WO2015124949A1

WO2015124949A1 - Ceramic waveguide filter apparatus

Info

Publication number: WO2015124949A1
Application number: PCT/GB2015/050508
Authority: WO
Inventors: Michael Guess
Original assignee: Radio Design Limited
Priority date: 2014-02-24
Filing date: 2015-02-23
Publication date: 2015-08-27
Also published as: GB2544365A; GB201403180D0

Abstract

Ceramic waveguide filter apparatus is provided including a ceramic body portion with at least one resonating means contained therein and/or associated therewith. The at least one resonating means is capable of undergoing resonance at a particular electromagnetic frequency or frequencies. One or more tuning means are provided with said apparatus for tuning the resonant frequency or frequencies of any or any combination of the at least one resonating means, the apparatus or the coupling between two or more resonating means.

Description

CERAMIC WAVEGUIDE FILTER APPARATUS

This invention relates to ceramic waveguide filter apparatus and to a method of use thereof.

Although the following description refers almost exclusively to ceramic waveguide filter apparatus for use as part of a telecommunications system or network, it will be appreciated by persons skilled in the art that the ceramic waveguide filter apparatus could be used in any suitable system or network as required.

Filters are electronic devices which allow an electromagnetic wave to be transmitted therethrough. They are designed in such a manner so as to allow signals at one or more pre-determined frequencies to pass through the device (passband frequencies) and to substantially prevent signals at frequencies other than the one or more pre-determined frequencies from passing through the device (stop band frequencies) . The frequency selectivity of a filter can be optimised by locating transmission zeros at both or either side of the passband frequency at finite, non-zero frequencies. A transmission zero can be defined as one or more frequencies at which attenuation of a filter is infinite. This improves the performance of the filter to stop interference and prevent blocking. However, conventional filters that provide the required frequency selectivity are typically large and there is a requirement in the industry to optimise both the size of the filter and the frequency selectivity of the filter. In an attempt to overcome this filter size problem, it is known to use ceramic waveguide filters.

An example of a conventional ceramic rectangular waveguide filter comprises a solid block of high permittivity low-loss ceramic, the exterior of which is coated in a conducting material, such as metal. The ceramic is typically formed by pressing and firing, and is then coated in a high conductivity adhesive paint. As the relative permittivity of the ceramic material is increased, the guide wavelength will reduce, thus also reducing the physical size of the filter for a specific resonant frequency, but this is offset by a reduction in resonator Q factor. This is particularly advantageous if an aim is to reduce the space required for the filter apparatus and/or apparatus with which the filter is associated in use.

Ceramic filters can be provided in different forms. Figure l a shows an example of a first type of ceramic filter 2, which is the subject of co-pending British Patent Application 1320995.2, the features of which are incorporated herein by reference, in which a plurality of electrically conductive through holes 4 or blind holes are formed in the ceramic filter between two or more resonating structures 6, 8, 10 (also labelled 1 -3 in circles in the figures) . The provision of the electrically conductive through holes or blind holes 4 between the resonating structures 6- 10 allows both inter-coupling between adjacent or sequentially numbered resonator structures, and cross coupling between different, non-adjacent or non-sequentially numbered resonating structures to take place. The latter cross coupling produces one or more transmission zeros at finite, non-zero frequencies, which helps to allow optimisation of the frequency selectivity of the ceramic filter apparatus. The filter also typically has an input 12 coupled to the first resonating structure 6 for allowing the input of an electromagnetic wave therethrough, and an output 14 coupled to the last resonating structure 10 of the filter for allowing the output of an electromagnetic wave therefrom. By selecting appropriate values for the dimensions of the filter, each resonator structure will resonate at a specific frequency in the microwave spectrum. Figure l b shows an example of a second type of ceramic filter 16, in which a plurality of slots 18 are provided on the sides 20, 22 of the filter and form part of the outer perimeter of the filter. An opening of each slot 1 8 is continuous with the outer wall 20, 22 and the slot is directed inwardly of the filter housing in the direction 'a'. Thus, the filter housing (or the distance between the two outer side or narrow walls) is narrow at the location of the slots in the 'a' axis. The slots pass all the way from a top wall 24 to the bottom wall 26 with openings in each of said walls respectively. The provision of side slots 18 in the ceramic filter housing allows inter-coupling between adjacent resonators 6-10 (i.e. the sections of the filter housing between the side slots that appear rectangular when viewed in plan view from the top and are labelled 1 -3 in circles) , with the dimensions of the slots 18 determining the extent of the coupling. This ceramic filter 16 does not allow cross coupling between resonators within the filter wherein transmission zeros at finite, non-zero frequencies can be produced.

