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(11) | EP 0 678 928 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A dielectric resonator filter |
| (57) A dielectric resonator filter is provided which includes at least one microwave resonator
having a body member with a cylindrical conductive cavity of uniform diameter formed
therein, symmetrically disposed about a longitudinal axis, the cavity being divided
into two sections, of unequal lengths, by an integral inwardly projecting flange;
a cylindrical dielectric resonator having a coefficient of thermal expansion to match
that of the body member, the longitudinal axis of the resonator being co-axial with
the longitudinal axis of the cavity; two cylindrical support members for supporting
the dielectric resonator within the longer section of the cavity, the support members
being of quartz and located one on each side of the dielectric resonator; and securing
means for securing the two support members, with the dielectric resonator therebetween,
within the cavity, one of the support members being in an abutting relationship with
a surface of the inwardly projecting flange. |
[0001] This invention relates to a dielectric resonator filter having a particular, but not necessarily an exclusive, application in a dielectric demultiplexer for communication satellite payloads.
[0002] Satellite communication systems are used for a number of different purposes, for example, ground surveillance, and telecommunications. The cost of placing communication satellite payloads into orbit is very high and it is desirable to have compact, reliable and light weight resonator filter structures that are sufficiently rugged and stable to withstand both the high levels of vibration experienced by space hardware during the launch phase of a mission and also long term effects of repeated thermal cycling experienced over the duration of the mission. It is of importance to ensure in communication satellite payloads that a stable performance is maintained over a wide range of temperatures.
[0003] Furthermore, with communications satellite payloads, the main problem encountered in realising practical dielectric resonator filters is in supporting the dielectric resonator in a spatial central position within the cavity of the filter.
[0004] Ideally, the dielectric resonator should hang in free space but, in practice, it is necessary to provide a support structure for the resonator within the cavity. The support structures of known dielectric resonator filters degrade the unloaded electrical quality factor of the resonator. This is due to additional losses induced in the fabric of the support structure.
[0005] The resonator support structures used in dielectric resonator filters for communications satellite payloads must, as stated above, be sufficiently rugged and stable to withstand both the high levels of vibration experienced by space hardware during the launch phase of a mission and also the long term effects of repeated thermal cycling experienced over the duration of the mission.
[0006] In addition, the perturbation of the resonators electrical performance must be minimised and, in particular, all additional electrical losses, given rise to by the resonator support structure, must be minimised in order to achieve the extremely high levels of unloaded Q required by narrow band filters.
[0007] It is known from EP 0351840 A2 to support a cylindrical dielectric resonator in coaxial position within a resonator cavity using recessed support members, located one on each side of the resonator, and to clamp the support members, with the resonator therebetween, in an abutting relationship with a step in one part of a two-part cavity structure. However, with this arrangement, the clamping is effected by an end face of the other part of the cavity and the clamping pressure is a function of the length of the said one part of the cavity between the step and an end wall thereof. The dimensions of the two parts of the cavity are, therefore, critical and must be set at exactly the correct values otherwise the resulting clamping pressure could cause stressing of the support structure and thereby risk damage to the resonator structure. Furthermore, the nature of this cavity structure is such that the cavity dimensions cannot readily be trimmed to effect a change in the clamping pressure. Thus, if the cavity dimensions are not precisely set during the manufacturing process, the cavity structure may have to be scrapped. The result of this is that adhesives may be the only effective means of securing the resonator structure in the cavity of this prior art resonator.
[0008] It is an object of the present invention to overcome the foregoing problems by providing a dielectric resonator filter having a support structure for the dielectric resonator which has a high mechanical ruggedness, minimises thermally induced stress and has low electrical loss.
[0009] The thermally induced stress is minimised by closely matching the thermal expansion coefficients of all of the materials from which the filter and support structure are fabricated.
[0010] The low electrical loss is due to low loss tangents, low dielectric filling factors and the positioning of the support member within the cavity of the resonator so as to avoid areas of high electric field concentration.
