U.S. patent application number 13/302617 was filed with the patent office on 2012-05-17 for tunable microwave devices with auto adjusting matching circuit.
This patent application is currently assigned to PARATEK MICROWAVE, INC.. Invention is credited to Cornelis Frederik du Toit, Deirdre A. Ryan.
Application Number | 20120119843 13/302617 |
Document ID | / |
Family ID | 46332505 |
Filed Date | 2012-05-17 |
United States Patent
Application |
20120119843 |
Kind Code |
A1 |
du Toit; Cornelis Frederik ;
et al. |
May 17, 2012 |
TUNABLE MICROWAVE DEVICES WITH AUTO ADJUSTING MATCHING CIRCUIT
Abstract
An impedance matching circuit includes a matching network for
coupling to a variable load, where the matching network has a first
port and a second port, and where the variable load is coupled to
one of the first port or the second port. The matching network can
have one or more variable dielectric capacitors, where the one or
more variable dielectric capacitors are operable to receive one or
more variable voltage signals to cause the one or more variable
dielectric capacitors to change an impedance of the matching
network, and where the change in the impedance of the matching
network causes an increase in power transferred from the first port
to the second port or from the second port to the first port.
Inventors: |
du Toit; Cornelis Frederik;
(Ellicott City, MD) ; Ryan; Deirdre A.; (Poquoson,
VA) |
Assignee: |
PARATEK MICROWAVE, INC.
Nashua
NH
|
Family ID: |
46332505 |
Appl. No.: |
13/302617 |
Filed: |
November 22, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12952395 |
Nov 23, 2010 |
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13302617 |
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11245898 |
Oct 8, 2005 |
7865154 |
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12952395 |
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10938898 |
Sep 10, 2004 |
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11245898 |
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10455901 |
Jun 6, 2003 |
6864757 |
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10938898 |
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09909187 |
Jul 19, 2001 |
6590468 |
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10455901 |
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60219500 |
Jul 20, 2000 |
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Current U.S.
Class: |
333/17.3 |
Current CPC
Class: |
H01P 5/04 20130101; H03H
7/40 20130101; H03F 3/60 20130101; H01Q 1/50 20130101; H03F 1/56
20130101; H03H 7/38 20130101; H04B 1/0458 20130101; H01Q 1/242
20130101 |
Class at
Publication: |
333/17.3 |
International
Class: |
H03H 7/38 20060101
H03H007/38 |
Claims
1. An impedance matching circuit, comprising: a matching network
for coupling to a variable load; wherein the matching network
comprises a first port and a second port; wherein the variable load
is coupled to one of the first port or the second port; wherein the
matching network comprises one or more variable dielectric
capacitors; wherein the one or more variable dielectric capacitors
are operable to receive one or more variable voltage signals to
cause the one or more variable dielectric capacitors to change an
impedance of the matching network; and wherein the change in the
impedance of the matching network causes an increase in power
transferred from the first port to the second port or from the
second port to the first port.
2. The impedance matching circuit of claim 1, wherein each of the
one or more variable dielectric capacitors comprises a tunable
dielectric material.
3. The impedance matching circuit of claim 2, wherein the tunable
dielectric material comprises a composition of barium strontium
titanate.
4. The impedance matching circuit of claim 1, wherein at least one
of the one or more variable dielectric capacitors comprises: a
first conductor coupled to one of the first port or the second
port; a second conductor; a tunable dielectric material positioned
between the first conductor and the second conductor; and wherein
at least one of the first conductor or the second conductor, or
both are adapted to receive the one of the one or more variable
voltage signals to cause the change in the impedance of the
matching network.
5. The impedance matching circuit of claim 4, wherein the tunable
dielectric material comprises a composition of barium strontium
titanate.
6. The impedance matching circuit of claim 1, wherein at least one
of the one or more variable dielectric capacitors comprises a
tunable dielectric material.
7. The impedance matching circuit of claim 6, wherein the tunable
dielectric material comprises a composition of barium strontium
titanate.
8. An impedance matching circuit, comprising: a matching network
for coupling to a variable load; wherein the matching network
comprises a first port and a second port; wherein the variable load
is coupled to one of the first port or the second port; wherein the
matching network comprises one or more variable capacitors; wherein
the one or more variable capacitors are operable to receive one or
more variable voltage signals to cause the one or more variable
capacitors to change an impedance of the matching network; and
wherein the change in the impedance of the matching network causes
an increase in power transferred from the first port to the second
port or from the second port to the first port.
9. The impedance matching circuit of claim 8, wherein each of the
one or more variable capacitors comprises one or more variable
dielectric capacitors.
10. The impedance matching circuit of claim 9, wherein each of the
one or more variable dielectric capacitors comprises a tunable
dielectric material that comprises a composition of barium
strontium titanate.
11. The impedance matching circuit of claim 8, wherein the variable
load is an antenna.
12. The impedance matching circuit of claim 8, wherein at least one
of the one or more variable capacitors comprises: a first conductor
coupled to one of the first port or the second port; a second
conductor; a tunable dielectric material positioned between the
first conductor and the second conductor; and wherein at least one
of the first conductor and the second conductor are adapted to
receive the one or more variable voltage signals to cause the
change in the impedance of the matching network.
13. The impedance matching circuit of claim 8, wherein at least one
of the one or more variable capacitors comprises composition of
barium strontium titanate.
14. The impedance matching circuit of claim 8, wherein each of the
one or more variable capacitors comprises one or more variable
dielectric capacitors.
15. The impedance matching circuit of claim 14, wherein each of the
one or more variable dielectric capacitors comprises a tunable
dielectric material comprising a composition of barium strontium
titanate.
16. An impedance matching circuit, comprising: a matching network;
wherein the matching network comprises a first port and a second
port; wherein the matching network comprises one or more variable
reactance elements; wherein the one or more variable reactance
elements are operable to receive one or more variable voltage
signals to cause the one or more variable reactance elements to
change an impedance of the matching network; and wherein the change
in the impedance of the matching network causes a change in power
transferred from the first port to the second port or from the
second port to the first port.
