CONNECTION PLUG FOR A MICROWAVE UNIT

Abstract: A connection plug which is to be fitted to a casing (M) carrying a substrate plate (B, S), on which microwave components are mounted and mutually connected with the aid of striplines. Certain striplines have their end portions taken out to the edges of the substrate plate. The plug contains a coaxial conductor junction, known per se, between an incoming coaxial conductor (K) and an outgoing conductor (6b) towards the substrate plate. In accordance with the invention, the plug has a projecting part (3) carrying a substrate piece (8) with a stripline (12) which, when the plug is fitted, is in line with the end portion of a stripline (11) on the substrate plate (S). The coaxial junction can thus be tested before fitting, and the connection between stripline (11) of the substrate plate and the stripline of the substrate piece (8) can be readily carried out during fitting.

Description: TECHNICAL FIELD The present invention relates to a connection plug intended for fitting to a microwave unit for electrically connecting a flat conductor (stripline) on a substrate plate of the unit to an outside coaxial conductor and for forming a conductive junction between the substrate conductor and the outside coaxial conductor, the plug including a hollow body part, a flange part and a projecting part, said hollow body part being cylindrically formed for recieving the outside coaxial conductor and including a first coaxial conductor element, said flange part being formed with a cylindrical space for fixing of a second coaxial conductor element, said first and second elements constituting said junction. BACKGROUND ART Microwave units, i.e. on which microwave components are built up and which are intended for the frequency range 10-50 GHz, require special connection means for the connections from one unit to remaining units. Usually, coaxial conductors are used for electrical connection between the different units. Several microwave components may be mounted on a common substrate, and the connections between the different components on the substrate can then be rapidly provided, e.g. in the form of striplines. The problem which then occurs is obtaining a reliable junction between the coaxial conductors and the conductors of the substrate of the respective microwave unit. With incoming coaxial conductors it is already known to use connectors which are attached to the substrate wafer of the microwave unit along its short sides. Special connector implementations have been developed for this purpose which give reliable connection to the substrate wafer. One type of such connector is sold under the name of "K-Connector" by Wiltron with the designation "Part Number K100". Such a connector comprises a coaxial junction mounted in a plug which can be screwed to the microwave unit. Incoming coaxial conductors are connected to a first element comprising a central conductor with two projecting ends, of which one is the female connection for the outside coaxial conductor and the other is in contact with a central conductor in a glass bead, which is soldered to the stripline of the substrate. The glass bead then constitutes the coaxial junction between the outside conductor and the substrate, and is furthermore soldered to the microwave unit itself so that stable and good contact is obtained to the substrate conductor. US 4 186 358 discloses a connection device for connecting a coaxial cable to a microwave unit, comprising a coaxial connector having a protuding inner conductor, and a tuning screw arranged to be adjusted to control the electrical parameters of the device. The device forms part of the housing supporting the microwave unit and also includes an intermediate carrier carrying an intermediate substrate conductor connected to the inner conductor of the coaxial cable. The intermediate substrate conductor is connected to the microwave circuit via a looped metal band for compensating for thermal expansion of the microwave unit relative the intermediate carrier. US 4 724 409 discloses a connection device similar to the above mentioned. This device includes a connector having a first cylindrical end mounted in the wall of the microwave unit and a second semicircular end protuding into the unit. A central conductor is disposed through the connector and have a first cylindrical portion at the first end of the connector and a second semicylindrical portion at the second end of the connector. The semicylindrical portion of the central conductor is connected to the microwave circuit via a flexible conductive member for compensating for thermal expansion of the microwave unit relative the connector. US 3 553 607 discloses a connection plug for connecting a coaxial cable to a microwave unit, comprising a metallic flange connector