U.S. patent application number 15/729542 was filed with the patent office on 2018-05-10 for apparatus and methods related to ferrite based circulators.
The applicant listed for this patent is Skyworks Solutions, Inc.. Invention is credited to David Bowie Cruickshank, Brian Murray.
Application Number | 20180130585 15/729542 |
Document ID | / |
Family ID | 47089870 |
Filed Date | 2018-05-10 |
United States Patent
Application |
20180130585 |
Kind Code |
A1 |
Cruickshank; David Bowie ;
et al. |
May 10, 2018 |
APPARATUS AND METHODS RELATED TO FERRITE BASED CIRCULATORS
Abstract
Apparatus and methods related to ferrite based circulators are
disclosed. A ferrite disk used in a circulator can be configured to
reduce intermodulation distortion when routing radio-frequency
signals having closely spaced frequencies. Such a reduction in
intermodulation distortion can be achieved by adjusting
magnetization at the edge portion of the ferrite disk. By way of an
example, a ferrite disk with a reduced saturation magnetization
(4PiMs) edge portion can reduce intermodulation distortion. Example
configurations with such a reduced 4PiMs edge portions are
disclosed.
Inventors: |
Cruickshank; David Bowie;
(Rockville, MD) ; Murray; Brian; (Cork,
IE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Skyworks Solutions, Inc. |
Woburn |
MA |
US |
|
|
Family ID: |
47089870 |
Appl. No.: |
15/729542 |
Filed: |
October 10, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14950765 |
Nov 24, 2015 |
9793037 |
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15729542 |
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13463394 |
May 3, 2012 |
9214712 |
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14950765 |
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61483595 |
May 6, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01F 7/0273 20130101;
H01P 1/36 20130101; H04B 2001/485 20130101; H01P 1/387 20130101;
H01P 1/39 20130101; H01P 1/38 20130101; H04B 1/48 20130101 |
International
Class: |
H01F 7/02 20060101
H01F007/02; H01P 1/39 20060101 H01P001/39; H04B 1/48 20060101
H04B001/48; H01P 1/36 20060101 H01P001/36; H01P 1/387 20060101
H01P001/387; H01P 1/38 20060101 H01P001/38 |
Claims
1. (canceled)
2. A passive circulator, comprising: a ferrite plate that extends
laterally along a first plane and has a center portion and an edge
portion, the center portion having a first saturation magnetization
value and the edge portion having a second saturation magnetization
value that is lower than the first saturation magnetization value;
a magnet that extends along a second plane parallel to the first
plane, the magnet disposed relative to the ferrite plate to provide
a static magnetic field to the ferrite plate to magnetize the
ferrite plate, the magnetization configured to facilitate
transmission of a radio-frequency signal between a first location
and a second location along a perimeter of the ferrite plate based
on a standing wave pattern formed in the ferrite plate due to the
magnetization; and a housing that surrounds the magnet and the
ferrite plate and which provides a return path for the static
magnetic field, the housing comprising a hollow portion with an
inner dimension that is larger than a lateral dimension of the
magnet and a lateral dimension of the ferrite plate, and a plate
portion that extends along a third plane parallel to the second
plane so that the magnet is disposed between the plate portion and
the ferrite plate, the plate portion attached to the hollow portion
to seal an end of the hollow portion.
3. The circulator of claim 2 further comprising a flux conductor
disposed relative to the ferrite plate so that the ferrite plate is
disposed between the flux conductor and the magnet, the flux
conductor configured to provide resonator and matching network
functionalities.
4. The circulator of claim 2 further comprising a dielectric
structure disposed along an outer perimeter of the ferrite plate,
the dielectric structure configured to facilitate impedance
matching between a first electrical conductor and a second
electrical conductor.
5. The circulator of claim 2 wherein the ferrite plate is a ferrite
disk with a circular outer perimeter.
6. The circulator of claim 5 wherein the edge portion of the
ferrite disk is defined by a ring disposed about a center disk that
defines the center portion of the ferrite disk.
7. The circulator of claim 6 further comprising a dielectric ring
disposed about the ring.
8. The circulator of claim 2 wherein the ferrite plate is a single
piece disk.
9. A method for reducing intermodulation distortion, the method
comprising: providing a ferrite plate having a center portion
having a first saturation magnetization to allow passage of a
transmit signal between a first location and a second location of
the ferrite plate and passage of a receive signal between the
second location and a third location of the ferrite plate;
providing an edge portion of the ferrite plate having a second
saturation magnetization that is lower than the first saturation
magnetization to reduce intermodulation distortion occurring at the
edge portion of the ferrite plate; applying a static magnetic field
to the ferrite plate with a magnet, the magnet disposed relative to
the ferrite plate so that the magnet extends along a parallel plane
to the ferrite plate; and providing a return path for the magnetic
field with a housing that surrounds the magnet and the ferrite
plate, the housing comprising a hollow portion with an inner
dimension that is larger than a lateral dimension of the magnet and
a lateral dimension of the ferrite plate, and a plate portion that
extends along a third plane parallel to the magnet so that the
magnet is disposed between the plate portion and the ferrite plate,
the plate portion attached to the hollow portion to seal an end of
the hollow portion.
10. The method of claim 9 wherein the second saturation
magnetization of the edge portion reduces a third order product of
fundamentals of the transmit and receive signals to a level of at
least about -85 dBc.
11. The method of claim 10 wherein the reduction of the third order
product is to a level of at least about -90 dBc.
12. The method of claim 9 further comprising disposing a dielectric
structure along an outer perimeter of the ferrite plate to
facilitate impedance matching between a first electrical conductor
and a second electrical conductor.
