U.S. patent application number 11/148135 was filed with the patent office on 2005-10-13 for filter structure including circuit board.
This patent application is currently assigned to ADC Telecommunications, Inc.. Invention is credited to Lukkarila, Teppo, Sauder, David D..
Application Number | 20050225411 11/148135 |
Document ID | / |
Family ID | 25246068 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050225411 |
Kind Code |
A1 |
Sauder, David D. ; et
al. |
October 13, 2005 |
Filter structure including circuit board
Abstract
A cavity filter assembly is provided with at least one
structural cavity wall comprising a circuit board. The circuit
board may also contain other circuits and circuit elements such as
trim capacitors, inductors, low noise amplifier circuits and power
amplifiers that are part of the filter's function. Input and output
coupling structures and connectors may also be provided on the
circuit board. The circuit board may contain inter-stage coupling
circuits, signal traces, and coupling pads/structures. Further
embodiments are provided that incorporate test connectors and
directional couplers on the circuit board. In yet other embodiments
the filter's electrical characteristics are tunable with trim
elements mounted on the circuit board, such as capacitors or
inductors, in either mechanical or electrical manner. The filter's
electrical characteristics may also be tunable with mechanical
elements mounted through the circuit board.
Inventors: |
Sauder, David D.; (Shakopee,
MN) ; Lukkarila, Teppo; (Bloomington, MN) |
Correspondence
Address: |
FOGG AND ASSOCIATES, LLC
P.O. BOX 581339
MINNEAPOLIS
MN
55458-1339
US
|
Assignee: |
ADC Telecommunications,
Inc.
Eden Prairie
MN
|
Family ID: |
25246068 |
Appl. No.: |
11/148135 |
Filed: |
June 8, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11148135 |
Jun 8, 2005 |
|
|
|
09826246 |
Apr 4, 2001 |
|
|
|
6919782 |
|
|
|
|
Current U.S.
Class: |
333/202 ;
333/212 |
Current CPC
Class: |
H01P 1/2053 20130101;
H05K 1/18 20130101; H01P 1/208 20130101; H05K 1/0243 20130101 |
Class at
Publication: |
333/202 ;
333/212 |
International
Class: |
H01P 001/208 |
Claims
What is claimed is:
1. A filter assembly, comprising: an enclosure having at least one
cavity; at least one wall of the enclosure comprised of a circuit
board; a trace formed on the circuit board; and at least one
circuit element, coupled to the trace.
2. The filter assembly of claim 1, wherein the circuit board
further comprises a ground plane on a surface of the circuit board
that forms a portion of the inner surface of the enclosure.
3. The filter assembly of claim 1, wherein the circuit board
further comprises multiple circuit trace layers.
4. The filter assembly of claim 1, wherein the at least one circuit
element further comprises a low pass filter.
5. The filter assembly of claim 4, wherein the low pass filter
further comprises one of a circuit trace filter element and a
mechanical structure filter element.
6. The filter assembly of claim 1, wherein the filter assembly
further comprises: an input connector attached to the enclosure and
coupled to the at least one cavity; and an output connector
attached to the enclosure and coupled to the at least one
cavity.
7. The filter assembly of claim 1, wherein the filter assembly
further comprises: an input connector attached to the circuit board
and coupled to the at least one cavity; and an output connector
attached to the circuit board and coupled to the at least one
cavity.
8. The filter assembly of claim 1, wherein the at least one circuit
element further comprises an amplifier and wherein the filter
assembly further comprises: an input connector attached to the
circuit board and coupled to the at least one cavity; an output
connector attached to the circuit board coupled to an output of the
amplifier; and an output coupling pad mounted in the at least one
cavity and coupled to an input of the amplifier.
9. The filter assembly of claim 1, wherein the at least one circuit
element further comprises an amplifier and wherein the filter
assembly further comprises: an input connector attached to the
circuit board and coupled to an input of the amplifier; an input
coupling pad mounted in the at least one cavity and coupled to an
output of the amplifier; and an output connector attached to the
circuit board coupled to the at least one cavity.
10. The filter assembly of claim 1, wherein the filter assembly
further comprises: a first and a second low noise amplifier; an
input connector attached to the circuit board and coupled to an
input of the first low noise amplifier; an input coupling pad
mounted in the at least one cavity and coupled to an output of the
first low noise amplifier; an output coupling pad mounted in the at
least one cavity and coupled to an input of the second low noise
amplifier; and an output connector attached to the circuit board
coupled to an output of the second low noise amplifier.
