Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVEMENTS IN CAVITY FILTERS
Cross-Reference to Related Applications
This Patent Cooperation Treaty application claims the benefit of the
filing date of, and incorporates by reference, U.S.S.N. 60/165,369, filed
November 12, 1999.
Field of the Invention
This invention relates to cavity filters of the type used in high
frequency communication systems. It is disclosed in the context of an
application of
cavity filters for a satellite communication system, but has utility in other
applications
as well.
Background of the Invention
The use of dielectric "puck" resonators in cavity filters is well known.
Such devices are used in a variety of RF applications. The wireless RF bands
from
700 MHZ through 3 GHz, which include avionics, cellular/PCS, satellite base
stations, and industrial/scientific/medical (so-called ISM) frequency bands,
are
presented as illustrative applications for puck-type dielectric resonator
filters, but are
by no means the only applications for such devices.
A significant problem that is faced in the implementation of such
devices is that a number of the applications for such devices require high
power
handling capabilities. The dielectric resonators themselves are typically on
the order
of a few centimeters or so in diameter and a few centimeters or so in
thickness, and
the materials from which they are made have relatively low dielectric loss and
the
thermal behavior of good insulators. Since these devices are typically
employed in
communication systems, they must be implemented in ways which minimize
frequency drift about communication carrier frequencies, and so on. Thus,
controlling
the temperatures of such devices is of considerable concern and interest to
system and
component designers.
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Disclosure of the Invention
According to one aspect of the invention, a cavity filter includes a
cavity constituting an electrically conductive enclosure, at least one
resonator element
constructed from a dielectric material, and a support constructed from a
relatively low
loss dielectric support material for supporting the at least one resonator
element in a
desired orientation in the cavity. The support material has substantially
higher
thermal conductivity than the dielectric material.
Illustratively according to this aspect of the invention, the cavity filter
includes multiple cavities, each having at least one resonator element
constructed
from a dielectric material, a support constructed from a relatively low loss
dielectric
support material for supporting the at least one resonator element in a
desired
orientation in the cavity. The support material has substantially higher
thermal
conductivity than the dielectric material.
Further illustratively according to this aspect of the invention, the at
least one resonator element in each cavity includes a passageway.
Additionally illustratively according to this aspect of the invention, the
support in each cavity includes a passageway.
Illustratively according to this aspect of the invention, each enclosure
includes at least one first passageway between an interior of the enclosure
and the
exterior of the enclosure.
Additionally illustratively according to this aspect of the invention, the
support in each cavity includes a heat pipe.
Further illustratively according to this aspect of the invention, each
enclosure includes at least one second passageway remote from the first
passageway
between its interior and its exterior.
Additionally illustratively according to this aspect of the invention,
each cavity further includes a somewhat disk-shaped element constructed from a
very
low loss dielectric material having substantially higher thermal conductivity
than the
dielectric material from which the at least one resonator element is
constructed. The
somewhat disk-shaped element is in heat conducting contact with the at least
one
resonator element.
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Illustratively according to this aspect of the invention, each somewhat
disk-shaped element is in heat conducting contact with at least one of its
respective
support and its respective enclosure.
Further illustratively according to this aspect of the invention, the at
least one resonator element in each cavity is generally right circular
cylindrical in
shape. Each cavity further includes a generally right circular cylindrical
enclosure for
at least partially surrounding a respective at least one resonator element in
heat
conducting contact.
Additionally illustratively according to this aspect of the invention,
each cavity further includes an element having somewhat the configuration of a
hub
with radially outwardly extending spokes constructed from a very low loss
dielectric
material having substantially higher thermal conductivity than the dielectric
material
from which the at least one resonator element is constructed. Each somewhat
hub-
and-spokes configured element is in heat conducting contact with a respective
at least
one resonator element.
Illustratively according to this aspect of the invention, each somewhat
hub-and-spokes configured element is in heat conducting contact with at least
one of
its respective support and its respective enclosure.
Further illustratively according to this aspect of the invention, the at
least one resonator element in each cavity is generally right circular
cylindrical in
shape. Each cavity further includes a generally right circular cylindrical
enclosure for
at least partially surrounding a respective at least one resonator element in
heat
conducting contact.
Additionally illustratively according to this aspect of the invention,
each enclosure includes means, such as, for example, a groove, for engaging
the outer
extent of at least one of the spokes.