17. The impedance matching circuit of claim 16, wherein each of the
one or more variable reactance elements comprises one or more
variable capacitors.
18. The impedance matching circuit of claim 17, wherein each of the
one or more variable capacitors comprises one or more variable
dielectric capacitors.
19. The impedance matching circuit of claim 18, wherein each of the
one or more variable dielectric capacitors comprises a tunable
dielectric material.
20. The impedance matching circuit of claim 19, wherein the tunable
dielectric material comprises a composition of barium strontium
titanate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 12/952,395 filed Nov. 23, 2010; which is a
Continuation of U.S. patent application Ser. No. 11/245,898 filed
Oct. 08, 2005, now U.S. Pat. No. 7,865,154; which is a Continuation
in part of Ser. No. 10/938,898, filed Sep. 10, 2004; which is a
Continuation of Ser. No. 10/455,901, filed Jun. 06, 2003, now U.S.
Pat. No. 6,864,757; which is a Divisional of Ser. No. 09/909,187
filed Jul. 19, 2001, now U.S. Pat. No. 6,590,468; which is a
non-Provisional of 60/219,500, filed Jul. 20, 2000. U.S. patent
application Ser. No. 10/938,898, and U.S. Pat. No. 6,864,757, and
U.S. Pat. No. 6,590,468, and U.S. Provisional Application Serial
Number 60/219,500 are all incorporated herein by reference in their
entirety.
FIELD OF THE DISCLOSURE
[0002] The invention relates to the field of tunable microwave
devices. More specifically, the invention relates to impedance
matching circuits that utilize a bias voltage to alter the
permittivity of a tunable dielectric material.
BACKGROUND OF THE DISCLOSURE
[0003] Microwave devices typically include a plurality of
components that may have different characteristic impedances. In
order to propagate the microwave signal through the device with
minimal loss, the impedances of the various components are matched
to the characteristic impedance of the input and output signal. By
transitioning the impedances so that an input transmission line is
matched, most of the available power from the input is delivered to
the device. Historically, impedance matching techniques have
treated the matching of components with constant characteristic
impedances to a constant characteristic impedance of the input
line, e.g. to 50 .OMEGA.. Multi-stage matching circuits have been
utilized to obtain minimal reflection loss over a specified
frequency range of operation of a device. Numerous techniques, such
as the use of radial stubs, quarter wave transformers, and
multistage matching circuits with specific distributions, such as
Binomial or Tchebycheff, etc., have been developed in order to
achieve maximum power transfer from the input to the device.
[0004] However, the characteristic impedance of the tunable
components in tunable microwave devices is not a constant value.
The characteristic impedance of the tunable component varies over
the operating range of the device from a minimum to a maximum
impedance value. In tunable dielectric devices, a bias voltage
applied to tunable dielectric material provides the ability to
alter the dielectric constant. The change in the dielectric
constant provides a variation in the electrical path length of a
microwave signal. As the electrical properties of the tunable
dielectric material are varied, the characteristic impedance is
also affected.
[0005] In practice, a single characteristic impedance within the
tunable components minimum/maximum impedance range is selected.
This single impedance value is matched using one of the state of
the art impedance matching techniques. However, as the tunable
microwave device is operated, the impedance of the tunable
component varies from the matched impedance and a degradation in
the impedance match occurs.
[0006] Prior tunable dielectric microwave transmission lines have
utilized tuning stubs and quarter wave matching transformers to
transition the impedance between the input and output. The
technique is best for matching a fixed impedance mismatch. U.S.
Pat. No. 5,479,139 by Koscica et al. discloses quarter wavelength
transformers using non-tunable dielectric material for the purpose
of impedance matching to a ferroelectric phase shifter device.
Similar impedance matching configurations using non-tunable
dielectric substrate of background interest are shown in U.S. Pat.
No. 5,561,407, U.S. Pat. No. 5,334,958, and U.S. Pat. No.
5,212,463. The disadvantage of the above technique is that the
impedance match is optimal at one selective tuning point of the
device and degrades as the device is tuned through its range.
Hence, the reflection loss due to impedance match increases when
the device is tuned away from the matched point.
[0007] Another impedance matching approach for tunable devices is
presented in U.S. Pat. No. 5,307,033 granted to Koscica et al. That
patent discloses the use of spacing of a half wavelength between
elements or matching networks for the purpose of impedance
matching.
[0008] Still another approach utilizes quarter wavelength
transformers on tunable dielectric material as disclosed in U.S.
Pat. No. 5,032,805, granted to Elmer et al. Other impedance
matching configurations are shown in U.S. Pat. Nos. 6,029,075;
5,679,624; 5,496,795; and 5,451,567. Since it is also desirable to
reduce the insertion loss of the matching network, a disadvantage
of the above approach is that the quarter wavelength transformer on
tunable dielectric material increases the insertion loss.
[0009] The disclosures of all of the above-mentioned patents are
expressly incorporated by reference.
[0010] It would be desirable to minimize the impedance mismatch in
tunable microwave device applications. There is a need for a
technique for improving impedance matching for tunable microwave
components that achieves minimal reflection and insertion losses
throughout the range of operation of tunable devices.
SUMMARY OF THE INVENTION
[0011] This invention provides an impedance matching circuit
comprising a conductive line having an input port and an output
port, a ground conductor, a tunable dielectric material positioned
between a first section of the conductive line and the ground
conductor, a non-tunable dielectric material positioned between a
second section of the conductor line and the ground conductor, and
means for applying a DC voltage between the conductive line and the
ground conductor.
[0012] The invention further encompasses an impedance matching
circuit comprising a first ground conductor, a second ground
conductor, a strip conductor having an input port and an output
port. The strip conductor is positioned between the first and
second ground conductors and to define first and second gaps, the
first gap being positioned between the strip conductor and the
first ground conductor and the second gap being positioned between
the strip conductor and the second ground conductor. A non-tunable
dielectric material supports the first and second ground conductors
and the strip conductor in a plane. A connection point is provided
for applying a DC voltage between the strip conductor and the first
and second ground conductors. A plurality of tunable dielectric
layer sections are positioned between the strip conductor and the
first and second ground conductors so as to bridge the gaps between
the first and second ground conductors and the strip conductor at a
plurality of locations, leaving non-bridged sections in between,
defining a plurality of alternating bridged and non-bridged
co-planar waveguide sections.