11. A filter assembly, comprising: an enclosure having a cavity; at
least one wall of the enclosure comprised of a circuit board; and
at least one diagnostic circuit formed on the circuit board.
12. The filter assembly of claim 11, further comprising: a trace
formed on the circuit board; and at least one circuit element,
coupled to the trace.
13. The filter assembly of claim 11, wherein the diagnostic circuit
formed on the circuit board further comprises a signal tap.
14. The filter assembly of claim 11, wherein the diagnostic circuit
formed on the circuit board further comprises a directional
coupler, comprising: a signal line with an RF signal; and a
sampling line, wherein the sampling line is run in parallel to the
signal line and is physically proximate.
15. The filter assembly of claim 14, wherein the directional
coupler further comprises a terminating resistance.
16. The filter assembly of claim 14, wherein the directional
coupler further comprises a stub terminator.
17. The filter assembly of claim 14, wherein the sampling line is
implemented on a surface of the circuit board.
18. The filter assembly of claim 14, wherein the sampling line is
implemented on an internal layer of the circuit board.
19. The filter assembly of claim 14, wherein the sampling line is
implemented on a same circuit layer as the signal line.
20. The filter assembly of claim 14, wherein the sampling line is
implemented on a first circuit layer and the signal line is
implemented on a second circuit layer.
21. A filter assembly, comprising: an enclosure having at least one
cavity; at least one wall of the enclosure comprised of a circuit
board; and at least one tuning element, wherein the at least one
tuning element extends into the at least one cavity of the
enclosure.
22. The filter assembly of claim 21, further comprising: a trace
formed on the circuit board; and at least one circuit element,
coupled to the trace.
23. The filter assembly of claim 21, wherein the at least one
tuning element is formed on the circuit board.
24. The filter assembly of claim 21, wherein the at least one
tuning element is formed in the enclosure.
25. The filter assembly of claim 21, wherein the at least one
tuning element is formed in a wall of the enclosure.
26. A method of tuning a filter assembly, comprising: forming a
cavity body with at least one chamber with at least one opening in
the cavity body; covering the openings in the cavity body with
structural elements to enclose the at least one chamber, wherein at
least one structural element is a circuit board; and tuning the
electrical characteristics of the cavity body by selectively
adjusting an element on the circuit board.
27. The method of claim 26, further comprising: forming a trace on
the at least one circuit board; and coupling at least one circuit
element to the trace.
28. The method of claim 26, wherein the element on the circuit
board comprises a capacitor.
29. The method of claim 26, wherein the element on the circuit
board comprises an inductor.
30. The method of claim 26, wherein the element on the circuit
board comprises a mechanically adjustable tuning element, where the
mechanically adjustable tuning element extends into the at least
one chamber of the cavity body.
31. A method of making a filter assembly, comprising: forming a
cavity body with at least one cavity and with at least one opening
in the cavity body; forming a trace on a printed circuit board;
coupling an electronic component to the trace; and covering the at
least one opening in the cavity body with the printed circuit
board.
32. The method of claim 31, wherein coupling the electronic
component to the trace comprises coupling a low pass filter to the
trace.
33. The method of claim 32, wherein the low pass filter further
comprises one of a circuit trace filter element and a mechanical
structure filter element.
34. The method of claim 31, wherein coupling the electronic
component to the trace comprises coupling an amplifier circuit to
the trace.
35. The method of claim 34, wherein coupling the amplifier circuit
comprises coupling at least one of a low noise amplifier and a
power amplifier to the trace.
36. The method of claim 31, wherein forming the circuit board
further comprises forming a ground plane on a surface of the
circuit board that forms a portion of the inner surface of the
cavity body.
37. The method of claim 31, wherein forming the circuit board
further comprises forming multiple circuit trace layers.
38. The method of claim 31, wherein forming the circuit board
further comprises: forming an input connector attached to the
cavity body and coupled to the at least one cavity; and forming an
output connector attached to the cavity body and coupled to the at
least one cavity.
39. The method of claim 31, wherein forming the circuit board
further comprises: forming an input connector attached to the
circuit board and coupled to the at least one cavity; and forming
an output connector attached to the circuit board and coupled to
the at least one cavity.
