Claims
- 1. A thin film ferromagnetic resonance tuned filter comprising:
- a ferrimagnetic thin film;
- an input transmission line and an output transmission line coupled to said ferrimagnetic thin film; and
- a magnetic circuit applying DC magnetic field to said ferrimagnetic thin film, each of said input and output transmission lines being grounded at a grounded end respectively, wherein each distance between the center of said ferrimagnetic thin film and said grounded ends of each of said input and output transmission lines is selected one-tenth or above and less than one-fourth the wavelength of a wave transmitted in said transmission lines at an upper limit frequency of a tuning bandwidth.
- 2. A thin film ferromagnetic resonance tuned filter comprising:
- a first and a second ferrimagnetic thin films;
- an input transmission line coupled to said first ferrimagnetic thin film and grounded at one end thereof;
- an output transmission line coupled to said second ferrimagnetic thin film and grounded at one end thereof; and
- a magnetic circuit applying DC magnetic field to said first and second ferrimagnetic thin films, wherein a distance between the center of said first ferrimagnetic thin film and said grounded end and a distance between the center of said second ferrimagnetic thin film and said grounded end are selected one-tenth or above and less than one-fourth the wavelength of a wave transmitted in said transmission lines at an upper limit frequency of a tuning bandwidth.
- 3. A thin film ferromagnetic resonance tuned filter according to claim 2, further comprises a connecting transmission line coupled to said first and second ferrimagnetic thin films.
- 4. A thin film ferromagnetic resonance tuned filter according to claim 2, further comprises a third ferrimagnetic thin film provided to be coupled with said first and second ferrimagnetic thin films.
- 5. A thin film ferromagnetic resonance tuned filter comprising:
- ferrimagnetic thin films;
- an input signal transmission line and an output signal transmission line respectively coupled with said ferrimagnetic thin films; and
- a magnetic circuit for applying a DC magnetic field to said ferrimagnetic thin films;
- characterized in that one end of said input signal transmission line and one end of said output signal transmission line are extended to form extensions, the distance from the center of the ferrimagnetic thin film coupled with said input signal transmission line to the grounded end of the extension of said input signal transmission line, and the distance from the center of the ferrimagnetic thin film coupled with said output signal transmission line to the grounded end of the extension of said output signal transmission line being one-tenth or above and less than one-fourth the wavelength of a wave transmitted in said transmission lines at the upper limit frequency of a tuning frequency band, and that parts spaced apart by an interval greater than the interval between the center of the ferrimagnetic thin film coupled with said input signal transmission line and the center of the ferrimagnetic thin film coupled with said output signal transmission line, are provided at least in either the said extensions located on the same side as the coupling points of said input and output signal transmission lines coupled with the corresponding magnetic resonance thin films, or the mutually opposite other corresponding parts of said input and output signal transmission lines.
- 6. A thin film ferromagnetic resonance tuned filter comprising:
- ferrimagnetic thin films;
- an input signal transmission line and an output signal transmission line respectively coupled with said ferrimagnetic thin films; and
- a magnetic circuit for applying a DC magnetic field to said ferrimagnetic thin films;
- characterized in that one end of said input signal transmission line and one end of said output signal transmission line are extended to form extensions, the distance from the center of the ferrimagnetic thin films coupled with said input signal transmission line to the grounded end of said extension, and the distance from the center of the ferrimagnetic thin film coupled with said output signal transmission line to the grounded end of said extension, being one-tenth or above and less than one-fourth the wavelength of a wave transmitted in said transmission lines at the upper limit frequency of a tuning frequency band, that a divided part is formed at least in either the coupling portion of said input signal transmission line or the coupling portion of said output signal transmission line, and that parts spaced apart by an interval greater than the interval between the input signal transmission line and the center of the ferrimagnetic thin film coupled with said output signal transmission line, are provided at least in either the said extensions located on the same side as the centers of the ferrimagnetic thin films, or the mutually opposite other corresponding parts of said input and output signal transmission lines.
- 7. A thin film ferromagnetic resonance tuned filter according to claims 5 or 6, further comprises a connecting transmission line coupled to said first and second ferrimagnetic thin films.
- 8. A thin film ferromagnetic resonance tuned filter according to claims 5 or 6, further comprises a third ferrimagnetic thin film provided to be coupled with said first and second ferrimagnetic thin films.
