U.S. patent application number 13/632911 was filed with the patent office on 2014-09-11 for increasing the minimum rejection bandwidth of a yig-tuned notch filter using a shunt yig resonator.
The applicant listed for this patent is Teledyne Wireless, LLC. Invention is credited to Marinus L. Korber.
Application Number | 20140253261 13/632911 |
Document ID | / |
Family ID | 50384594 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140253261 |
Kind Code |
A2 |
Korber; Marinus L. |
September 11, 2014 |
INCREASING THE MINIMUM REJECTION BANDWIDTH OF A YIG-TUNED NOTCH
FILTER USING A SHUNT YIG RESONATOR
Abstract
A Yttrium Iron Garnet (YIG) tuned band reject filter using one
or more Shunt YIG resonators provides for much wider minimum
rejection bandwidths without increasing maximum 3 db bandwidths or
spurious response. Various configurations of a tunable shunt YIG
tuned band reject filter achieves a wide rejection bandwidth at the
low end of the tuning range while keeping the maximum 3 db
bandwidth, normally occurring at the high end of the tuning range,
to a minimum.
Inventors: |
Korber; Marinus L.; (San
Carlos, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Teledyne Wireless, LLC |
Thousand Oaks |
CA |
US |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20140091882 A1 |
April 3, 2014 |
|
|
Family ID: |
50384594 |
Appl. No.: |
13/632911 |
Filed: |
October 1, 2012 |
Current U.S.
Class: |
333/202;
333/219.2 |
Current CPC
Class: |
H03H 2007/013 20130101;
H01P 1/201 20130101; H01P 1/218 20130101 |
Class at
Publication: |
333/202;
333/219.2 |
International
Class: |
H01P 1/20 20060101
H01P001/20 |
Claims
1. A filter, comprising: a plurality of Yttrium Iron Garnet (YIG)
resonators arranged in series; and at least one YIG resonator
configured as at least one shunt to the plurality of YIG resonators
arranged in series to provide a tunable filter.
2. The filter of claim 1, wherein the plurality of YIG resonators
comprise a plurality of stages of a band reject filter.
3. The filter of claim 2, wherein each stage includes an impedance
inverter.
4. The filter of claim 3, wherein each stage further includes at
least one of an inductor and a capacitor.
5. The filter of claim 3, wherein the inverter comprises a quarter
wave impedance inverter.
6. The filter of claim 2, wherein each stage includes at least one
of an inductor and a capacitor.
7. The filter of claim 1, wherein the tunable filter comprises a
band reject filter.
8. The filter of claim 1, wherein said at least one YIG resonator
is configured as a shunt resonator to ground.
9. The filter of claim 1, wherein said at least one YIG resonator
comprises an end shunt resonator.
10. The filter of claim 1, wherein said at least one YIG resonator
comprises two YIG resonators each configured as an end shunt
resonator.
11. The filter of claim 1, wherein said at least one YIG resonator
comprises a shunt resonator, the shunt resonator configured to be
connected between two of the series YIG resonators.
12. The filter of claim 1, wherein said at least one YIG resonator
comprises a plurality of shunt resonators, at least one of the
plurality of shunt resonators connected between at least one pair
of series YIG resonators.
13. The filter of claim 1, wherein said at least one YIG resonator
comprises a plurality of shunt resonators, each of the plurality of
shunt resonators connected between different pairs of series YIG
resonators.
14. The filter of claim 1, wherein the tunable filter comprises a
band reject filter having a notch that decreases in depth as
frequency increases.
15. The circuit of claim 14, wherein the tunable filter comprises a
band reject filter having a low impedance at resonance and a wider
minimum rejection bandwidth while having a narrower maximum 3 db
bandwidth, as compared with a series only YIG filter.
16. A filter, comprising: a plurality of impedance inverters in
series; and at least one shunt Yttrium Iron Garnet (YIG) resonator
connected between at least two of the plurality of impedance
inverters.
17. The filter of claim 16, further comprising at least one of: a
capacitor and an inductor connected between the at least one shunt
YIG resonator and at least one of the two impedance inverters.
18. The filter of claim 16, further comprising at least one YIG
resonator connected in series with the plurality of impedance
inverters.
19. The filter of claim 16, wherein at least one of the plurality
of inverters comprises a quarter wave impedance inverter.
20. The filter of claim 16, wherein the plurality of impedance
inverters comprises at least three impedance inverters and the at
least one shunt YIG resonator comprises at least two shunt YIG
resonators, each of the at least two shunt resonators connected
between a pair of impedance inverters.
