CONNECTOR FOR COAXIAL CABLE

Abstract: A coaxial plug (1,6) intended for use in a junction between a coaxial conductor located externally of an apparatus box (16,17) and a stripline with a conductive earthing plane located within the box, the stripline and earthing plane each being arranged on a respective side of an insulating plate (15), the centre pin of the coaxial plug (1, 6) being intended for connection with the stripline and the conductive outer casing of the coaxial plug being intended for connection with the earthing plane. An impedance-correct junction which is short in relation to the wavelength of the transmitted signal can be obtained without needing to solder or glue the conductors. This is achieved by providing the coaxial plug (1, 6) with an outwardly protruding part (13) which extends from one end wall of the plug in contact with the conductive outer casing thereof and which presents an at lest substantially planar surface (14) which enables the connections (19, 21) in the junction to be made by so-called bonding techniques. The plug may also comprise two parts of which one comprises a standard plug (1) and the other comprises an intermediate component intended for use as an intermediary (6) between the standard plug and the stripline with its earthing plane to which the plug is to be connected.

Description: TECHNICAL FIELD This invention relates to a coaxial plug for use in a junction between a coaxial conductor located externally of an apparatus box and a stripline located within the box and having a conductive earthing plane, or surface, the stripline and earthing plane being arranged on a respective side of an insulating plate, and the centre pin of the plug being intended for connection with the stripline, and the conductive outer casing of the plug being intended for connection with the earthing plane or surface. BACKGROUND ART Reflection phenomena occur when the impedance of the junction, or transition, between a coaxial plug and a stripline according to the above is incorrect. In order for the junction to have correct impedance, it is necessary for the junction to exhibit at each cross-section thereof the same characteristic impedance as that of coaxial conductor and the stripline with its earthing plane. An impedance-correct junction is difficult to achieve, however, for reasons of a practical and mechanical nature. When the length of the junction is considerably shorter than the wavelength of the transmitted signal, it is possible to use a junction with incorrect impedance without reflection becoming unacceptably high. In this regard the length of the junction should be at most 5-10% of the wavelength of the signal, which in the case of a 30GHz-signal, the wavelength of which on a substrate having a high dielectric constant is about 3mm, means that the junction should have at maximum a length of some tenths of a millimetre. The greatest problem encountered in the construction of a junction according to the aforegoing is one of providing a short earthing plane junction in relation to wave-length, i.e. a short connection between the outer casing of the coaxial conductor and the earthing plane associated with the stripline. One conceivable method is to solder or glue metal foil onto the earthing plane (surface) and onto a part of the earthing wire of the coaxial plug, the earthing wire being placed around (although not in contact with) the central pin on the transverse wall of the plug. This method, however, is unsuitable when the stripline is located within a hermetically sealed apparatus box together with non-encapsulated chips, since glue give off gases which are liable to damage the chips, and since soldering gives rise to problems related to flux residues. Consequently, glue should not be used at all, and welding, when carried out, should be done prior to mounting the chips. In certain contexts, inter alia when the electrical equipment is to be used in satellites or space vehicles, manufac­ turing methods and materials, e.g. synthetic resins, which are liable to produce deleterious gases are sometimes not allowed at all. The conventional method of obtaining an earthing plane junction would seem to be one which involves the use of the metallic connection extending between the earthing plane of the stripline and the bottom of the apparatus box. This results, however, in long and unsafe earthing plane connections which have incorrect impendance. In addition, problems are caused by the mutually different coefficients of linear expansion of a hard substrate, e.g. a ceramic, and the apparatus box, causing the substrate to crack readily. A soft substrate, e.g. teflon, is more durable than a hard substrate, but cannot be used in hermetically sealed apparatus boxes due to the aforesaid generation of gases. DISCLOSURE OF INVENTION The objective