Priority Claims (2)
| Number |
Date |
Country |
Kind |
| 61-283512 |
Nov 1986 |
JPX |
|
| 62-107350 |
Apr 1987 |
JPX |
|
BACKGROUND OF THE INVENTION:
This is a continuation of application Ser. No. 127,014, filed Nov. 27, 1987 (now abandoned).
The present invention relates to a thin film ferromagnetic resonance tuned filter comprising, for example, a tuned filter using ferrimagnetic resonance of YIG thin film.
FIG. 9 diagrammatically illustrates a known thin film ferromagnetic resonance tuned filter employing ferromagnetic resonance thin films. The ferromagnetic resonance tuned filter is a two-stage band pass filter having a pair of YIG thin films Y.sub.1 and Y.sub.2 serving as magnetic resonators. An input signal transmission line L.sub.1 and an output signal transmission line L.sub.2 are magnetically coupled with the YIG thin films Y.sub.1 and Y.sub.2, respectively. A connecting transmission line L.sub.1 2 extending across the input and output signal transmission lines L.sub.1 and L.sub.2 is coupled magnetically with the YIG thin films Y.sub.1 and Y.sub.2. The YIG thin films Y.sub.1 and Y.sub.2 are coupled with the signal transmission lines L.sub.1 and L.sub.2 at positions near the respective grounded ends P.sub.1 and P.sub.2 of the signal transmission lines L.sub.1 and L.sub.2, respectively, in order that the YIG thin films Y.sub.1 and Y.sub.2 are coupled strongly with the signal transmission lines L.sub.1 and L.sub.2 , respectively.
In such construction the range of variation of the bandwidth is one to two octaves at most when a DC magnetic field applied to the YIG thin films Y.sub.1 and Y.sub.2 is varied to use the ferromagnetic resonance tuned filter as a variable frequency tuned filter.
The narrowness of the variation of the bandwidth of such a two-stage YIG tuning filter will be examined hereinafter. Suppose that the unloaded Q of each of the YIG thin films Y.sub.1 and Y.sub.2 is Qu, the external Q resulting from the coupling of the YIG thin films Y.sub.1 and Y.sub.2 respectively with the signal transmission lines L.sub.1 and L.sub.2 is Qe, the apparent external Q resulting from the extension of the distance between the coupling point of the input signal transmission line L.sub.1 and the YIG thin film Y.sub.1, and the grounded end P.sub.1 and the distance between the coupling point of the output signal transmission line L.sub.2 and the YIG thin film Y.sub.2, and the grounded end P.sub.2 is Qe.sup.eff, and the coupling coefficient between the two YIG thin films Y.sub.1 and Y.sub.2 is k. Then, Qu, Qe, Qe.sup.eff and k are expressed by functions of frequency f as follows.
In a state of critical coupling, the insertion loss of the filter reaches the minimum value while the reflection loss of the same reaches the maximum value at the center of the pass band.
However, in a state of overcoupling where
As undercoupling is enhanced in a state of undercoupling where
FIG. 10 shows the results of simulation characteristics tests of a filter basically having the constitution shown in FIG. 9. In FIG. 10, curves 10RL, 10IL and 10BW indicate the variation of the reflection loss, the insertion loss and a 3 dB bandwidth, respectively, with frequency. In this case, a critical frequency, namely, a frequency where the filter is in a state of critical coupling, is approximately 1 GHz. When the frequency decreases from the critical frequency, overcoupling is enhanced to deteriorate the filter characteristics, the insertion loss at the center of the pass band increases and the reflection loss at the center of the pass band decreases, and when the frequency increases from the critical frequency, undercoupling is enhanced to deteriorate the filter characteristics, the insertion loss increases and the reflection loss decreases, because the coupling coefficient k of the YIG thin films varies in proportion to frequency, while the distance l is sufficiently small and hence, as obvious from expression (3), Qe.sup.eff is fixed at Qe independently on frequency. As obvious from FIG. 10, when a required reflection loss is 10 dB or above, namely, when voltage standing wave ratio is 2 or below, the variable bandwidth is 0.65 GHz to 1.5 GHz, namely, 1.2 octaves and, when the reflection loss is 6 dB or above, namely, when the voltage standing wave ratio is 3 or below, the variable bandwidth is 0.5 GHz to 1.9 GHz, namely, 1.9 octaves. FIG. 11 shows the measured filter characteristics of this filter, in which curves 11RL, 11IL and 11BW indicate the variation of the measured reflection loss, the measured insertion loss and the measured 3 dB bandwidth. It is obvious that the curves shown in FIG. 11 resemble the corresponding curves shown in FIG. 10 closely.