[0013] The matching circuits form tunable impedance transformers
that are able to match a constant microwave source impedance
connected at the input port to a varying load impedance connected
at the output port, thereby reducing signal reflections between the
microwave source and a variable load impedance.
[0014] This invention provides an impedance matching circuit
capable of matching a range of impedance values to a tunable
microwave device in order to reduce reflections from impedance
mismatch during tuning of the microwave device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a plan view of a first embodiment of the auto
adjusting matching network of this invention in the form of the
microstrip;
[0016] FIG. 2 is a cross-sectional view of the embodiment of FIG. 1
taken along line 2-2, showing a microstrip line geometry;
[0017] FIG. 3 is a cross-sectional view of the embodiment of FIG. 1
taken along line 3-3, showing a microstrip line geometry;
[0018] FIG. 4 is a plan view of a second embodiment of the auto
adjusting matching network of this invention in the form of the
stripline;
[0019] FIG. 5 is a cross-sectional view of the embodiment of FIG. 4
taken along line 5-5, showing a stripline geometry;
[0020] FIG. 6 is a cross-sectional view of the embodiment of FIG. 4
taken along line 6-6, showing a stripline geometry;
[0021] FIG. 7 is a cross-sectional view of a third embodiment for
the auto adjusting matching network of this invention based on a
coaxial geometry;
[0022] FIG. 8 is a cross-sectional view of the embodiment of FIG. 7
taken along line 8-8, showing the coaxial transmission line
geometry;
[0023] FIG. 9 is a plan view of another embodiment for the auto
adjusting matching network of this invention including multiple
partial stages on tunable material;
[0024] FIG. 10 is a plan view of another embodiment for the auto
adjusting matching network of this invention based on a slotline or
(inline geometry, and including multiple partial stages;
[0025] FIG. 11 is a cross-sectional view of the embodiment of FIG.
10 taken along line 11-11, showing a slotline geometry;
[0026] FIG. 12 is a plan view of another embodiment for the auto
adjusting matching network of this invention based on a co-planar
waveguide geometry, and including multiple partial stages;
[0027] FIG. 13 is a cross-sectional view of the embodiment of FIG.
12 taken along line 13-13, showing a coplanar waveguide geometry;
and
[0028] FIG. 14 is a block diagram showing a matching network of
this invention coupled to a tunable dielectric device.
DETAILED DESCRIPTION OF THE DRAWINGS
[0029] The preferred embodiments described herein are each designed
for use within a certain arbitrary frequency range. For this reason
all references to a "wavelength" will refer to the center frequency
of the design.
[0030] Referring to the drawings, FIG. 1 is a plan view of a first
embodiment of an auto adjusting matching network of this invention
in the form of the microstrip circuit 10. FIG. 2 is a
cross-sectional view of FIG. 1 taken along line 2-2, showing the
microstrip line geometry. FIG. 3 is a cross-sectional view of FIG.
1 taken along line 3-3.
[0031] The device has two ports 12 and 14 for input and output of a
guided electromagnetic wave. It includes a multi-stage microstrip
line 16, having sections 18 and 20 of various widths and lengths,
deposited on a non-tunable dielectric substrate 22, which in turn
is supported by ground plane 24; and a microstrip line section 26
deposited on a voltage tunable dielectric substrate 28 which in
turn is supported by ground plane 30. A biasing electrode 32 in the
form of a high impedance microstrip line is connected to microstrip
section 20.
[0032] The biasing electrode 32 serves as a means for connecting an
external variable DC bias voltage supply 34 to the auto-adjusting
impedance matching circuit. The connection of the biasing electrode
32 to the circuit is not limited to microstrip section 20, but may
be made to any other part of the circuit that is electrically
connected to microstrip line section 26. Ground planes 24 and 30
are electrically connected to each other. While ground planes 24
and 30 are shown as separate elements, it should be understood that
they may alternatively be constructed as a single ground plane.
[0033] The microstrip line section 26, which comprises a conducting
strip, is directly supported by a dielectric layer 28, which is the
voltage tunable layer. A ground plane 30 supports the dielectric
layer 28. The microstrip line 26 is less than a quarter wavelength
long and forms an approximately quarter wavelength long transformer
when joined to section 20 of the matching network on the
non-tunable dielectric substrate 22.
[0034] The non-tunable stages 36 and 38 of the matching network 10
form a multistage matching circuit 40 directly supported by the
non-tunable dielectric layer 22. The multi-stage matching circuit
40 can be any number of stages of varying widths and lengths, not
limited to quarter wavelength sections. If the non-tunable and
tunable substrates 22 and 28 respectively are not of the same
height, the last stage 38 of the matching network, which abuts the
tunable dielectric 28, would be electrically connected to
microstrip line section 26 via a step 42.
[0035] FIG. 4 is a plan view of a second embodiment of the auto
adjusting matching network 44 of the invention in the form of a
stripline. FIG. 5 is a cross-sectional view of FIG. 4 taken along
line 5-5, showing a stripline geometry. FIG. 6 is a cross-sectional
view of FIG. 4 taken along line 6-6.
[0036] The device 44 has two ports 46 and 48 for input and output
of the guided electromagnetic wave. It comprises a stripline 50
having sections 52 and 54 of various widths and lengths embedded in
a non-tunable dielectric substrate 56 supported by top and bottom
ground planes 58 and 60, an additional section 62 of stripline 50
embedded in a tunable dielectric substrate 64 supported by top and
bottom ground planes 66 and 68, and a biasing electrode 70 in the
form of a high impedance stripline is connected to stripline
section 54.