Illustratively according to this aspect of the invention, the apparatus
further includes a manifold for supplying a cooling fluid to each said cavity.
The
manifold is coupled to each said cavity through that respective cavity's
respective first
through hole.
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Further illustratively according to this aspect of the invention, the
apparatus further includes a device for establishing a pressure differential
between the
first and second through holes.
Additionally illustratively according to this aspect of the invention, the
apparatus includes a pressure sensor for sensing a pressure in the manifold.
Additionally illustratively according to this aspect of the invention, the
apparatus includes a coolant fluid temperature control unit for treating the
flow of
cooling fluid prior to the introduction of the cooling fluid into the
manifold.
Illustratively according to this aspect of the invention, a circuit is
provided for the recovery and recirculation of the cooling fluid.
Further illustratively according to this aspect of the invention, the
circuit includes the coolant fluid temperature control unit.
Illustratively according to this aspect of the invention, the apparatus
further includes a thermostat for controlling the coolant fluid temperature
control unit.
According to another aspect of the invention, a method For controlling
the temperature of a cavity filter including providing a f rst passageway into
a cavity
of the cavity filter, and introducing into the cavity a low dielectric loss,
substantially
non-polar fluid.
Further illustratively according to this aspect of the invention, the
method includes providing a second passageway into the cavity, and removing
the
fluid through the second passageway.
Additionally illustratively according to this aspect of the invention,
introducing the fluid into the cavity and removing the fluid from the cavity
together
include continuously recirculating the fluid.
Illustratively according to this aspect of the invention, continuously
recirculating the fluid includes passing the fluid through a fluid temperature
control
device.
Further illustratively according to this aspect of the invention, the
method includes monitoring a temperature of the fluid and controlling the
fluid
temperature control device based upon the monitored temperature of the fluid.
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Illustratively according to the invention, the cooling fluid includes a
low dielectric loss, substantially nonpolar gas or mixture of low dielectric
loss,
substantially nonpolar gases.
Additionally or alternatively illustratively according to the invention,
S the cooling fluid includes a low dielectric loss, substantially nonpolar
liquid or
mixture of low dielectric loss, substantially nonpolar liquids.
Brief Descriptions of the Drawings
The invention may best be understood by referring to the following
detailed description and accompanying drawings which illustrate the invention.
In the
drawings:
Fig. 1 illustrates a partly diagrammatic, exploded perspective view of a
resonator constructed according to the invention;
Fig. 2 illustrates a partly diagrammatic, fragmentary sectional view,
taken generally along section lines 2-2, of the resonator illustrated in Fig.
1;
Fig. 3 illustrates a partly diagrammatic, fragmentary sectional view of
an alternative construction to the construction illustrated in Fig. 2;
Fig. 4 illustrates a partly diagrammatic, fragmentary sectional view of
a further enhancement to the construction illustrated in Fig. 2 or Fig. 3;
Fig. 5 illustrates a pautly diagrammatic, fragmentary sectional view of
another alternative construction to the construction illustrated in Fig. 2;
Fig. 6 illustrates a partly diagrammatic, fragmentary sectional view of
another alternative construction to the construction illustrated in Fig. 2;
and,
Fig. 7 illustrates a partly diagrammatic, fragmentary sectional view of
another alternative construction to the construction illustrated in Fig. 2.
Detailed Descriptions of Illustrative Embodiments
A resonator element is enclosed in a thermally relatively highly
conductive, very low loss dielectric material. To aid in the control of the
temperature
of a cavity filter including the resonator, the enclosure may be augmented by
other
temperature controlling measures, such as refrigeration systems, cooling fluid
circulation systems, and the like. In some embodiments, the cooling fluid is
air. In
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others, more exotic coolants can be circulated through the cavities containing
such
resonators.
Referring now to Figs. 1-2, a cavity filter 8 includes one or more
cavities 10, each configured as a generally rectangular prism having
electrically
S conductive walls 12, 14, 16, 18, 20 and 22. While the illustrated cavities
10 are
generally rectangular prism shaped, it should be understood that any
appropriately
shaped cavity(ies) may be used in the implementation of the invention. In
addition to
being electrically conductive, walls 12, 14, 16, 18, 20 and 22 are thermally
conductive. Each resonator cavity 10 houses one or more dielectric resonator
elements 24-1, . . . 24-n, which illustratively are dielectric puck resonators
of
generally right circular cylindrical shape. Again, it should be understood
that, while
puck-type resonator elements 24-1, . . . 24-n are illustrated, any resonant
structures)
may be used in the implementation of the invention.