21. The filter of claim 16, wherein the filter comprises a band
reject filter.
22. A device utilizing the circuit of claim 1, wherein the device
comprises one of a communication device, a signal processing
device, a microwave device, a wireless transmission device, a
wireless reception device or an imaging device.
23. A device utilizing the circuit of claim 16, wherein the device
comprises one of a communication device, a signal processing
device, a microwave device, a wireless transmission device, a
wireless reception device or an imaging device.
24. A filter comprising: a plurality of Yttrium Iron Garnet (YIG)
resonators arranged in series; and at least one YIG resonator
configured as at least one shunt to the plurality of YIG resonators
arranged in series to provide a tunable filter, wherein the tunable
filter provides a notch that decreases in depth and width as
frequency increases.
25. The filter of claim 24, wherein the tunable filter provides a
minimum rejection bandwidth that increases while the maximum 3 dB
notch bandwidth over a tuning band decreases.
Description
BACKGROUND OF THE DISCLOSURE
[0001] 1.0 Field of the Disclosure
[0002] The disclosure is directed generally to a method and
apparatus for tunable notch filters and, more particularly, to a
method and apparatus for microwave tunable notch filters, tunable
oscillators and tunable filters, and the like, employing Yttrium
Iron Garnet (YIG) spheres.
[0003] 2.0 Related Art
[0004] Yttrium Iron Garnet (YIG) filters may include YIG tuned band
pass or YIG tuned band reject filters. YIG tuned band reject
filters may be know also as YIG tuned notch filters. A fixed tuned
non-YIG notch filter is used throughout the realm of electronics.
For example, a non-YIG notch filter might be used to block data
noise in household digital subscriber line (DSL) systems. Also, a
non-YIG notch filter may also be used as a fixed frequency filter
in sophisticated microwave systems to block an unwanted high power
signal while passing another signal at a close frequency.
[0005] YIG tuned notch filters serve a similar purpose in the
microwave realm, e.g., about 500 MHz to about 50 GHz. A basic
difference, however, is the ability if a YIG tuned notch filter to
tune over a wide frequency range and not just reject a "fixed" band
of frequencies, as occurs in fixed tuned non-YIG notch filter, for
example. In one aspect, it is this frequency agility of YIG tuned
filters that make this technology advantageous and appealing.
[0006] In a military application, such as a self-protection jammer,
for example, the YIG tuned notch filter may be part of a system
that protects the aircraft's surveillance receiver from being
overloaded or damaged by the airplane's own high power fire control
radar, and since the fire control radar may be "hopping around" to
different frequencies, the YIG notch filter may be an ideal
protection device since, in turn, it can be tuned to these
frequencies and jam a high power signal.
[0007] A notch filter, fixed tuned or YIG tuned has both a pass
band and a stop band or notch. The pass band is typically very wide
and is the band over which the input RF-signal may pass with the
lowest possible attenuation. The stop band (the notch) is typically
very narrow, relative to the pass band, and in the case of a YIG
tuned notch filter, the frequency range over which the notch tunes
may or may not be coincident with the pass band range, but will
always be within the pass band tuning range.
[0008] Accordingly, there is a need for a better technique for
providing a YIG tuned notch filter in which the minimum rejection
bandwidth increases while the maximum 3 dB Notch bandwidth over the
tuning band decreases.
SUMMARY OF THE INVENTION
[0009] The disclosure meets the foregoing need and provides for an
improved YIG tuned band reject filter. The improved YIG band reject
filter provides a much reduced ratio between the minimum rejection
bandwidth and the maximum 3 dB bandwidth across the entire band. By
arranging some or all YIG resonators in a shunt resonance
configuration, a new type of YIG tuned band reject filter with a
much wider minimum reject bandwidth (as compared with prior
available filters) may be achieved. Moreover, a much narrower
maximum 3 dB bandwidth and much lower tracking spur amplitude may
be achieved.
[0010] In one aspect, a filter is provided comprising a plurality
of Yttrium Iron Garnet (YIG) resonators arranged in series and at
least one YIG resonator configured as at least one shunt to the
plurality of YIG resonators arranged in series to provide a tunable
filter. The tunable filter may comprise a band reject filter having
a wider minimum rejection bandwidth while having a narrower maximum
3 db bandwidth, as compared with a conventional YIG Tuned Notch
filter in which all the YIG resonators are connected in series.
[0011] In one aspect a filter may be provided that includes a
plurality of impedance inverters in series, and at least one shunt
Yttrium Iron Garnet (YIG) resonator connected between at least two
of the plurality of impedance inverters.