40. The method of claim 31, wherein forming the circuit board
further comprises: forming a first and a second low noise
amplifier; forming an input connector attached to the circuit board
and coupled to an input of the first low noise amplifier; forming
an input coupling pad mounted in the at least one cavity and
coupled to an output of the first low noise amplifier; forming an
output connector attached to the circuit board coupled to an output
of the second low noise amplifier; and forming an output coupling
pad mounted in the at least one cavity and coupled to an input of
the second low noise amplifier.
41. The method of claim 31, wherein forming the circuit board
further comprises forming an inter-stage coupling circuit, the
inter-stage coupling circuit comprising: at least one input
coupling structure mounted in the at least one cavity; and at least
one output coupling structure mounted in the at least one cavity
and coupled to the at least one input coupling structure.
42. The method of claim 41, wherein forming the inter-stage
coupling circuit further comprises forming a signal trace on the
circuit board.
43. The method of claim 42, wherein forming the signal trace
further comprises one of forming the signal trace in an internal
circuit layer of the circuit board and forming the signal trace in
a surface circuit layer of the circuit board.
44. A method of making a filter assembly, comprising: forming a
cavity body with at least one chamber with at least one opening in
the cavity body; covering the openings in the cavity body with
structural elements to enclose the at least one chamber, wherein at
least one structural element is a circuit board; and forming at
least one test circuit on the at least one circuit board.
45. The method of claim 44, further comprising: forming a trace on
the at least one circuit board; and coupling at least one circuit
element to the trace.
46. The method of claim 44, further comprising forming the test
circuit with a connector.
47. The method of claim 44, wherein forming the test circuit on the
circuit board further comprises forming a signal tap.
48. The method of claim 44, wherein forming the test circuit formed
on the circuit board further comprises a forming a directional
coupler, comprising: forming a signal line; and forming a sampling
line, wherein the sampling line is run in parallel to the signal
line and is physically proximate.
49. The method of claim 48, further comprising forming the
directional coupler with a terminating resistance.
50. The method of claim 48, further comprising forming the
directional coupler with a stub terminator.
51. The method of claim 48, further comprising forming the sampling
line on a same circuit layer as the signal line.
52. The method of claim 48, further comprising forming the sampling
line on a first circuit layer and forming the signal line on a
second circuit layer.
53. A microwave system, comprising: an antenna; a RF system; and a
filter assembly coupled to the antenna and to the RF system,
wherein the filter assembly comprises: an enclosure having at least
one cavity; at least one circuit board comprising a wall of the
enclosure; a trace formed on the at least one circuit board; and at
least one circuit element coupled to the trace.
54. The microwave system of claim 53, wherein the circuit board
further comprises a ground plane on a surface of the circuit board
that forms a portion of the inner surface of the enclosure.
55. The microwave system of claim 53, wherein the at least one
circuit board further comprises multiple circuit trace layers.
56. The microwave system of claim 53, wherein the at least one
circuit element further comprises a low pass filter.
57. The microwave system of claim 56, wherein the low pass filter
further comprises one of a circuit trace filter element and a
mechanical structure filter element.
58. The microwave system of claim 53, wherein the at least one
circuit element further comprises an amplifier.
59. The microwave system of claim 58, wherein the amplifier is one
of a low noise amplifier and a power amplifier.
60. The microwave system of claim 53, wherein the filter assembly
further comprises: an input connector attached to the enclosure and
coupled to the at least one cavity; and an output connector
attached to the enclosure and coupled to the at least one
cavity.
61. The microwave system of claim 53, wherein the filter assembly
further comprises: an input connector attached to the circuit board
and coupled to the at least one cavity; and an output connector
attached to the circuit board and coupled to the at least one
cavity.
62. The microwave system of claim 58, wherein the filter assembly
further comprises: an input connector attached to the circuit board
and coupled to the at least one cavity; an output connector
attached to the circuit board coupled to an output of the
amplifier; and an output coupling pad mounted in the at least one
cavity and coupled to an input of the amplifier.
63. The microwave system of claim 58, wherein the filter assembly
further comprises: an input connector attached to the circuit board
and coupled to an input of the amplifier; an input coupling pad
mounted in the at least one cavity and coupled to an output of the
amplifier; and an output connector attached to the circuit board
coupled to the at least one cavity.