Resonator elements 24-l, . . . 24-n have through holes 25-1, . . . 25-n
which illustratively are of generally right circular cylindrical shape
extending through
them from one, 26-1, . . . 26-n, of their respective generally parallel
surfaces to the
other, 28-I, . . . 28-n, of their respective generally parallel surfaces. A
supporting post
or pillar 30 extends from one, 12, of the walls of each cavity I 0 toward the
center
thereof. Post 30 is constructed from a very low loss dielectric material and
has a
through hole 32. Wall 12 is also provided with a generally centrally located
passageway 34. Illustratively, passageway 34 may be surrounded by, for
example, a
counterbore 36 for receiving an end of post 30 configured to be received in
counterbore 36, for example, by threading the adjacent surfaces of both post
30 and
counterbore 36, or by a suitable low dielectric loss adhesive. Counterbore 36
typically does not extend all the way through wall 12. Wall 12 is also
provided with a
number, two in the illustrated embodiment, of through holes 38 disposed
outwardly
from passageway 34.
The end of post 30 remote from wall 12 is configured to receive a stack
containing a somewhat disk-shaped enclosure element 40, one or more dielectric
resonator elements 24-l, . . . 24-n, one or more somewhat disk-shaped elements
42-1,
. . . 42-(n-1), and a somewhat disk-shaped enclosure element 44. Element 40 is
configured to seat on a step 46 provided around the perimeter of post 30 at a
distance
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from its end remote from wall 12 substantially equal to the combined thickness
of the
resonators) 24-1, . . . 24-n, elements) 42-1, . . . 42-(n-1), where such
elements) 42-I,
. . . 42-(n-1 ) is (are) present, and enclosure elements 40 and 44. The outer
perimeter
48 of enclosure element 40 provides a seat for a generally right circular
cylindrical
enclosure sleeve 50 which is configured to slide with little clearance over
the
perimetrally outer surfaces 52-I, . . . 52-n, 54-1, . . . 54-(n-I), 56 of
resonators) 24-1,
. . . 24-n, elements) 42-1, . . . 42-(n-1), where present, and enclosure
element 44.
The adjacent surfaces of post 30, enclosure element 40, resonators)
24-1, . . . 24-n, elements) 42-l, . . . 42-(n-1), and enclosure element 44 are
as smooth
and close in tolerance as they can be made by accepted manufacturing
techniques for
the materials involved, and the assembly requirements for the illustrated
embodiment.
Resonators) 24-1, . . . 24-n illustratively is (are) constructed from barium,
zinc,
tantalum oxide. Post 30, enclosure element 40, elements) 42-1, . . . 42-(n-I
), and
enclosure element 44 illustratively are constructed from beryllia, aluminum
nitride or
boron nitride. Beryllia has a thermal conductivity which approximates that of
aluminum and is about six-tenths that of copper. Aluminum nitride and boron
nitride
have somewhat lower thermal conductivities, but are somewhat easier to work
with.
Beryllia has a dielectric loss constant which approximates that of sapphire.
Aluminum nitride's and boron nitride's dielectric loss constants are somewhat
higher,
but are satisfactory for this application. Machining beryllia to close
tolerances is
problematic. Consequently, low dielectric loss resins, such as Vary Flex two
component epoxy, type HV, available from Sigma Plastronics, P. O. Box 649,
Whitmore Lake, MI, 48189, may be used between the adjacent surfaces of
resonators) 24-1, . . . 24-n and post 30, enclosure element 40, spacers) 42-I,
. . . 42-
(n-I), and enclosure element 44 to reduce discontinuities that might otherwise
affect
the performance of the cavity filter 8. When the cavity filter 8 is assembled
in this
way, the through holes 25-1, . . . 25-n, 32, 34 align to provide a passageway
into
cavity 10 through wall 12 for the introduction of a low dielectric loss,
nonpolar
cooling fluid, such as air or a liquid such as FluorinertT"i liquid FC-40
available from
3M Specialty Materials Lab, Performance Materials Division, 3M Center, 236-2B-
Ol,
St. Paul, MN, 55144-1000. The fluid is exhausted from the cavity 10 through
holes
38. In this way, the fluid circulates through aligned through holes 32 and 34,
through
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cavity 10 to remove heat from resonators) 24-1, . . . 24-n and post 30,
enclosure
element 40, elements) 42-1, . . . 42-(n-1), and enclosure element 44, and
outward
through holes 38.