of the present invention is to provide a coaxial plug of the aforesaid kind which enables a junction to be obtained which is of the correct impedance and short in relation to the wavelength of the transmitted signal without needing to use glue or synthetic resin materials. In addition, it shall be possible to connect the coaxial plug to the stripline without damaging non-­ encapsulated chips previously connected to the stripline. This is achieved by providing the coaxial plug with an outwardly projecting part which extends from the plug in the axial direction thereof in contact with the outer casing of said plug and which presents at least one substantially planar surface, therewith to enable the connections in the junction to be made with the aid of bonding techniques. The characterizing features of the invention are set forth in the following claims. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to a number of embodiments thereof illustrated in the accompanying drawings, in which Figures 1 and 2 are respectively a side view and an end view of a known coaxial plug; Figures 3 and 4 are respectively a side view and an end view of a sleeve-­ like component according to the present invention intended for use as an intermediate component between the coaxial plug illustrated in Figures 1 and 2 and a stripline; Figures 5 and 6 illustrate an alternative embodiment of the sleeve-like component according to Figures 3 and 4; Figure 7 illustrates a coaxial plug according to Figures 1 and 2 connected to a sleeve-like component according to Figures 3 and 4; Figure 8 is a side view of the plug and the sleeve-­ like component according to Figure 7, the sleeve-like component also being connected to a stripline in an apparatus box; Figure 9 illustrates the arrange­ ment according to Figure 8 seen from beneath the box externally thereof; Figure 10 illustrates a coaxial plug according to Figures 1 and 2 connected to a sleeve-like component according to Figures 5 and 6; and Figure 11 is a side view of the plug and the sleeve-like component according to Figure 10, the component of this embodiment also being connected to a stripline in an apparatus box. BEST MODES FOR CARRYING OUT THE INVENTION Figures 1 and 2 illustrate in side view and end view respectively a conventional cylindrical coaxial plug 1 of the so-called spark plug type. The plug comprises a centre pin 2, a dielectric 3 and an electrically conductive outer casing 4, provided with a screwthreaded part 5. Figures 3 and 4 are a respective side view and an end view of a cylindrical sleeve-like component 6 according to the invention. The component 6 is made of metal and is intended for use as an intermediary between a coaxial plug of the kind illustrated in Figures 1 and 2 and a stripline located in an apparatus box. The intermediate component 6 is open at one end 7 thereof, while the other carries an end wall 8. The reference numerals 9 and 10 respectively designate a broad and a narrow part of the sleeve-like component, and the reference numeral 11 designates the annular transverse wall formed at the juncture between these two parts. The axial length of the narrower part 10 preferably coincides with the thickness of the apparatus-box wall in which the stripline to be connected with an external coaxial cable is located. The broken lines in Figure 3 indicate the inner walls of the sleeve-like component, these walls forming a cylinder having an end wall as its one end. The sleeve-like component thus has a uniform internal diameter along the whole of its length. This diameter is somewhat larger than the diameter of the coaxial plug 1 to which the aforesaid component is to be connected. The internal length of the sleeve-like component is somewhat shorter than the distance between the end wall of the plug 1, from which the centre pin 2 projects, and the end of the screwthreaded plug part 5 facing said end wall (Figure 1). When the coaxial plug is inserted into the intermediate component, the central pin will project slightly through a hole 12 located in the centre of the end wall 8. The intermediate member 6 also has a part 13 which projects from the outer surface of the end wall 8 in the axial direction of said intermediate component. The part 13 has an essentially flat configuration, presenting a planar surface 14, and in one practical embodiment projects approximately 6mm from the end wall 8. The part 13 may have a width of about 3 mm. The whole or aperture 12 in the end wall 8 continues into the part 13 as a groove 12a. The hole 12 and the groove 12a are dimensioned so as to form, together with the centre pin of the coaxial plug, a conductor having a characteristic conductor-impendance which coinci­ des with that of the plug. An alternative embodiment of the sleeve-like component 6 (the intermediate component) shown in