EP1903631A1

EP1903631A1 - Coaxial cavity resonator

Info

Publication number: EP1903631A1
Application number: EP07018585A
Authority: EP
Inventors: Gianpietro Villa; Vittorio Tansini; Mario Bandera; Giampietro Magni; Fabio Tansini
Original assignee: Kathrein Werke KG; MT Srl
Current assignee: Kathrein SE
Priority date: 2006-09-22
Filing date: 2007-09-21
Publication date: 2008-03-26
Also published as: ITMI20061803A1

Abstract

It is hereby disclosed a head (52) of a resonator element for a coaxial cavity resonator, formed of an electrically conductive material, and having an outer lateral surface (521), a top side (522) and a bottom side (523), characterized in that said head (52) defines by its shape at least one open cavity (8) formed in said bottom side (523).

Description

There is herein disclosed a coaxial cavity resonator to be used over a frequency range from 10 MHz to 4 GHz.
Coaxial cavity resonators are widely used in telecommunications, e.g. in the fabrication of passive filters or oscillators.
Traditional coaxial cavity resonators have a resonator element, generally of cylindrical shape, within a resonant cavity.
In an attempt to reduce the size of resonators, mushroom-shaped resonator elements are known, i.e. having a mushroom head possibly of electrically conductive material.
In these devices, the electric field is concentrated between the resonator head and the cavity cover.
Nevertheless, the resonators so formed have limits in terms of size reduction while maintaining maximum CW (continuous wave) and PEP (peak envelope) powers.
International patent application PCT/SE99/01368 by ALLGON AB discloses a coaxial resonator of the type having a mushroom resonator element, which comprises one or more metal or dielectric rings coaxially arranged around the resonator element.
These ring elements allow overall size reduction of the resonator element and thus the resonator.
Prior art resonators still suffer from certain drawbacks.
Particularly, the need arises to further reduce the size of such devices.
Furthermore, there is the need to improve the quality or Q factor of devices of equal overall size.
Also, the need is felt to minimize insertion losses in devices of equal overall size.
Finally, there is the need to maintain the maximum operating power with the minimum size.
The purpose of the present inventors is to find a solution to at least some of prior art drawbacks and particularly the problems as set out hereinbefore.
This purpose is achieved by a resonator element head as defined in claim 1, by a resonating element as defined in claim 6 and by a coaxial resonator as defined in claim 10.
Further advantages may be further achieved by the features of the dependent claims.
A possible embodiment, as set out in the attached claims, will be described hereafter with reference to the accompanying drawings, in which:

Figure 1 is a front sectional view of a resonator element head, for a coaxial cavity resonator, according to a first embodiment;
Figure 2 is a perspective view the same head as shown in Figure 1;
Figure 3 is a front sectional view of a resonant cavity, including a step for a resonator element, which is adapted to receive the resonator head of Figures 1 and 2;
Figure 4 is a front sectional view of a resonator element for a coaxial cavity, according to a second possible embodiment;
Figure 5 is a perspective view of the resonator element as shown in Figure 4;
Figure 6 is a front sectional view of a coaxial cavity resonator having a resonator element as shown in Figure 5, including a tuning screw attached to the cover;
Figures 7, 8, 9 and 10 are longitudinal sectional views showing further possible embodiments of a resonator element.