Thus, in the known YIG thin film tuned filter, the 3 dB bandwidth varies greatly with the variation of the center frequency, which is unfavorable to the application of the YIG thin film tuned filter to a system, and the known YIG thin film tuned filter has a problem in spurious characteristics that the filter response is enhanced relatively by a spurious mode when the uniform mode of the YIG thin film resonance is a stat of undercoupling.
The present invention expands greatly the variable frequency band of the magnetic resonance tuning filter such as the foregoing YIG thin film magnetic resonance tuning filter, reduces the variation of the 3 dB bandwidth attributable to the variation of the center frequency, maintains the 3 dB bandwidth fixed over the entire range of variable frequency band to provide a magnetic resonance thin film tuning filter advantageous in application to a system. Furthermore, the present invention improves the spurious characteristics of the magnetic resonance thin film tuning filter so that the magnetic resonance thin film tuning filter has satisfactory spurious characteristics over the entire variable frequency band, by maintaining the magnetic resonance thin film tuning filter in a state close to critical coupling in most part of the variable frequency band and in a state of overcoupling at the upper and lower ends of the variable frequency band to suppress the deterioration of the spurious characteristics by undercoupling state.
Accordingly, it is object of the present invention to provide an improved thin film ferromagnetic resonance tuned filter.
It is another object of the present invention to provide a thin film ferromagnetic resonance tuned filter having an expanded variable frequency band.
It is further object of the present invention to provide a thin film ferromagnetic resonance tuned filter having an expanded variable frequency band in which 3 dB bandwidth is stabilized.
It is still further object of the present invention to provide a thin film ferromagnetic resonance tuned filter having an improved isolation characteristics.
It is yet further object of the present invention to provide a thin film ferromagnetic resonance tuned filter having expanded variable frequency band in compact size.
According to one aspect of the present invention, there is provided a thin film ferromagnetic resonance tuned filter which comprises: a ferrimagnetic thin film, an input transmission line and an output transmission line coupled to said ferrimagnetic thin film, and a magnetic circuit applying DC magnetic field to said ferrimagnetic thin film, each of said input and output transmission lines being grounded at grounded end respectively, wherein each distance between a coupling point of said ferrimagnetic thin film and each of said input and output transmission lines and said grounded ends of each of said input and output transmission lines is selected one-tenth or above and less than one-fourth the wavelength of a wave transmitted in said transmission lines at an upper limit frequency of a turning bandwidth.
According to another aspect of the present invention, there is provided a thin film ferromagnetic resonance tuned filter which comprises:
a first and a second ferrimagnetic thin films, an input transmission line coupled to said first ferrimagnetic thin film and grounded at one end thereof, an output transmission line coupled to said second ferrimagnetic thin film and grounded at one end thereof, and
a magnetic circuit applying DC magnetic field to said first and second ferrimagnetic thin films, wherein a distance between a coupling point of said first ferrimagnetic thin film and said input transmission line and said grounded end and a distance between a coupling point of said second ferrimagnetic thin film and said output transmission line and said grounded end are selected one-tenth or above and less than one-fourth the wavelength of a wave transmitted in said transmission lines at an upper limit frequency of a tuning bandwidth.
Further, the extended portions of the transmission lines may be bent not to form a parallel portion to another transmission line to improve isolation characteristics.
US Referenced Citations (5)
Foreign Referenced Citations (2)
| Number |
Date |
Country |
| 196918 |
Oct 1986 |
EPX |
| 2131628 |
Jun 1984 |
GBX |
Non-Patent Literature Citations (3)
| Entry |
| 1987 IEEE MTT-S International Microwave Symposium Digest, Jun. 1987, pp. 371-374. |
| Carter, IRE Transactions on Microwave Theory and Techniques, "Magnetically-Tunable Microwave Filters Using Single-Crystal Yttrium-Iron-Garnet Resonators", pp. 252-260, May 1961. |
| Simpson et al., The European Microwave Conference, "Tunable Microwave Filters Using YIG Grown by Liquid Phase Epitaxy", pp. 590-594, Sep. 13, 1974. |
Continuations (1)
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Number |
Date |
Country |
| Parent |
127014 |
Nov 1987 |
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Patent Grant
4945324