[0012] In one aspect, a filter is provided that includes a
plurality of Yttrium Iron Garnet (YIG) resonators arranged in
series and at least one YIG resonator configured as at least one
shunt to the plurality of YIG resonators arranged in series to
provide a tunable filter, wherein the tunable filter provides a
notch that decreases in depth and width as frequency increases.
[0013] Additional features, advantages, and embodiments of the
disclosure may be set forth or apparent from consideration of the
following detailed description, drawings, and claims. Moreover, it
is to be understood that both the foregoing summary of the
disclosure and the following detailed description are exemplary and
intended to provide further explanation without limiting the scope
of the disclosure as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings, which are included to provide a
further understanding of the disclosure, are incorporated in and
constitute a part of this specification, illustrate embodiments of
the disclosure and together with the detailed description serve to
explain the principles of the invention. No attempt is made to show
structural details of the disclosure in more detail than may be
necessary for a fundamental understanding of the disclosure and the
various ways in which it may be practiced. In the drawings:
[0015] FIG. 1A is an illustration of a YIG resonator in magnetic
air gap, according to the prior art;
[0016] FIG. 1B is a schematic of an equivalent circuit of FIG.
1A;
[0017] FIG. 1C is a schematic showing an equivalent circuit of FIG.
1B above resonance;
[0018] FIG. 2 is an exemplary graph illustratively showing the
simulated electrical behavior of a YIG resonator as a one port
circuit showing both real and imaginary part of the YIG resonator
frequency response;
[0019] FIGS. 3A-3C are schematics of a shunt connected YIG
resonator, according to principles of the invention;
[0020] FIGS. 4A-4D are graphs showing measured frequency response
of the conventional 500 MHz to 2 GHz YIG tuned band reject
resonator of FIGS. 1A-1C;
[0021] FIGS. 5A-5D are graphs representing measured results of the
tunable band reject filter of FIGS. 3A-3C;
[0022] FIG. 6 shows an example schematic drawing of a seven stage
conventional YIG tuned band reject filter, according to the prior
art;
[0023] FIG. 7 shows an example schematic drawing of a seven stage
tuned YIG band reject filter, configured according to principles of
the invention;
[0024] FIG. 8 shows the measured frequency response of the
conventional YIG tuned band reject filter of FIG. 6, and also the
measured frequency response of the seven stage tuned YIG band
reject filter of FIG. 7, centered at about 500 MHz;
[0025] FIG. 9 shows the measured frequency response of the
conventional YIG tuned band reject filter of FIG. 6, and also the
measured frequency response of the seven stage tuned YIG band
reject filter of FIG. 7, centered at about 1000 MHz;
[0026] FIG. 10 shows the measured frequency response of the
conventional YIG tuned band reject filter of FIG. 6, and also the
measured frequency response of the seven stage tuned YIG band
reject filter of FIG. 7, centered at about 2000 MHz;
[0027] FIG. 11 shows the measured frequency response of the
conventional YIG tuned band reject filter of FIG. 6, and also the
measured frequency response of the seven stage tuned YIG band
reject filter of FIG. 7, centered at about 2600 MHz;
[0028] FIG. 12 shows an example of a schematic of a tunable shunt
YIG tuned band reject filter, configured according to principles of
the invention;
[0029] FIG. 13 shows an example of a schematic of a tunable shunt
YIG tuned band reject filter, configured according to principles of
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0030] It is understood that the disclosure is not limited to the
particular methodology, protocols, etc., described herein, as these
may vary as the skilled artisan will recognize. It is also to be
understood that the terminology used herein is used for the purpose
of describing particular examples only, and is not intended to
limit the scope of the disclosure. It is also to be noted that as
used herein and in the appended claims, the singular forms "a,"
"an," and "the" include the plural reference unless the context
clearly dictates otherwise. Thus, for example, a reference to "a
YIG resonator" may be a reference to one or more YIG resonators and
equivalents thereof known to those skilled in the art.