including a dielectric bead with a central opening, in which a conductive pin is force-fitted. The pin constitutes a connection for the coaxial conductor and includes a flat tab portion protuding through the connector for connection to the microwave circuit. Connection is achieved by screwing the connector to the microwave substrate so that the tab is pressed against a microwave strip conductor. Electrical contact can be further enhanced by a clamping slab screwed to the connector and pressing the tab against the conductor. DISCLOSURE OF INVENTION In the above-mentioned mounting of an outside coaxial conductor to a substrate, a substrate stripline is soldered to a coaxial junction with dielectric material in mechanical unit. In additon, the dielectric material is soldered to the unit for obtaining a stable soldering point between the substrate stripline and the dielectric material. This requires a special soldering technique, and it is very important that soldering is completely satisfactory to obtain good microwave contact at frequencies up to 40 GHz. A microwave unit generally has several coaxial inputs, e.g. five such inputs, to the substrate. It is practically impossible to make test measurement of the contacts for the different connections before the inner components of the unit have been put in place, and therefore a reliable test measurement of the contacts is never obtained before assembly. For example, if the unit has five contact sites and one of these has poor contact the unit is spoiled and cannot be used. It is not possible to change a connector and substrate which has been soldered on once, if soldering has been poorly executed. The entire unit must be rejected. The entire unit is only fully serviceable if all the contact sites are completely satisfactory, which is not known with certainty after soldering, since, as explained above, test measurements on the individual contact sites cannot be carried out. The present invention intends to solve the above-mentioned problem in soldering coaxial connections to the different contact sites. With the aid of the connection plug in accordance with the invention the sensitive and special soldering of the coaxial junction (the glass bead) is carried out before the complete plug is connected to the substrate stripline. This means that test measurements of the contact site made by the plug can be carried out before it is connected to the substrate stripline, and thereafter approve or reject the plug before its use as a microwave connection. A plug thus approved can be subsequently readily mounted and connected to the substrate stripline without any subsequent test measurement being needed. The connection plug in accordance with the invention is characterized as disclosed by the characterizing portion of claim 1. BRIEF DESCRIPTION OF THE DRAWING The invention will now be descibed in more detail, and with reference to the accompanying drawing, where: Figure 1 illustrates a microwave unit seen from above and fitted with a plurality of plugs in accordance with the invention; Figures 2 a-2c illustrate the inventive plug in side view, front view and a view from above. BEST MODES FOR CARRYING OUT THE INVENTION In Figure 1 there is illustrated in a view from above the mechanical construction of a microwave unit with a casing M, in which a support plate B is mounted. The support plate B is screwed to the casing M in a suitable way and carries a substrate S on which the different microwave components are mounted. Conductors in the form of striplines are provided on the substrate S to the different components. These are not shown in detail, since they are no part of the invention, with the exeption of certain end portions 11 which are described in more detail below. Five connection plugs P1-P5 are mounted on the casing M for enabling the connection of outside coaxial conductors K to the striplines 11 of the substrate. The plugs P1-P5 may be inserted into, and clamped in holes along the short sides of the casing M. In addition, a plurality of DC leads-through D1-D5 are screwed to the casing M. In accordance with the invention, each plug is provided with a piece or bit of substrate 8 of the same material as the substrate S and with a conductor 12 which is in line with a substrate stripline 11 in the assembled state of the plug. Figure 2 a shows in more detail from one side a cross section of a plug in accordance with the invention. It essentially comprises three parts: a cylindrical hollow body part 1, a cylindrical flange part 2 and a part 3 projecting out from the body part 1. The body part 1 has a cylindrical, internally threaded cavity for meshing with a threaded sleeve 4. The sleeve 4 constitutes the ground conductor for the incoming coaxial conductor K and inside the sleeve 4 there is a