United States Patent 1 1 Moore et al.

[ June 19, 1973 YIG FILTER HAVING A SINGLE SUBSTRATE WITH ALL TRANSMISSION LINE MEANS LOCATED ON A COMMON SURFACE THEREOF [75] Inventors: Robert A. Moore, Severna Park;

Theodore M. Nelson, Catonsville,

both of Md.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Aug. 17, 1970 [21] Appl. No.: 64,361

[52] US. Cl. 333/73 R, 333/76, 333/84 M [51] Int. Cl. HOlp 3/08, H03h 7/08 [58] Field of Search... 3-33/73 R, 24.1, 24.2,

[56] References Cited UNITED STATES PATENTS 3,448,409 6/1969 Moose et al 333/84 M 3,585,531 6/1971 Degenford et al.... 333/10 x 3,417,294 12/1968 Steidlitz 333/84 x 3,022,470 2/1962 Oliner 333/24.2x 3,102,244 8/1963 Seidel 333/24 2 3,458,837 7/1969 Ngo 333173 OTHER PUBLICATIONS Lewin A Resonance Absorption lsolator," in Microstrip for 4GC/S Proceedings of lEE Part B Supplement 1957; Title Page & pp. 364-365.

Ferrites Can be Replaced With Yttrium Iron Garnet, in Electronic Design, Aug. 6, l958, single page. Matthaei, Magnetically Tunable Band-Stop Filters, in IEEE Transactions on Microwave Theory and Techniques, March, 1965; pp. 203-212.

Barret Microwave Printed Circuits-A Historical Survey, in IRE Transactions on Microwave Theory and Techniques, March, 1955; Cover Page and pp. l-7 Mariner Introduction to Microwave Practice Aca demic Press, Inc., New York, 1961; Title Page & pp. 33-35.

Primary ExaminerRudolph V. Rolinec Assistant Examiner-Marvin Nussbaum Att0rneyF. H. Henson, E. P. Klipfel and J. L. Wiegreffe [57] ABSTRACT One or more non-overlapping transmission line conductors fabricated on one planar surface of a single slab of an electric material mounted on a ground plane. At least one YlG resonator element is located in a cavity formed in the surface of the substrate facing the ground plane. The YIG resonator element, moreover, is positioned in close proximity to said one or more transmission line conductors a selected distance below the outer surface of the substrate and below the transmission line circuitry.

l0'Claims, 11 Drawing Figures PATENTED JUN-1 3. 740 675 sum 2 or z err YIG FILTER HAVING A SINGLE SUBSTRATE WITH ALL TRANSMISSION LINE MEANS LOCATED ON A COMMON SURFACE THEREOF BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to magnetically tunable filters and more particularly to magnetically tunable bandpass and band stop filters which utilize ferrimagnetic resonators in combination with deposited or etched microstrip line conductors on a dielectric substrate.

2. Description of the Prior Art The basic principles and theory of operation of ferrimagnetic resonators used as filters in waveguides, strip transmission lines and the like appears in a publication entitled Design of Magnetically Tunable Microwave Filters Using Single Crystal Yttrium-Iron-Garnet Resonators," by P. S. Carter, Jr. appearing in the IRE Transactions by Microwave Theories and Techniques, Volume MTT-9, pages 252-260 (May, 1961). Also reference is made to a text entitled Mlcrowave Filters, Impedance-Matching Networks and Coupling Structures, George L. Matthaei, et al., McGraw-Hill, Inc., 1964, pp. 1043-1085, inclusive.

Ordinarily, strip transmission line YIG filters are comprised of overlapping or crossing strip transmission lines at right angles to each other with a YIG sphere located between the transmission line at the point of overlap. If the point of overlap is an RF short circuit and a'magnetic field of the proper magnitude is applied to the YIG sphere at right angles to the two transmission lines, filtering and power limiting will occur. Such apparatus is mentioned as being known prior art in U.S. Pat. No. 3,289,112 issued to Charles E. Brown. This patent, however, additionally discloses the concept of locating the YIG sphere beneath the overlapping lines in a cavity of one of the dielectric wall members instead of between the overlapping striplines. The overlapping striplines are printed on a pair of opposing dielectric wall members and the two lines are peeled back and extended through one of the two dielectric wall members to a ground plane associated therewith in order to form an RF short circuit for signals applied to the conductors. While the Brown patent teaches a novel means of coupling two stripline elements to a single pole or resonator and has an advantage over certain types of YIG filters in that the YIG sphere need not be between the two coupled lines, it has the disadvantage of most types of YIG filters in that it is restricted to a single YIG sphere coupling both lines and therefore only single pole filters can be realized by this technique.

SUMMARY OF THE INVENTION The present invention is an improvement in apparatus ofthe type referred to above and is particularly suitable for fabrication into integrated circuitry. In the present invention a single or multi-pole YIG filter is disclosed which comprises a single dielectric substrate mounted on a ground plane so that its inner face is contiguous with one surface of the ground plane. One or more non-overlapping microstrip line conductors are fabricated on the outer face of the substrate and terminate at input and output couplers of electromagnetic energy located at the edges of the substrate. A selected number, one or more, YIG resonator elements are located in a cavity formed. in the inner face of the substrate so that said selected number of resonator elements are positioned beneath the outer face in close proximity to said one or more line conductors. A magnetic field is applied substantially orthogonal to the outer face to tune said selected number of YIG resonators to provide a predetermined filtering action of electromagnetic signals being transmitted between said input and output couplers.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a first embodiment of the subject invention and being illustrative of a single pole bandstop filter;

FIG. 2(a) is a fragmentary view of FIG. 1 taken along the line 22 illustrating the location of a YIG sphere in the substrate;

FIG. 2(b) is a fragmentary view of FIG. 1 taken along the line 22 illustrating a YIG disc resonator element mounted in the substrate;