Filters per se with high performance (high levels of attenuation and rapid roll off) require high accuracy in the resonant frequency of the constituent resonating elements and the couplings between the resonating elements. This high level of accuracy is often beyond that which can be achieved by standard manufacturing techniques. In terms of ceramic waveguide filter apparatus, manufacturing tolerances apply to the dimensions and the dielectric constant and impact the filter response that can be achieved in such filter apparatus.

It is therefore an aim of the present invention to provide ceramic waveguide filter apparatus that overcomes the abovementioned problems, such that the tolerances associated with cost effective manufacturing techniques can be overcome and a desired filter performance can be achieved.

It is a further aim of the present invention to provide a method of manufacturing and/or using ceramic waveguide filter apparatus that overcomes the abovementioned problems, such that the tolerances associated with cost effective manufacturing techniques can be overcome and a desired filter performance can be achieved.

According to a first aspect of the present invention there is provided ceramic waveguide filter apparatus, said apparatus including a ceramic body portion with at least one resonating means contained therein and/or associated therewith, the at least one resonating means capable of undergoing resonance at a particular electromagnetic frequency or frequencies, and wherein one or more tuning means are provided with said apparatus for tuning the resonant frequency or frequencies of any or any combination of the at least one resonating means, the apparatus or the coupling between two or more resonating means.

Thus, the present invention provides tuning means or a tuning mechanism for ceramic waveguide filter apparatus to allow adjustment of the resonant frequency of the resonating means, the apparatus and/or the coupling between resonating means, thereby allowing the desired filter performance to be achieved in a cost effective manner and without changing the manufacturing tolerances of the apparatus.

Although tuning screws are known for use in resonant cavities of conventional cavity waveguide filters for tuning the resonant frequency of the resonant cavities, the use of tuning means in ceramic waveguide filter apparatus has not been done before. The technology associated with ceramic waveguide filter apparatus is different to that of cavity waveguide filters and the provision of tuning means in ceramic waveguide filter apparatus is a non-obvious advance in this technical field.

Preferably the one or more tuning means are inserted into the ceramic body portion at one or more locations consisting of or defining the at least one resonating means to allow external adjustment of the resonating frequency of one or more of the resonating means and/or apparatus as required.

Preferably one or more apertures, channels, holes, blind holes, through holes and/of the like are formed or defined in the ceramic body portion for the location of at least part of the tuning means therein or therewith in use.

A through hole is typically a hole defined within the ceramic body portion (i.e. within the external surfaces or boundaries of the body portion) passing between one side wall or surface of the body portion to another side wall or surface of the body portion. The through hole typically has openings in both said side walls of surfaces of the body portion. Preferably the side walls or surfaces are opposite side walls or surfaces.

A blind hole is typically a hole defined within the ceramic body portion (i.e. within the external surfaces or boundaries of the body portion) . It typically only has a single opening in one surface or side wall of the body portion.

Preferably the one or more apertures, channels, holes, blind holes, through holes and/or the like are non-metallised, substantially non-metallised, non-electrically conductive or substantially non-electrically conductive and/or are formed so as to allow the tuning means to interact with the electromagnetic field generated within the filter apparatus in use. The tuning means can be in any suitable form to allow adjustment of the resonating frequency or frequencies of one or more resonating means within the apparatus and/or the apparatus itself. For example, the tuning means can be in any form to allow relative movement of at least part of the tuning means with respect to the ceramic body portion.