13. A passive circulator module for isolating transmit and receive
RF signals from each other, the module comprising: a ferrite plate
that extends laterally along a first plane and has a center portion
and an edge portion, the center portion having a first saturation
magnetization value and the edge portion having a second saturation
magnetization value that is lower than the first saturation
magnetization value; a magnet configured to provide a static
magnetic field to the ferrite plate to magnetize the ferrite plate
to facilitate transmission of a radio-frequency signal between a
first location and a second location along a perimeter of the
ferrite plate based on a standing wave pattern formed in the
ferrite plate due to the magnetization, the magnet extending along
a second plane parallel to the first plane; a housing that
surrounds the magnet and the ferrite plate to provide a return path
for the static magnetic field, the housing comprising a hollow
portion with an inner dimension that is larger than a lateral
dimension of the magnet and a lateral dimension of the ferrite
plate, and a plate portion that extends along a third plane
parallel to the second plane so that the magnet is disposed between
the plate portion and the ferrite plate, the plate portion attached
to the hollow portion to seal an end of the hollow portion; and
signal ports coupled to a transmit radio-frequency signal, a
receive radio-frequency signal, and an antenna.
14. The module of claim 13 wherein the hollow portion and the plate
portion are separate pieces.
15. The module of claim 13 further comprising a dielectric
structure disposed along an outer perimeter of the ferrite
plate.
16. The module of claim 13 wherein the ferrite plate is a single
piece disk.
17. The module of claim 13 wherein the ferrite plate is a ferrite
disk with a circular outer perimeter.
18. The module of claim 17 wherein the edge portion of the ferrite
disk is defined by a ring disposed about a center disk that defines
the center portion of the ferrite disk, the ring having an inner
diameter greater than or equal to an outer diameter of the center
disk.
19. The module of claim 18 further comprising a dielectric ring
disposed about the ring.
20. A wireless device, comprising: a transmitter circuit; a
receiver circuit; an antenna configured to transmit signals from
the transmitter circuit and to receive signals for the receiver
circuit; and a passive circulator for isolating transmit and
receive signals between the transmitter and receiver circuits,
including (a) a ferrite plate that extends laterally along a first
plane and has a center portion and an edge portion, the center
portion having a first saturation magnetization value and the edge
portion having a second saturation magnetization value that is
lower than the first saturation magnetization value; (b) a magnet
extending along a second plane parallel to the first plane and
disposed relative to the ferrite plate to provide a static magnetic
field to the ferrite plate to magnetize the ferrite plate to
facilitate transmission of a radio-frequency signal between a first
location and a second location along a perimeter of the ferrite
plate based on a standing wave pattern formed in the ferrite plate
due to the magnetization; (c) a magnetic circuit configured to
provide a return path for the magnetic field, the magnetic circuit
at least partially defined by a housing that surrounds the magnet
and the ferrite plate, the housing comprising a hollow portion with
an inner dimension that is larger than a lateral dimension of the
magnet and a lateral dimension of the ferrite plate, and a plate
portion that extends along a third plane parallel to the second
plane so that the magnet is disposed between the plate portion and
the ferrite plate, the plate portion attached to the hollow portion
to seal an end of the hollow portion; and (d) signal ports coupled
to the transmitter circuit, the receiver circuit, and the
antenna.
21. The wireless device of claim 20 wherein the wireless device
includes a base station.
Description
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS
[0001] Any and all applications for which a foreign or domestic
priority claim is identified in the Application Data Sheet as filed
with the present application are hereby incorporated by reference
under 37 CFR 1.57.
BACKGROUND
Field
[0002] The present disclosure generally relates to circulators,
and, more particularly to ferrite-based circulators configured to
reduce intermodulation distortion.
Description of the Related Art
[0003] A circulator is a radio-frequency (RF) device typically
having three or four ports, where RF power entering one port is
routed to another port. When an RF signal is being routed between
two selected ports, it can be desirable to isolate other port(s)
from such a signal. Accordingly, a circulator is sometimes also
referred to as an isolator. In RF applications, circulators are
typically used to route to-transmit and received signals to and
from an antenna. Such signals can involve different frequencies;
and thus, intermodulation distortion can arise.
SUMMARY
[0004] In accordance with a number of implementations, the present
disclosure relates to a passive circulator having a ferrite plate
that extends laterally and having a perimeter to define a center
portion and an edge portion. The center portion has a first
saturation magnetization value and the edge portion having a second
saturation magnetization value that is less than the first
saturation magnetization value. The passive circulator further
includes a magnet assembly disposed relative to the ferrite plate
to provide a static magnetic field to the ferrite plate to
magnetize the ferrite plate, with the magnetization configured to
facilitate transmission of a radio-frequency signal between first
and second locations along the perimeter of the ferrite plate based
on a standing wave pattern formed in the ferrite plate due to the
magnetization. The passive circulator further includes first and
second electrical conductors disposed relative to the first and
second locations to facilitate the transmission of the
radio-frequency signal between the first and second locations.
[0005] In some embodiments, the circulator can further include a
magnetic circuit for the magnet assembly, with the magnetic circuit
configured to provide a return path for the magnetic field.
[0006] In a number of embodiments, the circulator can further
include an inner flux conductor disposed relative to the ferrite
disk and configured to provide resonator and matching network
functionalities.
[0007] According to some embodiments, the circulator can further
include a dielectric structure disposed along and outside of the
perimeter, with the dielectric structure configured to facilitate
impedance matching between the first and second electrical
conductors.
[0008] According to a number of embodiments, the perimeter of the
ferrite disk can have a shape such as a circular shape or a
triangular shape.
[0009] Some embodiments of the passive circulator can be configured
where ferrite disk is formed as a single piece disk, or includes a
first piece having the first saturation magnetization value and a
second piece having the second saturation magnetization value. In
some of such latter configurations, the second piece of the ferrite
disk can form a ring about the second piece.