[0011] The invention provides a dielectric resonator filter including at least one microwave resonator having a body member with a cylindrical conductive cavity of uniform diameter formed therein, symmetrically disposed about a longitudinal axis; and a cylindrical dielectric resonator supported in the cavity and having the longitudinal axis thereof coaxial with the longitudinal axis of the cavity characterised in that, the filter further includes an inwardly projecting flange formed integrally with a side wall of the cavity, the location of the flange being off-set relative to the longitudinal centre of the cavity whereby the cavity sections on each side of the flange are of unequal length; two cylindrical support members for supporting the dielectric resonator within the longer section of the cavity, the support members being of a dielectric material and located one on each side of the dielectric resonator; and securing means for securing the two support members, with the dielectric resonator therebetween, within the larger section of the cavity, at least part of the securing means being located within the cavity in an abutting relationship with one of the support members, the other support member being in an abutting relationship with a surface of the inwardly projecting flange, the longitudinal centres of the cavity and the dielectric resonator being substantially in alignment.
[0012] In a preferred arrangement, each of the support members is in the form of an annular disc having a cylindrical recess formed in a surface thereof into which a respective one of the ends of the dielectric resonator is located.
[0013] In one embodiment of the present invention, the body member of the filter is preferably, but not necessarily, of a thermal conductivity higher than that of the dielectric resonator. With this embodiment, the securing means include an annular disc located within the longer section of the cavity in an abutting relationship with the said one of the support members, the surface of the annular disc remote from the said one of the support members being securely connected, at four equi-spaced positions around the periphery thereof, to the wall of the cavity. The annular disc is preferably of a silver plated material, for example, brass, aluminium, steel, or a nickel-iron alloy, which is securely connected to the cavity wall, at each of the four positions, by either soldering or brazing. In a preferred arrangement, the soldered, or brazed, connections cover an arc of not less than two millimetres.
[0014] In another embodiment of the present invention, a dielectric resonator filter is provided wherein the securing means of the filter include a clamping member comprising a tubular body member located within the longer section of the cavity, at one end of the body member, the outer peripheral surface of the tubular body member being a sliding fit in the cavity, the tubular body member having an integral flange at one end thereof, wherein the flange member is in an abutting relationship with the body member of the filter, at the said one end thereof, and wherein the length of the tubular body member, between the flange member and the other end thereof, is such that the two support members, with the dielectric resonator therebetween, are securely clamped in an abutting relationship with the said surface of the inwardly projecting flange of the cavity, by the said other end of the tubular body member. In a preferred arrangement, the filter includes means for temporarily securing the flange member in an abutting relationship with the body member.
[0015] In a further embodiment of the present invention, the filter includes means secured within the cavity, at the other end thereof, to provide a symmetrical structure. In a preferred arrangement the means for providing a symmetrical structure include a tubular member located within the shorter section of the cavity, at the other end of the body member, the outer peripheral surface of the tubular member being a sliding fit in the cavity, the tubular member having an integral flange member at one end thereof, wherein the flange member is in an abutting relationship with the body member of the filter, at the said other end thereof, and wherein the length of the tubular member, between the flange member and the other end thereof, is less than the length of the cavity between the said other end thereof and the inwardly projecting flange of the body member.
[0016] Preferably, the cylindrical support members are of quartz, the dielectric resonator is of barium magnesium tantalate and the body member is of a silver plated material, for example, silver plated titanium, a nickel-iron alloy or beryllium.
[0017] The invention also provides a method of assembly for a dielectric resonator according to the present invention including the steps of supporting the body member, with the longer section of the cavity uppermost and the longitudinal axis thereof substantially vertical; inserting one of the support members into the cavity of the body member, with the recessed surface thereof uppermost, whereby it is supported by the inwardly projecting flange; inserting one end of the dielectric resonator into the recess of the said one of the support members; inserting the other one of the support members into the cavity of the body member, with the recessed surface thereof lowermost, whereby the other end of the dielectric resonator is located in the recess of the said other one of the support members; tinning one side of the annular disc of the securing means, at four equi-spaced positions around the periphery of the disc; inserting the tinned disc into the cavity of the body member, with the tinned side uppermost, whereby the disc is supported by the said other one of the support members; clamping the assembled components together exerting a minimum amount of pressure on the assembly, the pressure applied to the assembly being adjustable; heating the assembled components; applying pressure to the heated assembly; applying fillets of solder to the four equi-spaced positions; removing the pressure applied to the assembled components, on cooling of the four solder joints; allowing the assembled components to cool to room temperature; and after cooling, cleaning the assembly.