In one example, the tuning means is in the form of a screw, such as for example a screw, threaded screw and/or a non-threaded screw.

The tuning screw and/ or tuning means can be formed from any or any combination of suitable materials, such as for example, plastic, metal, ceramic and/or the like.

In one embodiment locking means or a locking mechanism is provided with the tuning means for locking the tuning means in a required or user selected position with respect to the ceramic body portion. For example, the locking means can include a locking nut. The locking nut can be threaded or non-threaded as required.

In one embodiment the tuning means are self-locking and no additional locking means are required to lock the tuning means in a required or user selected position with respect to the ceramic body portion.

In one embodiment one or more spaces or air gaps are created between the tuning means and one or more walls of the ceramic body portion defining the aperture, channel, holes, through holes, blind holes and/or the like in which at least part of the tuning means is located in use. Preferably at least a lower section or a part of the tuning means is located in free space within the aperture, channel, holes, through holes, blind holes and/ or the like.

In one embodiment the tuning means includes one or more support means or support members on which at least part of the tuning means is supported in use. The one or more support means typically allows contact, support and/or are located between at least part of the tuning means, locking means, and/or an outer or external surface of the ceramic body portion. Preferably the one or more support means is formed from or includes an electrically conductive material or materials.

The support means can include any or any combination of one or more bush connections, printed circuit board (PCB), plate member, metallised plate member and/or the like.

In one embodiment two or more spaced apart tuning means are provided in the apparatus and one or more support means or members extend between the two or more tuning means. For example, the support means can be arranged such that at least part of each of the tuning means is located through a corresponding aperture in the support means. Preferably two or more resonating means are provided in the apparatus and a tuning means is associated with, provided with or between each resonating means.

If two or more tuning means are provided, each tuning means could be of the same type or different type to another tuning means.

In the example where the support means is in the form of a PCB, this has the added advantage that electrically conductive tracks and/or one or more electronic components can be provided on the PCB. This can save space within the unit in which the ceramic waveguide filter is located in use.

In one embodiment the support means is soldered and/or adhered to at least part of the ceramic body portion.

In one embodiment one or more apertures are defined in the support means for location of at least part of the tuning means therethrough in use. The walls defining the one or more apertures can be threaded or non-threaded as required.

In one embodiment the one or more tuning means are provided at a location between two or more resonating means.

In one embodiment one or more electrically conductive apertures, channels, holes, blind holes, through holes and/or slots are defined in the ceramic body portion or forming parts of one or more sides walls of the ceramic body portion at a location between two or more resonating means. The electrically conductive apertures, channels, holes, blind holes, through holes and/or slots are preferably separate to an distinct from the apertures, holes, blind holes, through holes in which the tuning means are located in use.

In a further embodiment two or more electrically conductive apertures, channels, holes, blind holes and/or slots are defined in the ceramic body portion or forming parts of the sides walls of the ceramic body portion at a location between said two or more resonating means. In one example, the one or more tuning means are provided a spaced distance apart between the two or more of the electrically conductive apertures, channel, holes, blind holes and/or slots located between the two or more resonating means. A slot, in one example, can be a recess that is continuous or substantially continuous with an external surface of the body portion (for example the external surface of the body portion is shaped so as to form a slot or recess) .

In one embodiment each resonating means has at least one tuning means associated therewith.

The ceramic body portion can be formed from a continuous, substantially continuous, substantially solid block of ceramic material and/or solid block of ceramic material. Alternatively, two or more solid or substantially solid and/or continuous blocks of ceramic material could be joined or arranged together to produce a filter having the same or substantially the same function and/or performance if required.

The body portion of ceramic material is designed to operate as a dielectrically loaded waveguide filter where the addition of electrically conductive through apertures, channels, holes, blind holes, slots, and/or side slots at appropriate positions and/or of appropriate dimensions enables the realisation of all the desired resonator main-line coupling and/or cross couplings necessary to realise an nth order waveguide bandpass filter (where n = the number of resonators) with arbitrary located transmission zeros in the complex frequency domain.