[0010] According to a number of implementations, the present
disclosure relates to a method for reducing intermodulation
distortion. The method includes providing a ferrite medium having a
first saturation magnetization to allow passage of a transmit
signal between first and second locations of the ferrite medium and
passage of a receive signal between the second and a third location
of the ferrite medium. The method further includes providing an
edge portion of the ferrite medium with a second saturation
magnetization that is lower than the first saturation magnetization
to reduce intermodulation distortion occurring at the edge portion
of the ferrite medium.
[0011] In some implementations, the reduced intermodulation
distortion can include a reduction of a third order product of
fundamentals of the transmit and receive signals to a level of at
least about -85 dBc. Such a reduction of the third order product
can be to a level of at least about -90 dBc.
[0012] In various embodiments, the present disclosure relates to a
passive circulator module for isolating transmit and receive RF
signals from each other. The module includes a ferrite disk having
a center and an edge, and having a first saturation magnetization
value between the center and a first radius that is between the
center and the edge and a second saturation magnetization value
between the first radius and the edge. The module further includes
a magnet assembly configured to provide a static magnetic field to
the ferrite disk to magnetize the ferrite disk. The module further
includes signal ports coupled to the transmit RF signal, the
receive RF signal, and an antenna.
[0013] In some embodiments, the module can further include a
housing configured to contain the ferrite disk, the magnet
assembly, and at least a portion of the signal ports.
[0014] In some embodiments, the module can further include a
dielectric ring disposed along the outside of the edge of the
ferrite disk. Such a ferrite disk can be formed as a single piece
disk.
[0015] In some embodiments, the module can further include a
circular disk having the first radius and a circular ring having an
inner diameter greater than or equal to the first radius and an
outer diameter at the edge of the ferrite disk.
[0016] In accordance with a number of embodiments, the present
disclosure relates to a passive ferrite based isolator for
isolating transmit and receive wireless signals from each other
when sharing a common antenna. The isolator has a reduced
intermodulation distortion of a third order product of fundamentals
of the transmit and receive signals at a level of at least about
-85 dBc.
[0017] In some implementations, the present disclosure relates to a
wireless device having a transmitter circuit, a receiver circuit,
and an antenna configured to transmit signals from the transmitter
circuit and to receive signals for the receiver circuit. The
wireless device further includes a ferrite based circulator for
isolating transmit and receive signals between the transmitter and
receiver circuits. The circulator includes a ferrite disk having a
center and an edge, and having a first saturation magnetization
value between the center and a first radius that is between the
center and the edge and a second saturation magnetization value
between the first radius and the edge. The circulator further
includes a magnet assembly configured to provide a static magnetic
field to the ferrite disk to magnetize the ferrite disk. The
circulator further includes signal ports coupled to the transmitter
circuit, the receiver circuit, and the antenna.
[0018] In some embodiments, the wireless device can include a
mobile telephone.
[0019] In some implementations, the present disclosure relates to a
disk assembly for a radio-frequency circulator. The disk assembly
includes a ferrite disk having a first saturation magnetization
value. The disk assembly further includes a first piece dimensioned
to form a perimeter around the ferrite disk, and has a second
saturation magnetization value that is less than the first
saturation magnetization value. The disk assembly further includes
a second piece dimensioned to form a perimeter around the second
piece. The second piece includes a desired dielectric material. The
ferrite disk and the first and second pieces are configured to
provide desired magnetization at or near an edge portion of the
disk assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIGS. 1A and 1B schematically depict examples of 3-port and
4-port circulators.
[0021] FIGS. 2A and 2B show examples of magnetic fields that can be
applied to the example circulators of FIGS. 1A and 1B to achieve
desired routing functionalities.
[0022] FIG. 3 shows an example circulator having a pair of ferrite
disks disposed about an inner conductor and between a pair of
magnets.
[0023] FIG. 4 shows an example of significant radial component in
magnetization that can exist at or near the edge portion of the
example circulator of FIG. 3.
[0024] FIG. 5 shows that interactions of intermodulation signals in
circulators can occur primarily at the edge portion of ferrite
disks.
[0025] FIG. 6 shows a process that can be implemented to control
magnetization of a ferrite device to reduce intermodulation
distortion (IMD).
[0026] FIG. 7 shows an example process that can be implemented in
the context of a circular disk shaped ferrite as a more specific
example of the process of FIG. 6.
[0027] FIG. 8 shows another example process that can be implemented
as a more specific example of the process of FIG. 6, where one or
more structures can be positioned at or near the radial edge of the
ferrite disk to obtain a desired magnetization.
[0028] FIG. 9 shows an example configuration that can result from
the process of FIG. 8.
[0029] FIG. 10 shows an example of IMDs that can result from two
fundamental frequencies f.sub.1 and f.sub.2 that are relatively
close to each other in frequency space.
[0030] FIG. 11 shows an example test setup for generating and
measuring IMDs such as those of FIG. 10.
[0031] FIG. 12 shows examples of IMD measurement results.
[0032] FIGS. 13A-13C show an example passive circulator device
having one or more features described herein and packaged as a
modular device.
[0033] FIGS. 14A-14H show more detailed measurement results.
[0034] FIG. 15 schematically shows an example radio-frequency
device where a circulator or an isolator having one or more
features described herein can be implemented.
[0035] FIGS. 16A-16C show various views of an example ferrite-based
disk having one or more features described herein, and how such a
disk can be assembled.
[0036] FIG. 17 shows that in some implementations, the
ferrite-based disk of FIG. 16 can be obtained by cutting a
plurality of pieces from a longer assembly.
DETAILED DESCRIPTION OF SOME EMBODIMENTS
[0037] The headings provided herein, if any, are for convenience
only and do not necessarily affect the scope or meaning of the
claimed invention.