Referring to the annexed drawings, Figures 1 and 2 show a head 52 of a resonator element for a coaxial cavity resonator.
The head 52 is made of an electrically conductive material (such as aluminum, brass and is preferably silver-plated) and has an outer lateral surface 521, a top side 522 and a bottom side 523.
The head 52 defines by its shape at least one open cavity 8, formed in the bottom side 523, i.e. the side that is designed to face towards the bottom of the resonant cavity.
The transverse dimension of the head 52 is inversely proportional to the operating frequency.
The term "inversely proportional" as used herein shall not be intended in a strictly algebraic sense, but only in a qualitative sense.
Preferably, the open cavity 8 has a substantially and/or generally annular conformation.
The head 52 may be mounted in a resonant cavity 3, such as the one as shown in Figure 3, that already has a stem or support 51 integral with the bottom of the resonant cavity.
While Figure 3 shows a body 2 having a resonant cavity 3 with the stem 51 being part of the body 2, this design shall be apparently intended without limitation.
Therefore, the stem 51 may also be a component separate from the body 2 joined thereto by mechanical coupling, welding, gluing or else.
The diameter of the stem 51 is directly proportional to the resonance frequency, i.e. the smaller the diameter the lower the resonance frequency.
The transverse dimension of the stem 51 is dependent on the transverse dimension of the head 52.
The head 52 and the stem 51, which are electrically connected to each other, form a resonator element 5.
The outer lateral surface 521 is higher than traditional heads, and the annular cavity 8 can be formed thereby.
The height of the outer lateral surface 521 is inversely proportional to the resonance frequency (the greater the height the lower the resonance frequency) and inversely proportional to the quality or Q factor.
Under identical conditions of resonance frequency and quality or Q factor, the cavity 8 on the bottom side 523 of the head 52 of the resonator 5 and the outer surface 521 allow the operating power to be increased.
Furthermore, the presence of the cavity 8 and the outer surface 521 allow the size of the resonator element 5 and the resonant cavity 3 to be minimized with the quality or Q factor being substantially unaltered.
In a possible embodiment, the top surface 522 of the head 52 of the resonator element 5 is substantially and/or generally flat and parallel to the cover 4.
This is a preferred feature in case of extreme size reduction of the resonator.
The lateral surface 521 may have a larger area than the top surface 522.
Thus, the total coupling of the resonator 5 in the cavity 3 is further increased, thanks to the prevalent addition (unlike traditional solutions) of the coupling with the walls of the resonant cavity 3 to the coupling with the cover 4 only.
In the embodiment as shown in Figures 4 and 5, a resonator element 5 is provided, that has a head 52 with a stem 51 joined thereto.
The free end of the stem 51 may be equipped with fastener means 512 such as a threaded blind hole.
Otherwise, the free end of the stem 51 may be secured to the bottom of the resonant cavity by other means, such as by welding or gluing.
The head 52 is usually joined to the stem 51 in a coaxial position.
In the embodiments of the figures, the head 52 has a tubular portion 524 with a portion of the stem 51 therein.
In the embodiments of the figures, the head 52 of the resonator has a blind hole 12 at the top side 522, which is designed to receive a tuning screw 11 for fine resonance frequency adjustment.
Figure 6 shows a coaxial cavity resonator 1 comprising an electrically conductive body 2 (e.g. made of aluminum or brass of preferably of a silver-plated material) with at least one resonant cavity 3 therein.
The resonant cavity 3 has an opening 31 and a bottom 32.
A cover 4 of electrically conductive material (such as aluminum or brass and preferably of a silver-plated material) is further provided for closing the opening of the resonant cavity 3.
At least one resonator element 5 of an electrically conductive material is held in the resonant cavity 3, and is mechanically and electrically joined to the bottom 32 of the resonant cavity 3.
The resonator element 5 has a stem 51, which extends axially along an axis X, and has an end 522 secured to the bottom 32 of the resonant cavity 3.
The resonator element 5 further has a head 52 attached to the stem 51, which has an outer lateral surface 521, a top side 522 opposite to the stem 51 and a bottom side 523.
The head 52 defines by its shape at least one cavity 8 facing towards the bottom 32 of the resonant cavity 3.
In a possible embodiment, the cavity 8 has a substantially and/or generally annular extension around the axis of extension X.
In a possible embodiment, the head 52 has a tubular portion 524 (of cylindrical or prismatic shape) with a portion of the stem 51 therein.
The resonator 1 further has means 11, 12 for fine adjustment of the resonance frequency of the resonator element 5.
In the embodiment as shown in Figure 6, the means 11, 12 for adjusting the resonance frequency of the resonator element 5 include a screw 11 passing through the cover 4, having a free end to be fitted in a blind hole 12 formed on the top side 522 of the head 52.
Those of ordinary skill in the art will appreciate that the resonator as disclosed herein requires no use of dielectric materials.
The present resonator may be used over a frequency range from 10 MHz to 4 GHz, e.g. in the fabrication of filters, duplexers, multiplexers.
In resonators as disclosed herein, the electric field concentrates in the space between the outer lateral surface 521 of the head 52 of the resonator 5 and the inner walls of the resonant cavity 3 of the body 2.
The low electric field on the head of the resonator causes the influence of the cover 4 on the resonant cavity 3 to be dramatically reduced, wherefore the resonant cavity 3 shall no longer be silver plated (thereby affording a considerable cost reduction).
Silver plating is also not required on the resonator head 52, due to its poor contribution to the Q factor.
On the other hand, the magnetic field concentrates in the stem 51.
The above greatly simplifies coupling of multiple resonators in a filter, and consequently facilitates filter calibration.