[0031] Unless otherwise defined, all technical and scientific terms
used herein have the same meanings as commonly understood by one of
ordinary skill in the art to which the disclosure pertains. The
examples of the disclosure and the various features and
advantageous details thereof are explained more fully with
reference to the non-limiting examples that are described and/or
illustrated in the accompanying drawings and detailed in the
following description. It should be noted that the features
illustrated in the drawings are not necessarily drawn to scale, and
features of one example may be employed with other examples as the
skilled artisan would recognize, even if not explicitly stated
herein. Descriptions of well-known components and processing
techniques may be omitted so as to not unnecessarily obscure the
examples of the disclosure. The examples used herein are intended
merely to facilitate an understanding of ways in which the
disclosure may be practiced and to further enable those of skill in
the art to practice the examples of the disclosure. Accordingly,
the examples herein should not be construed as limiting the scope
of the invention, which is defined solely by the appended claims
and applicable law. Moreover, it is noted that like reference
numerals reference similar parts throughout the several views of
the drawings.
[0032] In general, for many applications, a significant requirement
for a YIG tuned notch filter is to have a wide minimum rejection
bandwidth, typically at the 40 db rejection point, although it
could be at other rejection points such as the 30 dB or the 50 dB,
depending on a specific application requirement, for example.
Another significant requirement of the same YIG tuned notch filter
may include that the maximum 3 dB bandwidth throughout the band be
kept to a minimum. Moreover, another significant requirement for a
YIG tuned notch filter may include that the tracking spur amplitude
be kept to a minimum. In prior art solutions, these requirements
typically conflict with each other. In the prior art, coupling a
YIG-tuned band reject filter for a wider minimum rejection
bandwidth has a detrimental effect filter performance by widening
the 3 dB bandwidth and increasing tracking spur amplitude.
[0033] In one aspect, the present disclosure provides an improved
YIG tuned band reject filter that is configured to provide a much
reduced ratio between the minimum rejection bandwidth and maximum 3
dB bandwidth across the entire band. By using one or more YIG
resonators in a shunt resonance configuration, a new type of YIG
tuned band reject filter with a much wider minimum rejection
bandwidth (compared to prior art filters) and at the same time a
much narrower maximum 3 dB bandwidth and much lower tracking spur
amplitude may be achieved.
[0034] FIG. 1A is an illustration of a YIG resonator in magnetic
air gap; FIG. 1B is a schematic of an equivalent circuit of FIG.
1A, and FIG. 1C is a schematic showing an equivalent circuit of
FIG. 1B above resonance. The inductor, capacitor and resistor of
the YIG resonator equivalent circuit of FIG. 1B represent intrinsic
inductor, capacitor and resistor values of the YIG resonator. The
actual values of the inductor, capacitor and resistor of the YIG
resonator may be understood to be dependent on factors such as
resonator size, unloaded Q, operating frequency, and other factors
such as coupling loop diameter. The YIG resonator of FIGS. 1A-1C
may be serially connected between a source and a load.
[0035] FIG. 1A illustrates a physical representation of a single
resonator in a magnet air gap that may comprise an electromagnetic
with air gap, and a single YIG sphere surrounded by a wire
"coupling loop." The YIG sphere inside the wire loop in FIGS. 1A
and 1B may be serially connected between a source and load such as
represented by the respective source and load resistors. The
parallel resonant circuit if FIG. 1B represents the YIG resonator.
The YIG resonator resonant frequency is a linear function of the
magnetic field strength in the air gap. The input impedance of the
parallel resonant circuit of FIG. 1B is very high at resonance and
very low away from resonance. Therefore, it makes a suitable
tunable notch filter, as the high impedance at resonance of the
circuit of FIG. 1B blocks a narrow band of frequencies from passing
from the source to the load through the resonator, and the narrow
band to be blocked can be different depending on the frequency to
which the YIG sphere is tuned. The low impedance outside of
resonance passes signals with little attenuation.
[0036] FIG. 1C shows the electrically equivalent circuit of the YIG
parallel resonance on the high side of the resonance center
frequency. The high side of the YIG resonance, or of any parallel
resonant circuit, behaves like a frequency sensitive capacitor. The
capacitance is in series with the YIG coupling loop inductance. The
series combination forms a series resonant circuit. The series
resonance shown in FIG. 1C may not be very significant in standard
prior art performance YIG tuned reject performance, but is a
significant aspect for a shunt YIG tuned band reject filter, when
configured according to principles of the invention.
[0037] FIG. 2 is an exemplary graph illustratively showing the
simulated electrical behavior of a YIG resonator as a one port
circuit showing real and imaginary part of the YIG resonator
frequency response. The graph of FIG. 2 is a simulation of circuit
B of FIG. 2, which is an equivalent circuit of the physical circuit
A of FIG. 2, while circuit C of FIG. 2 represents the electrical
equivalent of circuit B above resonance. Circuit B is electrically
equivalent of circuit A and comprises a wire YIG coupling loop
inductance in series with the YIG sphere (resonator) parallel
resonant circuit represented schematically by an inductance, a
capacitance and a resistance in parallel. The parallel resonance
circuit represents the YIG resonator. Below resonance, a parallel
resonant circuit looks like a frequency sensitive inductor. At
resonance, a parallel resonator has a purely resistive impedance.