[0038] In some implementations, circulators are passive devices
utilized in radio-frequency (RF) applications to, for example,
selectively route RF signals between an antenna, a transmitter, and
a receiver. If a signal is being routed between the transmitter and
the antenna, the receiver preferably should be isolated.
Accordingly, a circulator is sometimes also referred to as an
isolator; and such an isolating performance can represent the
performance of the circulator.
[0039] In some embodiments, a circulator can be a passive device
having three or more ports (e.g., ports for antenna, transmitter
and receiver). FIGS. 1A and 1B schematically show an example of a
3-port circulator 100 and a 4-port circulator 104. In the example
3-port circulator 100, a signal is shown to be routed (arrow 102)
from port 1 to port 2; and port 3 can be substantially isolated
from such a signal. In the example 4-port circulator 104, a signal
is shown to be routed (arrow 106) from port 1 to port 2; and
another signal is shown to be routed (arrow 108) from port 3 to
port 4. The two junctions of the signal paths in the example of
FIG. 1B can be substantially isolated from each other. Other
configurations of 3 and 4-port circulators, as well as circulators
having other numbers of ports, can also be implemented.
[0040] In some implementations, a circulator can be based on
ferrite materials. Ferrites are magnetic materials having very high
ohmic resistance. Accordingly, ferrites have little or no eddy
current when subjected to changing magnetic fields, and are
therefore suitable for RF applications.
[0041] Ferrites can include Weiss domains, where each domain has a
net non-zero magnetization. When there is no external magnetic
field influencing a ferrite object, the Weiss domains are oriented
substantially randomly, so that the ferrite as a whole has a net
magnetization of approximately zero.
[0042] If an external magnetic field of sufficient strength is
applied to the ferrite object, the Weiss domains tend to align
along the direction of the external magnetic field. Such a net
magnetization can influence how an electromagnetic wave propagates
within the ferrite object.
[0043] For example, and as depicted in FIGS. 2A and 2B, suppose
that a circular disk shaped ferrite object 110 is subjected to a
substantially static external magnetic field directed along the
axis (perpendicular to the plane of paper) of the disk. In the
absence of such an external field (not shown), an RF signal input
into Port 1 and propagating perpendicular to the disk axis splits
into two rotating waves with a substantially same propagation
speed. One wave rotates clockwise around the disk, and the other
counter-clockwise around the disk, so as to yield a standing wave
pattern. If Ports 2 and 3 are positioned equally spaced azimuthally
relative to Port 1 (about 120 degrees from each other), the
standing wave pattern results in approximately half of the incoming
wave leaving each of Ports 2 and 3.
[0044] In the presence of such an external magnetic field, the
propagation speeds of the two rotating waves are no longer the
same. Because of the difference in the propagation speeds, the
resulting standing wave pattern can yield a situation where
substantially all of the energy of the incoming wave is passed to
one of the two ports while the other port is substantially
isolated.
[0045] For example, FIG. 2A shows a configuration where the axial
static magnetic field (not shown) yielding a rotated standing wave
pattern relative to the incoming wave propagation direction (along
Port 1). Examples of electric field lines corresponding to such a
standing wave pattern are depicted as 112 (along a plane of the
disk) and 114, 116 (along the axis of the disk). The example
rotated standing wave pattern results in a substantial null in
electric field strength at Port 3, thereby yielding substantial
isolation of Port 3. On the other hand, Port 2 is depicted as
having a similar (inverted) wave pattern as that of the input at
Port 1, and therefore transmits energy from Port 1 to Port 2.
[0046] FIG. 2B shows another example where an axial static magnetic
field (not shown) yields a rotated standing wave pattern, such that
a wave input through Port 1 is passed to Port 3 as an output, and
Port 2 is substantially isolated. In some implementations, the two
rotated standing wave patterns can be achieved by providing
magnetic fields that are higher and lower than a field value that
results in a resonance in the precession of ferrite domains.
[0047] FIG. 3 shows an example configuration of a circulator device
130 having a pair of ferrite disks 132, 134 disposed between a pair
of cylindrical magnets 142, 144. The magnets 142, 144 can be
arranged so as to yield generally axial field lines through the
ferrite disks 132, 134. The magnetic field flux that passes through
the ferrite disks 132, 134 can complete its circuit (depicted by
arrows) through return paths provided by 148, 152, 150 and 146 so
as to strengthen the field applied to the ferrite disks 132, 134.
In some embodiments, the return path portions 148 and 146 can be
disks having a diameter larger than that of the magnets 142, 144;
and the return path portions 152 and 150 can be hollow cylinders
having an inner diameter that generally matches the diameter of the
return path disks 148, 146. The foregoing parts of the return path
can be formed as a single piece or be an assembly of a plurality of
pieces.
[0048] The example circulator device 130 can further include an
inner flux conductor 140 disposed between the two ferrite disks
132, 134. Such an inner conductor can be configured to function as
a resonator and matching networks to the ports (not shown).
[0049] The example circulator device 130 can further include a high
relative dielectric (Er) material 136, 138 disposed between the
edge portion of the ferrite disks 132, 134 and the return path
portions 150, 152. Such a high Er dielectric can be formed as a
ring dimensioned to fit between the corresponding ferrite disk and
the outer return path portion.
[0050] In some implementations, such a dielectric ring can be part
of a composite ferrite/dielectric TM resonator, where the
dielectric replaces some of the ferrite. A high dielectric constant
material can be used to keep the diameter of the composite
approximately the same as a ferrite-only resonator at a desired
frequency. In some embodiments, such a dielectric material can have
a dielectric constant value between about 16 and 30, but are not
necessarily confined to that range. For example, a dielectric
constant value as high as about 50 can also be utilized. In some
implementations, such a dielectric can provide a non-magnetic gap
between the ferrite and the return path magnetic field to thereby
improve the IMD reduction performance over a configuration where
the ferrite extends further out to the return path.