[0018] In a preferred method, the clamping of the assembled components is effected by means of a clamping plate situated on top of the tinned annular disc, the pressure is applied to the assembled components by a clamping screw connected to the clamping plate, the clamping screw generates a torque of 0.1nM, and the heating of the assembled components is effected at a temperature of 90 degrees centigrade for a period of two minutes.
[0019] The dielectric resonator filters according to the present invention have a particular, but not necessarily and exclusive application, in the dielectric resonator demultiplexer covered by our co-pending UK Patent Application Number 9400698.8 in that the compact, rugged and stable structure of the filters facilitate vertical mounting of cascaded filter arrangements thereby minimising the 'footprint' of the demultiplexer, i.e. the space occupied by the demultiplexer.
[0020] The foregoing and other features according to the present invention will be better understood from the following description with reference to the accompanying drawings, in which:
Figures 1 and 2 diagrammatically illustrate, respectively in a front view and cross-sectional side view, one arrangement for a dielectric resonator filter according to the present invention;
Figures 3 and 4 diagrammatically illustrate, respectively in a front view and cross-sectional side view, another arrangement for a dielectric resonator filter according to the present invention; and
Figures 5(A) and (B) diagrammatically illustrate, respectively in a front view and cross-sectional side view, part of the dielectric resonator filter illustrated in Figures 3 and 4 of the accompanying drawings.
[0021] As is diagrammatically illustrated in Figures 1 and 2 of the drawings, respectively in a front view and cross-sectional side view, one arrangement for a dielectric resonator according to the present invention includes a body member 1 having a cylindrical cavity 2 formed therein and a cylindrical dielectric resonator 3 located within the cavity 2. The dielectric resonator 3 is of a material, for example, barium magnesium tantalate, having a coefficient of thermal expansion to match that of the body member 1. As can be seen from the drawings, the longitudinal axes of the dielectric resonator 3 is co-axial with the longitudinal axis of the cavity 2. The cavity 2 is of uniform diameter and has an integral inwardly projecting flange 4. The dielectric resonator 3 is supported within the cavity 2 by two cylindrical support members 5, located one on each side of the dielectric resonator 3. The support members 5 are of a dielectric material, for example, a ceramic material, plastic or quartz but are preferably made from quartz.
[0022] As can be seen in Figure 2 of the accompanying drawings, each of the support members 5 is in the form of an annular disc having a cylindrical recess formed in a surface 6 thereof into which a respective one of the ends of the dielectric resonator 3 is located.
[0023] As is best illustrated in Figure 2 of the accompanying drawings, the resonator assembly comprising the two support members 5, with the dielectric resonator 3 situated therebetween, is securely retained within the cavity 2 by means of the annular disc 7. The resonator assembly is securely clamped between the annular disc 7 which is in an abutting relationship with the adjacent support member 5, and the inwardly projecting flange 4 which is in an abutting relationship with the adjacent support member 5. The assembly is arranged such that the longitudinal centre of the dielectric resonator 3 is in alignment with the longitudinal centre of the cavity 2. Clearly, the alignment of the longitudinal centres of the cavity 2 and dielectric resonator 3 is effected by the position of the flange 4 in association with the thickness of the supports 5 and the depth of the recesses formed therein.
[0024] As is best illustrated in Figure 1 of the accompanying drawings, the annular disc 7 is securely connected to the cavity at four equi-spaced positions 8 around the periphery to the wall of the cavity 2. The annular disc 7 is preferably made of a silver plate material, such as brass, or a nickel-iron alloy, and the connection of a silver plated disc 7 to the cavity wall is preferably effected by either brazing, or soldering, i.e. silver soldering. The soldered, or brazed, connections 8 preferably cover an arc of not less than two millimetres.
