Patent Application
20180219268
This invention relates generally to filter components and, more specifically, relates to the tuning of dielectric triple-mode filters.
This section is intended to provide a background or context for the invention to be disclosed below. The description to follow may include concepts that could be pursued, but have not necessarily been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated below, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section.
In general, a dielectric filter is composed of a number of resonating structures and energy coupling structures which are arranged to exchange radio-frequency (RF) energy among themselves and input and output ports. The pattern of interconnection of these resonators to one another and to the input and output ports, the strength of these interconnections, and the resonant frequencies of the resonators determine the response of the filter.
During the design process for a dielectric filter, the arrangement of the parts, the materials from which the parts are made, and the precise dimensions of the parts are determined such that an ideal filter so composed will perform the desired filtering function. If a physical filter conforming exactly to this design could be manufactured, the filter would perform exactly as intended by the designer.
However, in practice, the precision and accuracy of manufacture of both the materials and the parts are limited, resulting in departures in the values of resonant frequencies and coupling strengths from desired values, These departures, in turn, cause the response of the dielectric filter to differ from that predicted by an ideal filter model. Often, the departures from an ideal response are sufficiently large to bring the filter outside of its design specification. Because of this, it is desirable to make use of some means for adjusting the resonator frequencies and coupling strengths to bring the filter response within the design specification.
This is particularly the case for a class of dielectric filters in which TE (transverse electric) single-mode and triple-mode ceramic-filled cavities are combined. Filters of this type are tuned by making modifications to multiple faces of the components, including faces which will be bonded together in the assembled filter. However, this prevents full tuning of a filter subsequent to bonding, because, at that time, the bonded faces are no longer accessible.
As is recognized by those of ordinary skill in the art, triple-mode cuboid resonators can be tuned by lapping controlled amounts of material from three mutually orthogonal faces of the cuboid, and subsequently resilvering those faces. This allows the frequencies of all three modes of a triple-mode cuboid resonator to be independently adjusted. Single mode slab-shaped cuboid resonators can be tuned by lapping controlled amounts of material off one or more of the narrow faces, subsequently resilvering those faces.
An alternate method to tune triple-mode cuboid resonators is to drill holes in three mutually orthogonal faces, and then either to silver the walls of the holes or to leave the holes unsilvered. This method also allows independent adjustment of all three mode frequencies. In contrast, a single-mode slab-shaped cuboid resonator can be adjusted by drilling a hole or holes into one or both of the large flat faces.
Another method is to cut slots in the silver on at least two mutually orthogonal faces. This method also allows independent adjustment of all three frequencies. A single-mode slab-shaped cuboid resonator can also be adjusted by cutting one or more slots on one or more of the narrow faces, the slots being oriented parallel to the large faces.
As noted above, however, filter components cannot be tuned after the components have been bonded together, because, after bonding, an insufficient number of faces is accessible. The present invention addresses this deficiency in the prior art.
This section contains examples of possible implementations and is not meant to be limiting.
In an exemplary embodiment, the present invention is a pair of joined dielectric resonator components of an RF filter. The pair of joined dielectric resonator components comprises a first dielectric resonator component and a second dielectric resonator component.
The first dielectric resonator component includes a first block of dielectric material, the first block of dielectric material having a coating of a first conductive material. The first dielectric resonator component is a slab-shaped cuboid having one dimension with a magnitude less than the substantially equal magnitudes of the other two dimensions.
The second dielectric resonator component includes a second block of dielectric material, the second block of dielectric material having a coating of a second conductive material. The second dielectric resonator component is a generally cube-shaped cuboid with three dimensions of substantially equal magnitude.
The first dielectric resonator component is joined to the second dielectric resonator component by bonding a first face of the first dielectric resonator component, the first face having dimensions of substantially equal magnitude, to a second face of the second dielectric resonator component, so that the dimension of the first dielectric resonator component having a magnitude less than the substantially equal magnitudes of the other two dimensions is perpendicular to the first and second faces.
The first face has a first coupling aperture formed by removing a portion of the coating of first conductive material from the first block of dielectric material, and the second face has a second coupling aperture formed by removing a portion of the coating of second conductive material from the second block of dielectric material. The first coupling aperture and the second coupling aperture are aligned with one another when the first face is bonded to the second face.