Figures 3 and 4 is illustrated in Figures 5 and 6, in which the sleeve-like component is referenced 6a and corresponding elements are designated by the same reference numerals as those used in the preceding Figures. The difference between the Figure 3 and 4 embodiment of the intermediate component and the Figure 5 and 6 embodiment is that with the intermediate component of this latter embodiment the outwardly projecting part, here referenced 13a, is located around the hole 12. The intermediate component of the Figure 5 and 6 also presents the aforesaid planer surface 14 however. The hole 12 continues through the part 13a and is dimensioned so as to form, together with the centre pin of the coaxial plug, a coaxial conductor having the same characteristic conductor-impedance as the plug. Figure 7 illustrates a coaxial plug according to Figures 1 and 2 connected to a sleeve-like intermediate component according to Figures 3 and 4. In this case, the coaaxial plug is inserted into the intermediate component 6 with one end wall of the plug in abutment with the inner surface of the end wall 8 of the component. The center pin of the plug suitably terminates edge to edge with the distal end surface of the outwardly projecting part 13, as seen from the plug, although it may, for example, optionally extend beyond said distal end surface. The assemblies, plug and component, are intended to be, e.g., soldered together, as explained hereinafter. The narrower part 10 of the intermediate component is intended to be placed into and secured in an aperture which extends through a wall of the apparatus box such that annular transverse wall 11 abuts the outer surface of said wall. Figures 8 and 9 illustrate the coaxial plug 1 and the intermediate component 6 according to Figure 7, the intermediate component also being connected to a stripline in an apparatus box. Figure 8 illustrates the arrangement in side view, whereas Figure 9 is a view taken from the outer under surface of the box. The box walls and bottom are referenced 16 and 17 respectively. The stripline is located in the upper side of an insulating plate 15, as illustrated in Figure 8, the opposite side (the lower), of which plate incorporates a conductive earthing plane attached to the box bottom. The intermediate component 6 is secured in the apparatus box with the aid, e.g., of a solder joint, with the narrower part 10 of the component located in a through-passing aperture in the wall 16 and with the annular transverse wall 11 of said component in abutment with the outer surface of the wall, as described above. To this end, the intermediate component 6 is conveniently provided with two diametrically opposed holes in the proximity of the end wall 8, through which holes a soldering compound can be introduced, such as to secure the intermediate member to the box wall 16 and to secure the plug 1 in the intermediate component. One of these holes is referenced 18. The end wall 8 of the component 6 lies opposite the inner surface of the wall 16 and the outwardly projecting shoulderlike part 13 thus protrudes slightly into the box. Consequently, the plate 15 must either be spaced from the wall 16 or provided with a recess for accomodating the outwardly projecting part 13. The earthing plane, or surface, is bonded to the planar surface 14 of the outwardly projecting part 13 with the aid of a plurality of so-called bonding wires 19. These are affixed by means of a bonding process in which two points are mutually connected by pressing a conductive material, e.g. gold or aluminium, onto the first point while applying high pressure and optionally also heat, whereafter the conductive material - in the form of thin wire or strip - is pressed against the second point. This bonding process results in molecular adhesion and can be used with advantage in the vicinity of non-encapsulated chips, since it obviates the need of glue or soldering materials, which may be liable to damage the chips. Optionally, the bond in the earthing plane junction can be effected with a single bonding wire, instead of a plurality of wires. The bond connections may also be effected with strips or bands, instead of with wire. Neither is it necessary for the surface 14 to be completely planar in order for the bond connections to be affixed thereto, but may be slightly curved for example. An aperture 20 is formed through the bottom of the box, adjacent a box wall, in order to facilitate attachment of the bonding wires. This aperture can be sealed with a further bottom plate, which is secured to the box in a known manner, e.g. by laser welding. The centre pin of the coaxial plug is connected with the conductor on the upper surface of the insulating plate with the aid of one or more bonding wires 21. Figure 10 illustrates a coaxial plug according to Figures 1 and 2 connected