64. The microwave system of claim 53, wherein the filter assembly
further comprises: a first and a second low noise amplifier; an
input connector attached to the circuit board and coupled to an
input of the first low noise amplifier; an input coupling pad
mounted in the at least one cavity and coupled to an output of the
first low noise amplifier; an output connector attached to the
circuit board coupled to an output of the second low noise
amplifier; and an output coupling pad mounted in the at least one
cavity and coupled to an input of the second low noise
amplifier.
65. The microwave system of claim 53, wherein the filter assembly
further comprises: a first filter stage and a second filter stage
formed in the enclosure, wherein the first and second filter stage
each have at least one cavity; an input connector attached to the
circuit board and coupled to the first filter stage; an output
coupling structure mounted in the at least one cavity of the first
filter stage and coupled to an input of a low noise amplifier; an
input coupling structure mounted in the at least one cavity of the
second filter stage and coupled to an output of the low noise
amplifier; and an output connector attached to the circuit board
coupled to the at least one cavity of the second filter stage.
66. The microwave system of claim 53, wherein the at least one
circuit formed in the at least one circuit board comprises an
inter-stage coupling circuit, the inter-stage coupling circuit
comprising: at least one input coupling structure mounted in the at
least one cavity; and at least one output coupling structure
mounted in the at least one cavity and coupled to the at least one
input coupling structure.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of U.S. patent
application Ser. No. 09/826,246, filed Apr. 4, 2001 (Attorney
Docket No. 100.169US01), titled "FILTER STRUCTURE INCLUDING CIRCUIT
BOARD" and commonly assigned, the entire contents of which is
incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates generally to the field of
communications and, in particular, to a filter structure including
a circuit board.
BACKGROUND
[0003] Wireless telecommunications systems transmit signals to and
from wireless terminals using radio frequency (RF) signals. A
typical wireless system includes a plurality of base stations that
are connected to the public switched telephone network (PSTN) via a
mobile switching center (MSC). Each base station includes a number
of radio transceivers that are typically associated with a
transmission tower. Each base station is located so as to cover a
geographic region known colloquially as a "cell." Each base station
communicates with wireless terminals, e.g. cellular telephones,
pagers, and other wireless units, located in its geographic region
or cell.
[0004] A wireless base station includes a number of modules that
work together to process RF signals. These modules typically
include, by way of example, mixers, amplifiers, filters,
transmission lines, antennas and other appropriate circuits. One
type of filter that finds increased use in wireless base stations
is known as a microwave cavity filter.
[0005] Microwave cavity filters generally are formed from a
machined, extruded, or cast body structure with enclosing walls to
complete the filter cavity structure. The microwave signal
generally enters the filter through an input connector and is
coupled to an internal coupling pad or structure, and thus inserts
it into the cavity structure of the filter. The filtered signal is
extracted at the terminal end of the filter with another coupling
pad or structure. Structures, such as resonators and/or tuning
elements, that affect the electrical characteristics of the filter
can be attached internally to the filter. Adjustment of the
electrical characteristics of the filter can sometimes require the
removal of a filter structural panel in order to gain access to the
internally mounted elements.
[0006] Additional electronic circuitry, used with the filter is
typically contained in one or more assemblies that are separate
from the filter structure. This circuitry can include such things
as inductors and capacitors to affect the electrical
characteristics of the filter, low noise amplifiers (LNA's) and
power amplifiers. These elements, being in separate assemblies from
the filter body, require the use of connectors and cabling to
couple them to the filter. The requirement of separate assemblies,
connectors, and cabling can add expense, complexity, and source of
undesired signal loss to the filter.
[0007] For the reasons stated above, and for other reasons stated
below which will become apparent to those skilled in the art upon
reading and understanding the present specification, there is a
need in the art for a filter with a simpler design and reduced
number of components that provides lower costs, less complexity,
more reliability, and easier tuning.
SUMMARY
[0008] The above mentioned problems with cavity filters and other
problems are addressed by embodiments of the present invention and
will be understood by reading and studying the following
specification.
[0009] Embodiments of the present invention provide a filter
assembly that includes a circuit board that is attached to the
filter assembly as a cover for the cavity allowing electric
circuits to be implemented on the circuit board thereby reducing
difficulties in connecting the electric circuits to the filter
assembly.