Above resonance, the YIG resonator of circuit A and circuit B looks
like a frequency sensitive capacitor. Above resonance, the coupling
loop inductance and that equivalent above resonance capacitance
form the series resonance circuit C. A parallel resonator looks
like a frequency sensitive capacitor above resonance, which is a
significant aspect to understanding the principles of the
invention.
[0038] The graph of FIG. 2 shows a real part of the input
impedance, RE(ZIN), as line 10 and also an imaginary part of the
input impedance, IM(ZIN), as line 15. The imaginary part 15 of the
input impedance IM(ZIN) of the YIG parallel resonator is inductive
below resonance and capacitive above resonance. The wire coupling
loop has inductance. The YIG resonator as noted above and seen in
the graph of FIG. 2 looks like a capacitor on the high-side of the
YIG's parallel resonance. The combination of the coupling loop
inductance in series with the equivalent capacitance on the
high-side of the YIG resonance form a series resonance circuit as
shown in circuit C of FIG. 2. This series resonance remains at a
substantially fixed offset from the center frequency of the main
YIG resonance as it tunes over any particular frequency range. This
series resonance may be seen on the graph of FIG. 2 where the
imaginary part of the impedance travels through zero. This series
resonance remains at a substantially fixed offset from the main YIG
resonance as the main resonance is tuned through the band. This
series resonance is well known in the art and is generally
considered an unwanted parasitic that degrades the performance of
YIG tuned band pass filters and plays a small role in notch shape
of prior art YIG-tuned band reject filters. However, this series
resonance provides a significant aspect to understanding the
principles for a shunt YIG-tuned band reject filter configured
according to principles of the invention.
[0039] FIGS. 3A-3C are schematics of a shunt connected YIG
resonator, according to principles of the invention. FIG. 3A shows
a physical representation of a YIG sphere inside a coupling loop
placed in shunt with a source and load. FIG. 3B is an electrical
schematic and is the equivalent circuit of FIG. 3A. FIG. 3C is a
schematic of an equivalent of FIG. 3B when modeled above the center
of FIG. 3B's main resonance, and is also a resonant circuit as
understood by those skilled in the art. FIG. 3C is a series
resonant circuit placed in shunt with a source and load. A series
resonance circuit acts like a low impedance at resonance. This low
impedance reflects much of the energy coming from the source back
to the source and blocks it from reaching the load. Some energy is
also dissipated in the resonator. Also, since the series resonance
of FIG. 3C is a result of the YIG coupling loop inductance
resonating with the YIG resonator's high side capacitance, it
provides a tunable band reject or notch filter. The notch depth and
notch width decreases with increasing frequency. This behavior
(decreasing notch depth with increasing frequency) may be explained
by the fact that the impedance of the YIG resonator at resonance
and off resonance, at a fixed offset, increases with increasing
frequency. The measured notch frequency response of the shunt band
reject filter of FIG. 3B is explained more fully in reference to
FIGS. 5A-5D below.
[0040] FIGS. 4A-4D are graphs showing measured frequency response
(S21) of the band reject filter of FIG. 1B. FIGS. 4A-4D show an
example of a resulting notch of the series connected YIG resonator
of FIG. 1B as a function of frequency. The resulting notch of these
examples may be centered at, for example, 500 MHz, 750 MHz, 1000
MHz and 2000 MHz respectively. The minimum notch depth always takes
place at the low end of the tuning range, in this series of
examples, at about 500 MHz shown in FIG. 4A, and the maximum notch
depth always takes place at the high end, in this example, at about
2 GHz as shown in FIG. 4D. The series YIG resonance may have a high
impedance at resonance thereby resulting in a notch that increases
in depth with increasing frequency (e.g., from 500 MHz of FIG. 4A
to 2000 MHz of FIG. 4D). This behavior (increasing notch depth with
increasing frequency) may be explained by the fact that the
impedance of the YIG resonator at resonance and off resonance
increases with increasing frequency. The divisions of the y-axis
each represent e.g., 5 db and the divisions of the x-axis each may
represent e.g., 10 MHz in FIGS. 4A-4D.