To promote the exposure of all cavities 10 in an array of such cavities
to the same cooling capacity, thereby increasing the likelihood that the
dielectric
properties of all cavities will remain substantially uniform, a manifold 62 is
provided
adjacent cavities 10. The cooling fluid is supplied to the manifold 62 from,
for
example, a pump or blower 64 under the control of a manifold 62 pressure
sensor 66.
Sensor 66 increases the likelihood of uniform flow rates of the cooling fluid
through
the cavities 10 if the dimensions of the cavities 10 and through holes 25-l, .
. . 25-n,
32, 34 and 60 are chosen to provide substantially uniform flow rates among the
cavities 10. To increase the likelihood of a constant temperature of the
cooling fluid,
the other variable which will affect the cooling of the cavities, a coolant
fluid heat
exchanger/conditioning unit 68 treats the flow of cooling fluid prior to the
introduction of the cooling fluid into the manifold 62. Conditioning unit 68
operates
under the control of, for example, a thermostat 70. If the cooling fluid is
air, the
conditioning unit may be an air conditioner. Air flowing from cavities 10
through
holes 60 can be exhausted to atmosphere, or recycled through the air
conditioner 68,
as dictated by the needs of a particular application. If a cooling fluid such
as
FluorinertTM fluid is used, this material quite likely will have to be
recycled, owing to
cost, envirommental concerns, and so on.
In another embodiment of the invention illustrated in Fig. 3, a cavity
filter 108 includes cavities 110, each configured as a generally rectangular
prism
having electrically conductive walls 112, 114, 116, 118, 120 and 122. Again,
while
the illustrated cavities 110 are generally rectangular prism shaped, it should
be
understood that any appropriately shaped cavity may be used in the
implementation of
the invention. In addition to being electrically conductive, walls 112, 114,
116, 118,
120 and 122 are thermally conductive. Each resonator cavity 110 houses one or
more
dielectric resonator elements 124-l, . . . 124-n, which illustratively are
dielectric puck
resonators of generally right circular cylindrical shape. Again, it should be
understood that, while puck-type resonator elements 124-l, . . . 124-n are
illustrated,
any resonant structures) may be used in the implementation of the invention.
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Resonator elements 124-1, . . . 124-n have through holes which
illustratively are of generally right circular cylindrical shape extending
through them
from one to the other of their respective generally parallel surfaces for
receiving a
supporting post or pillar 130. Supporting post or pillar 130 extends from one,
112, of
the walls of cavity 110 toward the center thereof. Post 130 is constructed
from a very
low loss dielectric material and has a through hole 132. Wall 112 is also
provided
with a generally centrally located through hole 134. Wall 112 is also provided
with a
number, illustratively two, of through holes 138 disposed outwardly from
through
hole 134.
The end of post 130 remote from wall 112 is configured to receive a
stack containing an enclosure element 140 having somewhat the configuration of
a
hub 141 with radially outwardly extending spokes 143, one or more dielectric
resonator elements 124-1, . . . 124-n, one or more elements 142-1, . . . 142-
(n-1), each
having somewhat the configuration of a hub 145-1, . . . 145-(n-1) with
radially
outwardly extending spokes 147-1, . . . 147-(n-1 ), and an enclosure element
144
having somewhat the configuration of a hub 149 with radially outwardly
extending
spokes 151. Element 140 is configured to seat on a step 146 provided around
the
perimeter of post 130 at a distance from its end remote from wall 112
substantially
equal to the combined thickness of the resonators) 124-l, . . . 124-n,
elements) 142-
1, . . . 142-(n-1 ), where such elements) is (are) present, and enclosure
elements 140,
144. A number of generally right circular cylindrical enclosure sleeves 150-1,
. . .
