WO2002075839A1

WO2002075839A1 - Microwave coupler

Info

Publication number: WO2002075839A1
Application number: PCT/GB2002/001321
Authority: WO
Inventors: Barry George Morton Helme; Paul Tresise
Original assignee: Quasar Microwave Technology Limited
Priority date: 2001-03-20
Filing date: 2002-03-18
Publication date: 2002-09-26
Also published as: GB0106834D0; GB2373642A; GB0125234D0; EP1374333A1

Abstract

The coupler (1) can be mounted directly on the back of a microwave dish antenna (42) to carry a pair of microwave radios (46 and 47), e,g, in a hot standby configuration. The coupler is generally planar with the radios mounted on opposite sides coupled with respective connectors, the dish being coupled to a further connector on an end face. In a preferred form the coupler includes a pair of opposed plates containing respective microwave waveguides. One waveguide leads from a first radio to the antenna but the second waveguide leading from the second radio has a blind end containing a microwave termination element. The two waveguides are coupled through a microwave window which is preferably formed in a shim between the two plates. Each connector may contain a polarising assembly and a transition element which can only be inserted in a limited number of orientations.

Description

MICROWAVE COUPLER

TECHNICAL FIELD OF THE INVENTION

This invention relates to microwave couplers for use in radio communication installations.

BACKGROUND

In line-of-sight communication links in which a microwave dish antenna is supported on a mast, a microwave radio transceiver is generally mounted on the mast along with the antenna so that the transmission line linking the antenna to the radio is as short as possible. Such links are increasingly being installed in remote locations, and many installations now use a hot standby system in which a second radio is mounted on the mast coupled to the same antenna so that in the event that the primary radio fails the second will still function to provide uninterrupted communication until the faulty unit can be repaired. Similar configurations may be used in other situations, e.g. for radio burn-in tests.

The present invention seeks to provide a new and inventive means of mounting and coupling the various units in such an installation, which makes the mounting of the various units neat and simple and minimises stresses on the antenna mounting whilst still allowing considerable flexibility in the overall configuration of the system.

SUMMARY OF THE INVENTION

The present invention proposes a microwave coupler having a coupler body provided with:

- mounting means,

- an antenna connector,

- first and second microwave radio connectors, and

- transmission lines enclosed within the body linking the antenna connector to both radio connectors.

In a preferred form of the coupler the mounting means includes provision for mounting the coupler body directly on the back of a microwave antenna with the antenna connector engaged with a complimentary connector on the antenna. To minimise mechanical stresses such provision preferably includes a pair of mounts disposed on opposite sides of the antenna connector.

The mounting means preferably includes provision for mounting respective microwave radio units on the coupler body each coupled directly to a respective radio connector.

The antenna connector is preferably mounted in a different face of the coupler body relative to the two radio connectors, which are preferably mounted in two different faces of the coupler body. In a preferred configuration the two radio connectors are preferably mounted in mutually opposed side faces of the coupler body and the antenna connector is mounted in an end face of the body.

The body is preferably of a substantially planar configuration, and may contain a first waveguide transmission line leading from the first radio connector to the antenna connector, and a second waveguide transmission line leading from the second radio connector to a blind end, the first and second waveguides being in microwave communication via window means. The coupler body preferably includes a plurality of opposed metal plates and the first and second waveguides are formed in respective plates.

Since the dimensions of the window means affects the microwave coupling such window means preferably includes an apertured metal shim which is located between the two plates. The shim can be formed with greater accuracy and lower cost than could be achieved by machining the plates. Furthermore, by adjusting the dimensions of the window means different coupling values may be accommodated by a common set of primary and secondary plates.

In another form of the coupler, the first and second waveguides are formed side-by-side in the same plate. The coupling between the transmission lines may be achieved by window means which includes an aperture formed in a wall separating the two transmission lines. The window means can, by way of example, take the form of a single or multiple slots depending on the coupling value and particular performance requirements. In order to prevent undesirable microwave reflections the blind end of the second waveguide preferably contains a microwave termination element. Such a termination element may contain a particulate microwave-absorbing material, e.g. iron particles, in a microwave-transparent matrix, e.g. rubber. With such an arrangement a certain amount of electrical isolation is provided between the primary and secondary radios. This enables removal of either of the radios while the other remains operational.

The size of the body can be reduced, thereby minimising mechanical loading to the antenna, if the blind end of the transmission line containing the termination element is folded to lie alongside the portion containing the window means.

Any of the three connectors may comprise connector body which is releasably joined to the coupler body. The connectors can thus be easily changed to mate with different forms of radio or antenna connectors, or they can be removed to allow a length of transmission line to be coupled to the body for connection to a separately-mounted radio or antenna.