[0010] More particularly, in one embodiment a filter assembly is
provided. The filter assembly includes an enclosure having a cavity
wherein at least one wall of the enclosure is comprised of a
circuit board. The circuit board includes a trace formed on the
circuit board and at least one circuit element coupled to the
trace.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a side view that represents an embodiment of a
cavity filter assembly according to the teachings of the present
invention.
[0012] FIG. 2 is a side view that represents a printed circuit
board for a cavity filter assembly according to the teachings of
the present invention.
[0013] FIG. 3 is a top view that represents a directional coupler
according to the teachings of the present invention.
[0014] FIGS. 4, 5, and 6 are perspective views that represent
embodiments of a cavity filter assembly according to the teachings
of the present invention.
[0015] FIGS. 7, 8, 9, and 10 are schematic views that illustrate
various embodiments of cavity filters coupled with amplifiers
according to the teachings of the present invention.
[0016] FIG. 11 is a schematic view of a microwave system and
antenna incorporating an embodiment of a cavity filter assembly
according to the teachings of the present invention.
[0017] FIG. 12 is a top view of a low pass filter according to the
teachings of the present invention.
[0018] FIG. 13 is a perspective view that represent an embodiment
of a cavity filter assembly according to the teachings of the
present invention.
DETAILED DESCRIPTION
[0019] In the following detailed description, reference is made to
the accompanying drawings that form a part hereof, and in which is
shown by way of illustration specific illustrative embodiments in
which the invention may be practiced. These embodiments are
described in sufficient detail to enable those skilled in the art
to practice the invention, and it is to be understood that other
embodiments may be utilized and that logical, mechanical and
electrical changes may be made without departing from the scope of
the present invention. The following detailed description is,
therefore, not to be taken in a limiting sense.
[0020] I. Filter Structure
[0021] Embodiments of the present invention provide filter
assemblies with one or more cavities that are typically formed out
of a machined, extruded, or cast body. In addition, one or more
structural walls of the filter assembly are formed of a printed
circuit board (PCB) material with the remainder of the cavity walls
formed in a conventional manner. This arrangement allows circuit
elements to be incorporated on the circuit board and simplifies
connection to the filter. This simplification saves connectors and
cables, and combines all elements of the circuit into one
assembly.
[0022] FIG. 1 is a cross sectional, side view that represents an
embodiment of a filter assembly, indicated generally at 100,
according to the teachings of the present invention. Microwave
signals enter the filter assembly 100 through an input connector
122 and are injected into cavity 102 of the filter assembly 100.
After having passed through the filter assembly 100, the signal is
extracted from the filter assembly 100 and is placed on an output
connector 124. The filter assembly 100 is shown with three cavity
chambers 102, 104, and 106, that include resonator structures 108,
110, and 112, respectively. In other embodiments, other appropriate
numbers of cavity chambers and resonators are used, depending on
the filter function that is desired. A first cover plate 114 is
shown forming a wall of the filter assembly 100 and contains tuning
elements 116, 118, and 120.
[0023] A second cover plate 126 of the filter assembly 100
comprises a printed circuit board (PCB). Input connector 122 and
the output connector 124 are coupled to filter assembly 100 through
second cover plate 126. Advantageously, the second cover plate 126
is adapted to receive additional circuit elements such as
inter-stage coupling 128 and coupling pads/structures 130 and 132.
In other embodiments, other circuit elements are coupled to the
second cover plate 126. For example, additional circuit elements
include, in some embodiments, one or more of capacitors, inductors,
low noise amplifiers (LNA's), power amplifiers, low pass filters,
and the like. This placement of circuits and circuit elements on
the second cover plate 126 allows the elimination of separate
circuit assemblies, connectors, and cabling to accommodate these
elements into the filter assembly. Additionally, inter-stage
coupling elements and tuning components are optionally incorporated
into the second cover plate 126 to allow the function of the filter
assembly 100 to be affected. In any given filter assembly, any one
or more of these additional circuit elements can be
incorporated.
[0024] In the filter assembly 100, a RF signal enters the filter
assembly through input connector 122 and is injected into cavity
102 of the filter assembly 100. The RF signal travels through
filter cavities 102, 104, and 106 and is filtered. The filtered
signal is extracted from the cavity 106 of the filter assembly 100
and is coupled to the output connector 124.
