin. Once a female element finger has been distorted, as illustrated in Figures 1 or 2 of the drawing, it will usually not make contact, at its end, on later connections even though the male and female elements are centered. This is because severe deflections take the fingers past the point where they can recover and spring back to their original position. This type of female element failure does not occur in the SMA female connector because the female element of the SMA connector is surrounded by a plastic dielectric (typically teflon) that prevents the fingers from being distorted outwardly as shown in Figures 1 and 2 of the drawing.

One solution to the female element failure problem for miniature air dielectric coaxial connectors was proposed by Wiltron Co. and is described in an article entitled "Connector Relieves Nagging SMA Measurement Problems" Microwaves, Vol. 18, No.1, January 1979, pp.

97-99. As described, the female element consists of two concentric tubes, with the inner tube slotted, to form fingers which are biased to make contact with both the outer tube and the mating male pin. The outer tube is unslotted and prevents the fingers from being distorted outward by an off-centre male pin. However, this solution is not entirely satisfactory since the female element is difficult and costly to manufacture, requiring extremely tight dimensional tolerances and complicated twisted biasing of the fingers.

In accordance with the present invention there is provided a centre conductor element for a female coaxial connector comprising two concentric tubular inner and outer portions, said inner portion providing for centering of the mating male pin, said outer portion extending beyond said inner portion and being slotted to form a plurality of fingers, said fingers being resiliently biased inward to contact the mating male pin past the end of said inner portion, said outer and inner portions being rigidly connected at the opposite end from the place of contact.

The invention will be illustrated by the following description of preferred embodiments of the invention with reference to the accompanying drawings, in which: Figure 1 is a cross sectional view of the engaging male and female elements of an APC-3.5 connector illustrating an off-centre male pin and the resulting deformation of the female part upon engagement; Figure 2 is a cross sectional view of the engaging male and female elements of an APC--3.5 connector illustrating a male pin at and angle with the centre line of the female and the resulting deformation of th female part upon engagement; Figure 3 is a cutaway cross sectional view of the female element of the present invention engaged with a mating male pin; Figure 4 is a view taken along lines 4-4 of Figure 3;; Figure 5 is a cutaway cross sectional view of the inner centering tube of the present invention; Figure 6 is an end view of the inner centering tube of Figure 5; Figure 7 is a cross sectional view of the outer slotted contact tube of the present invention; Figure 8 is an end view of the outer tube of Figure 7; Figure 9 is a cutaway view of an air dielectric coaxial connector utilising the male and female elements shown in Figure 3; Figure 10 is a cutaway cross sectional view like Figure 3 but showing an alternative embodiment of the inner centering tube of Figure 5; and Figure 11 is a cutaway cross sectional view like Figure 3 but showing an alternate embodiment of both inner and outer tubes.

Referring now to the drawings, and particularly to Figures 1 and 2, there is shown a male portion 10 having a centre line 11 and female portion 12 having a centre line 1 3 which, respectively, form the male and female ends of the centre conductor at a junction of an ultra-high frequency coaxial connector. As is well known in the art, and as will be explained in connection with the description of Figure 9, the usual coaxial connector has a male connector unit and a female connector unit, each having an outer conductive shell and an inner centre conductor insulative supported within the outer shell. The outer shells are normally connected by being butted together as shown in Figure 9, and form no part of this invention.The ends of the centre conductor, shown in Figures 1 and 2, are connected by sliding the male portion 10 into the female portion 12.

Figure 1 illustrates the problem attendant when the male pin is off-centre, i.e. centre lines 11 and 13 are parallel but not coincident, and Figure 2 illustrates the problem attendant when the male pin is at an angle with respect to the centre line, i.e. centre lines 11 and 1 3 are at an angle with respect to one another. As a result, contact finger 1 2a is forced outwardly so that contact takes place only at 1 2c, and finger 1 2b is allowed to flex inwardly and make contact only at 1 2d. In both cases, the contact between the male and female parts is not at the ends of the fingers and near to the shoulders 1 5, as it should be.

Such a failure of the fingers to make contact, at their ends, with the male pin causes undesirable reflections. Also, the severe deflection of finger 1 2a will often cause it to fail mechanically and take a permanent "set".

Misalignment of the male pin with the female element as in Figures 1 or 2 illustrates the prior art problem which could only be solved by either the complicated female element proposed by the Wiltron Co. or by modifying the connector design and tightening mechanical tolerances to allow for less "play" during connection and consequently less misalignment of the female element with the male pin. Modifying the APC-3.5 connector design and tightening its mechanical tolerances is not always desirable because of increased cost and also because the APC-3.5 would no longer be compatible with the standard SMA connector.