The first dielectric resonator component and the second dielectric resonator component thereby form a linear stack having two end faces and four side faces. The linear stack is thereby oriented in a direction in common with the one dimension of the first dielectric resonator component having a magnitude less than substantially equal magnitudes of the other two dimensions.
A first hole is provided at a point along a center line of a side face of the first dielectric resonator component in the direction of orientation of the linear stack, and a second hole is provided substantially in the center of a side face of the second dielectric resonator component to tune a resonant frequency of the pair of joined dielectric resonator components.
In the attached Drawing Figures:
The word “exemplary” as used herein means “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described in this Detailed Description are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims.
In accordance with the present invention, an array of tuning holes drilled into a single face of a cuboid triple-mode dielectric resonator component is sufficient to enable all three lowest-order modes of the resonator component to be independently adjusted.
All of the in-band resonant frequencies of all of the components of a filter composed of a linear stack of cuboid dielectric resonator components, possibly including one or more triple-mode resonator components, can be independently adjusted by drilling an array of tuning holes in one or more of the outer faces of the components. If required in a particular application or use of the filter, all of the holes can be provided on a single side of the linear stack.
Additional holes may be drilled in at least one outer face to enable couplings between the dielectric resonator components to be adjusted, when the couplings are implemented with apertures near one or more of the outer faces of the cuboids.
However, when coupling apertures are provided in the center of the bonded faces, the coupling through a central aperture cannot be adjusted in this manner because the distance between the central aperture and an outer face is too large for a hole in the outer face to have any effect.
As noted above, once the dielectric resonator components of a filter have been bonded together, their planar contact surfaces are no longer accessible, thereby preventing any tuning operations requiring access to those surfaces. The tuning method of the present invention has the advantage that all of the in-band resonant frequencies and all of the couplings resulting from apertures close to the outer edges of the dielectric resonator component can be adjusted, even after the dielectric resonator components of the filter have been bonded together.
Turning now to the figures identified above,
The three lowest-order resonant modes are commonly referred to as the TE011, TE101, and TE110 modes; the directions of their electric fields are parallel to the X-axis, the Y-axis, and the Z-axis, respectively, TE being the abbreviation for “Transverse Electric”. The TE011, TE101, and TE110 modes may alternatively be referred to as the X-mode, the Y-mode, and the Z-mode, respectively.
When the magnitudes of the three dimensions of the dielectric resonator component 10 are close to one another, the resonant frequencies of the three lowest-order resonant modes will also be close to one another. In such a case, the dielectric resonator component 10 may be used as a triple-mode resonator, when the three mode frequencies lie within the passband of the filter. Similarly, when the magnitudes of two of the three dimensions of the dielectric resonator component 10 are close to one another, the frequencies of two of the three lowest-order resonant modes will also be close to one another. Such a dielectric resonator component 10 may be used as a dual-mode resonator. Alternatively, the frequency of the third lowest-order resonant mode may be the in-band frequency, in which case the dielectric resonator component 10 may be used as a single-mode resonator. Finally, when the magnitudes of all three dimensions of the dielectric resonator component 10 are substantially different from one another, all three lowest-order resonant frequencies will be different from one another. When one of these resonant frequencies is in-band, such a dielectric resonator component 10 may also be used as a single-mode resonator. All of the in-band resonant frequencies of the above dielectric resonator components 10 will require careful adjustment to ensure that the completed filter is tuned.
We will consider the case where a cuboid dielectric resonator component 10 is a thin slab-shaped component, wherein the magnitude of one of its three dimensions is significantly smaller than the other two. Further, we will assume that this component has a magnitude such that that the lowest-frequency resonant mode is in-band, so that the cuboid dielectric resonator component 10 may be used as a single-mode resonator. Referring to the face labels in
Now we will consider another cuboid dielectric resonator component to have three dimensions of similar magnitude, so that all three lowest-frequency resonant modes are in-band. The three resonant modes of interest are then TE011 (X-mode), TE101 (Y-mode), and TE110 (Z-mode). As with the thin slab-shaped component described above, when the triple-mode cuboid dielectric resonator component is placed in a linear filter stack with Face 1 and Face 4 oriented toward neighboring dielectric resonator components, only Faces 2, 3, 5, and 6 will be accessible. Tuning holes or other structures cannot be placed on Faces 1 or 4 after those faces of the cube-shaped component are bonded to those of other dielectric resonator components.