[0037] The connection of biasing electrode 70 to the circuit is not
limited to stripline section 54, but may be made to any other part
of the circuit that is electrically connected to stripline section
62. The biasing electrode 70 serves as means for connecting the
auto adjusting impedance matching circuit to an external adjustable
DC voltage bias source 72. Ground planes 66 and 68 may or may not
be the same ground planes as for the tunable microwave device to
which the matching circuit is connected. Ground planes 66 and 68
are electrically connected to the ground planes of the tunable
microwave device. Ground planes 66 and 68 are electrically
connected to ground planes 58 and 60.
[0038] The stripline section 62, which is a conducting strip, is
directly embedded in the tunable dielectric layer 64, which is the
voltage tunable layer. Ground planes 66 on the top and 68 on the
bottom support the dielectric layer 64. The stripline 62 is less
than a quarter wavelength long and forms an approximate quarter
wavelength long transformer when joined to section 54 of the
matching network in the non-tunable dielectric substrate 56.
[0039] The non-tunable stages 76 and 78 of the matching network 44
form a multistage matching circuit 80 directly supported by the
non-tunable dielectric layer 56. The multi-stage matching circuit
80 can be any number of stages of varying widths and lengths, not
limited to and including quarter wavelength sections. The last
stage 78 of the matching network, which abuts the tunable
dielectric 64, is electrically connected to microstrip line section
62.
[0040] FIG. 7 is a longitudinal cross-sectional view of a third
embodiment of the invention for the auto adjusting matching network
based on a coaxial geometry. FIG. 8 is a cross-sectional view of
FIG. 7 taken along line 8-8, showing the coaxial transmission line
geometry.
[0041] The device 82 of FIGS. 7 and 8 has two ports 84 and 86 for
input and output of the guided electromagnetic wave. It comprises a
center conductor 88 having sections 90 and 92 of various diameters
and lengths surrounded by a non-tunable dielectric substrate 94,
which in turn is surrounded by ground conductor 96. An additional
center conductor section 98 is surrounded by a tunable dielectric
substrate 100, which in turn is surrounded by ground conductor 102.
A thin biasing electrode 104 enters the co-axial structure through
a small hole 106 and is connected to the central conductor 88.
[0042] The connection of biasing electrode 104 to the circuit is
not limited to the center conductor section 92, but may be made to
any other part of the circuit that is electrically connected to
center conductor section 98. The biasing electrode 104 serves as a
means for connecting an external adjustable DC voltage bias source
74 to the auto-adjusting impedance matching circuit. Ground
conductor 102 may or may not be the same ground conductor as for a
tunable microwave device to which the matching circuit would be
connected. Ground conductor 102 is electrically connected to the
ground conductor of the tunable microwave device. Ground conductors
96 and 102 are electrically connected to each other.
[0043] The center conductor section 98 is surrounded by a
dielectric layer 100, which is the voltage tunable layer. The
voltage tunable dielectric layer 100 is enclosed by a ground
conductor 102. The center conductor section 98 is less than a
quarter wavelength long and forms a composite impedance transformer
approximately a quarter wavelength long when joined to section 92
of the matching network in the non-tunable dielectric 94.
[0044] The matching network 109 is a multi-stage matching circuit
surrounded by a dielectric layer 94, which is a non-tunable
dielectric. The dielectric layer 94 is enclosed by a ground
conductor 96. The multi-stage matching circuit can be any number of
stages of varying widths and lengths, not limited to and including
quarter wavelength sections. The last stage 108 of the matching
circuit, which abuts the tunable dielectric 100, is electrically
connected to the center conductor 98.
[0045] An extension to the first embodiment is shown in FIG. 9, as
a matching circuit having multiple tunable stages 112, 114, 116,
and multiple non-tunable stages 154, 156, 114a and 116a. The device
has two ports 118 and 120 for input and output of a guided
electromagnetic wave. It includes a matching microstrip line
section 122, deposited on a non-tunable dielectric substrate 124;
multiple pairs of microstrip sections 126, 128 and 130, 132 and
134, 136 deposited on pairs of non-tunable and tunable dielectric
substrates 124, 138 and 140, 142 and 144, 146 respectively; a
biasing electrode 148 in the form of a high impedance microstrip
line connected to microstrip section 126; and a ground plane (not
shown). The dielectric substrates are supported by the ground
plane, which may include different electrically connected sections
to adapt to the different thicknesses of the substrates 124, 140
144 and 138, 142, 146.
[0046] The connection of biasing electrode 148 to the circuit is
not limited to microstrip section 126, but may be made to any other
part of the circuit that is electrically connected to microstrip
line sections 128, 132 and 136. The biasing electrode 148 connects
the auto-adjusting impedance matching circuit to an adjustable DC
voltage bias source 152. The ground plane may or may not be the
same ground plane as for the tunable microwave device to which the
matching circuit is connected.
[0047] Each of the microstrip line sections 128, 132 and 136 is
less than a quarter wavelength long and forms an approximately
quarter wavelength long impedance transformer when joined to
microstrip sections 126, 130 and 134 respectively.
[0048] The non-tunable stages of the matching network 154, 156 form
a multi-stage matching circuit 158 directly supported by the
non-tunable dielectric layer 124. The multistage matching circuit
can be any number of stages of varying widths and lengths, not
limited to quarter wavelength sections. Microstrip section 126 of
the last stage 156 of the non-tuning part of the matching network,
which abuts the tunable stage 112, is electrically connected to
microstrip line section 128. The latter abuts non-tunable tunable
stage 114a and is electrically connected to microstrip line section
130. The latter abuts tunable stage 114 and is electrically
connected to microstrip line section 132. The latter abuts
non-tunable tunable stage 134 and is electrically connected to
microstrip line section 134. The latter abuts tunable stage 116 and
is electrically connected to microstrip line section 136.
[0049] The multiple stage pairs in FIG. 9 ensure impedance matching
over a wider frequency and impedance range than the more simple
geometry of FIG. 1. It should be understood that a similar
extension to multiple stage pairs can be made for the second
(stripline) and third (co-axial) embodiments as well.
