GB2189652A - Adaptor for connecting a coaxial transmission line to a parallel plate transmission medium - Google Patents

Abstract

An adaptor for connecting a coaxial transmission line to a parallel plate transmission medium comprises a coaxial connector (6), which is adapted to be connected to a coaxial transmission line and which is provided with stripline connection means, and a stripline circuit connected to the coaxial connector (6) by said connection means. The stripline circuit comprises a metal body (1) having an overlying dielectric layer (2) in which a conductive track (3) is etched and which is partially covered by a further metal body (4). A parallel plate transmission medium can be engaged with the stripline circuit so that one plate is in face to face contact with the exposed track (3) and the other plate butts against the side of the metal body (4) to form a ground connection. In this way, connection between a coaxial transmission line and a parallel plate transmission medium can be established without any exposed leads or dangling contacts. <IMAGE>

Description

SPECIFICATION Adaptor for connecting a coaxial transmission line to a parallel plate transmission medium This invention relates to an adaptor for connecting a coaxial transmission line to a parallel plate transmission medium.

Such a connection is generally not possible because the media are usually mechanically incompatible. The present invention, however, aims to achieve such a connection by means of an adaptor to which both a coaxial transmission line and a parallel plate transmission medium can be connected.

According to the invention, there is provided an adaptor for connecting a coaxial transmission line to a parallel plate transmission medium which comprises a coaxial connector adapted to be connected to a coaxial transmission line and provided with strip line connection means and a stripline circuit connected to the coaxial connector by said connection means, wherein the stripline circuit is provided with an exposed track which is engageable with a parallel plate transmission medium to establish an electrical connection between said medium and a coaxial transmission line via said stripline circuit and coaxial connector.

The stripline connection means of the coaxial connector may comprise a launching pin or tab and the coaxial connector may be of the type SMA, SMB, type N or any similar type.

The adaptor is desirably constructed in such a manner that a rectangular sheet can be flush with a ground connection and the exposed track.

Preferably, the stripline circuit is supported on a metal body part of which is cut way to provide the exposed track for the parallel plate transmission medium. The metal body will provide a R.F. earth connection for the said parallel plate transmission medium.

The adaptor is desirably arranged to establish face to face electrical contact between the exposed track and one of the parallel plates of a parallel plate transmission medium. The adaptor may also be arranged to establish a ground connection at right angles to the exposed track or to the other parallel plate by means of a clamping device. In the latter case, the clamping device may comprise a clamp plate mounted on the metal body, a spindle extending through the clamp plate, a wheel eccentrically mounted on the spindle and a lever arranged to operate the wheel, said wheel being arranged to bear against the other parallel plate through operation of the lever.

A dielectric layer may be provided to establish a capacitive contact for the ground connection and/or between the exposed track and the said one parallel plate.

The characteristic impedance of the stripline circuit should be the same as that of the coaxial transmission line to be connected to the coaxial connector. A metal spacer may be provided between the coaxial connector and the stripline circuit depending on the type of connector used. The characteristic impedance through the spacer should, however, be unchanged.

The invention also extends to transmission connection means comprising a pair of adaptors as above described in which a first adaptor is fixedly mounted on a metal base plate adapted to receive a parallel plate transmission medium and a second adaptor is slidably mounted on the metal plate, means being provided for moving the second adaptor into clamping engagement with the parallel plate transmission medium and to force the latter against the first adaptor whereby the medium is clamped between the two adaptors.

The invention will now be further described, by way of example, with reference to the drawings, in which: Figure 1 is a perspective view of one embodiment of an adjuster according to the invention; Figure 2 is a section taken on the line Il-Il in Figure 1 in the direction of the arrows; Figure 3 is a side elevation showing the mounting of a parallel plate transmission medium on the adaptor shown in Figures 1 and 2; Figure 4 is a perspective view of a modified form of adaptor according to the invention; Figure 5 is a plan view of the adaptor shown in Figure 4 indicating the position of a parallel plate resonator mounted thereon; Figure 6 is a perspective view showing two adaptors of the type shown in Figure 4 connected to opposite ends of a parallel plate resonator to form a resonator test jig;; Figure 7 shows an arrangement for establishing an earth connection using two adaptors according to the invention; and Figure 8 shows clamp means for establishing electrical contact between a parallel plate transmission medium and an adaptor according to the invention.

