AU754390B2 - An adjustable coupling arrangement for aperture coupled cavity filters - Google Patents

Description

V Wr P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

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ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: AN ADJUSTABLE COUPLING ARRANGEMENT FOR APERTURE COUPLED CAVITY FILTERS The following statement is a full description of this invention, including the best method of performing it known to us: Technical Field This invention relates to microwave filters and in particular to coupling arrangements for aperture coupled cavity filters.

In highly selective bandpass filters which use adjacent cavity resonators coupled by apertures in common walls, the magnitudes of such couplings are very critical parameters. An example of such a bandpass filter is disclosed in our copending International Application No. PCT/AU99/01071.

In order to achieve these necessary critical parameters it is known to provide a high degree of manufacturing precision. However, this solution is unattractive for large filters.

Summary of Invention °.It is therefore an object of the present invention to provide an adjustable °i coupling aperture arrangement for adjusting the coupling between cavity resonators over a wide range of coupling values, the coupling being adjusted externally using a 15 tool that does not disturb the filter's characteristics.

According to the invention, in a microwave filter comprising an electrically conductive housing within which is disposed at least two cavity resonators coupled oooo° by aperture means in a substantially planar wall common to both said resonators, there is provided an adjustable coupling aperture arrangement including aperture 20 means comprising at least one slit of predetermined dimensions, the at least one slit communicating with a respective access hole in said housing via an associated passageway that lies within the boundary of said wall's major surfaces, wherein said at least one slit is provided with a movable metal slug that is slideably retained by opposite longitudinal edges of the slit, whereby said slug can be engaged and slideably manipulated by a tool means, introduced into said access hole and guided to said slug via said passageway, into a position in which electrical contact between said slug and said edges of the slit produces a desired change in effective electrical length of the slit.

Brief Description of the Drawings In order that the invention may be readily carried into effect, embodiments thereof will now be described in relation to the accompanying drawings, in which: Figure 1 is a top view of a cavity wall within a circular filter housing, the cavity wall being provided with an adjustable coupling iris.

Figure 2 is a top view of the cavity wall shown in Figure 1, showing radial passageways connecting slits of the coupling iris to the filter housing exterior.

Figure 3 is a side view of Figure 2.

Figure 4 is a top view of an expanded adjustment slug.

Figure 5 is a top view of a contracted adjustment slug.

Figure 6 is an end view of an adjustment slug.

Figure 7 is a side view of a cavity wall showing an adjustment slug located within a slit of the coupling iris.

Detailed Description Referring to Figures 1 and 2, the adjustable coupling aperture arrangement comprises an electrically conductive wall 24 coaxially located within a filter housing 25. Wall 24 is provided with a cruciform iris 26 comprising a central zone 27 having four slits 28, 29, 30 and 31 extending outwardly therefrom. Each slit is connected by S a radial passageway 32, 33, 34 and 35 to respective apertures 25a, 25b, 25c and in the filter housing permitting access to the slits from the exterior of the filter .oo.oi housing. The passageways are within the boundary of the wall's opposite surfaces.

ooolo In each slit is arranged a captive, movable, rectangular metal slug 36, 37, 38 and 20 39.

Referring to Figures 4 7, each rectangular slug comprises two sections A and B each in the form of general trapezoids whose respective non-parallel sides and 41 interface. The two sections are held together by a screw 42. One section, A, is provided with a threaded hole (not shown), which cooperates with the screw's thread when the screw is disposed in a bore hole in section B. The screw is provided with a slotted bayonet head 43 which allows the screw to be engaged by a tool (not shown) having a T-shaped end to allow the screw to be rotated as well as allowing the associated slug to be moved linearly.

A groove 44, 45 is provided in a side of each section A and B such that when a slug is assembled by screwing the sections together, opposite parallel grooves are formed for slideably engaging the edges of respective slits Due to cooperation between sections A and B, the width between the sides provided with the grooves is maximum when the screw is tightened as shown in Figure 4, and minimum when the screw is loosened as shown in Figure 5. Referring to Figure 7, the width is such that the slug is slideably retained in a slit when the screw is loosened, and fixedly grips and makes electrical contact with opposite edges of the slit when the screw is tightened, thereby affecting the electrical length of the slit.

In operation, slugs 36, 37, 38 and 39 are located in respective slits. Desired filter transmission and reflection characteristics are obtained, using a vector network analyser and manipulating the slugs with the tool inserted into respective passageways 32, 33, 34 and 35 via associated apertures 25a, 25b, 25c and While it is preferable to use four slugs to maintain symmetry in two principal planes, it will be understood that this is not an essential requirement.

Further, in filter arrangements where only a single slit is required, either one or two slugs could be used.

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Claims (7)

1. In a microwave filter comprising a housing within which is disposed at least two cavity resonators coupled by aperture means in a substantially planar wall common to both said resonators, an adjustable coupling aperture arrangement including aperture means comprising at least one slit of predetermined dimensions, the at least one slit communicating with a respective access hole in said housing via an associated passageway that lies within the boundary of said wall's major surfaces, wherein said at least one slit is provided with a movable metal slug that is slideably retained by opposite longitudinal edges of the slit, whereby said slug can be engaged and slideably manipulated by a tool means, introduced into said access hole and guided to said slug via said passageway, into a position in which electrical contact between said slug and said edges of the slit produces a desired change in effective electrical length of the slit.

S2. An adjustable aperture arrangement as claimed in claim 1, wherein said slug 15 includes a screw operated locking means arranged to be actuated by said tool means for locking said slug in said position.

3. An adjustable aperture arrangement as claimed in claim 2, wherein said slug e is a rectangular-shaped block having a groove in each of two opposite parallel sides for cooperating with opposite edges of said slit for slideably retaining and gripping said block therein, said block being formed from a first trapezoid-shaped section and a second trapezoid-shaped section assembled together, with each section's non-parallel side interfacing, by a screw having a head and a threaded section, said screw's threaded section freely passing through a hole in the first trapezoid section to cooperate with a threaded hole provided in the second trapezoid-shaped section, whereby the width between said grooves can be varied by a turning adjustment of said screw with said tool means engaging the screw's head to change the positional relationship between the said interfacing non-parallel sides to cause the slug to be either slideably retained within the slit for manipulation, or fixedly locked in electrical contact with said edges of said slit.

4. An adjustable aperture arrangement as claimed in claim 3, wherein said aperture means comprises four slits of predetermined dimensions, extending outwardly from a central zone, each slit including a said slug, and each slit communicating with a respective said access hole via an associated said passageway.

An adjustable aperture arrangement as claimed in claim 4, wherein said planar wall is substantially circular in shape.

6. An adjustable aperture arrangement as claimed in any one of claims 3, 4 or wherein the screw head includes a bayonet socket for cooperating with a tool having a T-shaped end.

7. An adjustable aperture arrangement substantially as herein described with reference to Figures 1 7 of the accompanying drawings. An adjustable aperture arrangement as claimed in any one of claims 1 to 7, operatively incorporated in a waveguide filter arrangement. :ooo o DATED THIS THIRD DAY OF NOVEMBER 2000 ALCATEL ooo* oo••. lOOOO