WO1995001658B1

WO1995001658B1 - Tunable resonator for microwave oscillators and filters

Info

Publication number: WO1995001658B1
Application number: PCT/EP1994/002154
Authority: WO
Filing date: 1994-07-01
Publication date: 1995-02-23

Abstract

Tunable resonator consisting of a cylindrical cavity containing a cylindrical dielectric resonator (DR) connected to a metal tuning screw by means of a cylindrical dielectric spacer placed between the screw and the DR and connected rigidly to the latter. The tuning screw penetrates into a hole made in axial direction in the upper wall of the cavity. Said wall exhibits on the edge of the hole a toroidal extension toward the interior of the cavity. As concerns tuning, starting from a condition in which resonance frequency fr of the resonator is minimal, i.e. when the DR is at the centre of the cavity, a rotation of the metal tuning screw which results in approach of the DR to the toroidal extension produces a significant increase in fr. There are also described microwave filters comprising multiple resonators which are the object of the present invention coupled together by means of irises.

Claims

AMENDED CLAIMS[receivedbytheInternationalBureauon24January1995(24.01.95); originalclaims 1-20replacedbynewclaims 1-18 (5pages)]

1. Tunable microwave resonator consisting essentially in a cavity (5) delimited by walls (l',l",2 ) and including a cylindrical dielectric resonator (6) rigidly connected to a tuning screw (3) by an interposed dielectric support (7) , acting as a spacer, penetrating in a hole (F) made in a first (1') of said walls; said tunable resonator comprising means designed to excite in the cavity and in the dielectric resonator one or more resonant modes of an electromagnetic field and to take the current induced by said resonant modes to transfer them outside the cavity, characterized in that said first wall (1') comprises a toroidal extension (8) at the edge of said hole (F) extending for an appropriate length (Ht) inside said cavity (5) , said toroidal extension (8) increasing tuning range of the microwave resonator, reducing thermal effect on the resonance frequency, and increasing mechanical stability.

2. Tunable microwave resonator in accordance with claim 1, characterized in that said toroidal extension (8) has an outside diameter approximately equal to the diameter of said cylindrical dielectric resonator (6) and a lenght (Ht) indicatively comprised between one-fifth and one-third, but preferably one-fourth, of the distance (He) between said first wall and a second wall of the cavity (5) parallel to the first.

3. Tunable microwave resonator in accordance with claims 1 or 2, characterized in that said dielectric support (7) has a length (Hs) such that when said tuning screw (3) is rotated in an initial position so that resonance frequency is minimal for said tunable microwave resonator, said cylindrical dielectric resonator (6) is placed near the centre of said cavity (5) and the end of said tuning screw (3) does not penetrate in said cavity.

4. Tunable microwave resonator in accordance with any of the above claims, characterized in that said cylindrical dielectric resonator (6) completes a small translation along its axis of cylindrical symmetry, remaining near the centre of the cavity (5), during rotations of said tuning screw (3) which cause a change in resonance frequency of said tunable microwave resonator from one end to the other of the tuning range.

5. Tunable microwave resonator in accordance with claim 1, characterized in that said walls (l',l",2 ) are metallic and said toroidal extension (8) is of dielectric material, with high dielectric constant, rigidly connected to said first wall (1').

6. Tunable microwave resonator in accordance with claim 1, characterized in that said walls (l',l",2 ) are of dielectric material and said toroidal extension (8) is of metallic material rigidly connected to said first wall (1').

7. Tunable microwave resonator in accordance with any of the above claims, characterized in that the materials making up said dielectric support (7) and said toroidal extension (8) have respective thermal expansion coefficients such that their thermal elongations are approximately the same.

8. Tunable microwave resonator in accordance with any of the above claims, characterized in that said cavity (5) is preferably cylindrical in form.

9. Microwave filter consisting essentially of a hollow body (9, 9') comprising resonant cavities (10) arranged in succession in which are included respective dielectric resonators (6) positioned in said cavities (10) through as many tuning screws (3) and interposed dielectric supports (7), acting as spacers, penetrating in first holes (F) made in the walls (9) of the cavities (10) ; also comprising an input gate for a microwave signal to be filtered and an output gate for a filtered signal, said gates being without distinction located opposite a second (11') and a third hole (11") made in the walls (9) separating a first and a last cavity of said succession (10) from the outside of the filter, each remaining cavity (10) being electromagnetically coupled to a preceding and following cavity (10) of said succession by means of fourth holes (11) made in respective dividing walls, characterized in that the walls (9) of said resonant cavities comprise a toroidal extension (8) at the edge of said first holes (F) extending for an appropriate length (Ht) inside the cavities (10) , said toroidal extensions (8) increasing tuning range of the microwave filter, reducing thermal effect on the pass-band central frequency, and increasing mechanical stability.