to a sleeve-like intermediate component according to Figures 5 and 6. The resultant assembly differs from the corresponding assembly illustrated in Figure 7, insomuch as the centre pin of the coaxial plug projects out through the hole in the outwardly projecting part 13a which, as beforementioned, is located around the pin. Figure 11 shows the assembly of Figure 10 connected to a stripline in an apparatus box. The arrangement is shown in side view and differs from the corresponding arrangement of Figure 8, insomuch as the centre pin of the plug projects slightly over the stripline on the plate 15. When seen from beneath, this arrangement has essentially the same appearance as the arrangement illustrated in Figure 9. The illustrated bond connections provide between the coaxial plug and the stripline a junction which is short and has a correct impedance, this bond being achieved without the need of soldering subsequent to mounting the components, e.g. non-encapsulated chips, in the box. In addition, the relative movement between the box and the stripline resulting from the mutually different thermal expansion coefficients are taken-up by the bonding wires. Modifications can be made within the scope of the following claims. For example, the coaxial plug may be of a kind different to that illustrated. One example in this regard resides in the type of plug having a plate in the end thereof from which the centre pin extends. It will be understood that in this case the intermediate component must also be given a flat side surface commensurate with this form of plug. The coaxial plug and the intermediate component may also have the form of a single unit, i.e. the form of a coaxial plug having the same external configura­ tion as, for example, the interconnected assemblies illustrated in Figures 7 and 10. In the case of less stringent cleanliness requirements, e.g. in the absence of encapsulated chips, other connections than bond connections may, of course, be used.

Claims: 1. A coaxial plug (1, 6, 6a) intended for use in a junction between a coaxial conductor located ecternally of an apparatus box (16,17) and a stripline with a conductive earthing plane located within the box, the stripline and earthing plane each being located on a respective side of an insulating plate (15), and the plug having a centrally located pin (2) intended for connection with the stripline, and in which the conductive outer casing (4) of the plug is intended for connection with the earthing plane, characterized in that the coaxial plung (1, (6, 6a) has a part (13, 13a) which projects outwardly in contact with the conductive outer casing (4) of the plug from the end wall (8) from which the centre pin (2) extends, and in that the outwardly projecting part presents at a location remove from the centre pin an at least substantially planar surface (14) which will enable bonded connections (21, 19) to be used between the central pin (2) and the stripline and between said surface (14) and the earthing plane respectively. 2. A coaxial plug according to claim 1, characterized in that the end wall (8) comprises a conductive circular plate having a hole (13) through which the centre pin (2) protrudes without being in contact with the defining surfaces of the hole. 3. A coaxial plug according to claim 1 or 2, characterized in that the outwardly projecting part (13) comprises an at least substantially rectangular plate having an U-shaped groove (12a) through which the centre pin protrudes without being in contact with the groove defining surfaces. 4. A coaxial plug according to claim 3, characterized in that the centre pin (2) and the outwardly projecting part (13) extend at least substantially equal distances from said end wall (8). 5. A coaxial plug according to claim 3, characterized in that the centre pin (2) extends further from the end wall (8) than does the outwardly projecting part (13). 6. A coaxial plug according to claim 1 or 2, characterized in that the outwardly projecting part (13) surrounds the centre pin (2) and has a hole (12) through which the pin protrudes without being in contact with the defining surfaces of said hole. 7. A coaxial plug according to any of claims 1-6, characterized in that the plug comprises two part, of which one part comprises a standard plug (e.g. 1) and the other part comprises a component intended for use as an intermediary (6, 6a) between the standard plug and the stripline with its conductive earthing plane with which the coaxial plug is to be connected. 8. A coaxial plug according to claim 7, characterized in that said other part (6, 6a) is of sleeve-like construction so as to fit a cylindrical standard plug (1).

Inventors: AXELL, CLAES ERIC SIGVARD
Applicants: TELEFONAKTIEBOLAGET L M ERICSSON
Application year: 1986
Main classification: H01R9
IPC codes: H01R9