150-(n-1) are configured to slide with little clearance over the perimetrally
outer
surfaces 152-l, . . . 152-n of resonators) 124-1, . . . 124-n. The adjacent
surfaces of
post 130, enclosure element 140, resonators) 124-1, . . . 124-n, elements) 142-
1, . . .
142-(n-1), and enclosure element 144 are as smooth and close in tolerance as
they can
be made by accepted manufacturing techniques for the materials involved, and
the
assembly requirements for the illustrated embodiment. The perimetrally outer
extents
of the spokes of spacer elements 142-1, . . . 142-(n-1) may be accommodated in
grooves provided in the sidewalls 114, 116, 118, 120. Again, low dielectric
loss
resins can be used between the adjacent surfaces of elements 142-l, . . . 142-
(n-1) and
the walls of the grooves to enhance the performance of cavity filter 108. The
spokes
143, 147-1, . . . 147-(n-1), 151 may be aligned in a plane perpendicular to
the plane of
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Fig. 3, or they may not, as the performance requirements of a particular
application
dictate. Alignment of the spokes results in less restricted flow of coolant
through
cavity 110, and less turbulence in that flow. Other orientations may result in
less
restricted flow of coolant through cavity 110, but may also result in
increased cooling
of the contents of cavity 110.
Again, when the cavity filter 108 is assembled in this way, the through
holes 125-l, . . . 125-n, 132, 134 align to provide a passageway into cavity
110
through wall 112 for the introduction of a cooling fluid such as air or a low
loss,
nonpolar liquid such as FluorinertTM fluid. The fluid is exhausted from the
cavity 110
through holes 138. In this way, the fluid circulates through aligned holes 125-
1, . . .
125-n, 132 and 134, through cavity 110 to remove heat from resonators) 124-1,
. . .
124-n and post 130, enclosure element 140, elements) 142-l, . . . 142-(n-1),
and
enclosure element 144, and outward through holes 138. It will be appreciated
that in
this embodiment it may be necessary to have removable walls 112, 116, 120, for
example, in order to assemble cavity filter 108.
As another alternative to, or in combination with the above discussed
cooling scheme, the walls 12, 14, 16, 18, 20, 22 of cavity 10 and 112, 114,
116, 118,
120, 122 of cavity 110 can be provided with through holes 160 for the flow of
a
coolant. The coolant may be a less exotic coolant, such as water or any of the
currently commercially available halogenated hydrocarbon refrigerants or non-
halogenated refrigerants, or it may be something more exotic, such as, for
example,
liquid carbon dioxide, liquid nitrogen, or the like.
As another alternative to, or in combination with the above discussed
cooling schemes, some one or more of the walls 12, 14, 16, 18, 20, 22 of
cavity 10
and walls 112, 114, 116, 118, 120, 122 of cavity 110 may be constructed of a
more
thermally conductive material such as, for example, copper. Of course, such a
more
thermally conductive material may need to be passivated against the
environment in
which it is going to reside. For example, if copper is used and will be
exposed to
atmosphere, the copper may need to be coated with, for example, silver to
prevent the
formation of thermally non-conductive copper oxides.
As another alternative, or in combination with any one or more of the
above cooling schemes, one or more Peltier effect devices may be provided on
the
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outside of one or more of the walls 12, 14, 16, 18, 20, 22 of cavity 10 and
112, 114,
116, 118, 120, 122 of cavity 110. As another alternative for cooling, and with
reference to Fig. 5, posts 30, 130 can be configured as heat pipes 162 which
extend
not only upward within cavities 10, 110, but also downward and out to the
exteriors of
cavities 10, 110. The exterior ends I 64 of heat pipes 162 can be equipped
with heat
sinks 166 (illustrated diagrammatically) as necessary to meet the heat
dissipation
requirements of a particular application.
In another embodiment of the invention illustrated in Fig. 6, a cavity
filter 208 includes cavities 210, each configured as a generally rectangular
prism
having electrically conductive walls 212, 214, 216, 218, 220 and 222. Again,
while
the illustrated cavities 210 are generally rectangular prism shaped, it should
be
understood that any appropriately shaped cavity may be used in the
implementation of
the invention. In addition to being electrically conductive, walls 212, 214,
216, 218,
220 and 222 are thermally conductive. Each resonator cavity 210 houses one or
more
dielectric resonator elements 224-1-1, 224-1-2; . . . 224-n-1, 224-n-2, which
illustratively are dielectric puck resonators of generally right circular
cylindrical
shape. Again, it should be understood that, while puck-type resonator elements
224-
1-1, 224-1-2; . . . 224-n-l, 224-n-2 are illustrated, any resonant structures)
may be
used in the implementation of the invention.