[0050] FIG. 10 is a plan view of another embodiment for the auto
adjusting matching network 160 based on a slotline or finline
geometry, and including multiple partial stages 162, 164, and 166.
FIG. 11 is a cross-sectional view of FIG. 10 taken along line
11-11, showing a slotline geometry.
[0051] The device 160 has two ports 168 and 170 for input and
output of the guided electromagnetic wave. It includes two
conducting coplanar conductors 172 and 174, supported by
non-tunable dielectric layer 176, and separated by a gap 178 to
form a slotline (or finline if integrated into a waveguide)
geometry. For comparison with the first, second and third
embodiments, one of these coplanar conductors 174 can be considered
to be the ground conductor. The slot 178 may be of uniform width,
or it can be of non-uniform width as shown in FIG. 10. At multiple
locations (three shown in FIGS. 10) 162, 164 and 166, the slot is
bridged by a tunable dielectric layer 180, 182 and 184, which can
be deposited on the supporting dielectric layer 176 using thick or
thin film technology prior to depositing the metal layers 172 and
174 on the supporting dielectric layer 176. Between locations 162,
164 and 166, there remain sections 186 and 188 as well as 190a and
190b, which are not bridged with a tunable material layer. Planar
conductor 172 is connected to an adjustable DC voltage bias source
192, and planar conductor 174 is connected to DC ground. The
coplanar conductors may or may not be the same coplanar conductors
as for the tunable microwave device to which the matching circuit
is connected.
[0052] Each of the tunable slotline sections 162, 164 and 166 is
less than a quarter wavelength long, but together with the
non-tunable intermediate sections 186, 188, 190a and 190b which are
also typically shorter than a quarter wavelength long, these
cascaded slotline sections form a cascaded network that may be a
multiple of quarter wavelengths long. The network can be made
longer by simply adding more pairs of tunable and non-tunable
slotline sections. By careful choice of the relative lengths of
each tunable and non-tunable slotline section, the cascaded network
forms a tunable impedance matching network over a wide frequency
band.
[0053] The slotline sections 186, 188 190a and 190b may also be
bridged by a tunable layer, similar to the tunable sections 162,
164 and 166, but which may be less tunable. Reduced tunability in
regions 186, 188 190a and 190b can be achieved by using a material
that is less tunable and/or by using wider slot gaps to reduce the
bias field strength in these regions. Instead of using different
types of materials in the strongly tunable and lesser tunable slot
regions, a tunable material can be deposited which may have varying
tunability along the slot length.
[0054] FIG. 12 is a plan view of another embodiment for the auto
adjusting matching network 194 based on a co-planar waveguide
geometry, and including multiple partial stages. FIG. 13 is a
cross-sectional view taken along line 13-13 in FIG. 12, showing a
coplanar waveguide geometry.
[0055] The device 194 has two ports 196 and 198 for input and
output of the guided electromagnetic wave. It includes two coplanar
conducting ground conductors 200, 202 and a central strip conductor
204, supported by non-tunable dielectric layer 206, and separated
by gaps 208 and 210 to form a co-planar waveguide geometry. The
slots 208 and 210 may be of uniform width, or they can be of
non-uniform width as shown in FIG. 12. At multiple locations 212,
214 and 216, the slots 208 and 210 are bridged by a tunable
dielectric layers 218 220 and 222, which can be deposited on the
supporting dielectric layer 206 using thick or thin film technology
prior to depositing the metal layers 200 and 202 and 204 on the
supporting dielectric layer 206. Between locations 212, 214 and
216, there remain sections 224, 226 as well as 228a and 228b, which
are not bridged with a tunable material layer. Strip conductor 204
is connected to an adjustable DC voltage bias source 230, and
planar ground conductors 200 and 202 are connected to DC ground.
The coplanar conductors 200 and 202 and strip 204 may or may not be
the same coplanar conductors as for the tunable microwave device to
which the matching circuit is connected.
[0056] Each of the tunable co-planar waveguide sections 212, 214
and 216 is less than a quarter wavelength long, but together with
the non-tunable intermediate sections 224, 226, 228a and 228b,
which are also typically shorter than a quarter wavelength long,
these cascaded co-planar waveguide sections form a cascaded network
that may be a multiple of quarter wavelengths long. The network can
be made longer by simply adding more pairs of tunable and
non-tunable co-planar waveguide sections. By careful choice of the
relative lengths of each tunable and non-tunable section, the
cascaded network forms a tunable impedance matching network over a
wide frequency band.
[0057] The slots in co-planar waveguide sections 224, 226, 228a and
228b may also be bridged by a tunable layer, similar to the tunable
sections 212, 214 and 216, but in that case the layer may be less
tunable. Reduced tunability in regions 224, 226, 228a and 228b can
be achieved by using a material that is less tunable and/or by
using wider slot gaps to reduce the bias field strength in these
regions. Instead of using different types of materials in the
strongly tunable and lesser tunable slot regions, a tunable
material can be deposited which may have varying tunability along
the co-planar waveguide length.
[0058] FIG. 14 is a block diagram showing a matching network 10
constructed in accordance with this invention coupled to a tunable
microwave device 232. The tunable microwave device 232 could be one
of many devices which have varying input/output characteristic
impedances such as tunable phase shifters, delay lines, filters,
etc. In the arrangement shown in FIG. 14, the adjustable external
DC voltage source is used to supply bias voltage to the matching
network 10 and the tunable microwave device 232 in tandem. As the
voltage supplied by the external DC voltage source changes, the
characteristic input/output impedance of the tunable dielectric
device will also change. At the same time the impedance
characteristics of the matching network will change to maximize
power transfer from/to the microwave source/load 234 to/from the
tunable microwave device 232. Alternatively, the tunable microwave
device 232 and the matching network 10 can be controlled by two
different external DV voltage sources.