Preferably the entire exterior surface, substantially the entire exterior surface of the ceramic material, or at least the external area of the filter in which the resonating means are provided, is metallised and/ or is provided with an electrically conductive material, layer(s) and/or coating(s) thereon. This is typically with the exception of the non-metallised surface of the tuning means apertures, holes and/or the like. In one embodiment the entire or substantially entire electrically conductive through apertures, channels, holes and/or blind holes are provided with an electrically conductive material, layer(s) and/or coating(s) and/or are metallised thereon. Thus, the interior walls of the apertures, channels, holes and/or blind holes have one or more metal layers provided thereon in one example. The provision of the electrically conductive through apertures, channels, holes, and/or blind holes allows the same to act in an equivalent manner to metallic rods provided in conventional air filled waveguide filters.

In one embodiment the entire surface of substantially the entire surface of the slots or side slots are metallised.

Preferably the electrically conductive material, layer(s) and/or coating(s) used on the exterior of the ceramic body and/or the walls of the through apertures, channels, holes, blind holes and/or slots is metallic material, one or more metallic layers and/or one or more metallic coatings.

Preferably the ceramic material used in the filter body is a high permittivity ceramic material.

Preferably the high permittivity ceramic material has a relative permittivity of between approximately 10-100.

Typically any number of electrically conductive through apertures, holes, channels, blind holes and/or side slots are defined in the ceramic housing body between the resonating means.

Preferably the filter apparatus includes input coupling means or member(s) and output coupling means or member(s) . The input coupling means is/are typically coupled to the first resonating means of the filter and allows for the input of an electromagnetic wave therethrough. The output coupling means is/are typically coupled to the last resonating means of the filter and allows for the output of an electromagnetic wave therefrom.

Preferably each resonating means is a portion of the ceramic body of the filter which is capable of undergoing resonance at a particular electromagnetic frequency or frequencies. Preferably each resonating means is substantially cuboid in shape.

The tuning means can be located on any one or more external surfaces of the ceramic body portion, such as for example, a top wall, base wall, side wall, end wall and/ or the like.

According to a second aspect of the present invention there is provided a method of using ceramic waveguide filter apparatus, said apparatus including a ceramic body portion with at least one resonating means contained therein and/or associated therewith, the at least one resonating means capable of undergoing resonance at a particular electromagnetic frequency or frequencies, and wherein said method includes the step of tuning the resonant frequency or frequencies of any or any combination of the at least one resonating means, the apparatus or the coupling between two or more resonating means using tuning means to reach a desired or pre-determined resonant frequency or frequencies.

According to further independent aspects of the present invention there is provided a telecommunication system including a ceramic waveguide filter apparatus and a method of use thereof. The telecommunication system can include any or any combination of one or more masts, antenna, base station transceiver means, cabling and/or the like to allow one or more receive and/ or transmit radio frequency signals to pass through the same, to be received and/or transmitted therefrom. According to one aspect of the present invention there is provided ceramic waveguide filter apparatus, said apparatus including a ceramic body portion with one or more resonating means contained therein and/or associated therewith, and wherein support means are joined to at least a part of the ceramic body portion, said support means in the form of a printed circuit board.

The provision of a printed circuit board (PCB) mounted to a ceramic waveguide filter allows one or more electronic components to be connected to the waveguide and/or the PCB, it reduces space within the unit in which the apparatus is to be placed in use and reduces the connectivity of the unit. This aspect may or may not be provided with tuning means as required.

Embodiments of the present invention will now be described with reference to the following figures:

Figures la-lb (PRIOR ART) show simplified perspective views of two different conventional types of ceramic waveguide filters;

Figures 2a-2c show a perspective view, a cross sectional view and a top plan view of a ceramic waveguide filter according to an embodiment of the present invention respectively;

Figure 3 shows a cross sectional view of a ceramic waveguide filter according to a further embodiment of the present invention;

Figure 4 shows a cross sectional view of a ceramic waveguide filter according to a yet further embodiment of the present invention; Figure 5 is a perspective view of ceramic waveguide filter apparatus according to a different aspect of the present invention.