[0025] The assembly of the dielectric resonator filter illustrated in Figures 1 and 2 of the drawings is a very delicate operation which must be effected in a clean environment, wearing cotton cloves to avoid contamination of the various component parts during assembly. The assembly is preferably effected using a specially constructed assembly jig.
[0026] In particular, quartz support members 5 are extremely fragile and must, therefore, be well supported during the assembly process and be handled with extreme care, for example, using plastic tweezers.
[0027] The method of assembly for the dielectric resonator filter of Figures 1 and 2 includes the steps of:
- locating the end 9 of the body member 1, i.e. the end nearest the flange 4, on a suitable support so that the longitudinal axis of the body member 1 is substantially vertical;
- inserting one of the support members 5 into the cavity 2 of the body member 1, with the recessed surface thereof uppermost, whereby it is supported by the flange 4;
- inserting one end of the dielectric resonator 3 into the recess of the said one of the support members 5;
- inserting the other one of the support members into the cavity 2 of the body member 1, with the recessed surface thereof lowermost, whereby the other end of the dielectric resonator 3 is located in the recess of the said other one of the support members 5;
- tinning one side of the annular disc 7 using, for example, silver loaded solder, at four equi-spaced positions 8 around the periphery of the disc, the solder deposit at each of the four positions 8 covering an arc of not less than 2 millimetres;
- inserting the annular disc 7 into the cavity 2 of the body member 1, with the tinned side uppermost, whereby the disc 7 is supported by the said other one of the support members 5;
- holding the assembled components together by means of a clamping plate, placed on top of the disc 7, but exerting a minimum amount of pressure on the assembly, the pressure applied to the clamping plate being adjustable by operation of a clamping screw;
- heating the assembled components to a temperature of 90 degrees centigrade for a period of two minutes;
- applying pressure to the heated assembly by means of the clamping plate, i.e. by turning the clamping screw to generate a torque of 0.1nM;
- applying fillets of solder to the four equi-spaced positions 8;
- removing the pressure applied to the assembled components, on cooling of the four solder joints;
- allowing the assembled components to cool to room temperature; and
- after cooling, cleaning the assembly.
[0028] The body member 1 of the dielectric resonator filter, manufactured by the foregoing method, preferably, but not necessarily, has a thermal conductivity higher than that of the dielectric resonator 3. With this arrangement, the heating of the assembled components means that the expansion of the body member 1 will be greater than the expansion of the dielectric resonator 3 and, on cooling, after the annular disc 7 is securely connected in place by the soldering, the support member 5/dielectric resonator 3 assembly is subject to further stressing and is more securely held in position. Thermal cycling of the assembly, during operation of the filter, will not affect the clamping action of the assembly because the temperature changes will be gradual and the difference in the coefficients of thermal expansion of the body member 1 and the dielectric resonator 3 will not be sufficiently large to affect the clamping action.
[0029] The only difference between the dielectric resonator filter, diagrammatically illustrated in Figures 3 and 4 of the accompanying drawings, and the dielectric resonator filter, diagrammatically illustrated in Figures 1 and 2 of the accompanying drawings, is in the manner in which the resonator assembly, comprising the dielectric resonator 3 and the support members 5, is clamped in position against the surface of the inwardly projecting flange 4.
[0030] As is best seen in Figure 4 of the accompanying drawings, the resonator assembly is clamped in position by means of a clamping member 9 which, as is diagrammatically illustrated in Figure 5(A) and 5(B) of the drawings, comprising a tubular body member 10 and a flange member 11 located at one end 13 thereof. As with the dielectric resonator filter of Figures 1 and 2 of the drawings, the longitudinal centres of the dielectric resonator 3 and the cavity 2 are in alignment. The body member 10 is located within the longer section of the cavity 2. The outer peripheral surface of the body member 2 is a sliding fit in the cavity and the integral flange 11, at the said one end 13 thereof, is in an abutting relationship with the body member 1. The length of the body member 10, between the flange member 11 and the other end 12 thereof, is such that the two support members 5, with the dielectric resonator 3 therebetween, are securely clamped in an abutting relationship with the surface of the inwardly projecting flange 4, by the said other end 12 of the tubular body member 10, when pressure is applied to the end 13 of the clamping member 9 by an adjacent cavity.