Referring now to Figures 3 through 8, which illustrates the present invention, there is shown a centre conductor terminating in male portion 20 which is mated with the centre conductor terminated in a female portion 22. The terminating portion of male portion 20 is of conventional construction and has a cylindrical male element 24 of a uniform main diameter and a cylindrical forward portion 26 of a first reduced diameter which terminates in a tapered point 28. The junction between the two diameters form a first annular radial shoulder 30.

The terminating female portion 22 includes a cylindrical female element 32 which has a tubular forward portion 34 of a second reduced external diameter and has an internal diameter 36 selected to slidingly receive cylindrical forward portion 26.

The junction between the two diameters forming a second annular radial shoulder 38. The external surface of tubular forward portion 34 has a cylindrical section 40 and a tapered section 42.

There is further provided a tubular contact finger sleeve 46 which has an external diameter equal to the uniform main diameter of cylindrical male element 20 and cylindrical female element 22, and has an internal diameter 48 which is selected to slidingly fit over cylindrical section 34 of female element 22. Sleeve 46 is provided with four lengthwise slots 50 which extend about halfway along the entire length of sleeve 46 and which form four flexible spring fingers which, as best seen in Figure 3, are substantially coextensive with tapered section 42 of female element 22 and extend beyond it. In this manner, the fingers can be inwardly biased, the tapered section providing the space therefor. The fingers, designated by reference character 52, are provided with inwardly extending contact segments 54 which make contact with cylindrical forward portion 26 of male portion 20.

In the preferred embodiment of the invention, sleeve 46 is made of heat treated berylliumcopper to provide good spring action. Also, contact segments 54 are formed by leaving a reduced diameter at the spring end of sleeve 46 prior to providing slots 50. Sleeve 46 is placed on reduced diameter section 40 of female element 32 after a small amount of solder paste has been deposited on section 40 near shoulder 38. The sleeve is put flush with annular shoulder 38, and element 32 and sleeve 46 are heated until the solder flows joining sleeve 46 permanently to female element 32. Sleeve 46 could also be press fitted or welded in place on element 32. For best results the entire female element 22 is gold plated.

Referring to Figure 3, it can be seen that the tubular portion 34 provides primarily for the centering of male cylindrical portion 26 with respect to tubular contact finger sleeve 46, thus preventing reflections and mechanical failure of finger sleeve 46.

Referring now to Figure 9, there is shown a cutaway view of an air dielectric coaxial connector constructed in accordance with the present invention. A male connector unit 70 comprises an outer shell 72 and a centre conductor 74 insulative supported within the outer shell, and a female connector 75 comprises an outer shell 76 and a centre conductor 78 insulatively supported within the outer shell. Centre conductor 74 is terminated in the conventional male portion 80 which is in all respects similar to male portion 20 shown in Figure 3, and centre conductor 78 is terminated in a female portion 82 which in all respects is similar to the one shown in Figure 3 as 22. Female portion 22 is provided with tubular contact finger sleeve 46 to effect a good highfrequency connection which has a minimum of reflection and therefore only a minimal VSWR varient.

Figure 10 shows an alternate embodiment of tubular portion 34 in which a tubular extension 90 is provided which has a reduced diameter portion 91 instead of the tapered portion 42. The purpose is the same, namely to allow spring fingers 46 to be inwardly biased for good electrical contact with male element 20.

Figure 11 shows a further alternate embodiment of tubular portion 34 and of sleeve 46 in which a tubular extension 93 is provided which is of uniform radial thickness along its length, i.e. is neither tapered as in Figure 5 nor has a reduced diameter end portion as in Figure 1 0.

Further, sleeve 46 is provided with an enlarged internal tubular portion proximate to contact segments 54 to allow contact fingers 52 to be inwardly biased for good electrical contact with male portion 20.

In all the illustrated embodiments of this invention, the female portion 22 is provided with a forwardly extending tubular extension for mechanically or structurally receiving and centering the male pin, and a sleeve with inwardly biased contact fingers for electrically contacting the male pin.

There has been described a centre conductor element for a female coaxial connector having two concentric tubes with the inner tube providing for centering of the mating male pin, and the outer tube being slotted to form fingers which extend past the end of the inner tube and are biased inwardly to cause contact points at their ends to radially contact the male pin.

Amongst the advantage of the particular connectors described above are improved reliability and ruggedness, simple design, ease of manufacture, and electrical performance that is free of resonances (mode free) and minimises reflections for frequencies in excess of 26 GHz.

Furthermore, the connectors have a centre conductor female element that is compatible with the APC-3.5 and the SMA and similar male coaxial connectors, and improves the reliability and mechanical ruggedness of the resulting connector with no degradation in electrical performance.