Resonator elements 224-1-1, 224-I-2; . . . 224-n-I, 224-n-2 have
through holes which illustratively are of generally right circular cylindrical
shape
extending through them from one to the other of their respective generally
parallel
surfaces. The through holes in the inner resonator elements 224-I-l, . . . 224-
n-I
receive a supporting post or pillar 230. Supporting post or pillar 230 extends
from
one, 212, of the walls of cavity 210 toward the center thereof. Post 230 is
constructed from a very low loss dielectric material and has a through hole
232. Wall
212 is also provided with a generally centrally located through hole 234. Wall
212 is
also provided with a number, illustratively two, of through holes 238 disposed
outwardly from through hole 234.
The end of post 230 remote from wall 212 is configured to receive a
stack containing an enclosure element 240. Element 240 is configured to seat
on a
step 246 provided around the perimeter of post 230 at a distance from its end
remote
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from wall 212 substantially equal to the combined thickness of the resonators)
224-l,
. . . 224-n, elements) 242-l, . . . 242-(n-1), where such elements) is (are)
present, and
enclosure elements 240, 244. A number of generally right circular cylindrical
enclosure sleeves 250-1-1, . . . 250-(n-1)-1 are configured to slide with
little clearance
over the perimetrally outer surfaces 252-1-l, . . . 252-n-1 of resonators) 224-
1-l, . . .
224-n-1 and inside the perimetrally inner surfaces 252-1-2, . . . 252-n-2 of
resonators)
224-1-2, . . . 224-n-2. A generally right circular cylindrical enclosure
sleeve 250 is
configured to slide with little clearance over the perimetrally outer surfaces
252-I-2, .
. . 252-n-2 of resonators) 224-1-2, . . . 224-n-2. The adjacent surfaces of
post 230,
enclosure element 240, resonators) 224-1-l, 224-1-2; . . . 224-n-l, 224-n-2,
elements) 242-l, . . . 242-(n-1), and enclosure element 244 are as smooth and
close in
tolerance as they can be made by accepted manufacturing techniques for the
materials
involved, and the assembly requirements for the illustrated embodiment. Again,
low
dielectric loss resins can be used between the adjacent surfaces of elements
230, 240,
224-1-l, 224-1-2; . . . 224-n-1, 224-n-2, 242-1, . . . 242-(n-1), and 244 to
enhance the
performance of cavity filter 208.
Again, when the cavity filter 208 is assembled in this way, the through
holes 225-1, . . . 225-n, 232, 234 align to provide a passageway into cavity
210
through wall 212 for the introduction of a cooling fluid such as air or a low
loss,
nonpolar liquid such as FluorinertTM fluid. The fluid is exhausted from the
cavity 210
through holes 238. In this way, the fluid circulates through aligned holes 225-
l, . . .
225-n, 232 and 234, through cavity 210 to remove heat from resonators) 224-1-
l,
224-1-2; . . . 224-n-1, 224-n-2, post 230, enclosure element 240, elements)
242-I, . . .
242-(n-1), and enclosure element 244, and outward through holes 238.
Yet another embodiment of the invention is illustrated in Fig. 7. In the
embodiment illustrated in Fig. 7, supporting post or pillar 230a is threaded
for
threadably engaging wall 212a and the inner circumferential surfaces of
resonator
elements 224a-1-1; . . . 224a-n-1. Post 230a is threaded at end 270 past the
point of
step 246a, for threaded engagement with the inner circumferential surfaces of
enclosure element 240a and dielectric resonator elements 224a-1-1; . . . 224a-
n-1.
Additionally, in this embodiment post 230a is threaded at its lower end 260
for
threaded engagement with threads provided for this purpose in wall 212a of
cavity
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210. All elements are configured with close tolerances providing little
clearance
between the threads. Low dielectric loss resins can be used between the
surfaces of
the elements to enhance the performance of the cavity filter 208, as described
above.
Of course, other cooling schemes are possible with cavity filters of the
type illustrated and described.