[0051] Non-limiting examples of materials that can be utilized for
the various parts of the foregoing example circulator device 130
are described herein in greater detail.
[0052] As described herein (e.g., in reference to FIGS. 2A and 2B),
a disk-based circulator generally has an intrinsically symmetrical
RF field distribution in the ferrite disk. The static magnetic
field, however, can change considerably at the edge portion of the
ferrite disk. FIG. 4 shows such an example, where magnetization
vector directions are shown for a ferrite disk subjected to a
substantially uniform static magnetic field in the axial direction.
As seen in the axial view (along the Z direction), the vector
directions at or near the edge portion have significant radial
components.
[0053] It has been reported that interactions of intermodulation
signals in circulators occur primarily at the edge of the disks.
Such an effect is depicted in FIG. 5, where a rectangular loop
represents a coupling between an RF field and magnetization for an
intermodulation of signals associated with an input (port 1) and an
output (port 2). More particularly, such a coupling can contribute
to a third order intermodulation product having a frequency
2.omega..sub.1-.omega..sub.2, where .omega..sub.1 and .omega..sub.2
are the frequencies of the input and output signals,
respectively.
[0054] In some situations, and as described herein in reference to
FIG. 3, a static magnetic field can be distorted by the shape of
the magnet and/or the presence of a magnetic return path in the
circulator. In the example of FIG. 4, the deviation of
magnetization vector directions away from the axial direction along
the edge portion can be due to such a distortion.
[0055] In some situations, such a distortion can influence how well
saturated the edge of a ferrite is, and hence its susceptibility to
nonlinear behavior in the presence of RF fields. For example, a
reduced axial field at or near the ferrite's edge portion can
result in the ferrite to drop back towards the resonance absorption
peak, thereby increasing the insertion loss. At low microwave
frequencies relative to the ferrite's saturation magnetization
(also referred to as 4.pi.Ms or 4PiMs), low field loss is also
possible even above resonance.
[0056] In some situations, the foregoing nonlinear behavior can
result in intermodulation distortion (IMD) resulting from two or
more signals mixing within a device to produce undesirable
higher-order products. These unwanted higher-order signals can fall
within transmitting or receiving bands and cause interference (also
referred to as intermodulation distortion).
[0057] Accordingly, in some implementations, it is desirable to
control the magnetization of a ferrite based device so as to reduce
the amount of IMD. FIG. 6 shows a process 180 that can be
implemented to achieve such a feature. In block 182, a ferrite
material can be provided. In block 184, the ferrite material and/or
its surrounding can be configured to yield a desired magnetization
of the ferrite material when subjected to a static magnetic
field.
[0058] For the purpose of description herein, a circular disk
shaped ferrite material is utilized to demonstrate various features
of the disclosure. It will be understood, however, that one or more
features of the present disclosure can also be implemented in other
shaped ferrites, including, for example, a non-circular slab such
as a triangular shaped slab, as well as other non-slab shaped
objects.
[0059] In the context of a circular disk shaped ferrite, a process
190 of FIG. 7 can be a more specific example of the process 180 of
FIG. 6. In block 192, a ferrite disk can be provided. In block 194,
one or more surfaces of the ferrite disk can be treated to obtain a
desired magnetization when subjected to a static magnetic field. An
example of such a surface treatment is described herein in greater
detail.
[0060] In another example, a process 200 of FIG. 8 can be
implemented, where in block 202, a ferrite disk can be provided. In
block 204, one or more structures can be disposed at or near the
radial edge of the ferrite disk to obtain a desired magnetization
when subjected to a static magnetic field. An example of such a
structure is described herein in greater detail.
[0061] FIG. 9 shows that in some implementations, a circulator
device 210 can be configured to have one or more features that can
yield a desired magnetization of one or more ferrite disks 212,
214. One or more of the ferrite disks 212, 214 can have one or more
surfaces treated so as to yield or contribute to the desired
magnetization.
[0062] In the circulator device 210, a pair of cylindrical magnets
252, 254 is shown to provide a static magnetic field for
magnetization of the ferrite disks 212, 214. The magnetic field
flux that passes through the ferrite disks 212, 214 can complete
its circuit (depicted by arrows) through return paths provided by
264, 274, 272 and 262 so as to strengthen the field applied to the
ferrite disks 212, 214. In some embodiments, the return path
portions 264 and 262 can be disks having a diameter larger than
that of the magnets 252, 254; and the return path portions 274 and
272 can be hollow cylinders having an inner diameter that generally
matches the diameter of the return path disks 264, 262. The
foregoing parts of the return path can be formed as a single piece
or be an assembly of a plurality of pieces.
[0063] The example circulator device 210 can further include an
inner flux conductor 240 disposed between the two ferrite disks
212, 214. Such an inner conductor can be configured to function as
a resonator and matching networks to the ports (not shown).
[0064] The example circulator device 210 can also include a high
relative dielectric (Er) material 232, 234 disposed between the
edge portion of the ferrite disks 212, 214 and the return path
portions 272, 274. Such high Er dielectric material 232, 234 can be
formed as a ring dimensioned to fit within the inner walls of the
outer return path portions 272, 274.
[0065] In some implementations, the example circulator device 210
can include structures 222, 224 disposed at or near the edge
portions of the ferrite disks 212, 214. In the example shown, each
of the structures 222, 224 can be a ring dimensioned to fit between
the high Er dielectric ring (232 or 234) and the outer edge of the
ferrite disk (212 or 214).
[0066] In some implementations, each of the rings 222, 224 can be
formed from a material having a lower saturation magnetization
(4PiMs) than that of the ferrite disk (212 or 214). Combined, each
of the ferrite disk and the lower-4PiMs ring can yield a
magnetizable disk having a reduced 4PiMs at the edge portion. As
described herein, such a combination can yield a reduction in the
IMD of the circulator device 210.