[0025] In one embodiment of the filter assembly 100, a filter body
is constructed with one or more chambers, having one or more
openings in the filter body in various positions. The one or more
filter body openings are covered with at least one or more PCB
covers. Any remaining openings are covered in a conventional manner
to complete the filter structure. The PCB typically will have one
or more circuits implemented on it and a ground plane implemented
on the surface of the PCB that faces and covers the opening in the
body of the filter body assembly. In additional embodiments,
multiple circuit trace layers are implemented into the PCB to
accommodate more complex circuits.
[0026] II. Tuning of the Filter
[0027] The characteristics of the filter assembly 100 are
electrically adjusted or tuned in a variety of manners. One such
manner is by the inclusion of circuit elements on the circuit board
126, such as trimming capacitors and inductors, that affect the
electrical characteristics of the filter assembly 100. In one
embodiment, these trimming capacitors and inductors are adjusted
physically to quickly allow the electrical characteristics of the
filter to be tuned to the desired characteristics.
[0028] In one embodiment, these tuning elements of the filter are
electrically adjustable, allowing for non-mechanical and/or remote
adjustment of the electrical characteristics of the filter.
[0029] In one embodiment, the filter assembly 100 electrical
characteristics are adjusted and/or tuned with mechanical elements
wherein the position of the mechanical elements may be adjusted
internal to the filter cavities thus changing the characteristics
of the filter. For example, filter assembly 100 includes tuning
elements which are physically embodied as screws 116, 118, and 120
that extend through the body of the filter assembly allowing for
adjustment of the characteristics of each chamber of the filter
assembly 100.
[0030] III. Printed Circuit Board
[0031] FIG. 2 is a cross sectional, side view of one embodiment of
a printed circuit board (PCB) 126' suitable for use with the filter
assembly 100 of FIG. 1. The PCB 126' is typically formed with a
contiguous ground plane 200 on an inner surface 228 that covers an
opening of an associated filter assembly body. In one embodiment,
circuit elements that are a functional part of the filter assembly
are incorporated onto PCB 126' and represented by elements 202,
204, 206, and 208. The PCB 126' of this embodiment is made of
conventional materials and processes to form an appropriate circuit
board to be used as one wall of a filter assembly. As such, it is
possible to construct the PCB 126' of this embodiment with as many
circuit layers as necessary to accommodate circuits desired to be
used in conjunction with the filter assembly on the PCB 126'. The
complexity and cost of such a circuit board are typically related
to the number of circuit layers in the PCB 126'. The ability to
incorporate circuit elements onto the PCB 126' that forms a
structural wall of the filter allows such elements such as low
noise amplifiers (LNAs), power amplifiers, and tuning capacitors
and inductors to be placed directly onto the wall of the filter
assembly. This placement of circuits and circuit elements on the
PCB 126' allows the elimination of separate circuit assemblies,
connectors, and cabling to accommodate these elements into the
filter assembly. Additionally, inter-stage coupling elements and
tuning components are optionally incorporated into the PCB 126' to
allow the function of the filter assembly to be affected. As shown
in FIG. 2, connectors 210, 212, and 214 and coupling
pads/structures 216 and 218 are also incorporated into the PCB of
the embodiment. Inter-stage coupling in the filter is accomplished
in this embodiment with traces etched into the PCB 126'. These
etched signal paths are either on a surface or on an internal trace
of the PCB 126'. If the signal path/inter-stage coupling line is an
internal trace other circuit elements and signal lines could be
placed over the top of it on the PCB and do not have to be routed
around. Coupling the internal trace 220 with the signal coupling
pads/structures 216 and 218 is accomplished with a through layer or
"blind" via in the PCB 226 and 224. In one embodiment, additional
connector 212 is included on the PCB 126' for electrical connection
and communication with the filter and the circuitry on the PCB
126'. This connector allows for easy incorporation of test taps
into the PCB 126' and filter assembly of FIG. 2 with devices such
as a directional coupler 222.