[0059] The first preferred embodiment of the auto adjusting
matching network uses a microstrip geometry. The second preferred
embodiment of the auto-adjusting matching circuit has a stripline
geometry, the third has a coaxial geometry, the fourth has a
slotline or finline geometry and the fifth has a co-planar
waveguide geometry.
[0060] In some embodiments, this invention provides a multi-stage
impedance circuit functionally interposed between a conductor line
and an entry point of a tunable microwave device, wherein the
multi-stage impedance matching circuit reduces the signal
reflection of a microwave signal propagating through the tunable
impedance transformer into the microwave device, by matching the
wave impedance of a microwave signal at the entry point, to the
microwave source impedance.
[0061] This invention provides electrically controlled
auto-adjusting matching networks that contribute to the tunable
applications of microwave devices, while improving upon the range
of operation of such devices. It overcomes the problem of matching
to a microwave transmission line with a varying characteristic
impedance. It is well suitable for tunable phase shifters, delay
lines, and impedance matching for power amplifiers used as
general-purpose microwave components in a variety of applications
such as handset power amplifiers, radar, microwave instrumentation
and measurement systems and radio frequency phased array antennas.
The devices are applicable over a wide frequency range, from 500
MHz to 40 GHz.
[0062] The invention provides an impedance matching circuit having
minimal reflection loss and reduced insertion loss over the tuning
range of the device.
[0063] The auto-adjusting matching circuits of this invention may
have a dual function. The main objective of the auto-adjusting
matching circuit is to operate as an impedance matching network.
Additionally, the auto-adjusting matching circuit has the ability
to contribute to the tunable range of the microwave device to which
it is coupled. Hence, the auto-adjusting matching circuit may
incorporate tunable applications in its design as well. For
example, the length of a tunable phase shifter may be decreased
since the matching network provides a small amount of tunable phase
shift through its operating range. Thus, both objectives also lead
to a decrease in the insertion loss.
[0064] The present invention is advantageous because it has wide
application to tunable microwave transmission line applications
that make use of a static electric field to produce the desired
tuning effect. This invention is also applicable to tunable
microwave device applications that operate over a frequency band or
at a single frequency.
[0065] The auto-adjusting matching circuit according to the present
invention may or may not contribute to the design criteria of the
tunable application and may use a common DC Voltage bias or a
different DC Voltage bias. The invention minimizes reflection loss
and increases the useable bandwidth of the microwave
application.
[0066] The auto-adjusting matching circuit is a multi-stage
impedance matching circuit that includes both non-tunable and
tunable dielectric material. For example in one preferred
embodiment, the impedance matching transformer stage supported by
the tunable dielectric material is less than a quarter wavelength
long and is connected to the adjacent transformer supported by the
non-tunable dielectric to form a composite quarter wavelength
impedance transformer. Individual sections of such a composite
quarter wave transformer can be referred to as "partial stages".
The matching transformers are tuned in tandem with the microwave
device, in order to obtain low insertion loss as well as reducing
the reflections from impedance mismatch. Thus, minimal insertion
loss in the matching network is achieved. Additionally, the
reflections from impedance mismatch due to the tuning of the
microwave device are also minimized.
[0067] The auto-adjusting matching circuit is a two-port device,
which in its simplest form includes a conducting matching network
supported by a low-loss, conventional non-tunable dielectric
substrate which in turn is a supported by a first ground conductor;
at least one conducting partial-stage supported by a low-loss
voltage-tunable dielectric layer, which in turn is supported by a
second ground conductor; and a biasing electrode for connection to
an external variable DC voltage source, preferably by way of a
microwave choke.
[0068] The partial-stage on the tunable dielectric layer and the
adjoining partial stage non-tunable dielectric layer together can
form an approximate quarter wavelength long impedance transformer.
The port leading to the partial stage supported by the tunable
dielectric can be connected at the input or output of a tunable
microwave device. The other port of the auto-adjusting matching
circuit, which is connected to the matching section supported by
the non-tunable dielectric substrate, forms a microwave signal
input/output port, which has a substantially constant
characteristic impedance.
[0069] The low-loss voltage-tunable dielectric layer of the
partial-stage of the matching circuit may be comprised of the same
tunable dielectric material as the tunable microwave device to
which it is connected, or it may be comprised of a different
tunable dielectric material. The auto-adjusting matching circuit
may be biased with the same bias voltage as the tunable microwave
device to which it is connected, or it may have a separate bias
voltage applied. If more than one tunable material is used, i.e.
one tunable dielectric material for the microwave tunable device
and another for the partial-stage of the matching circuit, each may
have its own separate bias voltage source or use a common (shared)
bias voltage source.
[0070] As is well known, the bandwidth of the impedance matching
network may be improved by additional matching stages. The
additional matching stages may each be comprised of a partial stage
supported by a tunable dielectric substrate in series with a
partial stage supported by a non-tunable dielectric substrate. The
tunable dielectric substrate sections for the additional matching
stages may be comprised of the same tunable dielectric material as
the first tunable partial-stage, or it may be comprised of a
different tunable dielectric material.
[0071] The microwave matching section, which is supported by the
tunable dielectric substrate for the dual purpose of reducing
signal reflections and providing good transmission to and from the
microwave transmission line application as well as contributing to
the tunability of the application, may be a partial stage less than
a quarter wave length long, or may include more than one matching
section and is not limited to the use of one tunable dielectric
substrate.
[0072] The biasing electrode may be connected to the auto-adjusting
matching circuit by way of a microwave choke such as a high
impedance transmission line, or by a highly inductive wire attached
directly to the auto-adjusting matching circuit at any point that
is ultimately electrically connected to the partial stage supported
by the tunable dielectric.
[0073] The first and second ground conductors are electrically
connected and if both are of a planar construction, they should
preferably form one continuous ground plane. The non-tunable
matching stages are electrically connected to the tunable
partial-stage.