cylindric, electrically conductive body 5 engaging against the inner wall of the sleeve 4, and is thus in contact with the ground conductor. Inside this body there is a dielectric, concentric layer. A central conductor towards the incoming coaxial conductor K consists of a hollow pin 5a, which can be connected mechanically to the central conductor of the incoming coaxial conductor. Inside the flange part 2 there is a cylindrical space for a glass bead 6, which together with the body 5 forms a coaxial air-glass junction between the incoming coaxial conductor and the substrate. The glass bead 6 has a central conductor towards the body 5 in the form of a pin 6a, and when the plug is fitted, this pin projects into the central conductor 5b of the body 5. The central conductor of the glass bead towards the substrate comprises the same pin 6b, which projects out a distance through an opening in the flange part 2 towards the substrate piece 8. The glass bead 6 is fixed in its position inside the part 2 by soldering, which is carried out via a capillary hole 7 on the upper side of the flange part. The cylindrical body 5 constitutes an adapter for the central conductor of the incoming coaxial conductor and the central conductor 6a, 6b of the glass bead 6, and forms together with it a coaxial conductor air-glass (or other dielectric) junction from the incoming coaxial conductor to the substrate conductor. The ground contact is obtained by the side surfaces of the body 5 engaging tightly against the glass bead sheath in the fitted state. The above-described coaxial conductor junction/adaption device is described in detail in the specification from WILTRON mentioned in the introduction. The half-cylindrical part 3 projecting out from the body part 1 and from the flange part 2 has a flat upper side. The substrate piece 8 (starting substrate) is glued on to this flat surface. A flat conductor 12 (Figure 2b) is arranged on the substrate piece 8, and is connected, for example soldered, to the central conductor 6b of the glass bead. The conductor 12 has a position such that when the plug is fitted to the casing M, the conductor 12 is directly opposite a conductor 11 on the substrate plate S (Figure 1). Figure 2a further illustrates how a bond 10 is made between the conductor 12 on the substrate piece 8 and the conductor 11 on the substrate 8. This bond can be readily carried out after the plug has been fitted, e.g. with the aid of supersonics, heat and pressure, so that the bond wire (AU) melts into the striplines 11, 12. Figure 2c illustrates the plugs seen from the left in Figure 2a. The inventive plug thus comprise a unit corresponding to a known plug with the coaxial junction 5 and 6 and a starting substrate piece 8 attached to the part 3. The delicate soldering of the glass bead inside the plug and to the starting substrate 8 has already been done. Before fitting, a plurality of manufactured plugs is tested with regard to their microwave properties, e.g. for 40 GHz and 18 GHz: a) Plugs which can be used for 40 GHz, and thereby for 18 GHz. b) Plugs which can only be used for 18 GHz. c) Plugs which cannot be used for 18 GHz or 40 GHz. These plugs are rejected. After testing the properties of a plurlity of manufactured plugs have thus been determined, and those that meet given requirements (40 GHz) can be fitted into a microwave unit, and may also be replaced. The unit will never be spoiled due to the connector mounting.

Claims: A connection plug intended for fitting to a microwave unit (M) for electrically connecting a conductor (11) on a substrate plate (S) of the unit to an outside coaxial conductor (K) and for forming a conductive junction between the substrate conductor (11) and the outside coaxial conductor (K), the plug including a hollow body part (1), a flange part (2) and a projecting part (3), said hollow body part (1) being cylindrically formed for recieving the outside coaxial conductor (K), including a first coaxial conductor element (5, 5a, 5b), said flange part (2) being formed with a cylindrical space for fixing of a second coaxial conductor element (6, 6a, 6b), said first and second elements constituting said junction, characterized in that the projecting part (3) is formed as a half cylinder projecting from the flange part (2) and having a flat surface on which a substrate piece (8) is attached, the substrate piece (8) including a conductor (12) electrically connected to the central conductor (6b) of said second coaxial element (6), said conductor (12) of said substrate piece (8) being connectable to the conductor (11) of the substrate plate (S) when the plug is fitted to the microwave unit (M).

Inventors: LINDAHL, PER ANDERS ARE
Applicants: TELEFONAKTIEBOLAGET L M ERICSSON
Application year: 1989
Main classification: H01P5
IPC codes: H01P5