In the drawings, like parts are denoted by like reference numerals.

Reference will first be made to Figures 1 and 2 of the drawings in which the adaptor comprises a metal body 1 over one surface of which is laid a layer of dielectric insulation 2 containing a conductive track 3. Overlying the dielectric layer 2 is a further metal body 4, pert of this metal body and of the dielectric layer 2 being cut away to expose the track 3.

A launching pin or tab 5 of a coaxial connector 6 is connected to the track 3, a spacer 7 being provided between the connector 6 and the metal bodies 1 and 4.

As shown in Figure 3, a parallel plate transmission medium comprising a thick metal plate 11 having on one face a dielectric insulator layer 12 and a metal conductor 13 is connected to the adaptor by laying the medium on the exposed dielectric layer 2 and exposed track 3 so that one end of the plate 11 butts against the metal body 4 with the metal conductor 13 in contact with the exposed track 3. A conventional coaxial cable (not shown) can be connected to the coaxial connector 6 so that a connection between the cable and the parallel plate transmission medium is established by means of the adaptor. As will be seen from Figure 3, the electrical connection for one plate 13 of the parallel plate transmission line is made to the exposed track 3 whilst the electrical connection to the other plate 11 is made by sideways contact to the metal body 4.The electrical connections may be metal to metal but, if capacitive coupling is required, a thin layer of insulation may be provided either against the metal body or over the exposed track. Care is required to make good contact.

A modified form of adaptor according to the invention is shown in Figure 4 in which the metal body 4 is provided with a wedgeshaped protrusion 8. This is considered desirable to make a good ground connection close to the R.F. launch point as can be seen from Figure 5 in which a parallel plate resonator is indicated by the dotted lines.

Turning now to Figure 6, two adaptors of the type shown in Figures 4 and 5 are shown connected to either end of a parallel plate resonator to form a resonator test jig suitable for the measurement of the dielectric constant of the insulator dielectric.

The parallel plate resonator shown in Figure 6 preferably consists of a brass plate 11 having a thickness of about 0.32 cm (1/8") and about 14.175gm (1/2or) of copper electrodeposited on its lower face to form the metal layer 13. The dielectric consists of Rogers 6010.2 PTFE/Ceramic composite with a dielectric constant of 10.2 nominal. The size of the parallel plate resonator is 25.4cm (10") + 0.25 cm (0.1") x 10.8 cm (41/4") + 0.25 cm (0.1"). An adaptor having a wedge shaped protrusion 8 is fitted to either end of the parallel plate resonator, the protrusions serving to make a good ground connection close to the R.F. launch point.Each coaxial connector 6 comprises a Radial R125-501 SOohm connector spaced from the striplne circuit by respective spacers 7 with a hole designed to provide the outer conductor of a 50 ohm coaxial iine.

The width of the strip line centre conductor 3 is chosen for 50 ohm characteristic impedance using 0.64 cm (1/4") aluminium clad Rogers 5880 substrate with tracks etched into 28.35 gm (loz) copper cladding. The aluminium claddings are placed outermost. Thus, the characteristic impedance of 50 ohms is maintained frcm the exposed connector through to the coaxial line.

A method of maintaining a good earth contact is shown in Figure 7 in which a metal base plate 14 supports two coaxial/parallel plate adaptors according to the invention. One adaptor 1 a is fixed to the base plate 14 while the other 1 b is permitted to slide along a slot 15 in the base plate. Pressure is maintained in the direction of the arrow shown (thereby giving good earth connections to both adaptors) by a screw 16 in the baseplate which bears against the metal body of the sliding adaptor 1b which lies in the slot 15. The metal base plate 14 is partly covered with a soft plastic layer (not shown) which does not affect electrical performance but presents the parallel plate resonator 11, shown in dotted lines in Figure 7, from being accidentally scratched by the metal baseplate 14.

