EP1054473A2

EP1054473A2 - 50-ohmic coaxial connector for radio frequencies

Info

Publication number: EP1054473A2
Application number: EP00302059A
Authority: EP
Inventors: Manuel Perez
Original assignee: TRT Lucent Technologies SA
Current assignee: TRT Lucent Technologies SA
Priority date: 1999-05-19
Filing date: 2000-03-14
Publication date: 2000-11-22
Also published as: EP1054473A3

Abstract

The connector according to the invention comprises a female part (1) designed to be installed at the output from equipment at the end of a cable (C1), and a male part (5) for connection to an external cable (C2).

The female and male parts (1, 5) comprise metallic bodies (10, 50) that lock together by means of a nut (55) and form the connection between the peripheral conductors of cables (C1, C2), the central conductors being connected by a pin (61) and a tubular clamp (25). The end (12) of the female part (1) has an edge at the end of an external chamfer (12a), which is applied in contact with an annular surface (51) at the connection end of the male part (5).

Description

This invention relates to a 50 Ω connector for the connection of coaxial cables, designed specifically for radio transmission applications.
This connector was developed to satisfy a need arising in the field of cordless telephony.
This technology is currently growing quickly, according to which subscribers are connected by radio to a base station included in the network (DECT system). In practice, an antenna is provided at the end of the subscriber's installation for communication with the base station (the RFP), and a subscriber unit (called the CTA) physically connected to the antenna.
Up to now, the distance of the subscriber from the base station remained within limits of the order of a maximum of five kilometers, which did not require high performances of the said subscriber radio transmission means, and particularly the said antenna-unit physical connection for matching it. Therefore, priority was given to economic aspects in making this connection using a coaxial cable, a connector for external connection to the antenna with an impedance of 50 Ω and a connector for a connection inside the unit, also with an impedance of 50 Ω. Thus, apart from the higher quality connector for connection to the antenna for which no saving is possible since it is located on the outside, a standard type of 75 Ω cable and a 75 Ω connector are usually used for connection to the CTA unit, which is an inexpensive model known as an F type connector according to the IEC international standard. Despite its low cost, this coaxial cable has the advantage that it has a relatively high performance within the useful radio frequency range, since its linear attenuation is about 0.3 dB/m. However globally, the adaptation of the connection remains mediocre, with an average SWR (the ratio of transmitted power to reflected power) of the order of 19 dB.
One method of improving matching of the connection is to use components that all have an impedance of 50 Ω. This solution has become even more attractive since the Bieffe S.R.L. Company developed and markets a new relatively inexpensive 50 Ω coaxial cable (reference CO150af) with performances approximately equivalent to the performances of the 75 Ω cable mentioned above (loss per meter of about 0.3 dB) for the same diameter of 7 mm.
However there was a missing link before this solution can be used satisfactorily, namely a 50 Ω connector satisfactory for connection to the CTA unit.
This invention was made in order to satisfy this need as well as possible, with the twofold objective of low cost and good connection quality.
Consequently, it was decided to use a connector designed inspired from the design of the 75 Ω F type connector mentioned above, due to the cost advantage of this connector, but improved in order to achieve significantly better performances.
Therefore, the invention consists of a 50 Ω coaxial connector for radio frequencies, characterized in that it comprises a female fixed connector part that will be fitted at the output from equipment such as an electronic unit, at the end of a coaxial cable from the said equipment, and a male connection part to an external coaxial cable, the female and male parts comprising tubular metallic bodies that lock one to the other by means of a nut and making the electrical connection of the peripheral conductors of the said coaxial cables, whereas the electrical connection between the central conductors in the coaxial cables is made by a pin of the male part cooperating with a tubular clamp in the female part, the connection end in the female part having an external chamfer, forced into contact with an annular surface at the end of the connection of the male part while locking.
According to other preferred characteristics of the female part:

the metallic body of the female part has an internal bore fitted with the following (working from the back towards the front); firstly a connector base with a connecting tail projecting backwards, and a dielectric part holding the axial connection clamp in position;
the edge of the connection end has a peripheral lip crimped onto the said dielectric part holding the axial connection clamp in position; or as a variant, the connection end has an internal return defining a transverse annular contact surface at the end of the said chamfer.

According to other preferred characteristics of the male part:

its metal body forms a connecting tail at the back, the cable being attached to the said back part by means of a crimped sleeve which advantageously forms an integral part of the said body and may have one or several openings serving as a visualization window for checking that the cable is correctly fitted;
its metal body supports the connector locking nut, this nut being provided with a seal on the inside designed to form a sealed connection between the chamfered surface at the connection end of the female part and the transverse annular surface at the connection end of the male part;
in one variant embodiment, a sealing means is provided at the back in the form of a grommet.