Referring now to
In the calculations, both the thin slab-shaped dielectric resonator component 20 and the generally cube-shaped dielectric resonator component 30 were assumed to be made from a dielectric material having a dielectric constant of 45. Both the thin slab-shaped dielectric resonator component 20 and the generally cube-shaped dielectric resonator component 30 were also assumed to have a coating of a conductive material, such as silver. The dimensions of the holes 22, 32 were 1.5 mm in diameter and 1.0 mm deep. The dimensions of the generally cube-shaped dielectric resonator component 30 were 17.7 mm×18.0 mm×18.3 mm in the X-, Y-, and Z-directions, respectively, while the dimensions of the slab-shaped dielectric resonator component 20 were 4 mm×18.0 mm×18.3 mm in the X-, Y-, and Z-directions, respectively. The positions of the holes 22, 32 relative to the center of Face 6 are given in the following Table 1:
It will be noted, referring to
The calculated shifts in the resonant frequencies of the X-mode, Y-mode, and Z-mode are shown in Table 2 below, for the generally cube-shaped dielectric resonator component 30, and Table 3, for the slab-shaped dielectric resonator component 20, to follow for both filled holes, wherein a coating of a conductive material is provided on the inner surface of the holes 22, 32, and for unfilled holes 22, 32, which are air-filled and capped with a metal cover.
786
754
1386
−5816
753
788
As may be noted in preceding Table 2, and as indicated by the use of italics, the calculations reveal that the X-mode can be controlled using filled holes 32 at positions B and H, the Y-mode using filled holes 32 at positions D and F, and the Z-mode using unfilled or filled hole 32 at position E. This combination of holes achieves good independent control. Unfilled holes 32 in the corners (A, C, G, and I) have negligible effect on the resonant frequencies of all modes, and, therefore, can be used to control couplings between adjacent dielectric resonator components as will be discussed below. Filled holes 32 in the corners have only a small effect on the resonant frequencies, and may be used to control the couplings between adjacent dielectric resonator components if care is taken to compensate for their effect on the resonant frequencies.
The calculated shifts in the resonant frequencies are for the X-mode in following Table 3 for the slab-shaped dielectric resonator component 20.
Based on the results provided in Table 3, all of the holes 22 increase the resonant frequency of the X-mode, although the holes on the X-centerline (B, E, and H) do so most effectively.
Based on the results of the calculations described above, an effective set of tuning holes 32 to use for a cube-shaped dielectric resonator component 30 is a filled hole 32 at one or both of positions B and H to adjust the X-mode resonant frequency, a filled hole 32 at one or both of positions D and F to adjust the Y-mode resonant frequency, and either a filled or an unfilled hole 32 at position E to adjust the Z-mode resonant frequency. These provide three degrees of freedom which, while not completely independent, are reasonably orthogonal. With the aid of a tuning matrix of the sort disclosed in U.S. patent application Ser. No. 15/227,169, filed Aug. 3, 2016, the teachings of which are incorporated herein by reference, it is straightforward to calculate the hole depths required to achieve a desired set of resonant frequency changes. One method to calculate needed tuning is use coupling matrix extraction from a measured filter s-parameters. A calculated matrix is just compared to a target coupling matrix, and all clear deviations are corrected by a calculated drill tuning. This method is also suitable for coupling tuning.
Since there is only one resonant frequency (X-mode) to adjust in a slab-shaped dielectric resonator component 20, a hole 22 at almost any position (A to I) on one of the narrow faces will cause a resonant frequency shift. However, the most effective positions are on the X-centerline of the face, such as Face 6, as indicated with italics for filled holes at positions B, E, and H in Table 3 above.