Referring to figures 2a-4, there is illustrated ceramic waveguide filter apparatus 2 of a type similar to that shown in figure la. In accordance with a first aspect of the present invention, tuning means 30 are provided with the filter apparatus 2 to allow the resonating frequency of the apparatus to be adjusted to a desired frequency response, as will be described in more detail below. It will be appreciated that the tuning means of the present invention could be applied to a ceramic waveguide filter 16 of a type shown in figure lb and achieve the same advantages.

As has previously been described with reference to figure la, ceramic waveguide filter apparatus 2 comprises a body portion made from ceramic material. Three resonating structures 6-10 are defined within the body portion and are sequentially labelled 1-3 in circles. A pair of spaced apart, electrically conductive or metallised through holes 4 are defined between resonators 1 and 2 and between resonators 2 and 3. The metallised holes 4 pass from a top surface 24 of the filter 2 to a base surface 26 and have openings in said top and base surfaces 24, 26. It is to be noted that the metallised through holes 4 could be blind holes if required.

An input 12 is coupled to the first resonating structure 6 for allowing the input of an electromagnetic wave therethrough, and an output 14 is coupled to the last resonating structure 10 of the filter for allowing the output of an electromagnetic wave therefrom.

A recess or blind hole 32 having an opening defined in a top surface 24 of the ceramic body portion is provided for the location of tuning means 30 therein. More particularly, in this example, the tuning means is located in resonating structure 8 (or 2 in a circle) substantially centrally of the top surface 24. However, it will be appreciated that the tuning means could be located at any suitable position on the ceramic body portion as required. The blind hole 32 only extends part way through the ceramic body portion below surface 24. The blind hole 32 is typically substantially non-metallised.

The tuning means 30 in this example comprises a threaded tuning screw 34, locking means in the form of a locking nut 36 and support means in the form of a bush connector 38. In particular, the threaded tuning screw 34 comprises a head portion 34' which is used to rotate and adjust the screw 34 relative to the ceramic body portion of the filter 2 in use to adjust the resonant frequency of the filter, and a threaded portion 34" protruding below the head portion for location in the hole 32 of the filter 2.

The bush connector 38 is located on the external surface 24 of the ceramic body portion and is typically soldered to the metallised outer surface thereof in one example. The locking nut 36 is located on an upper surface of the bush connector 38 and the head portion 34' of the screw protrudes above the locking nut. Both the bush connector 38 and the locking nut 36 have apertures defined therein and the walls defining the apertures are threaded to engage with the threaded portion 34" of the tuning screw in use.

The tuning screw can be formed from any suitable material, such as metal, plastic or ceramic.

The locking nut 36 may not be necessary if the support means or bush connector and/ or the tuning means or tuning screw could be self locking.

Figure 3 shows a similar arrangement of a ceramic filter 2 to that in figures 2a-2c but the blind hole 32 in which the tuning means are mounted in use is a through hole 32'. The through hole 32' has openings in both the top surface 24 and the base surface 26.

Figure 4 shows a similar arrangement of a ceramic filter 2 to that in figures 2a-2c but a number of tuning means 30 are provided for tuning the resonant frequency of the filter. More particularly in this example, two tuning means are provided; one tuning means in each of the two centrally located resonating structures. Rather than having individual bush connectors 38 associated with each individual tuning screw 34, support means in the form of a single plate 40 is provided which extends between the two tuning means. A plurality of apertures are defined in the plate 40 for the location of the tuning screws therethrough in use. The inner side walls defining the apertures could be threaded or non-threaded as required. The plate 40 could be soldered to an outer surface of the filter as required, such as for example the top surface 24.

The plate 40 could be formed from PCB material, metal and/ or the like.

According to a further aspect of the present invention there is provided a ceramic waveguide filter , of a type described in figures la or lb. The filter 2 or 16 is mounted on a PCB 42, as shown in figure 5.