The characteristics and advantages of the invention mentioned above, and others, will become more obvious after reading the following description with reference to the attached drawings in which:
Figures 1a and 1b are diagrammatic views of an axial section of the female and male parts respectively of a connector according to the invention;
Figure 2 is a partial diagrammatic view of an axial section showing a variant of the male part in figure 1a;
Figure 3 is a partial diagrammatic view of an axial section showing another embodiment of the ends of the male and female connection parts; and
Figure 4 is a diagrammatic axial view of another variant of the male part.
The same references have been used to denote the same elements, in all drawings and in all cases.
Firstly, figures 1a and 1b show overall views of a 50 Ω connector according to the invention, designed to connect an external coaxial cable C2 (50 Ω cable such as the reference mentioned above, the Bieffe S.R.L. CO150af) to a cable C1 inside a piece of equipment, for example a CTA subscriber unit in a telephone installation, in the connection between the CTA unit and the antenna.
The fixed connector type female part 1 is designed to be installed in a crossing through a wall. Therefore, its tubular metallic body 10 has a back collar 13 at its back end 11, and in front of the collar and all the way to the front connection end 12, there is an external thread on which an assembly nut 14 can be screwed, and a connection locking nut 55 that pertains to the male part 5 in this example.
The front end 12 of the body 10 has an outside chamfer 12a which terminates with a lip 12b surrounding the orifice of the bore 15 inside body 10. The bore 15 has a first shoulder 16 at the back, and then a second shoulder 17 around an output orifice 18 at the back. The volume of the bore 15 is fully occupied by a rear metallic fixed connector base 20, and a dielectric part 23 in front of the connector base.
The fixed connector base 20 fits intimately between the shoulder 16 with which it is in contact and the shoulder 17. Its rear part forms a connecting tail 21 passing through the orifice 18 and projecting axially backwards from body 10. The fixed connector base 20, with its connecting tail 21, comprises an axial duct 22 with the same diameter as the internal dielectric of the coaxial cable C1 to be connected.
The dielectric part 23 at the front of the fixed connector base 20 in bore 15 is in contact with the shoulder 16. It is fixed in place by the lip 12b being crimped onto its front end. Its center comprises a bore in which a contact element 25 is inserted. This element is a clamp, the front part of which is of the tubular type and which contains a plurality of extended jaws designed to provide a perfect quality contact with the corresponding element of the male part 5.
For the connection of cable C1, the dielectric inside the cable passes through the duct 22 in the fixed connector base 20 until it stops in contact with the back end of the contact clamp 25 that was crimped on the end of the internal conductor, the connecting tail 21 being slid into the peripheral conductor and the external casing fixed by means of a crimping sleeve 26.
The male part 5 comprises a tubular body 50 with an external collar 52 at its front connection end 51 and an internal return 53 defining an axial orifice 54 bordered on the outside by an annular transverse surface 51a. The collar 52 acts as a stop for the base of the locking nut mentioned above 55, which is engaged free to rotate on body 50. On the outside, the rear part of the body 1 is shaped with peripheral steps, to form a connecting tail 56 for the peripheral conductor and the external casing of a cable C2 to be connected. The connecting tail 56 is limited towards the front by a peripheral shoulder 57.
On the inside, between the back end 58 and as far as the return 53, the body 50 has a bore 59 with a diameter corresponding to the inside diameter of the internal dielectric of the cable C2 to be connected. Most of the length of the bore 59 is empty, but at the back, in contact with the return 53 at the front, it contains a small dielectric part 60 that will support the axial contact element, in this case a pin 61, of which the front part 61a projecting on the outside is shaped to provide a maximum quality contact in the clamp 25 of the female part 1. The overall shape of the dielectric part 60 is a thick ring fixed at the bottom of the bore 59 and defining an axial duct through which the pin 61 passes.
The rear tubular part 61b of the pin 61 has a larger cross-section than the cross-section of the front part 61a and is separated from it by a shoulder 61c. The front part 61a of the pin 61 is engaged in the dielectric part 60 and the back wall of this dielectric part forms a support for shoulder 61c.
For the connection of cable C2, the internal conductor of the cable fits intimately into the back part 61b of pin 61, until the internal dielectric of the cable comes into contact with the back end of the pin, the back connection part 56 of the body 1 being slid into the peripheral conductor and the outside casing of the cable C2 finally blocked by a crimping sleeve 62.
As can be seen in the drawing, the back end of pin 61 and the shoulder 57 limiting the connection part 56 of the body 50 at the front end are advantageously approximately in the same transverse plane, in order to enable and facilitate connection of cable C2 with the necessary precision to obtain the expected performances. Figure 1b shows that despite the simplicity of the structure and the small number of parts in the male part 5, the assembly works together so that the only way to connect the cable is an optimum connection respecting the best conditions for the relative positions of the various elements.
Secondly, when the male part 5 and the female part 1 are fitted together, the connection quality is excellent both for internal conductors in the cables through the clamp-pin assembly and for their peripheral conductors through the fixed connector base 20, the body 10 of the female part and the body 50 of the male part, with an improved contact quality between the connection ends 12 and 51 due to the chamfer 12a on the end of the female part.
Figure 2 illustrates an improvement made to the male part 5 in figure 1b, this improvement consisting of designing the sleeve 62 as an integral part of the body 50, therefore defining a deep annular groove with the rear part forming a connecting tail 56, into which the peripheral conductor and the outside casing of cable C2 can fit. As shown, the wall of the sleeve 62 advantageously has one or several small openings 62a near the front part, in other words at the bottom of the said groove, that acts as a visualization window to check that cable C2 is correctly installed when it is connected.
In figure 3, the front end 12 of the female part always has an outside chamfer 12a, but which in this case is extended by a straight internal return 12c instead of lips 12b in the example shown in figure 1b. Parts inside the body 50 are then put into place starting from its back end, a crimping lip being enclosed on the rear edge of the fixed connector base 20 and fixing the assembly in place.
In the male part 5, figure 3 also shows its locking nut 55 with a peripheral groove 55a in which a seal 65 will be fitted to make the seal between the chamfered surface 12a of the female part 1, and the plane annular surface of the end 51 of the male part 5.
In the example embodiment in figure 4, the male part 5' also comprises sealing means at its back end in the form of a grommet. Instead of forming a connecting tail, the back part 56' of the body 50' is threaded so that the grommet nut 66' can be fitted onto it.
The front part of body 50' and the pin 61', are essentially the same as described above, and therefore there is no need for them to be described again. However in its back part, the inside bore 59' has a first shoulder 67' for fixing an annular part made of a dielectric 69' retaining the back end of pin 61', and a second shoulder 68' for packing behind the dielectric part 69', a connecting tail 70' separated from the body 50' but intimately fitting into it to provide good electrical continuity between them. As in the previous case, a free space is formed in the body 50' around the back part of the pin 61', between the front dielectric part 60' and the dielectric part 69'.
The front end of the connecting tail 70' fitted into the body 50' forms a collar limiting the connection part itself, and onto which the sealing ring 71' of the grommet fits. For the connection of cable C2, the internal dielectric of the cable engaged in the connecting tail 70' comes into contact with the back surface of the dielectric part 69'. As in the previous case, the layout of the male part 5' is such that it is very easy to install cable C2 in the best possible way.
In the above mentioned application of the connection of an antenna to a CTA subscriber unit, tests have shown a very significant improvement due to the use of the 50 Ω connector according to the invention together with the cable mentioned above made by the Bieffe S.R.L company to make a connection entirely in 50 Ω, the gain in matching (average SWR) compared with connections made at the present time using equipment in the same price range possibly being of the order of 5 dB or more. Furthermore, and comparatively, the performance of a 50 Ω connector according to the invention is almost equal to an existing N type 50 Ω connector (IEC international standard) although its cost is very significantly lower, of the order of 4 times less.