[0031] As with the arrangement of Figures 1 and 2, it is important to ensure that the pressure applied to the fragile support members 5 of the resonator assembly by the clamping member 9 is the minimum required to effect the clamping action. The pressure that is actually applied being controllable by variation of the length of the tubular body member 10 between the flange member 11 and the end 12. This length can be accurately set by skimming the surface of the clamping member 9, at the end 12 thereof, in a special jig i.e. the gradual removal of material from the end 12 to an accuracy of + or - 5 µ.
[0032] In a preferred arrangement, the clamping member 9 is a silver plated member having an overall length of approximately 3 mm, the internal diameter of the tubular member 10 being approximately 12.5 mm.
[0033] With the arrangement according to Figures 3 and 4 of the drawings, the resonator assembly is easy to remove, if problems occur, in that there are no soldered joints. In addition, and very importantly, the resonant frequency of the cavity 2 can be set by skimming the surface of the clamping member 9, at the end 13 thereof, rather than the cavity itself. This is a cost effective arrangement because of the vast difference in the cost of the clamping member 9 in comparison to the vastly more expensive body member 1.
[0034] During filter alignment, i.e. prior to the clamping action being affected by an adjacent cavity, the dielectric resonator filter according to Figures 3 and 4 of the drawings, may include means (not illustrated) for temporarily securing the flange member 11 in an abutting relationship with the body member 1. This could be effected by a suitable adhesive.
[0035] In addition, the dielectric resonator filter, according to Figures 3 and 4 of the drawings, may include means, secured within the shorter section of the cavity 2, to provide a symmetrical structure.
[0036] As is illustrated in dotted detail in Figure 4 of the accompanying drawings, the means for providing a symmetrical structure include a tubular member 23 located within the shorter section of the cavity 2. The outer peripheral surface of the tubular member 23 is a sliding fit in the cavity 2. The tubular member 23 has an integral flange, at one end thereof, in an abutting relationship with the body member 1. The length of the tubular member 23, between the flange member and the other end thereof, is less than the length of the shorter section of the cavity 2 and does not, therefore, affect the clamping action of the filter arrangement.
[0037] The dielectric resonator filter according to the present invention also includes, as is diagrammatically illustrated in Figures 1 to 4 of the accompanying drawings, coupling screw holes which extend into the cavity 2 on radial planes 14 and 15, that are at 45° to the two orthogonal dual mode electrical field orientations of the cavity 2 i.e. in substantial alignment with the solder fillets 8. The filter will also include two resonance tuning screws, each one of which will extend into the cavity 2 on a radial plane, i.e. the planes 16 and 17, and the plane indicated by the line X-X, that are coincident with a respective one of the two orthogonal mode electrical field orientations of the filter.
[0038] Screw-threaded holes (see, for example, screw-threaded hole 19 in Figures 2 and 4 of the drawings) would be provided in the body member 1 for the coupling and tuning screws to enable the position of the screws to be adjusted, i.e. the extent to which the screws extend into the cavity 2 is adjustable. As, and when, a desired position is reached the screws are respectively locked in position by locking nuts (not illustrated).
[0039] A coaxial input connector for the cavity 2 would also be provided and would be connected to the boss 18 of the body member 1. The probe of the input connector would enter the cavity 2 through the hole 20 in the boss 18.
[0040] In practice, the dielectric resonator filter includes a plurality of the dielectric resonators, illustrated in Figures 1 to 4 of the drawings, connected in cascade with resonant energy coupling means interposed between each pair of adjacent dielectric resonators. The body member 1 is provided with flanges 21 to facilitate the cascaded couplings. The flanges 21 are each provided with a hole 22 to facilitate the bolting together of the cascaded resonators.
[0041] The resonant energy coupling means referred to above which, in practice, is in the form of a planar member with a coupling iris formed therein, for example, a cruciform shaped aperture, would be interposed between the flanges 21, and provided with a number of through holes in alignment with the holes 22.