[0074] The objective of a matching network is to ensure that a
guided electromagnetic wave entering one port (as such defined as
the input port) will enter the microwave device and leave it at the
other port (output), with minimum residual reflections at each
port. The ground plane is kept at zero voltage, while a voltage
bias is applied to the electrodes. The voltage bias causes a DC
electric field across the voltage tunable dielectric, which affects
the dielectric permittivity of the medium. Since the characteristic
impedance of the microstrip is inversely proportional to the square
root of the effective dielectric permittivity of the medium around
the strip, the biasing voltage can be used to control the
characteristic impedance of the auto-adjusting matching network. In
this way, the characteristic impedance of the invention can be
controlled by the voltage bias. The advantages of this invention
are low insertion loss and improved bandwidth operation for tunable
devices.
[0075] Tunable dielectric materials have been described in several
patents. Barium strontium titanate (BaTiO.sub.3--SrTiO3), also
referred to as BSTO, is used for its high dielectric constant
(200-6,000) and large change in dielectric constant with applied
voltage (25-75 percent with a field of 2 Volts/micron). Tunable
dielectric materials including barium strontium titanate are
disclosed in U.S. Pat. No. 5,427,988 by Sengupta, et al. entitled
"Ceramic Ferroelectric Composite Material-BSTO--MgO"; U.S. Pat. No.
5,635,434 by Sengupta, et al. entitled "Ceramic Ferroelectric
Composite Material-BSTO-Magnesium Based Compound"; U.S. Pat. No.
5,830,591 by Sengupta, et al. entitled "Multilayered Ferroelectric
Composite Waveguides"; U.S. Pat. No. 5,846,893 by Sengupta, et al.
entitled "Thin Film Ferroelectric Composites and Method of Making";
U.S. Pat. No. 5,766,697 by Sengupta, et al. entitled "Method of
Making Thin Film Composites"; U.S. Pat. No. 5,693,429 by Sengupta,
et al. entitled "Electronically Graded Multilayer Ferroelectric
Composites"; U.S. Pat. No. 5,635,433 by Sengupta entitled "Ceramic
Ferroelectric Composite Material BSTO--ZnO"; U.S. Pat. No.
6,074,971 by Chiu et al. entitled "Ceramic Ferroelectric Composite
Materials with Enhanced Electronic Properties BSTO--Mg Based
Compound-Rare Earth Oxide". These patents are incorporated herein
by reference.
[0076] The electronically tunable materials that can be used in the
present invention include at least one electronically tunable
dielectric phase, such as barium strontium titanate, in combination
with at least two additional metal oxide phases. Barium strontium
titanate of the formula Ba.sub.xSr.sub.1-xTiO.sub.3 is a preferred
electronically tunable dielectric material due to its favorable
tuning characteristics, low Curie temperatures and low microwave
loss properties. In the formula Ba.sub.xSr.sub.1-xTiO.sub.3, x can
be any value from 0 to 1, preferably from about 0.15 to about 0.6.
More preferably, x is from 0.3 to 0.6.
[0077] Other electronically tunable dielectric materials may be
used partially or entirely in place of barium strontium titanate.
An example is Ba.sub.xCa.sub.1-xTiO.sub.3, where x is in a range
from about 0.2 to about 0.8, preferably from about 0.4 to about
0.6. Additional electronically tunable ferroelectrics include
Pb.sub.xZr.sub.1-xTiO.sub.3 (PZT) where x ranges from about 0.05 to
about 0.4, lead lanthanum zirconium titanate (PLZT), PbTiO.sub.3,
BaCaZrTiO.sub.3, NaNO.sub.3, KNbO.sub.3, LiNbO.sub.3, LiTaO.sub.3,
PbNb.sub.2O.sub.6, PbTa.sub.2O.sub.6, KSr(NbO.sub.3) and
NaBa.sub.2(NbO.sub.3)5KH.sub.2PO.sub.4.
[0078] In addition, the following U.S. Patent Applications,
assigned to the assignee of this application, disclose additional
examples of tunable dielectric materials: U.S. application Ser. No.
09/594,837 filed Jun. 15, 2000, entitled "Electronically Tunable
Ceramic Materials Including Tunable Dielectric and Metal Silicate
Phases"; U.S. application Ser. No. 09/768,690 filed Jan. 24, 2001,
entitled "Electronically Tunable, Low-Loss Ceramic Materials
Including a Tunable Dielectric Phase and Multiple Metal Oxide
Phases"; U.S. application Ser. No. 09/882,605 filed Jun. 15, 2001,
entitled "Electronically Tunable Dielectric Composite Thick Films
And Methods Of Making Same"; and U.S. Provisional Application Ser.
No. 60/295,046 filed Jun. 1, 2001 entitled "Tunable Dielectric
Compositions Including Low Loss Glass Frits". These patent
applications are incorporated herein by reference.
[0079] The tunable dielectric materials can also be combined with
one or more non-tunable dielectric materials. The non-tunable
phase(s) may include MgO, MgAl.sub.2O.sub.4, MgTiO.sub.3,
Mg.sub.2SiO.sub.4, CaSiO.sub.3, MgSrZrTiO.sub.6, CaTiO.sub.3,
Al.sub.2O.sub.3, SiO.sub.2 and/or other metal silicates such as
BaSiO.sub.3 and SrSiO.sub.3. The non-tunable dielectric phases may
be any combination of the above, e.g., MgO combined with
MgTiO.sub.3, MgO combined with MgSrZrTiO.sub.6, MgO combined with
Mg.sub.2SiO.sub.4, MgO combined with Mg.sub.2SiO.sub.4,
Mg.sub.2SiO.sub.4 combined with CaTiO.sub.3 and the like.
[0080] Additional minor additives in amounts of from about 0.1 to
about 5 weight percent can be added to the composites to
additionally improve the electronic properties of the films. These
minor additives include oxides such as zirconnates, tannates, rare
earths, niobates and tantalates. For example, the minor additives
may include CaZrO.sub.3, BaZrO.sub.3, SrZrO.sub.3, BaSnO.sub.3,
CaSnO.sub.3, MgSnO.sub.3, Bi.sub.2O.sub.3/2SnO.sub.2,
Nd.sub.2O.sub.3, Pr.sub.2O.sub.11, Yb.sub.2O.sub.3,
Ho.sub.2O.sub.3, La.sub.2O.sub.3, MgNb.sub.2O.sub.6,
SrNb.sub.2O.sub.6, BaNb.sub.2O.sub.6, MgTa.sub.2O.sub.6,
BaTa.sub.2O.sub.6 and Ta.sub.2O.sub.3.