[0032] IV. Directional Couplers
[0033] Use of a printed circuit board as a wall of a filter
assembly allows test taps and directional couplers to be
incorporated without difficulty. Test taps are placed on the PCB
and routed through it to coupling pads placed in the appropriate
positions in the interior of the filter. Directional couplers can
also be incorporated and allow the sensing of the signal at a given
point of the filter. Typically, directional couplers are utilized
in high frequency RF circuits and filters to allow for an
unfiltered signal feed or a mid-point feed in the filter for
diagnostic purposes, monitoring, and tuning. FIG. 3 is a top view
of a portion of a PCB 126" that shows an example of a directional
coupler circuit. A signal line 300 containing a RF signal and a
directional coupler, consisting of a signal trace 306, are run
parallel to each other in close physical proximity. The RF signal
couples from the signal line 300 to the signal trace 306 of the
directional coupler. The sampled signal present on the directional
coupler signal trace 306 is then coupled externally through the
connector 304. The directional coupler is typically terminated with
a impedance matching resistor and/or a wavelength tuning stub,
shown as element 308. The RF signal is shown as entering the signal
line 300 through connector 302, although in other embodiments, the
signal is coupled to the signal line 300 through a coupling pad or
other such process.
[0034] V. Alternative Filter Structures
[0035] FIG. 4 shows a perspective view of an additional embodiment
of a filter assembly indicated generally at 458 according to the
teachings of the present invention. The filter assembly 458
comprises a filter body 402 with a PCB 400 that forms a cover. The
PCB 400 includes a ground plane 448 implemented on the surface 460
covering the opening 462 in the filter body 402. The filter
assembly 458 also contains resonators 404, 406, and 408 that are
mounted in the filter body 402 or the PCB 400. The filter assembly
458 also has input and output connectors 428 and 430, respectively,
and input and output coupling structures 432 and 434 that descend
into the filter body 402. An additional connector coupling 436 is
provided for a directional coupler 450.
[0036] In the filter assembly 458, the RF signal enters the filter
assembly 458 through the input connector 430 and is injected into
the filter body 402 via the input coupling structure 434. For
filter analysis purposes the input RF signal is sampled by the
input directional coupler 450 and is made available at connector
436. The filtered RF signal is extracted from the filter body 402
by coupling structure 432, coupling structure 432 is coupled to low
noise amplifier (LNA) 456 via trace 455. LNA 456 is further coupled
by trace 457 to output connector 428.
[0037] FIG. 5 is a perspective view that represents another
embodiment of a filter assembly 540 according to the teachings of
the present invention. The filter assembly 540 comprises a filter
body 502, a cover 500 that consists of a printed circuit board 542,
and resonators 504, 506, and 508 that are mounted in the filter
body 502. The filter assembly 540 also has input and output
connectors 528 and 530. Connectors 528 and 530 are coupled through
the PCB 542 to coupling structures 532 and 534 that descend into
the filter body.
[0038] In the filter of FIG. 5, adjustment of the filter
characteristics is accomplished by tuning elements that are
adjusted by screws 514, 516, 518, 520, and 522 that extend through
the PCB plate 500 into interior of the filter body.
[0039] FIG. 6 is a perspective view that represents another
embodiment of a filter assembly 640 according to the teachings of
the present invention. The filter assembly 640 of FIG. 6 shows an
implementation that is functionally divided into two filter stages,
first filter stage 622, and second filter stage 624, with a low
noise amplifier (LNA) 620 coupling the two stages.
[0040] The filter assembly 640 comprises a filter body 602 with
cavities 612, 614, 616,and 618, and resonator structures 604, 606,
608, and 610 that are mounted in the filter body 602. The first
filter stage 622 includes cavities 612 and 614, and the second
filter stage 624 includes cavities 616 and 618. It is noted that in
other embodiments, any appropriate number of cavities are included
to implement selected filter functions. The filter assembly 640,
additionally has a cover 600 that consists of a printed circuit
board, PCB 642, on which are mounted input and output connectors
628 and 630. Coupling structures 632, 634, 636, and 638 are mounted
to the PCB 642 and descend into the filter body. Coupling
structures 632 and 634 descend into the first filter stage 622, and
coupling structures 636 and 638 descend into the second filter
stage 624. Connectors 628 and 630 are coupled through the PCB 642
to coupling structures 632 and 638. A LNA 620 is mounted to the PCB
642 and coupled via traces 637 and 639 through the PCB 642 to
coupling structures 634 and 636.
[0041] In operation, the filter assembly 640 acts as two filters
coupled with a LNA. The RF signal enters the filter assembly 640
through the input connector 628 and is injected into the first
filter stage 622 of the filter body 602 via the input coupling
structure 632. The RF signal is extracted from the first filter
stage 622 by the coupling structure 634 and amplified by the
coupled LNA 620. The amplified RF signal is then injected into the
second filter stage 624 by coupling structure 636. The filtered RF
signal is extracted from the second filter stage 624 by coupling
structure 638 to the coupled output connector 630.