[0041] FIGS. 5A-5D are graphs representing measured notch frequency
response of the shunt connected YIG resonator of FIG. 3B, according
to principles of the invention. This is the measured frequency
response (S21) of a single shunt resonator YIG tuned band reject
filter. Unlike the prior art circuitry frequency response shown in
FIGS. 4A-4D, the shunt connected YIG resonator of FIG. 3B has its
maximum notch depth and bandwidth at the low end of the tuning
range (see, FIG. 5A) and the notch depth and notch bandwidth
decrease with increasing frequency (see, FIGS. 5B-5D). This
behavior (i.e., decreasing notch depth with increasing frequency)
may be explained by the fact that the impedance of the YIG
resonator at resonance and off resonance, at a fixed offset,
increases with increasing frequency. The divisions of the y-axis
may represent 5 db and the divisions of the x-axis represent e.g.,
10 MHz in FIGS. 4A-4D.
[0042] FIG. 6 shows an example schematic drawing of a seven stage
conventional YIG tuned band reject filter 100, according to the
prior art. Practical YIG tuned band reject filters of the prior art
may have many single resonators, e.g., multiple single resonator
band reject filters of FIGS. 1A and 1B connected in series. (A
single resonator band reject filter of FIGS. 1A and 1B typically
does not have a wide enough rejection bandwidth or notch depth to
serve usefully in typical applications where a wide notch bandwidth
and deep notch are required to block interfering signals). This
series configuration may create a notch filter with a much wider
rejection bandwidth and notch depth. The seven stage conventional
YIG tuned band reject filter 100 may comprise YIG resonators
20a-20g, quarter wave impedance inverters 25b-25g, YIG resonator
coupling loops 30a-30g and input/output matching lines 25a and 25h.
The filter 100 is an example of a prior art filter that may have a
notch that can tune from about 500 MHZ to about 2.6 GHZ. The YIG
resonators 20a-20g may be separated by a length of transmission
line that is a quarter wave long toward the upper end of the tuning
range and may serve as an impedance inverter between YIG resonators
20a-20g and also part of the matching network to insure a low loss
pass band. The measured frequency response of the prior art filter
100 of FIG. 6 is shown in relation to FIGS. 8-11, as explained more
fully below. FIGS. 8-11 also show the measured frequency response
of circuit 120 of FIG. 7, which is configured according to
principles of the invention, as explained more fully below.
[0043] YIG tuned band reject filters are typically specified to
have a minimum rejection bandwidth and a maximum 3 dB bandwidth in
the entire tuning band. The filter 100 of FIG. 6 is an example of
the state of the prior art. The filter 100 has a minimum 40 dB
rejection bandwidth of 4.4 MHz at 500 MHz center frequency. The
filter bandwidth, both rejection bandwidth and the 3 dB bandwidth,
grow as the notch is tuned to higher frequencies. The minimum
rejection bandwidth, 4.4 MHz at the 40 dB point at 500 MHz center
frequency, and the maximum 3 dB bandwidth of 220 MHz occurring at
the high end of the tuning range at 2600 MHz can be seen in FIGS.
8-11.
[0044] FIG. 7 shows an example schematic drawing of a seven stage
YIG-tuned band reject filter, configured according to principles of
the invention. The filter 120 of FIG. 7 uses two shunt resonators
35a and 35b in order to achieve a much wider minimum rejection
bandwidth. Essentially, the first and last YIG resonator of FIG. 6
have been replaced by shunt YIG resonators 35a and 35b. The filter
120 of FIG. 7 is a still seven stage YIG-tuned filter, albeit
improved, but now comprising five serially connected YIG resonators
20a-20e, two shunt resonators 35a, 35b, series resonator coupling
loop inductors 30b-30f, shunt resonator loop inductors 30a, 30g,
matching capacitors 40, and input-output matching lines 25a and
25g. Using this topology, several prototypes were built and tested,
all of the serially connected resonators are very de-coupled
relative to how tightly they were coupled in regard to circuit 100
of FIG. 6 in order to achieve the needed bandwidth in the filter
100 of FIG. 6.
[0045] In the filter 120 that is configured with shunt resonators
35a, 35b, the interior five serially connected resonators 20a-20e
contribute very little to the low end (500 MHz) rejection
bandwidth, while still having usable bandwidth at the high end,
i.e., about 2600 MHz. The input and output shunt resonators 35a,
35b have a very wide and deep notch at 500 MHz (FIG. 5A) relative
to the shallow notch of the prior art resonator (as shown in FIG.