[0067] Table 1 lists some non-limiting examples of materials or
features that can be utilized for the various parts of the
circulator 210 described in reference to FIGS. 3 and 9.
TABLE-US-00001 TABLE 1 Part(s) Example Material(s) and/or
Feature(s) Magnets (142, 144 in FIG. 3; Permanent magnets having
field strength 252, 254 in FIG. 9) sufficient to yield saturation
magnetization of ferrite disks when assembled. Return path (148,
152, 150, Steel, which is preferable when RF signals 146 in FIG. 3;
264, 274, 272, cause large eddy currents in good 262 in FIG. 9)
conductors such as soft iron. Inner conductor (140 in High RF
conductivity metal such as FIG. 3; 240 in FIG. 9) copper, brass,
silver etc. Ferrite disks (132, 134 in Yttrium iron garnet (YIG)
having a 4PiMs FIG. 3; 212, 214 in FIG. 9) of about 1780 Gauss
(referred to as "G113" herein) or any 4PiMs greater than the
ferrite rings 232, 234 High Er dielectric rings (136, Referred to
as "D30" herein. Dielectric 138 in FIG. 3; 232, 234 in constant
value can be between about 16 FIG. 9) and 30, or can be higher up
to about 50. Reduced-4PiMs rings (232, Garnet such as YIG with a
low 4PiMs of 234 in FIG. 9) about 1000 Gauss (referred to as
"G1010" or "G-1210" herein) or any 4PiMs significantly lower than
the ferrite disks 212, 214.
[0068] It will be understood that a number of other types of
materials and materials having different values or properties can
also be used to implement one or more features of the present
disclosure.
[0069] In the example described in reference to FIG. 9 and Table 1,
the reduced 4PiMs at the edge portion of a ferrite disk can be
provided by an addition of a ring having a lower 4PiMs value. Such
a ring configuration can be an example where the ferrite disk and
the ferrite ring form a ferrite assembly formed from separate
pieces. In some embodiments, a single-piece ferrite structure
(e.g., a disk) can also be used, where the single-piece structure
has two or more regions having different 4PiMs values. For example,
a center portion of a disk can have a first 4PiMs value, and an
edge portion can have a second 4PiMs value that is lower than the
first value.
[0070] To demonstrate improvements in IMD isolation performance
associated with one or more features of the present disclosure,
Applicant measured third order products resulting from two closely
spaced (in frequency) RF signals. An example of such an IMD is
depicted in FIG. 10, where two fundamental frequencies f.sub.1 and
f.sub.2 are relatively close to each other in frequency space.
Odd-numbered products form relatively close to the fundamentals;
and among such odd-numbered products, the third-order products are
typically the most dominant, and thus of greatest concern. Such
third-order products occur at frequencies centered at about
2f.sub.1-f.sub.2 and 2f.sub.2-f.sub.1.
[0071] Such IMDs can be formed and measured in a number of ways.
FIG. 11 shows an example test setup 300 where various
configurations of a circulator 302 can be tested. Two signal
generators can generate two fundamental signals having closely
spaced frequencies (f.sub.1 and f.sub.2). Each signal can be
conditioned (e.g., amplifier, dual isolator, and low-pass filter as
shown), then combined and fed into the circulator 302. An output
signal can be conditioned (e.g., attenuator and notch filter as
shown) and measured by, for example, a spectrum analyzer.
[0072] FIG. 12 shows examples of results obtained from the
foregoing investigation of the localization of the IMD effect. The
vertical scale denotes amplitude in dBc. The values of the various
bars shown correspond to average values of upper third-order peak
amplitudes.
[0073] The right-most bar ("G-113 Straight Ferrite") is for a
configuration similar to that of FIG. 3 without the dielectric
rings (136, 138). Moving to the left, the bar indicated as
"G-113/G-1210 Assembly" is for a configuration where a reduced
4PiMs ring (G-1210) is provided on the outside of the ferrite
(G-113). The bar indicated as "G-113/G-1210/D30 Triple Assy" is for
a configuration where both of the reduced 4PiMs ring (G-1210) and
the dielectric ring (D30) are provided on the outside of the
ferrite (G-113) (e.g., similar to FIG. 9). The bar indicated as
"G-113/D30 Assembly" is for a configuration the dielectric ring
(D30) is provided on the outside of the ferrite (G-113), but not
G-1210 (e.g., similar to FIG. 3). The left-most bar indicated as
"System IM" is representative of a detection limit of the
measurement system, and can be considered to be a theoretical
situation where no IMD contribution comes from the
circulator/isolator.
[0074] Experiments utilizing the foregoing circulator
configurations the example setup of FIG. 11 were performed at about
400 MHz and at about 900 MHz, with the fundamentals being separated
by about 5 MHz. The results depicted in FIG. 12 are for the 900 MHz
experiment; and following observations can be made. The presence of
the low magnetization ring (in the G-113/G-1210/D30 configuration)
resulted in an IMD reduction of about -92 dBc, which is an
improvement of about 5 dB in IMD isolation when compared to the
configuration without the low magnetization ring (G-113/D30) (about
-87 dBc). Without the low magnetization ring, the presence of the
dielectric ring (G-113/D30) performs better than the configuration
without the dielectric ring (G-112) (about -82 dBc). Without the
dielectric ring, the presence of the low magnetization ring
(G-113/G-1210) appears to make very little improvement over the
configuration without the low magnetization ring (G-113).
[0075] Relative to the "System IM" result (at about -97 dBc), the
G-113/G-1210/D30 configuration (about -92 dBc) shows the best
results among the configurations tested. When compared to the worst
of the example configurations (G-113 at about -82 dBc), the
improvement of about 10 dB can be realized. In some
implementations, an improvement of about 20 dB or more can also be
achieved.