Claims

1. A centre conductor element for a female coaxial connector comprises two concentric tubular inner and outer portions, said inner portion providing for centering of the mating male pin, said outer portion extending beyond said inner portion and being slotted to form a plurality of fingers, said fingers being resiliently biased inward to contact the mating male pin past the end of said inner portion, said outer and inner portions being rigidly connected at the opposite end from the place of contact.

2. An ultra-high frequency coaxial connector, in which a male connector unit and a female connector unit each having an outer conductive shell and an inner centre conductor insulatively supported within the outer shell are connected to one another, and in which the ends of the inner centre conductors terminate in male and female portions, and in which the male portion has a conventional cylindrical male element having a cylindrical forward portion extending from an annular shoulder and terminating in a tapered point, wherein the female portion comprises: a cylindrical female element having a tubular forward portion, the internal diameter and length of said tubular forward portion being dimensioned to slidingly receive a selected length of the end portion of said cylindrical forward portion of said male element; and a tubular contact finger sleeve having an internal diameter selected to engage said tubular forward portion, said sleeve terminating in a plurality of spring fingers which extend beyond the end of said tubular forward portion, said fingers having end portions which are dimensioned and biased to conductively contact the cylindrical forward portion of said male element proximate to said annular shoulder.

3. An ultra-high frequency coaxial connector, in accordance with Claim 2 in which said tubular forward portion terminates in a tapered forward section to allow for the inwardly biasing of said spring fingers.

4. An ultra-high frequency coaxial connector in accordance with Claim 2 in which said tubular forward portion terminates in a reduced outer diameter section to allow for the inwardly biasing of said spring fingers.

5. An ultra-high frequency coaxial connector in accordance with Claim 2 in which said sleeve has an increased internal diameter section and in which the ends of each finger have an inwardly extending contact extension, said increased internal diameter section allowing for inwardly biasing of said spring fingers.

6. An ultra-high frequency coaxial connector, in which a male connector unit and a female connector unit each having an outer conductive shell and an inner centre conductor insulatively supported within the outer shell are connected to one another, and in which the ends of the inner centre conductors terminate in male and female portions, and in which the male portion has a cylindrical male element of a uniform main diameter and a cylindrical forward portion of a first reduced idea meter terminating in a tapered point, the junction between the two diameters forming a first annular radial shoulder, wherein the female portion comprises:: a cylindrical female element of said uniform main diameter having a tubular forward portion of a second reduced external diameters and an internal diameter selected to slidingly receive the cylindrical forward portion of said male element, the junction between the two diameters forming a second annular radial shoulder, said external surface of said tubular forward portion having a cylindrical section commencing at said second annular shoulder and a tapered section terminating at the end of said tubular forward portion; and a tubular contact finger sleeve of said uniform main diameter for its external surface and having an internal diameter which is selected to slidingly fit over said cylindrical section of said tubular forward portion, said sleeve terminating in a plurality of spring fingers which are coextensive with said tapered section and extend beyond the end of said tubular forward portion, said fingers being located and biased and shaped so as to conductively contact the cylindrical forward portion of said male element proximate said first annular shoulder when said male and female elements are mated, said tapered section allowing said fingers to be inwardly spring biased for a good electrical contact with the cylindrical forward portion of the element.

7. An ultra-high frequency coaxial connector, in which a male connector unit and a female connector unit each having an outer conductive shell and an inner centre conductor insulatively supported within the outer shell are connected to one another, and in which the ends of the inner centre conductors terminate in male and female portions, and in which the male portion has a cylindrical male element and a cylindrical forward portion of a reduced diameter terminating in a tapered point, wherein the female portion comprises:: a cylindrical female element having a tubular forward portion of a reduced external diameter and an internal diameter selected to slidingly receive the cylindrical forward portion of said maleelement, said external surface of said tubular forward portion having a cylindrical section commencing at said second annular shoulder and tapered section terminating at the end of said tubular forward portion; and a tubular contact finger sleeve having an internal diameter which is selected to slidingly fit over said cylindrical section of said tubular forward portion, said sleeve terminating in a plurality of spring fingers which are coextensive with said tapered section and extend beyond the end of said tubular forward portion, said fingers being located and biased and shaped to conductively contact the cylindrical forward portion of said male element when said male and female elements are mated.

8. An ultra-high frequency coaxial connector in accordance with Claim 7 in which the ends of said fingers have inwardly extending contact extensions for contacting said cylindrical forward portion.

9. An ultra-high frequency coaxial connection in accordance with Claim 8 in which the contact surface of said contact extensions lie on a cylindrical surface having a diameter which is less than the diameter of the cylindrical forward portion of said male element.

10. A centre conductor element or an ultra-high frequency coaxial connector substantially as hereinbefore described with reference to and as shown in Figures 3 to 9 or Figure 10 or Figure 11 of the accompanying drawings.