4A). This may assure that the 500 MHz notch depth and notch
bandwidth of the full seven stage YIG tuned band reject filter 120
are very deep and wide even though all the series resonators
20a-20e are very decoupled to minimize the tracking spur
contributions as the filter 120 tunes towards to upper band
frequencies and finally to about 2600 MHz. So, the normally very
tight coupling needed to achieve wide minimum rejection bandwidth
with a prior art series connected YIG tuned band reject filter is
no longer needed once the end serial resonator(s) are replaced by a
shunt resonator (e.g., 35a, 35b), according to principles of the
invention. Now, very light coupling may be used on the serial
resonators (e.g., 20a-20e), thereby greatly reducing the amplitude
of the tracking spurs that widen the 3 dB bandwidth over most of
the tuning band. The very low end (e.g., 500 MHz) rejection
bandwidth due to the five serially connected resonators 20a-20e is
compensated for by the very deep notch depth and wide rejection
bandwidth that the two shunt resonators 35a, 35b contribute.
[0046] The frequency response (S21) of filter 120 is shown as line
130 and the frequency response of filter 100 of the prior art is
shown as line 135 at multiple frequencies in FIGS. 8-11. The two
frequency responses overlap. Although a 500 MHz-2600 MHz prototype
unit was constructed (i.e., filter 120) and tested to demonstrate
the principles of the invention, the principles of the invention
are not limited to this frequency range (i.e., 500 MHz-2600 MHz).
Rather, the principles of the invention may provide a substantial
improvement over the prior art at any frequency range that a
YIG-tuned band reject filter, or similar YIG based devices, can be
implemented.
[0047] The minimum rejection bandwidth at 500 MHz of filter 120 of
FIG. 7 is about 8.7 MHz, twice that of the prior art filter 100 of
FIG. 6 which is about 4.4 MHz at the 40 dB rejection point. At the
same time, the maximum 3 dB bandwidth of the filter 120 of FIG. 7
is less than half that of the prior art filter 100 of FIG. 6. The
prior art filter 100 has a 3 dB bandwidth of about 220 MHz at 2600
MHz, and the filter 120 of FIG. 7 has a 3 dB bandwidth of only
about 103 MHz at 2600 MHz.
[0048] The plots of FIGS. 8-11 (i.e., lines 130, 135) were recorded
by conventional lab test equipment (not shown) which had limited
dynamic range. The test equipment employed to measure the frequency
responses shown in FIGS. 8-11 included: a HP 8350B Sweep
Oscillator, a HP8757C Scalar Network Analyzer, a HP 6205C Dual DC
power supply, and an XL Microwave Sweeping Current Supply. Minimum
notch depth was measured with an Agilent N5320C Network Analyzer;
the minimum notch depth, for the filter 120 as plotted in FIGS.
8-11, occurring at 500 MHZ center frequency is 75 dB.
[0049] FIG. 8 shows the measured frequency response of the
conventional YIG tuned band reject filter of FIG. 6, and also the
measured frequency response of the seven stage tuned YIG band
reject filter of FIG. 7, across a frequency range of about 0.4000
GHz to about 0.6000 GHz, centered at about 500 Mhz. The performance
of the filter 120 of FIG. 7 is shown in FIG. 8 as line 130, while
the performance of the conventional seven sphere YIG band reject
filter 100 of FIG. 6 is shown as line 135. The line 135 of the
conventional seven stage filter of FIG. 6 may have a resulting 3 dB
notch bandwidth of about 27 MHz and a 40 dB notch bandwidth of
about 4.4 MHz. In comparison, the line 130 of the filter 120 of
FIG. 7 may have a resulting 3 dB notch bandwidth of about, e.g., 59
MHz and a 40 dB notch bandwidth of about, e.g., 8.7 MHz. The notch
depth of the conventional seven stage filter 100 of FIG. 6 may be
about 48 dB, while the actual notch depth of the tunable shunt YIG
tuned band reject filter 120 of FIG. 7 may actually exceed 75
dB.
[0050] FIG. 9 shows the measured frequency response of the
conventional YIG tuned band reject filter 100 of FIG. 6, and also
the measured frequency response of the seven stage tuned YIG band
reject filter 120 of FIG. 7, across a frequency range of, e.g.,
about 0.9000 GHz to about 1.1 GHz, centered at about 1000 Mhz. The
performance of the filter 120 of FIG. 7 is shown in relation as
line 130, while the performance of the conventional seven sphere
YIG band reject filter of FIG. 6 is shown as line 135. The line 135
of the conventional seven stage filter 100 of FIG. 6 has a
resulting 3 dB notch bandwidth of about, e.g., 96 MHz, and a 40 dB
notch bandwidth of about, e.g., 12 Mhz. In comparison, the line 130
of the tunable shunt YIG tuned band reject filter 120 of FIG. 7 may
have a resulting 3 dB notch bandwidth of about, e.g., 40 MHz, and a
40 dB notch bandwidth of about, e.g., 10 Mhz.