[0076] In some implementations, a passive circulator device having
one or more features can be packaged as a modular device. An
example of such a device is shown in FIGS. 13A-13C. A circulator
module 500 can include a circulator 510 packaged in a housing 502.
Such a housing 502 can be configured to facilitate mounting of the
module 500, via, for example, mounting holes 504. The example
circulator 510 of the module 500 is a 3-port circulator; and RF
signals to and/or from the circulator 510 can be passed through
electrical contacts 512, 514, 516. Various dimensions of the
example circulator module 500 are listed in Table 2.
TABLE-US-00002 TABLE 2 Dimension reference Approximate dimension D1
25.4 mm D2 25.4 mm D3 20.8 mm D4 20.8 mm D5 2.3 mm D6 2.3 mm D7 7.6
mm D8 0.6 mm D9 12.7 mm D10 9.0 mm (max) D11 3.8 mm D12 2.8 mm D13
3.0 mm D14 1.3 mm
[0077] For the purpose of description, the example single junction
circulator module 500 described in reference to FIG. 13 and Table 2
is referred to as a SKYFR-000700 module. In some embodiments, the
compact dimension (about 25 mm.times.25 mm) module 500 can be
designed to operate in the GSM band of 925 MHz-960 MHz. As
described herein, some configurations of the SKYFR-000700 module
can achieve IMD performance of better than about -90dBc with two CW
tones of +47 dBm, spaced 5 MHz apart.
[0078] For the purpose of demonstrating such an improved IMD
performance, the SKYFR-000700 module was configured with a
circulator having a triple assembly similar to the configuration
described herein as G-113/G-1210/D30 and having G-113 ferrite
disks, reduced magnetization rings G-1210, and dielectric rings
D30. For comparison, a circulator device (referred to as MFR000xxx
herein) was configured with a circulator having a configuration
similar to that of G113/D30 described herein.
[0079] The foregoing circulator modules SKYFR-000700 and MFR000xxx
were tested in a setup similar to the setup described in reference
to FIG. 11 under two frequency conditions. The first test condition
was as follows: F1=925 MHz, +47 dBm, CW tone; F2=930 MHz, +47 dBm,
CW tone. The second test condition was as follows: F1=955 MHz, +47
dBm, CW tone; F2=960 MHz, +47 dBm, CW tone.
[0080] Table 3 shows examples of results obtained from the
foregoing IMD measurements.
TABLE-US-00003 TABLE 3 Approx. Approx. Frequency IMD Module (MHz)
(dBc) See FIG.(s) MAFR- 925 -73 FIG. 14A: MAFR-000xxx at 925 MHz
000xxx MAFR- 960 -73 FIG. 14B: MAFR-000xxx at 955 MHz 000xxx SKYFR-
925 -92 FIG. 14C: SKYFR-000700 at 925 MHz 000700 FIG. 14D:
SKYFR-000700, close up of third order product at 935 MHz FIG. 14E:
SKYFR-000700, close up of third order product at 920 MHz SKYFR- 960
-91 FIG. 14F: SKYFR-000700 at 955 MHz 000700 FIG. 14G:
SKYFR-000700, close up of third order product at 950 MHz FIG. 14H:
SKYFR-000700, close up of third order product at 965 MHz
As one can see, IMD performance improvements of the SKYFR-000700
circulator module over the MAFR-000xxx device is more than 10 dB at
all of the tested frequencies.
[0081] In the context of the carrier wave power as a reference, a
circulator having one or more features of the present disclosure
can be configured to provide a third-order IMD level of at least
approximately -85 dBc, -86 dBc, -87 dBc, -88 dBc, -89 dBc, -90 dBc,
-91 dBc, -92 dBc, -93 dBc, -94 dBc, -95 dBc, -96 dBc, or -97
dBc.
[0082] As described herein, one or more features of the present
disclosure can be utilized to achieve improved IMD performance in
the example GSM band. Such one or more features can also be
utilized to achieve similar improvements in IMD performance in
other GSM bands, other cellular band, and/or other non-cellular
frequency ranges.
[0083] FIG. 15 shows that in some embodiments, one or more
circulators or isolators described herein can be implemented in a
radio-frequency (RF) device 600. The example RF device 600 can
include a transceiver 604 having a transmitter 606 and a receiver
608. The transmitter 606 can be configured to generate an RF signal
based on signals received from a baseband sub-system 602. The RF
signal generated by the transmitter 606 is shown to be amplified by
a power amplifier (PA) 610; and the amplified RF signal is shown to
be sent to an antenna 614.
[0084] In the example RF device 600, the antenna 614 is shown to
receive an incoming RF signal; and the received signal is routed to
an low-noise amplifier (LNA) 612. The amplified received signal is
then sent to the receiver 608 for processing; and the processed
signal can be passed on to the baseband sub-system 602.
[0085] In the foregoing path between the transmitter 606 and the PA
610, an isolator 210 can be provided to isolate the to-be-amplified
RF signal as it goes from port 1 to port 2. Such an isolation can
be achieved by connecting port 3 to an appropriately configured
termination path.
[0086] Similarly, in the foregoing path between the LNA 612 and the
receiver 608, an isolator 210 can be provided to isolate the
LNA-amplified signal as it goes from port 2 to port 1. Such an
isolation can be achieved by connecting port 3 to an appropriately
configured termination path.
[0087] In the foregoing example where the antenna 614 is shared for
both transmit and receive operations, routing of the amplified
signal (from the PA 610) and the received signal (to the LNA 612)
can be facilitated by a circulator 210 as shown. In the example,
port 2 is shown to be connected to the PA 610, port 2 is shown to
be connected to the antenna 614, and port 3 is shown to be
connected to the LNA 612. Thus, the amplified signal from the PA
610 enters port 1 of the circulator 210 and exits at port 2 to be
routed to the antenna 614. The received signal from the antenna 614
enters port 2 of the circulator 210 and exits at port 3 to be
routed to the LNA 612.