1. A dielectric resonator filter including at least one microwave resonator having a
body member (1) with a cylindrical conductive cavity (2) of uniform diameter formed
therein, symmetrically disposed about a longitudinal axis; and a cylindrical dielectric
resonator (3) supported in the cavity (2) and having the longitudinal axis thereof
co-axial with the longitudinal axis of the cavity (2) characterised in that, the filter
further includes an inwardly projecting flange (4) formed integrally with a side wall
of the cavity (2), the location of the flange (4) being off-set relative to the longitudinal
centre of the cavity (2) whereby the cavity sections on each side of the flange (4)
are of unequal length; two cylindrical support members (5) for supporting the dielectric
resonator (3) within the longer section of the cavity (2), the support members (5)
being of a dielectric material and located one on each side of the dielectric resonator
(3); and securing means (7; 9) for securing the two support members (5), with the
dielectric resonator (3) therebetween, within the larger section of the cavity (2),
at least part of the securing means (7; 9) being located within the cavity (2) in
an abutting relationship with one of the support members (5), the other support member
(3) being in an abutting relationship with a surface of the inwardly projecting flange
(4), the longitudinal centres of the cavity (2) and the dielectric resonator (3) being
substantially in alignment.
2. A dielectric resonator filter, as claimed in claim 1, characterised in that, the cylindrical
dielectric resonator (3) has a coefficient of thermal expansion to substantially match
that of the body member (1).
3. A dielectric resonator filter, as claimed in claim 1 or claim 2, characterised in
that, each of the support members (5) is in the form of an annular disc having a cylindrical
recess formed in a surface thereof into which a respective one of the ends of the
dielectric resonator (3) is located.
4. A dielectric resonator filter, as claimed in any one of the preceding claims, characterised
in that, the body member (1) is of a thermal conductivity higher than that of the
dielectric resonator (3).
5. A dielectric resonator filter, as claimed in claim 4, characterised in that, the securing
means include an annular disc (7) located within the longer section of the cavity
(2) in an abutting relationship with the said one of the support members (5), the
surface of the annular disc (7) remote from the said one of the support members (5)
being securely connected, at four equi-spaced positions (8) around the periphery thereof,
to the wall of the cavity (2).
6. A dielectric resonator filter, as claimed in claim 5, characterised in that, the securing
means include a silver plated annular disc (7) and in that the disc (7) is securely
connected to the cavity wall (2), at each of the four equi-spaced positions (8), by
either soldering or brazing.
7. A dielectric resonator filter, as claimed in claim 6, characterised in that, the soldered,
or brazed, connections cover an arc of not less than two millimetres.
8. A dielectric resonator filter, as claimed in claim 5 or claim 6, characterised in
that, the material of the silver plated annular disc (7) is either brass, aluminium,
steel, or a nickel-iron alloy.
9. A dielectric resonator filter, as claimed in any one of claims 1 to 3, characterised
in that, the securing means include a clamping member (9) comprising a tubular body
member (10) located within the longer section of the cavity (2), at one end of the
body member (1), the outer peripheral surface of the tubular body member (10) being
a sliding fit in the cavity (2), the tubular body member (10) having an integral flange
(11) at one end thereof, in that the flange (11) is in an abutting relationship with
the body member (1) of the filter, at the said one end thereof, and in that the length
of the tubular body member (10), between the flange (11) and the other end (12) thereof,
is such that the two support members (5), with the dielectric resonator (3) therebetween,
are securely clamped in an abutting relationship with the said surface of the inwardly
projecting flange (4) of the cavity (2), by the said other end (12) of the tubular
body member (10).
10. A dielectric resonator filter, as claimed in claim 9, characterised in that, the filter
includes means for temporarily securing the flange (11) in an abutting relationship
with the body member (1) of the filter.
11. A dielectric resonator filter, as claimed in claim 9 or claim 10, characterised in
that, the filter includes means (23) secured within the cavity (2), at the other end
thereof, to provide a symmetrical structure.