Claims

1. Ceramic waveguide filter apparatus, said apparatus including a ceramic body portion with at least one resonating means contained therein and/or associated therewith, the at least one resonating means capable of undergoing resonance at a particular electromagnetic frequency or frequencies, and wherein one or more tuning means are provided with said apparatus for tuning the resonant frequency or frequencies of any or any combination of the at least one resonating means, the apparatus or the coupling between two or more resonating means.

2. Apparatus according to claim 1 wherein the tuning means are inserted into the ceramic body portion at one or more locations defining or consisting of the at least one resonating means.

3. Apparatus according to claim 1 wherein one or more apertures, channels, holes, blind holes and/or through holes are formed or defined in the ceramic body portion for the location of at least part of the tuning means therein in use.

4. Apparatus according to claim 3 wherein the one or more apertures, channels, holes, blind holes and/ or through holes associated with the tuning means are non-metallised, are non-electrically conductive in form and/ or are formed so as to allow the tuning means to interact with electromagnetic field generated within the filter apparatus in use.

5. Apparatus according to claim 1 wherein the tuning means are arranged in such a manner so as to allow adjustment of the resonating frequency or frequencies of one or more resonating means witiiin the apparatus and/ or the apparatus itself.

6. Apparatus according to claim 1 wherein the tuning means is in the form of a screw, threaded screw and/ or non-threaded screw.

7. Apparatus according to claim 1 wherein locking means are provided with the tuning means for locking the tuning means in a required or user selected position with respect to the ceramic body portion.

8. Apparatus according to claim 7 wherein the locking means is in the form of a locking nut.

9. Apparatus according to claim 1 wherein the tuning means are self- locking.

10. Apparatus according to claim 1 wherein one or more spaces or air gaps are created between the tuning means and one or more walls of the ceramic body portion defining the aperture, channel, hole, through hole and/or blind hole in which at least part of the tuning means is located in use.

11. Apparatus according to claim 1 wherein the tuning means includes one or more support means or members on which at least part of the tuning means is supported in use.

12. Apparatus according to claim 11 wherein the one or more support means or members are formed from or include an electrical conductive material or materials.

13. Apparatus according to claim 11 wherein the support means or members include any or any combination of one or more bush connections, printed circuit board (PCB), plate member or metallised plate member.

14. Apparatus according to claim 1 wherein two or more tuning means are provided a spaced distance apart in the apparatus and a support means or member extends between the two or more tuning means.

15. Apparatus according to claim 1 wherein two or more resonating means are provided in the apparatus and tuning means are associated with, provided with or between each resonating means.

16. Apparatus according to claim 1 wherein one or more electrically conductive apertures, channels, holes, blind holes, through holes and/ or slots are defined in the ceramic body portion or forming parts of one or more side walls of the ceramic body portion at a location between two or more resonating means.

17. Apparatus according to claim 1 wherein the ceramic body portion is formed from a solid block of ceramic material or two or more solid blocks of ceramic material joined or arranged together to provide a filter.

18. Apparatus according to claim 1 wherein the ceramic body portion is formed from a high permittivity ceramic material having a relative permittivity of between 10-100.

19. Apparatus according to claim 1 wherein the entire exterior surface or substantially the entire exterior surface of the ceramic material, or at least the external area of the filter in which the resonating means are provided, is metallised and/or is provided with an electrically conductive material, layer and/ or coating thereon.

20. Apparatus according to claim 1 wherein the apparatus includes input coupling means and output coupling means for allowing the input and output of an electromagnetic wave therethrough in use.

21. A method of using ceramic waveguide filter apparatus, said apparatus including a ceramic body portion with at least one resonating means contained therein and/or associated therewith, the at least one resonating means capable of undergoing resonance at a particular electromagnetic frequency or frequencies, and wherein said method includes the step of tuning the resonant frequency or frequencies of any or any combination of the at least one resonating means, the apparatus or the coupling between two or more resonating means using tuning means to reach a desired or pre-determined resonant frequency or frequencies.