[0088] In some implementations, at least some of the isolators
and/or the circulator of FIG. 15 can include one or more features
as described herein to reduce IMD distortions. In some embodiments,
the example circulator 210 can benefit especially due to the same
device handling both transmit and receive signals thereby creating
a condition susceptible to IMDs.
[0089] In some embodiments, the RF device 600 can include a
wireless device. Such a wireless device can include a portable
device, or a device configured for stationary systems such as a
base station.
[0090] FIGS. 16A-16C show various views of an example ferrite-based
disk having one or more features described herein, and how such a
disk can be assembled. In an assembled form (FIGS. 16A and 16B), an
example ferrite-based disk 700 is shown to include a ferrite center
piece 212 which is surrounded by a ring 222 having a lower 4PiMs
value than that of the ferrite center 212. The reduced 4PiMs ring
222 is shown to be surrounded by a dielectric ring 232. The disk
700 can be one of the two disks (212, 222, 232; and 214, 224, 234)
described in reference to FIG. 9.
[0091] FIG. 16B shows that when assembled, the ferrite center 212
and the reduced 4PiMs ring 222 form a joint 702. Similarly, the
reduced 4PiMs ring 222 and the dielectric ring 232 form a joint
704. Depending on how the pieces are assembled, such joints can be
formed by, for example, an adhesive, shrink-fitting one part around
another, and/or press-fitting.
[0092] FIG. 16C shows that the unassembled pieces 212, 222, 232 can
be dimensioned appropriately to accommodate one or more assembly
techniques. The ferrite center piece 212 is shown to have an
overall diameter of d1. The reduced 4PiMs ring is shown to have an
inner diameter of d2 and an outer diameter of d3. The dielectric
ring is shown to have an inner diameter of d4 and an outer diameter
of d5.
[0093] By way of examples, if the ferrite center piece 212 and the
reduced 4PiMs ring 222 are to be press-fitted, then both can be
sintered appropriately to yield desired physical properties and
shrinkage, and then machined so that the dimensions d1 and d2 allow
press-fitting. In another example, if the same pieces are to be
assembled by an adhesive, the dimensions d1 and d2 can be selected
to accommodate such an adhesive.
[0094] In yet another example, suppose that the dielectric ring 232
is to be shrunk-fit around an assembly of the reduced 4PiMs ring
and the ferrite center (e.g., press-fit together with pre-shrunk
pieces). The inner diameter dimension d4 of the dielectric ring 232
in its unfired condition can be selected to be larger than the
outer diameter d3 of the reduced 4PiMs ring 222 in its fired
condition, to allow the outer ring to slip over the inner ring.
Then, firing of the assembly can shrink the outer ring (232) over
the inner ring (222). Additional details concerning such
"co-firing" methods can be found in U.S. Pat. No. 7,687,014, titled
"CO-FIRING OF MAGNETIC AND DIELECTRIC MATERIALS FOR FABRICATING
COMPOSITE ASSEMBLIES FOR CIRCULATORS AND ISOLATORS," which is
hereby incorporated herein by reference in its entirety.
[0095] FIG. 17 shows that in some implementations, the
ferrite-based disk 700 of FIG. 16 can be obtained by first
assembling longer pieces to yield a longer assembly 710. Then, a
plurality of disks 700 can be cut from the longer assembly 710.
Such cutting can be achieved in a number of known ways, and the cut
disks 700 can be finished to yield, for example, desired finish
and/or dimensions.
[0096] Unless the context clearly requires otherwise, throughout
the description and the claims, the words "comprise," "comprising,"
and the like are to be construed in an inclusive sense, as opposed
to an exclusive or exhaustive sense; that is to say, in the sense
of "including, but not limited to." The word "coupled", as
generally used herein, refers to two or more elements that may be
either directly connected, or connected by way of one or more
intermediate elements. Additionally, the words "herein," "above,"
"below," and words of similar import, when used in this
application, shall refer to this application as a whole and not to
any particular portions of this application. Where the context
permits, words in the above Detailed Description using the singular
or plural number may also include the plural or singular number
respectively. The word "or" in reference to a list of two or more
items, that word covers all of the following interpretations of the
word: any of the items in the list, all of the items in the list,
and any combination of the items in the list.
[0097] The above detailed description of embodiments of the
invention is not intended to be exhaustive or to limit the
invention to the precise form disclosed above. While specific
embodiments of, and examples for, the invention are described above
for illustrative purposes, various equivalent modifications are
possible within the scope of the invention, as those skilled in the
relevant art will recognize. For example, while processes or blocks
are presented in a given order, alternative embodiments may perform
routines having steps, or employ systems having blocks, in a
different order, and some processes or blocks may be deleted,
moved, added, subdivided, combined, and/or modified. Each of these
processes or blocks may be implemented in a variety of different
ways. Also, while processes or blocks are at times shown as being
performed in series, these processes or blocks may instead be
performed in parallel, or may be performed at different times.
[0098] The teachings of the invention provided herein can be
applied to other systems, not necessarily the system described
above. The elements and acts of the various embodiments described
above can be combined to provide further embodiments.
[0099] While certain embodiments of the inventions have been
described, these embodiments have been presented by way of example
only, and are not intended to limit the scope of the disclosure.
Indeed, the novel methods and systems described herein may be
embodied in a variety of other forms; furthermore, various
omissions, substitutions and changes in the form of the methods and
systems described herein may be made without departing from the
spirit of the disclosure. The accompanying claims and their
equivalents are intended to cover such forms or modifications as
would fall within the scope and spirit of the disclosure.
* * * * *