[0081] Thick films of tunable dielectric composites can comprise
Ba.sub.1-xSr.sub.xTiO.sub.3, where x is from 0.3 to 0.7 in
combination with at least one non-tunable dielectric phase selected
from MgO, MgTiO.sub.3, MgZrO.sub.3, MgSrZrTiO.sub.6,
Mg.sub.2SiO.sub.4, CaSiO.sub.3, MgAl.sub.2O.sub.4, CaTiO.sub.3,
Al.sub.2O.sub.3, SiO.sub.2, BaSiO.sub.3 and SrSiO.sub.3. These
compositions can be BSTO and one of these components or two or more
of these components in quantities from 0.25 weight percent to 80
weight percent with BSTO weight ratios of 99.75 weight percent to
20 weight percent.
[0082] The electronically tunable materials can also include at
least one metal silicate phase. The metal silicates may include
metals from Group 2A of the Periodic Table, i.e., Be, Mg, Ca, Sr,
Ba and Ra, preferably Mg, Ca, Sr and Ba. Preferred metal silicates
include Mg.sub.2SiO.sub.4, CaSiO.sub.3, BaSiO.sub.3 and
SrSiO.sub.3. In addition to Group 2A metals, the present metal
silicates may include metals from Group 1A, i.e., Li, Na, K, Rb, Cs
and Fr, preferably Li, Na and K. For example, such metal silicates
may include sodium silicates such as Na.sub.2SiO.sub.3 and
NaSiO.sub.3--5H.sub.2O, and lithium-containing silicates such as
LiAlSiO.sub.4, Li.sub.2SiO.sub.3 and Li.sub.4SiO.sub.4. Metals from
Groups 3A, 4A and some transition metals of the Periodic Table may
also be suitable constituents of the metal silicate phase.
Additional metal silicates may include Al.sub.2Si.sub.2O.sub.7,
ZrSiO.sub.4, KalSi.sub.3O.sub.8, NaAlSi.sub.3O.sub.8,
CaAl.sub.2Si.sub.2O.sub.8, CaMgSi.sub.2O.sub.6, BaTiSi.sub.3O.sub.9
and Zn.sub.2SiO.sub.4. Tunable dielectric materials identified as
Parascan.TM. materials, are available from Paratek Microwave, Inc.
The above tunable materials can be tuned at room temperature by
controlling an electric field that is applied across the
materials.
[0083] In addition to the electronically tunable dielectric phase,
the electronically tunable materials can include at least two
additional metal oxide phases. The additional metal oxides may
include metals from Group 2A of the Periodic Table, i.e., Mg, Ca,
Sr, Ba, Be and Ra, preferably Mg, Ca, Sr and Ba. The additional
metal oxides may also include metals from Group 1A, i.e., Li, Na,
K, Rb, Cs and Fr, preferably Li, Na and K. Metals from other Groups
of the Periodic Table may also be suitable constituents of the
metal oxide phases. For example, refractory metals such as Ti, V,
Cr, Mn, Zr, Nb, Mo, Hf, Ta and W may be used. Furthermore, metals
such as Al, Si, Sn, Pb and Bi may be used. In addition, the metal
oxide phases may comprise rare earth metals such as Sc, Y, La, Ce,
Pr, Nd and the like.
[0084] The additional metal oxides may include, for example,
zirconnates, silicates, titanates, aluminates, stannates, niobates,
tantalates and rare earth oxides. Preferred additional metal oxides
include Mg.sub.2SiO.sub.4, MgO, CaTiO.sub.3, MgZrSrTiO.sub.6,
MgTiO.sub.3, MgAl.sub.2O.sub.4, WO.sub.3, SnTiO.sub.4, ZrTiO.sub.4,
CaSiO.sub.3, CaSnO.sub.3, CaWO.sub.4, CaZrO.sub.3,
MgTa.sub.2O.sub.6, MgZrO.sub.3, MnO.sub.2, PbO, Bi.sub.2O.sub.3 and
La.sub.2O.sub.3. Particularly preferred additional metal oxides
include Mg.sub.2SiO.sub.4, MgO, CaTiO.sub.3, MgZrSrTiO.sub.6,
MgTiO.sub.3, MgAl.sub.2O.sub.4, MgTa.sub.2O.sub.6 and
MgZrO.sub.3.
[0085] The additional metal oxide phases may alternatively include
at least two Mg-containing compounds. In addition to the multiple
Mg-containing compounds, the material may optionally include
Mg-free compounds, for example, oxides of metals selected from Si,
Ca, Zr, Ti, Al and/or rare earths. In another embodiment, the
additional metal oxide phases may include a single Mg-containing
compound and at least one Mg-free compound, for example, oxides of
metals selected from Si, Ca, Zr, Ti, Al and/or rare earths.
[0086] This invention provides minimal loss auto-adjusting matching
circuits for application to microwave transmission line devices
that utilize a bias voltage for tuning Each embodiment of the
auto-adjusting matching circuit is comprised of a microwave
transmission line configuration, a tunable dielectric material,
means for connecting to a bias voltage, and a non-tunable low-loss
dielectric material. In operation, the auto-adjusting matching
circuit is placed adjacent to the tunable microwave device in order
to reduce the reflections from impedance mismatch.
[0087] The invention contemplates various dielectric materials,
tunable dielectric materials, tunable liquid crystals, bias line
geometries, matching stages, impedances of microstrip lines, and
operating frequencies of the auto-adjusting matching circuit. It
should be understood that the foregoing disclosure relates to only
typical embodiments of the invention and that numerous
modifications or alternatives may be made therein by those skilled
in the art without departing from the scope of the invention as set
forth in the appended claims.
* * * * *