Each of the releasably joined connector bodies preferably contains a chamber containing a polarising assembly. The polarising assembly is preferably adjustable to change the polarisation of microwaves passing through the connector. Furthermore, a transition element can be inserted into the chamber to permit connection with devices having waveguides of different cross-sectional shape. By changing the size of the spacer the polarising assembly and/or transition element can easily be changed to permit operation on different microwave frequencies. The orientation of the polarising assembly and transition element may be determined by a unique set of locating features such that they can only be assembled in a predetermined number of orientations.

Although the microwave transmission line will often be in the form of waveguide, other kinds of transmission line can be used, e.g. those which include electrical conductors and dielectrics such as a co-axial pair, or dielectrics and conductors which are formed as a flat strip such as stripline and microstrip. Additionally, some transmission line coupling values may be achievable by using waveguides without window means, for example 3dB hybrid.

More elaborate coupling configurations within the plates would enable more than two radio connectors to share the same antenna. For example 4:1 and 8:1 configurations may be achieved relatively simply.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings:

Figure 1 is a general exploded view of the main body of a microwave coupler in accordance with the invention;

Figure 2 is an end view of the assembled coupler, looking from the left in Fig. 1 ; Figure 3 is a section on the line A-A of Fig. 2;

Figure 4 is a side view of the assembled coupler, showing the internal structure in ghost outline;

Figure 5 is a general exploded view of one of the connectors used in the coupler;

Figure 6 is a similar view to Fig. 5 but showing an alternative configuration of the coupler;

Figure 7 is a general view of the coupler, in use, in a preferred configuration; and

Figures 8 to 10 are similar views to Fig. 7 showing the coupler in three alternative configurations.

DETAILED DESCRIPTION OF THE DRAWINGS

The microwave coupler to be described below can be used in hot standby applications, burn-in tests etc. Referring firstly to Fig.1 , the coupler includes a structural body 1 formed by pair of rectangular metal plates 2 and 3 of substantially identical outline which are secured together, e.g. by bolts inserted into holes 4. The body 1 thus has an end face 5 and a pair of opposed side faces 6 and 7 provided by the respective plates 2 and 3. In the embodiment being described, the plates 2 and 3 have a pair of out- turned flanges 8 and 9 at the end face 5 to which a mounting frame 10 for a dish antenna can be bolted as shown in Fig.2, although the configuration of the end face 5 can vary. (The coupler shown in Fig.s 7 and 8 described below, has a different configuration of end face.)

The end face 5 has a co-axial microwave antenna connector 12 mounted substantially centrally thereof to connect with a complementary connector fixed to a microwave dish antenna (not shown) which, in the embodiment under discussion, is secured to the mounting frame 10. In addition, a pair of co-axial microwave radio connectors 13 and 14 are mounted substantially centrally on the respective side faces 6 and 7 extending in opposite directions. Each of the side faces 6, 7 also includes mounting blocks 16 to which a microwave radio transceiver can be secured using clips 17 or equivalent mounting means, with a complimentary connector of the radio joined to the respective connector 13 or 14. It will be appreciated that the connectors 12-14 can be of any suitable configuration. They are secured to the body 1 by screws so that they can easily be removed and replaced with a different form of connector if required.

The internal configuration of the body 1 is best seen in Fig.s 3 and 4. A large area of the opposed faces 20, 21 of the two plates are machined away as indicated at 22 to reduce the weight of the coupler. In addition, one of the faces 21 of plate 3 contains a machined groove forming a rectangular- section microwave waveguide 23 (transmission line) leading from the antenna connector 12 and, via a 90° bend, to one of the radio connectors 14, to which the primary radio transceiver is connected. There is thus a direct microwave transmission path between the antenna and the primary radio. A secondary waveguide 24, again or rectangular section, is machined into the opposed face 20 of the plate 2, again leading via a 90° bend to the respective radio connector 13, to which a secondary or standby radio transceiver is connected in use. The waveguides 23 and 24 are separated by a thin metal shim 26 of an accurately determined thickness through which rows of window apertures 27 are formed by an accurate etching process. The windows 27 thus permit microwave communication between the antenna at connector 12 and the standby radio at connector 13. The secondary waveguide 24 is turned through a 180° bend 29, designed by computer simulation to minimise losses, which leads into a blind-ending portion 30 lying alongside the portion containing windows 27. This portion 30 contains a microwave termination device (not shown) formed of a rubber matrix loaded with iron particles and fixed in the waveguide using an adhesive. The termination device minimises return losses at all three ports by absorbing reflected signals. By machining an accurate 180° bend the overall size of the coupler can be reduced so that if the coupler is used with very compact radio units its size can be reduced accordingly, thereby saving valuable mast space.