12. A dielectric resonator filter, as claimed in claim 11, characterised in that, the
means for providing a symmetrical structure include a tubular member (23) located
within the shorter section of the cavity (2), at the other end of the body member
(1), the outer peripheral surface of the tubular member (23) being a sliding fit in
the cavity (2), the tubular member (23) having an integral flange member at one end
thereof, in that the flange member is in an abutting relationship with the body member
(1) of the filter, at the said other end thereof, and in that the length of the tubular
member (23), between the flange member and the other end thereof, is less than the
length of the cavity (2) between the said other end thereof and the inwardly projecting
flange (4) of the body member (1).
13. A dielectric resonator filter, as claimed in any one of the preceding claims, characterised
in that, the cylindrical support members (5) are of a ceramic material, plastic, or
quartz.
14. A dielectric resonator filter, as claimed in any one of the preceding claims, characterised
in that, the dielectric resonator (3) is of barium magnesium tantalate.
15. A dielectric resonator filter, as claimed in any one of the preceding claims, characterised
in that, the body member (1) is of a silver plated material.
16. A dielectric resonator filter, as claimed in claim 15, characterised in that, the
body member (1) is of either silver plated titanium, a nickel-iron alloy, or beryllium.
17. A dielectric resonator filter as claimed in any one of the preceding claims characterised
in that, the filter further includes a coupling screw which extends into the cavity
(2) on a radial plane (14, 15) that is at 45° to the two orthogonal dual mode electrical
field orientations of the cavity (2) and at least two resonance tuning screws each
one of which extends into the cavity (2) on a radial plane (16, 17) coincident with
a respective one of the said two orthogonal dual mode electrical field orientations,
the extent to which the coupling and tuning screws extend into the cavity (2) being
adjustable.
18. A dielectric resonator filter as claimed in any one of the preceding claims, characterised
in that, the filter further includes a plurality of cascaded dielectric resonators,
and resonant energy coupling means interposed between each pair of adjacent dielectric
resonators.
19. A method of assembly for a dielectric resonator filter as claimed in any one of the
preceding claims 5 to 8 characterised by the steps of supporting the body member (1),
with the longer section of the cavity (2) uppermost and the longitudinal axis thereof
substantially vertical; inserting one of the support members (5) into the cavity (2)
of the body member (1), with the recessed surface thereof uppermost, whereby it is
supported by the inwardly projecting flange (4); inserting one end of the dielectric
resonator (3) into the recess of the said one of the support members (5); inserting
the other one of the support members (5) into the cavity (2) of the body member (1),
with the recessed surface thereof lowermost, whereby the other end of the dielectric
resonator (3) is located in the recess of the said other one of the support members
(5); tinning one side of the annular disc (7) of the securing means, at four equi-spaced
positions (8) around the periphery of the disc (7); inserting the tinned disc (7)
into the cavity (2) of the body member (1), with the tinned side uppermost, whereby
the disc (7) is supported by the said other one of the support members (5); clamping
the assembled components together exerting a minimum amount of pressure on the assembly,
the pressure applied to the assembly being adjustable; heating the assembled components;
applying pressure to the heated assembly; applying fillets of solder to the four equi-spaced
positions (8); removing the pressure applied to the assembled components, on cooling
of the four solder joints; allowing the assembled components to cool to room temperature;
and after cooling, cleaning the assembly.
20. A method, as claimed in claim 19, characterised in that, the assembled components
are heated to a temperature of 90 degrees centigrade for a period of two minutes.
21. A method, as claimed in claim 19 or claim 20, characterised in that, the solder deposit
at each of the four positions (8) covers an arc of not less than 2 millimetres.
22. A method, as claimed in any one of the claims 20 to 21, characterised in that, the
clamping of the assembled components is effected by means of a clamping plate situated
on top of the tinned disc (7), and a clamping screw connected to the clamping plate
for applying pressure to the assembled components.
23. A multiplexer/demultiplexer including at least one dielectric resonator filter as
claimed in any one of the preceding claims 1 to 18.
24. A communication satellite payload including a demultiplexer as claimed in claim 23