[0042] FIG. 13 is a perspective view that represents an additional
embodiment of a filter assembly 1300 according to the teachings of
the present invention with connectors 1302 and 1304 coupled through
the filter body 1306 to coupling structures 1308 and 1310.
[0043] VI. Filter and Amplifier Configurations
[0044] Shown in FIGS. 7, 8, 9 and 10 are schematic diagrams of
common filter--amplifier configurations using filter assemblies
having a PCB cover with an amplifier attached to the PCB cover. In
FIG. 7 is shown an embodiment of a circuit with a filter 700
coupled with an amplifier 702, so that the input RF signal is
amplified after it is filtered. Shown in FIG. 8 is a system
configuration wherein the amplifier 800 proceeds the filter 802,
allowing amplification of the input RF signal before it is
filtered. FIG. 9 shows a filter--amplifier--filter arrangement
wherein the incoming RF signal is filtered by an initial filter
stage 900, then passed through an amplifier stage 902, before
passing through a final filter stage 904. A further
amplifier--filter--amplifier arrangement is shown in FIG. 10
wherein the incoming RF signal sequentially passes through an
amplifier 1000, a filter stage 1002, and then finally an amplifier
1004. Additional such arrangements of filters and amplifiers would
be apparent to those skilled in the art.
[0045] FIG. 12 is a top view of a portion of a PCB 126'", showing
examples of a common type of low pass filter such as would be used
in an embodiment of the filter assembly of the present invention.
The top view of FIG. 12 includes a signal line 1200 containing a RF
signal and a low pass filter 1202. The low pass filter 1202
contains a coupled series of alternating sections of wider circuit
traces 1206 and narrower circuit traces 1208 that are formed into
the PCB 126'". The RF signal is coupled from the signal line 1200
to the low pass filter 1202, where it is filtered by the electrical
transmission characteristics of the wider and narrower circuit
traces, 1206 and 1208. The filtered RF signal is then coupled from
the low pass filter 1202 to an output signal line 1204.
[0046] The RF signal in FIG. 12 is shown as entering the signal
line 1200 through connector 1210, although in other embodiments,
the signal is coupled to the signal lines 1200 through a coupling
pad, or circuit element, or other such process. Additional such
arrangements of filters and amplifiers would be apparent to those
skilled in the art.
[0047] VII. RF System with Filter
[0048] FIG. 11 is a schematic diagram of a system indicated at 1106
using a filter with a PCB cover according to the teachings of the
present invention. In the system 1106, a filter assembly 1100 is
coupled with an antenna 1102 and a RF system 1104. The filter
assembly 1100 includes a cavity filter body with PCB incorporated
to be at least one wall of the filter chamber to allow for circuit
elements to be incorporated on the PCB. The circuits that are
incorporated into the PCB include, but are not limited to one or
more of, an inter-stage coupling circuit, a low noise amplifier, a
power amplifier, coupling pads and structures, tuning elements,
capacitors, and inductors.
[0049] Conclusion
[0050] Embodiments of the present invention have been described.
The embodiments provide a filter assembly with at least one
structural cavity wall consisting of a circuit board. The circuit
board may also contain other circuits and circuit elements such as
trim capacitors, inductors, low noise amplifier circuits and power
amplifiers that are part of the filter's function. Other
embodiments are also provided that provide input and output
coupling structures and connectors on the circuit board. Additional
embodiments are provided wherein the circuit board contains
inter-stage coupling circuits, signal traces, and coupling
pads/structures. Further embodiments are provided that incorporate
test connectors and directional couplers on the circuit board. In
yet other embodiments the filter's electrical characteristics are
tunable with trim elements mounted on the circuit board, such as
capacitors or inductors, in either mechanical or electrical manner.
The filter's electrical characteristics may also be tunable with
mechanical elements mounted through the circuit board.
[0051] Although specific embodiments have been illustrated and
described in this specification, it will be appreciated by those of
ordinary skill in the art that any arrangement that is calculated
to achieve the same purpose may be substituted for the specific
embodiment shown. This application is intended to cover any
adaptations or variations of the present invention. For example,
multiple circuit boards may be utilized as structural cavity wall
elements in a filter. Further, the inter-stage coupling circuits
may contain additional circuit elements to alter the electrical
characteristics of the inter-stage coupling.
* * * * *