Claims

A head (52) of a resonator element for a coaxial cavity resonator, formed of an electrically conductive material, and having an outer lateral surface (521), a top side (522) and a bottom side (523), characterized in that said head (52) defines by its shape at least one open cavity (8) formed in said bottom side (523).
A head (52) of a resonator element as claimed in claim 1, wherein said open cavity (8) has a substantially and/or generally annular shape.
A head of a resonator element (5) as claimed in claim 1 or 2, wherein said top surface (522) of said head (52) is substantially flat.
A head of a resonator element (5) as claimed in claim 1 or 2 or 3, wherein said outer lateral surface (521) has a larger area than said top surface (522).
A head of a resonator element (5) as claimed in any one of the preceding claims, wherein said head (52) has a blind hole (12) at said top surface (522).
A resonator element (5) for a coaxial cavity resonator, having a head (52) as claimed in any one of the preceding claims, further comprising a stem (51) joined to said bottom side (523) of said head (52).
A resonator element (5) as claimed in claim 6, wherein said stem (51) is equipped with fastener means (512).
A resonator element (5) as claimed in claim 7 or 8, wherein said head (52) is coaxial with said stem (51).
A resonator element (5) as claimed in any one of claims 7, 8 and 9, wherein said head (52) has a tubular portion (524) with a portion of said stem (51) therein.
A coaxial cavity resonator (1) comprising:
- an electrically conductive body (2);

- at least one resonant cavity (3) formed in said electrically conductive body (2), said at least one resonant cavity (3) having an opening (31) and a bottom (32);

- a cover (4) for closing every opening (31) of said at least one resonant cavity (3), said cover (4) being formed of an electrically conductive material;

- at least one resonator element (5) of an electrically conductive material, which is mechanically and electrically connected to said bottom (32) of said resonant cavity (3), said at least one resonator element (5) having a stem (51) axially extending along an extension axis (X), and having an end (511) attached to said bottom (32) and a head (52) joined to said stem (51), which has an outer lateral surface (521) and a top surface (522), opposite to said stem (51),
characterized in that said at least one head (52) defines by its shape at least one cavity (8).
A resonator as claimed in claim 10, wherein said cavity (8) has a substantially and/or generally annular extension around said extension axis (X).
A resonator as claimed in claim 11, wherein said head (52) has a tubular portion (523) with a portion of said stem (51) therein.
A resonator as claimed in claim 10 or 11 or 12, wherein said outer lateral surface (521) of said head (52) has a larger area than said top surface (522) of said head (52).
A resonator as claimed in any one of claims 10 to 13, further having means (11, 12) for adjusting of the resonance frequency of said resonator element (5) .
A resonator as claimed in claim 14, wherein said means (11, 12) for adjusting the resonance frequency of said at least one resonator element (5) include a screw (11) passing through said cover (4), and a blind hole (12) formed in said head (52).