GB2359197A

GB2359197A - Enhanced performance waveguide diplexers

Info

Publication number: GB2359197A
Application number: GB9929206A
Authority: GB
Inventors: David Young
Original assignee: BSC Filters Ltd
Current assignee: BSC Filters Ltd
Priority date: 1999-12-11
Filing date: 1999-12-11
Publication date: 2001-08-15
Anticipated expiration: 2019-12-11
Also published as: GB9929206D0; GB2359197B

Abstract

A waveguide diplexer consisting of two extracted pole waveguide filters and a waveguide junction. Each waveguide filter has an asymmetrical generalized Chebyshev transfer function, the lower filter having transmission zeros near its upper skin and the upper filter having transmission zeros near its lower skirt. The transmission zeros are realized by waveguide stubs 2 coupled to either the narrow wall or the broad wall of the waveguide and situated at either one or both ends of the filter. The junction is either an H-plane T-junction, an E-plane T-junction, an H-plane tuning fork junction (see figure 3), an E-plane tuning fork junction (see figure 4), an H-plane Y-junction or an E-plane Y-junction. The junction may contain a matching element.

Description

1 Enhanced performance waveguide diplexers 2359197 This invention relates

to a method for improving the performance of a waveguide diplexer for use in commercial microwave point to point and point to multi-point systems.

Until now waveguide diplexers for commercial point to point and point to multi-point systems have used Chebyshev coupled cavity waveguide diplexers. This invention allows the required diplexer filtering to be achieved using less filter sections thereby improving the insertion loss.

This invention is a waveguide diplexer whose filter channels have an asymmetrical generalized Chebyshev transfer function with finite frequency transmission zeros given by extracted poles. The lower channel having increased selectivity on its upper skirt and the upper channel having increased selectivity on its lower skirt. The finite frequency transmission zeros are realized by waveguide stubs coupled to either the waveguide broad wall or narrow wall or a combination of both the waveguide broad wall and narrow wall. The waveguide stubs are located either at one end or at both ends of the filter and may all be on the same waveguide wall or on different waveguide walls relative to the diplexer common port. The waveguide stubs may be of different cross section to the main waveguide. The transmission zeros at infinity are realized by iris coupled waveguide bandpass cavities. The waveguide stubs are separated from each other and from the bandpass sections by phase shifters realized by lengths of waveguide. The diplexer junction may be an H-plane TJunction, an Eplane T-junction, an H-plane tuning fork junction (figure 3 shows an example of an H-plane tuning fork junction with the lid 13 removed), an E-plane tuning fork junction (figure 4 shows an example of an E-plane tuning fork junction with the lid 14 removed), an H-plane Y-junction or an E-plane Y-junction. The junction may or may not contain a matching element. A length of waveguide acting as a phase shifter may or may not be present between the junction and the first filter element in each arm.

Two examples of the invention will now be described with reference to the accompanying drawings: - Example 1: H-plane T-junction diplexer Figure 1 shows an example of the invention using a compensated H-plane T- Junction for a MHz diplexer, machined from a solid block of metal. The device is shown with the lid 1 removed.

Figure 2 shows the predicted insertion loss 11 and return loss 12 of the diplexer shown in figure 1.

Each filter in figure 1 is of order six with two finite frequency transmission zeros (extracted poles) placed close to one skirt. The extracted poles are realized by waveguide stubs 2, approximately a guide wavelength in length at the filter centre frequency, coupled to the narrow waveguide wall by an inductive iris 3. A single stub is located at either end of each filter, such that the filter element nearest the junction is 2 a waveguide stub. All the waveguide stubs are located on the wall opposite the waveguide common port 4. The four transmission zeros at infinity in each filter are realized by inductive iris coupled waveguide cavity bandpass resonators 5. These are separated from the waveguide stubs by phase shifters 6. Since the filters use a nonstandard waveguide cross section, the three diplexer ports 4,7 and 8 are stepped out to a standard waveguide size using quarter wave transformers 9. The H-plane T- junction contains an inductive vane 10 which operates as a matching element.

Example 2: H-plane tuning fork junction diplexer Figure 3 shows an example of an H-plane tuning fork junction Figure 5 shows an example of the invention using an H-plane tuning fork junction for a 38GHz diplexer.

Figure 6 shows the predicted insertion loss 28 and return loss 29 of the diplexer shown in figure 5.