Figure 8 shows an alternative method of maintaining a good electrical contact between the metal body 4 of an adaptor and the metal plate 11 of a parallel plate resonator. A clamp plate 17 is fitted on the top of the metal body 4 and a spindle 18 extends through the clamp plate. A wheel 19 is eccentrically mounted on the spindle 18 and is arranged to be operated by a lever 20. By operating the lever, the wheel 19 can exert a downwards pressure on the parallel plate resonator, as indicated by the arrow in Figure 8, to provide a good electrical contact. The wheel/clamp plate assembly may be made of metal to provide alternative or supplementary earth electrical contact.

The adaptor above described may be used with certain types of parallel plate transmission media, in particular those with a thick metal plate on one face, to launch or receive R.F. signals.

The adaptor according to the invention has the advantage that a matched R.F. transmission line, i.e. coax/stripline, is brought right up to the edge of the parallel plate transmission line by pressing into a right angle corner, i.e.

there are no exposed leads or dangling contacts. Further, since the parallel plate fits squarely into the adaptor, there is no danger of a point contact or tab scratching the plate.

Additionally, no soldering is required. The technique lends itself to simple clamping jig techniques. There is little danger of short circuiting the R.F. contacts and the most delicate part of the coaxial line, i.e. the pin or tab launcher, is completely protected inside the stripline circuit. The adaptor can handle virtually any thickness of dielectric insulator.

Claims (14)

1. An adaptor for connecting a coaxial transmission line to a parallel plate transmission medium which comprises a coaxial connector adapted to be connected to a coaxial transmission line and provided with stripline connection means and a stripline circuit connected to the coaxial connector by said con nection means, wherein the stripline circuit is provided with an exposed track which is engageable with a parallel plate transmission medium to establish an electrical connection between said medium and a coaxial transmission line via said stripline circuit and coaxial connector.

2. An adaptor according to claim 1, wherein the coaxial connector includes a launching pin or tab.

3. An adaptor according to claim 1 or claim 2, wherein the adaptor is constructed in such a manner that a rectangular sheet can be flush with a ground connection and the exposed track.

4. An adaptor according to claim 3, wherein the stripline circuit is supported on a metal body part of which is cut away to provide the exposed track for the parallel plate transmission medium.

5. An adaptor according to claim 4, wherein the adaptor is arranged to establish face to face electrical contact between the exposed track and one of the parallel plates of a parallel plate transmission medium.

6. An adaptor according to claim 5, wherein the adaptor is arranged to establish a ground connection at right angles to the exposed track.

7. An adaptor according to claim 5, wherein the adaptor is arranged to establish a ground connection to the other parallel plate by means of a clamping device.

8. An adaptor according to claim 7, wherein the clamping device comprises a clamp plate mounted on the metal body, a spindle extending through the clamp plate, a wheel eccentri caily mounted on the spindle and a lever arranged to operate the wheel, said wheel being arranged to bear against the other parallel plate through operation of the lever.

9. An adaptor according to any one of claims 6 to 8, wherein a dielectric layer is provided to establish a capacitive contact for the ground connection.

10. An adaptor according to any one of claims 5 to 9, wherein a dielectric layer is provided to establish a capacitive contact between the exposed track and the said one parallel plate.

11. An adaptor according to any one of claims 4 to 10, wherein the part of the metal body which is cut away is provided with a wedge-shaped protrusion which is engageable with a parallel plate transmission medium located on the adaptor.

12. An adaptor according to any preceding claim, wherein a spacer is provided between the coaxial connector and the stripline circuit.

13. Transmission connection means comprising a pair of adaptors as claimed in any preceding claim, wherein a first adaptor is fixedly mounted on a metal base plate adapted to receive a parallel plate transmission medium and a second adaptor is slidably mounted 6n the base plate, means being provided for moving the second adaptor into clamping engagement with the parallel plate transmission medium and to force the latter against the first adaptor whereby the medium is clamped between the two adaptors.

14. An adaptor for connecting a coaxial transmission line to a parallel plate transmission medium substantially as described herein with reference to the drawings.