Claims

50 Ω coaxial connector for radio frequencies, characterized in that it comprises a female fixed connector part (1) that will be fitted at the output from equipment such as an electronic unit, at the end of a coaxial cable (C1) from the said equipment, and a male connection part (5) for a connection to an external coaxial cable (C2), the female (1) and male (5) parts comprising tubular metallic bodies (10, 50) that lock end to end one to the other by means of a nut (55) and making the electrical connection of the peripheral conductors of the said coaxial cables (C1, C2), whereas the electrical connection between the central conductors in the coaxial cables is made by a pin (61) of the male part (5) cooperating with a tubular clamp (25) in the female part (1), the connection end (12) in the female part (1) having an edge at the end of external chamfer (12a), forced into contact with an annular surface (51) at the connection end of the male part (5) while locking.
Connector according to claim 1, characterized in that the metallic body (10) of the female part (1) has an internal bore (15) fitted with the following (working from the back towards the front); firstly a metallic fixed connector base (20) with a connecting tail (21) projecting backwards, and a dielectric part (23) holding the axial connection clamp (25) in position.
Connector according to claim 2, characterized in that the edge of the connection end (12) of the female part (1) is fitted with a peripheral lip (12b) at the end crimped onto the said dielectric part (23) holding the axial connection clamp (25) in position
Connector according to claim 2, characterized in that the connection end (12) of the female part (1) has an internal return (12c) defining a transverse annular contact surface at the end of said chamfer (12a).
Connector according to one of claims 1 to 4, characterized in that the metallic body (50) of the male part (5) forms a connecting tail at the back part (56), the cable (C2) being attached to the said back part (56) by means of a crimped sleeve (62).
Connector according to claim 5, characterized in that said sleeve (62) forms an integral part of the said metallic body (50).
Connector according to claim 6, characterized in that said sleeve (62) has one or several openings (62a) acting as a visualization window in order to ensure that the cable (C2) is correctly fitted.
Connector according to one of claims 1 to 7, characterized in that the metallic body (50) of the male part (5) supports the said locking nut (55), this nut (55) being provided on the inside with a seal (65) designed to form a sealed connection between the chamfered surface (12a) at the connection end (12) of the female part (1) and the transverse annular surface (51) at the connection end of the male part (5).
Connector according to one of claims 1 to 4 and 8, characterized in that the male part (5) is provided with a sealing means at the back in the form of a grommet (66', 71').