The common port of the H-plane tuning fork junction 18 is of a standard waveguide size whereas the filters ports 25 and 26 are of non-standard cross section. The device is machined from a solid block of metal. Figure 5 shows the device with the lid 15 removed. The two filters are separated by a septum 27. Each filter in figure 5 is of order seven with a single finite frequency transmission zero (extracted pole) placed close to one skirt. The extracted poles are realized by waveguide stubs 16 approximately a guide wavelength in length at the filter centre frequency, coupled to the narrow waveguide wall by an inductive iris 17. The single waveguide stubs are located at the ends of the filters furthest away from the waveguide common port 18. The six bandpass sections in each filter are realized by inductive iris coupled waveguide bandpass resonators 19. These are separated from the waveguide stubs by phase shifters 20. Both filters use waveguide of a non-standard cross section hence the waveguide ports 21 and 22 contain quarter wave transformers 23 to transform the waveguide to a standard size.

3

Claims

Claims 1 A waveguide diplexer whose filter channels have an asymmetrical generalized Chebyshev transfer function. The lower channel having increased selectivity on its upper skirt and the upper channel having increased selectivity on its lower skirt. The finite frequency transmission zeros are realized by waveguide stubs coupled to either the broad wall of the filter or the narrow wall of the filter or a combination of both the broad wall and the narrow wall and located either at one end of the filter or both ends. The waveguide stubs may all be on the same waveguide wall relative to the junction or on different waveguide, walls. The waveguide stubs may be of different width to the main wavgeuide. 2 A waveguide diplexer as described in claim 1 using an H-plane Tjunction, which may or may not be compensated. 3 A waveguide, diplexer as described in claim 1 using an E-plane TJunction, which may or may not be compensated. A waveguide, diplexer as described in claim 1 using an H-plane tuning fork junction (figure 3), which may or may not be compensated. A waveguide, diplexer as described as described in claim 1 using an Eplane tuning fork junction (figure 4), which may or may not be compensated. 6 A waveguide, diplexer as described in claim 1 using an H-plane Yjunction which may or may not be compensated. A waveguide diplexer as described in claim 1 using an E-plane Y-junction which may or may not be compensated. 8 A waveguide diplexer as described in claims 1 to 7 using none standard waveguide sizes and transforming to a standard waveguide, size at the three diplexer ports. 9 A waveguide diplexer as described in claims 1 to 8 using waveguide of any cross section.

1+ Amendments to the claims have been filed as follows 1. A waveguide diplexer having an upper frequency filter and a lower frequency filter each having an asymmetrical generalized Chebyshev transfer function, in which the transfer function of the lower frequency filter has increased selectivity on its upper skirt and the transfer function of the upper frequency filter has increased selectivity on its lower skirt, and in which finite frequency transmission zeros of the transfer functions are realized by waveguide stubs coupled to a waveguide wall.

2. A diplexer as claimed in claim 1, in which the waveguide stubs are coupled to the waveguide broad wall or the waveguide narrow wall, or both the waveguide broad wall and narrow wall.

3. A diplexer as claimed in claim 1 or 2, in which a waveguide stub is located at one end of a filter or at both ends of a filter.

4. A diplexer as claimed in claim 3, in which more than one waveguide stub is located at one end of a filter or at both ends of a filter.

5. A diplexer as claimed in any of claims 1 to 4, in which the waveguide stubs are all on the same waveguide wall relative to a junction of the diplexer.

6. A diplexer as claimed in any of claims 1 to 4, in which the waveguide stubs are on different waveguide walls.

A diplexer as claimed in any preceding claim, in which laveguide stubs have a width different to the width of,er cavities.

8. A diplexer as claimed in any preceding claim, in which the diplexer is configured as an H-plane T-junction.

9. A diplexer as claimed in any of claims 1 to 7, in which 5 the diplexer is configured as an E-plane T-junction.

10. A diplexer as claimed in any of claims 1 to 7, in which the diplexer is configured as an H-plane tuning fork j unction.

11. A diplexer claimed in any of claims 1 to 7, in which the diplexer is configured as an E-plane tuning fork junction.

12. A diplexer as claimed in any of claims 1 to 7, in which the diplexer is configured as an H-plane Y-junction.

13. A diplexer as claimed in any of claims 1 to 7, in which the diplexer is configured as an E-plane Y-junction.

14. A diplexer as claimed in any of claims 1 to 13, in which the diplexer is compensated.

15. A diplexer as claimed in any of claims 1 to 13, in which the diplexer is not compensated.

16. A diplexer as claimed in any of claims 1 to 15, in which the diplexer includes three diplexer ports of a standard waveguide size, parts of the diplexer have a non- standard waveguide size, and includes transformers connecting the ports to the non-standard waveguide size parts.

17. A diplexer as claimed in any preceding claim, in which the waveguide has any cross section.