As stated at the outset, a class of dielectric filters in which TE (transverse electric) single-mode and triple-mode ceramic-filled cavities are combined is of interest in the present application. This type of filter heretofore could not be fully tuned subsequent to bonding, because, the bonded faces are no longer accessible.
However, based on the calculations described above, a set of holes suitable for adjusting the resonant frequencies in a dielectric filter of this type is shown in
More specifically,
Similarly, in each of the slab-shaped dielectric resonator components 20, a hole 24, filled with a conductive material, is provided at a central position, analogous to position E in
The holes 24, 34 shown in
More specifically, in exemplary dielectric filter 50, approximately cube-shaped dielectric resonator component 30, holes 34, 36, are provided at three positions, analogous to positions B, E, and F in
As was the case in
In addition to the ability to adjust the resonant frequencies, the set of holes illustrated in
In this regard, reference is now made to
Similarly, referring to
When coupling apertures 26, 38 are in the corners, holes 22, 32 placed in the corners of the outer faces are very suitable for use as coupling adjustments. Referring to the resonant frequency shifts due to the corner hole positions (A, C, G, and I) in Table 2, for unfilled holes, the resonant frequency shifts are negligible, while, for filled holes, the resonant frequency shifts are significantly smaller than those for the other hole positions. As a result, the disturbance to the resonant frequencies caused by modifications to corner holes are small, and may be compensated by the other holes. Thus, the corner holes may be used to adjust the coupling strengths.
Since every hole changes multiple quantities, both resonant frequencies and electric-field couplings, it will be necessary to use a tuning matrix of the sort disclosed in the above-referenced U.S. patent application Ser. No. 15/227,169 to calculate the depth changes required in all of the holes to achieve the desired changes to all of the resonant frequencies and electric-field couplings. Unlike the situation described in U.S. patent application Ser. No. 15/227,169, where only resonant frequency adjustments are discussed, in the present case the quantities to be adjusted are resonant frequencies and couplings.
The couplings could be adjusted by placing the corner holes either in the slab-shaped dielectric resonator component 20 shown in
Even though a nine-hole embodiment has been shown, the essential methods described would also work with other arrangements of tuning holes. Accordingly, the present invention is not limited to the 3×3 hole pattern shown in
The general requirement for couplings to be adjusted is that the aperture be close to the edge of a bonding face, such as Face 1 or Face 4, and that a tuning hole be placed close to that aperture. The general requirement for resonant frequencies to be tuned depends on the mode concerned, as has been seen above, and will be further discussed below.
A filled hole placed somewhere in the middle of a face will cause the mode with electric field striking that face (Z-mode in the case of holes on Face 6) to decrease in resonant frequency, as illustrated by E in column 7 of Table 2. An unfilled hole in a similar location will cause the same mode frequency to increase, as illustrated by E in column 4 of Table 2.
A filled hole placed in the current stream due to a particular mode will cause the resonant frequency of that mode to increase. This is illustrated by B, E and H in column 5 of Table 2 for the X-mode. These holes run across the face in the X-direction, and are located in the center in the Y-direction as can be seen in
An unfilled hole placed in the current stream will have a negligible effect on the resonant frequencies of modes having minimal electric field in the location of the hole, such as the X-mode and Y-mode on Face 6. This is illustrated by the tiny resonant frequency shifts of the X-mode and Y-mode in columns 2 and 3 of Table 2.
To further illustrate the variation of resonant frequency shifts as the position of a hole is changed, plots showing these variations are shown below. They are based on calculations performed for a 17.9 mm×18.0 mm×18.1 mm cuboid with a dielectric constant of 45. The size of the hole was 1.0 mm in diameter and 1.0 mm deep.
In order to achieve a given resonant frequency shift, one may choose a certain combination of hole diameter and depth. A larger diameter hole will not need to be as deep as a smaller diameter hole in order to produce the same resonant frequency shift. This gives some freedom in choosing the drill diameter.
The available resonant frequency shifts from the present method are not very large compared with the shifts which are possible with lap tuning, such as are described in the above-referenced U.S. patent application Ser. No. 15/227,169, however they are still large enough to be useful when the filter is close to tuned at the time of bonding.
Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims.
It is also noted herein that while the above describes example embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.