[0051] FIG. 10 shows the measured frequency response of the
conventional YIG tuned band reject filter 100 of FIG. 6, and also
the measured frequency response of the seven stage tuned YIG band
reject filter 120 of FIG. 7, across a frequency range of about
1.9000 GHZ to about 2.1000 GHz, centered at about 2000 Mhz. The
performance of the filter 120 of FIG. 7 is shown in relation as
line 130, while the performance of the conventional seven sphere
YIG band reject filter 100 of FIG. 6 is shown as line 135. The line
135 of the conventional seven stage filter 100 of FIG. 6 may have a
resulting 3 dB notch bandwidth of about, e.g., 135 MHz, and a 40 dB
notch bandwidth of about, e.g., 27 Mhz. In comparison, the line 130
of the tunable shunt YIG tuned band reject filter 120 of FIG. 7 may
have a resulting 3 dB notch bandwidth of about, e.g., 67 MHz, and a
40 dB notch bandwidth of about, e.g. 15 Mhz.
[0052] FIG. 11 shows the measured frequency response of the
conventional YIG tuned band reject filter 100 of FIG. 6, and also
the measured frequency response of the seven stage tuned YIG band
reject filter 120 of FIG. 7, across frequency range of about 2.5000
GHz to about 2.7000 GHz, centered at about 2600 MHz. The
performance of the filter 120 of FIG. 7 is shown in relation as
line 130, while the performance of the conventional seven sphere
YIG band reject filter 100 of FIG. 6 is shown as line 135. The line
135 of the conventional seven stage filter 100 of FIG. 6 may have a
resulting 3 dB notch bandwidth of about, e.g., 220 MHz, and a 40 dB
notch bandwidth of about, e.g., 43 Mhz. In comparison, the line 130
of the tunable shunt YIG tuned band reject filter 120 of FIG. 7 may
have a resulting 3 dB notch bandwidth of about, e.g., 103 MHz, and
a 40 dB notch bandwidth of about, e.g., 21 Mhz.
[0053] FIG. 12 shows a schematic of a YIG tuned band reject filter
200, configured according to principles of the invention. The
filter 200 comprises all shunt resonators 35a-35g, impedance
inverters 25b-25g, input-output matching lines 25a and 25h,
capacitors 40 and shunt resonator loop inductors 30a-30g.
[0054] FIG. 13 shows a schematic of YIG tuned band reject filter
220, configured according to principles of the invention. The
filter 220 may comprise alternating shunt and series YIG
resonators. The filter 220 may comprise shunt resonators 35a-35d,
shunt resonator coupling loop inductors 30a, 30c, 30d, 30f, series
resonators 20a-20c, coupling loop inductors 30b, 30g and 30e and
input-output matching lines 25a and 25h.
[0055] The configuration of FIGS. 12 and 13 are examples of other
topologies that are possible using principles of the invention.
Other topologies are also contemplated.
[0056] The tunable shunt YIG resonator examples described herein
may also require commonly known supporting circuitry which might
include, for example: a power source, a signal acquisition circuit,
a processor, an output, and the like, to implement the principles
herein, as one of ordinary skill would understand. The tunable
shunt YIG resonators may be employed in most applications that
might warrant the use of tunable microwave filters. Moreover, the
tunable shunt YIG resonators may be employed in other types of
circuits such as, e.g., band pass filters or oscillators, or the
like. The various shunt YIG filters described herein may be
utilized in many types of application elements, e.g., in such
devices as Tunable Oscillators (YIG Oscillators) and Tunable
Filters (YIG Filters). The applications may include a device that
may include a tunable shunt YIG filter (e.g., circuit 120, 200,
220, or variation thereof). The device may include, but not limited
to, e.g., a communication device, a signal processing device, a
microwave device, a wireless transmission device, a wireless
reception device, an imaging device, or the like.
[0057] While the invention has been described in terms of exemplary
examples, those skilled in the art will recognize that the
invention can be practiced with modifications in the spirit and
scope of the appended claims. These examples given above are merely
illustrative and are not meant to be an exhaustive list of all
possible designs, embodiments, applications or modifications of the
invention.
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