10. Microwave filter in accordance with claim 9, characterized 2 5

in that said extensions (8) have an outside diameter approximately equal to the diameter of said cylindrical dielectric resonators (6) and a lenght (Ht) indicatively comprised between one-fifth and one-third, but preferably one-fourth, of the height (He) of the cavities (10) .

11. Microwave filter in accordance with claims 9 or 10, characterized in that said dielectric supports (7) have a length (Hs) such that when said tuning screws (3) are rotated in initial positions so that the resonance frequencies of said resonant cavities (10) are minimal, said dielectric resonators (6) are placed near the centres of the respective cavities (10) and the ends of said tuning screws (3) do not penetrate in said cavities (10).

12. Microwave filter in accordance with any of the above claims from 9 to 11, characterized in that the heights (Ht) of said toroidal extensions (8) have a value such that said cylindrical dielectric resonators (6) complete small translations along their axes of cylindrical symmetry while remaining near the centres of said resonant cavities (10) during rotations of said tuning screws (3) which cause a variation in said pass-band central frequency from one end to the other of the tuning range of the filter.

13. Microwave filter in accordance with claim 9, characterized in that said hollow body (9, 9') is metallic and said toroidal extensions (8) are of dielectric material, with high dielectric constant, rigidly connected to said body (9).

14. Microwave filter in accordance with claim 9, characterized in that said hollow body (9, 9') is of dielectric material and said toroidal extensions (8) are of metallic material rigidly connected to said body (9) .

15. Microwave filter in accordance with any of the above claims from 9 to 14, characterized in that the materials making up said dielectric supports (7) and said toroidal extensions (8) have respective thermal expansion coefficients such that their thermal elongations are approximately the same.

16. Microwave filter in accordance with any of claims 9 to 15, characterized in that said resonant cavities (10) arranged in succession are identical cavities preferably cylindrical in form, 2 6

aligned along an axis perpendicular to the axes of cylindrical symmetry of said cylindrical cavities (10) and passing near the centres thereof; and in that said second (11'), third (11") and fourth holes (11) are aligned along said axis with which are aligned said cylindrical cavities, and that said first holes (F) are made in correspondence of the axes of cylindrical symmetry of said resonant cavities.

17. Microwave filter in accordance with any of claims 9 to 15, characterized in that:

- said resonant cavities arranged in succession (14,15,16,17) are identical cavities preferably cylindrical in form;

- contiguous cavities (14,15) belonging to a first group are aligned along a first axis perpendicular to the axes of cylindrical symmetry of said cavities and passing near the centres of said cavities of the first group;

- contiguous resonant cavities (15,16,17) belonging to a second group are aligned along a second axis, perpendicular to the first axis, and perpendicular to the axes of cylindrical symmetry of said resonant cavities, and said second axis passing also near centres of said resonant cavities of the second group;

- a resonant cavity (14) placed at a first end of said first group of resonant cavities is said first resonant cavity of said succession;

- a resonant cavity (17) placed at a first end of said second group of resonant cavities is the last resonant cavity of said succession;

- said first and second groups of cavities are contiguous;

- a resonant cavity (15) placed at a second end of said first group coincides with a resonant cavity (15) placed at a second end of said second group;

- said second hole (18') is aligned along said first axis, said third hole (19') is aligned along said second axis, and said fourth holes (18,19) are aligned along the respective said first and second axes; and

- said first holes are made in correspondence of axes of cylindrical symmetry of respective resonant cavities.

18. Microwave filter in accordance with any of claims 9 to 15, characterized in that said resonant cavities arranged in succession constitute a single cavity corresponding to the cavity of a rectangular wave guide (20) having a cross section of dimensions such that the critical frequency of said guide is higher than the resonance frequency of said dielectric resonators (6) ; and in that said first holes (F) are made in correspondence of the centre line of a wall (20') of said rectangular wave guide (20), while respecting an appropriately predetermined mutual distance.

STATEMENT UNDER ARTICLE 19(1)

All the amendments introduced in the claims have no impact on the description and the drawings, because all the features claimed are also described.

More precisely:

in the preamble of the new claim 1 the feature concerning the presence of a tuning screw connected to a dielectric resonator by an interposed dielectric spacer has been inserted. So the claim is correctly delimited from the closest prior art, meeting the requirements of PCT rule 6.3(b) (i,ii) .

in the characterizing part of the new claim 1 the existing features have been replaced by the feature concerning the presence of a toroidal extension of the wall which is the true innovative and original features of the invention.

In the dependent claim 2 the features concerning the dimensions of the toroidal extension relatively to the height of the cavity and of the diameter of the dielectric resonator have been introduced.

In the dependent claims from 3 to 7, concerning a tunable microwave resonator, minor amendments have been introduced consequently.

In the claims from 8 to 14, concerning microwave filters, amendments like those of the tunable microwave resonator have been introduced.