GB2142481A

GB2142481A - A wave guide to microstrip microwave transition

Info

Publication number: GB2142481A
Application number: GB08317642A
Authority: GB
Inventors: Amitava Banerjee; Roger Hill
Original assignee: Decca Ltd
Current assignee: Decca Ltd
Priority date: 1983-06-29
Filing date: 1983-06-29
Publication date: 1985-01-16
Also published as: GB8317642D0

Abstract

A waveguide to microstrip microwave transition comprises a rectangular waveguide 1 having broad-wall longitudinal slots 2 and 3 at an open end thereof. A substrate plate 4, carrying a microstrip array antenna 5 can be located in the slot so as to extend across the waveguide perpendicular to the broad walls thereof. A length of microstrip line 8 extends from the array antenna into the open end of the waveguide and terminates in a coupling stub 9. A ground plane 7 provided on the opposite face of the substrate to the microstrip line extends right across the narrow dimension of the waveguide and terminates at a distance from the stub chosen to maximise the energy coupling. The waveguide and substrate may have interengaging threaded rings. <IMAGE>

Description

SPECIFICATION A waveguide to microstrip microwave transition This invention relates to a waveguide to microstrip microwave transition, and more specially wherein the microstrip is connected to a microstrip array antenna.

Microstrip array antennas offer a cheap and relatively simple method of producing both omni directional and wide beam radiators. It is known to connect a microstrip array antenna to a microwave waveguide by a coaxial cable. The coaxial cable has a connection in a broad wall of the waveguide and includes a stub member which is positioned so as to couple microwave energy between the waveguide and the microstrip array antenna. With use of this form of connection it is important that radiation is not radiated from the waveguide end with a conse quent energy loss. In addition the form of connection is not particularly robust thereby restricting its usage.

It is an object of the invention to provide a waveguide to a microstrip microwave transition which is both convenient and easy to use, and has a robust construction.

According to the invention there is provided a waveguide to microstrip microwave transition com prising a rectangularwaveguide having provided in an open end thereof longitudinal slots extending from the end into the broad walls of the waveguide; a microstrip substrate plate locatable into said slots so as to extend across the waveguide perpendicular to said broad walls; a length of microstrip line provided on one face of the substrate so as to extend into the open end of the waveguide and terminating in a stub located in the waveguide and capable of coupling microwave energy between the waveguide and the microstrip line; and a conducting plane provided on the opposite face of the substrate so as to extend right across the narrow dimension of the waveguide between said slots; an inner edge of the said plane extending perpendicularly to said broad walls at a predetermined distance from said stub to maximise said energy coupling. Conveniently the microstrip line is connected to a microstrip array antenna, and the stub is L shaped and located centrally with respect to the waveguide broad dimension. In this way the substrate plate carrying the microstrip can be easily removed and easily located within the waveguide end. By mounting the substrate plate into said slots it is convenient to orientate the array vertically to provide thereby wide beam azimuth coverage over a limited elevation, for example as an automatic transponder in a naviga tional aid system.Furthermore the conducting plane extending right across the narrow dimension of the waveguide acts as a reflector to substantially elimin ate radiation of microwave energy from the wave guide end. Preferably the waveguide end is sealed with a non-electrically conductive material to pre vent ingress of moisture into the waveguide. The substrate plate can be maintained in its position in the slots by including a connecting means compris ing a threaded flange provided at the waveguide end and a threaded ring associated with the substrate and capable of screwing on to the flange to urge thereby the substrate into the slots. Consequently a stable and robust waveguide to microstrip microwave transition is produced.

Examples of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 illustrates a waveguide to microstrip microwave transition; Figure 2 illustrates a waveguide to microstrip microwave transition including connecting means.

Referring to the drawings a rectangular microwave waveguide 1 has two longitudinal slots 2 and 3 extending from the end of the waveguide into the broad walls thereof. A substrate plate 4 is located into the slots.

The plate 4 has provided thereon a microstrip line 8 connecting to a microstrip array antenna 5 also provided on the substrate plate. The microstrip array antenna can be of various types, for example, a Derneryd Array (reference Derneryd, A.G., 'Linearly Polarised Microstrip Antennas', IEEE Trans. on Antenna and Propagation, 846 - 850, (Nov. 1976)).