It will be noted in Fig. 3 that each of the connectors 12-14 contains a cylindrical chamber 34 arranged co-axially with the microwave path through the respective connector. The chamber contains a set of components which are used to interface the coupler with a particular antenna or radio, as will now be described with reference to Fig.s 5 and 6. The chamber 34 of each connector (in this case antenna connector 12) contains an interface element 35 followed by a transition element 36 which can, for example, create a low loss transition between a circular antenna transmission line and the rectangular waveguide used in the coupler. This is followed by a spacer 37 forming a plain section of rectangular transmission line, which is in turn followed by two twist elements 38 and 39. These elements 38, 39 contain respective sets of locating holes 41 and 42 which co-operate with pins 43 on the body 1 to ensure that the plates can only be fitted in two orientations. In one orientation shown in Fig. 5, the elements align with the rectangular- section waveguide of the body 1 to maintain the polarisation of the microwaves on passing through the connector. However, by mounting the twist elements in their alternative configuration (Fig. 6) the waves undergo a total polarisation shift of 90° on passing through the connector. Thus, by unbolting the connector the user can easily reconfigure the connector to interface with antennas and radios of horizontal or vertical polarisation. It is similarly possible to change the elements 35 and 36 for different antennas. In addition, the elements 35, 36 and 38, 39 can be changed for operation on different microwave frequencies, the spacer also being changed to compensate for the different lengths of these elements.

A preferred use of the coupler is shown in Fig. 7. A microwave antenna 42 is mounted on a mast 43 via a mounting bracket 44 which is in turn secured by conventional mast clamps 45. The coupler body 1 is mounted on the rear of the antenna by means of mounting projections on opposite sides of the connector 12, with the connector 12 directly engaged with the antenna. Radios 46 and 47 are mounted on opposite sides of the body 1 , as described, engaged with the connectors 13 and 14. It will thus be appreciated that the installation utilises a minimum amount of mast space and avoids the requirement for separate interconnecting lengths of waveguide.

The coupler does however permit other configurations to be readily achieved where operating conditions dictate. For example, the coupler can be mounted separately on the mast as shown in Fig. 8. The connector 12, is unbolted so that a length of waveguide 50 can be bolted directly to the body 1 , the opposite end of the waveguide being connected to the antenna 42. In an alternative configuration shown in Fig. 9 the coupler can be mounted directly to the antenna 42 and one or both of the radios 46 and 47 can be mounted separately on the mast connected to the coupler by respective lengths of waveguide 51 and 52. Again, the respective connector 13, 14 is unbolted so that the waveguide can be bolted directly to the body of the coupler. Lastly, the coupler and radios can all be separately mounted as shown in Fig. 10.

It will be appreciated that the features disclosed herein may be present in any feasible combination. Whilst the above description places emphasis on those areas which, in combination, are believed to be new, protection is claimed for any inventive combination of the features disclosed herein.

Claims

1. A microwave coupler having a coupler body characterised by:

- mounting means,

- an antenna connector,

- first and second microwave radio connectors, and

2. A microwave coupler according to Claim 1, in which the mounting means includes provision for mounting the coupler body on the back of a microwave antenna with the antenna connector engaged with a complimentary connector on the antenna.

3. A microwave coupler according to Claim 1 , in which the mounting means includes provision for mounting respective microwave radio units on the coupler body each coupled directly to a respective radio connector.

4. A microwave coupler according to Claim 1 , in which the antenna connector is mounted in a different face of the coupler body relative to the two radio connectors.

5. A microwave coupler according to Claim 4, in which the two radio connectors are respectively mounted in two different faces of the coupler body.

6. A microwave coupler according to Claim 1 , in which the coupler body contains a first waveguide transmission line leading from the first radio connector to the antenna connector, and a second waveguide transmission line leading from the second radio connector to a blind end, the first and second waveguides being in microwave communication via window means.

7. A microwave coupler according to Claim 6, in which the coupler body includes a plurality of opposed metal plates and the first and second waveguides are formed in respective plates.

8. A microwave coupler according to Claim 6, in which the first and second waveguides are formed side-by-side in the same plate.

9. A microwave coupler according to Claim 1, in which at least one of the three connectors has a connector body which is releasably joined to the coupler body.

10. A microwave coupler according to Claim 9, in which the or each releasably joined connector body contains a chamber containing a polarising assembly.