However that shown was described in 'A twin line omnidirectional aerial configuration', 8th European Microwave Conference, Paris, September 1978 p.p.

307-311. The microstrip line terminates at its lower end with a L shaped stub 9. The line 8 is arranged so that when the plate 4 is located in the slots the line extends into the open end of the waveguide. The stub 9 is thereby located approximately centrally within the waveguide.

A conducting plane 7 is provided on the opposite face of the substrate to the microstrip line and is located such that when the substrate is positioned within the slots the conducting plane extends right across the narrow dimension of the waveguide between the slots and an inner edge of the plane extends perpendicularly to the broad walls of the waveguide. The stub ending is then located at a predetermined distance from the inner edge of the plane in orderto maximise the coupling of microwave energy between the waveguide and the microstrip line. The predetermined distance is preferably one quarter of the wavelength of the microwave radiation to be radiated.

As a consequence of the location of the plane microwave radiation is prevented from radiating from the waveguide end and microwave radiation is coupled from the waveguide to the microstrip array antenna by means of the microstrip line. In this way the microstrip substrate plate 4 can easily be removed from the waveguide end and easily replaced.

Furthermore the loss of energy by radiation of microwaves from the waveguide end is prevented by the conducting plane 7. The waveguide to microstrip microwave transition is secure and robust and allows quick assembly by insertion cf the substrate into the slots. The end of the waveguide can also be sealed with a non-electrically conducting material to seal the waveguide against entry of water.

Referring to Figure 2 a waveguide 1 is connected at its end to a threaded flange 12. The waveguide includes slots 2 and 3 to allow the location of the substrate plate. A threaded flange ring 10 includes a central aperture 11 through which the substrate plate can be inserted. The substrate plate is formed to be T shaped and the substrate plate is inserted through aperture 11 so that when the flange ring 10 is located above the flange 12 the section of the plate having a broader width is located between the ring and the flange. The broader section of the substrate plate includes the microstrip line and is consequently located with slots 2 and 3. When the flange ring 10 is screwed on to the flange 12 the flange ring urges the substrate into the slots and maintains the substrate plate therein. In this way the substrate plate is held into its position in the waveguide end in a secure and robust manner which allows quick assembly and disassembly.

It will be apparent that other forms of stub ending can be provided and it is not essential that the microstrip array antenna and conducting plane are provided on a common substrate. The conducting plane is provided to extend across the narrow dimension of the waveguide end between said slots and can be connected to the microstrip array antenna. As an alternative to a substrate carrying the microstrip antenna which is removeable and held in place as shown in Figure 2, it will be apparent that the substrate may conveniently be connected to the waveguide slots 2 and 3 by means of an adhesive.

Claims

1. A waveguide to microstrip microwave transition comprising a rectangular waveguide having provided in an open end thereof longitudinal slots extending from the end into the broad walls of the waveguide; a microstrip substrate plate locatable into said slots so as to extend across the waveguide perpendicular to said broad walls; a length of microstrip line provided on one face of the substrate so as to extend into the open end of the waveguide and terminating in a stub located in the waveguide and capable of coupling microwave energy between the waveguide and the microstrip line; and a conducting plane provided on the opposite face of the substrate so as to extend right across the narrow dimension of the waveguide between said slots; an inner edge of the said plane extending perpendicularlyto said broad walls at a predetermined distance from said stub to a maximise said energy coupling.

2. A waveguide to microstrip microwave transition as claimed in claim 1 wherein the microstrip line is connected to a microstrip array antenna.

3. A waveguide to microstrip microwavetransition as claimed in claim 1 or 2 wherein the stub is L shaped and located centrally with respect to the waveguide broad dimension.

4. A waveguide to microstrip microwave transition as claimed in any preceding claim wherein the waveguide end is sealed with a non-electrically conductive material.

5. A waveguide to microstrip microwavetransition as claimed in any preceding claim including connecting means arranged to hold the substrate in said slots.

6. A waveguide to microstrip microwavetransition as claimed in claim 5 wherein the connecting means comprises a threaded flange provided at the waveguide end and a threaded ring associated with the substrate and capable of screwing on to the flange to urge thereby the substrate into the slots.

7. A waveguide to microstrip microwave transition as claimed in claim 5 wherein the connecting means comprises an adhesive.

8. A waveguide to microstrip microwavetransition substantially as herein described with reference to the accompanying drawings.