FIG. 3 is a perspective view of a second embodiment, being illustrative of a single pole filter having two noncrossing microstrip line conductors on the outer face of the substrate;

FIG. 4 is a fragmentary view of the embodiment shown in FIG. 3 taken along the line 4-4 illustrating the location of a YIG sphere in relation to the two microstrip line conductors;

FIG. 5 is a perspective view of a third embodiment of the subject invention being'illustrative of a two pole filter and including two microstrip line conductors fabricated on the outer face of the substrate and terminating in a short circuit thereon;

FIG. 6 is a fragmentary view of FIG. 5 taken along the line 66 illustrating the location of two YIG resonators in relation to the microstrip line conductors;

FIG. 7 is a perspective view of a fourth embodiment of the subject invention similar to the embodiment shown in FIG. 5;

FIG. 8 is a fragmentary view of the embodiment shown in FIG. 7 taken along the line 8-8;

FIG. 9 is a partial cut away view of the embodiment shown in FIG. 7 modified to embody a three pole YIG filter; and

FIG. 10 is a partial cut away view of the embodiment shown in FIG. 7 modified to embody a four pole YIG filter.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2(a), a single microstrip line conductor 10 is deposited or etched on the outer face 12 of a dielectric substrate 14 which may be comprised of for example alumina, sapphire or some other ceramic material. The dielectric substrate 14 is mounted on a metallic ground plane 16 which is coextensive with its inner face 18. The microstrip line conductor 10 is of a substantially constant width and thickness and extends between opposite edges of the dielectric substrate l4 terminating at each end in an electrical connector 20 and 22 which is adapted to couple electromagnetic energy to and from the line conductor 10. A cavity 24 is fabricated into the inner face 18 directly beneath the line conductor 10 between the RF connectors 20 and 22. In the present embodiment the cavity 24 comprises a round dimple wherein a YIG sphere resonator element 26 is positioned so that it lies a predetermined distance, for example 0.005 inches below the upper surface 12 of the substrate 14. Additionally, the inner face 28 of the ground plane 16 contains a recess 30 including a dimple 32 for accepting the protrusion of the YIG sphere 26 when it is of such a size relative of the thickness of the substrate 14 that itwould otherwise prevent mating of the surfaces 18 and 28.

When RF signals are applied to the line conductor by means of the connectors 20 and 22 and a DC biasing magnetic field H of the proper magnitude is applied to the YIG sphere 26 substantially orthogonal to the line conductor 10, signals within a predetermined frequency range will not pass the point of the YIG sphere when it is at or near its point of resonance, thereby providing a bandstop filter. If for example RF energy is coupled into connector 20 only those frequencies which have been passed will exit at the other connector 22.

While it is desirable in certain applications to utilize a YIG sphere 28 such as shown in FIG. 2(a) as the resonator element, it sometimes becomes desirable to utilize a YIG resonator in the form of a disc which is shown in FIG. 2(b) and identified by reference numeral 34. In the embodiment shown, the disc 34 has a diameter substantially equal to the circular dimension of the cavity 25 and does not protrude below the inner face 18 of the substrate.

The second embodiment of the subject invention is shown in FIGS. 3 and 4. It comprises a single pole bandpass or bandstop filter including a pair of non-. overlapping microstrip line conductors 36 and 38 of substantially equal width dimensions fabricated on the outer face 12 of the dielectric substrate 14 so that a portion of their respective lengths run parallel to each other and then diverge into respective RF connectors located at the edges of the substrate. More particularly, microstrip line conductor 36 runs diagonally across a portion of the outer face 12 terminating in the RF connectors 40 and 42 while line conductor 38 also runs diagonally across the outer face 12 separated from the other conductor 36 by predetermined separation and terminating in respective RF connectors 44 and 46. Midway between the parallel portions of the two line conductors 36 and 38 is a selected number of, in this case one, YIG resonator elements shown as a YIG sphere 26 located in the substrate 14 beneath the outer face 12. Rather than being located directly beneath the line conductor 10 as shown in the embodiment in FIG. 1, the present embodiment locates the YIG sphere 26 between the parallel line portions of the conductors 36 and 38. By applying a DC biasing magnetic field I-I through the YIG sphere 26 selective coupling of electromagnetic energy occurs between the line conductors 36 and 38 because of the resonance characteristic of the YIG sphere. This configuration is adapted to provide low insertion loss bandpass coupling between the transmission lines 36 and 38.

For minimum insertion loss bandpass transmission an RF short must be applied at the location of the sphere 26. This can be provided in the embodiment shown in FIG. 3 for example, by external short circuits shown schematically by the reference numerals 41 and 45 directly connected from the connectors 40 and 44, respectively, to the ground plane 16. When this is done input signals applied to one of the opposite connectors 42 or 46 will be coupled out of the other connector. By selectively adjusting these short circuits for example by means of sliding shorts, not shown, the effect of the short circuit will be transformed on each line 36 and 38 to a position adjacent the sphere 26 wherein the tightest coupling will occur and best transmission effects will result. It should be noted, however, when desirable the short circuits could be applied to connectors 42 and 46 and connectors 40 and 44 utilized as the inputoutput ports for coupling between microstrip line conductors 36 and 38.

A third embodiment of the subject invention is shown in FIGS. 5 and 6 and comprises a first and a second microstrip line conductor 48 and 50 fabricated on the upper face 12 of the substrate 14 and which terminate in a short circuit 52 also fabricated on the upper face 12. The first line conductor 48 extends to one edge of the substrate 14 but turning at a substantially right angle inwardly of the edge to contact the short circuit 52. The second line conductor 50 extends to an adjacent edge of the substrate 14 and running in a substantially straight line to the short circuit 52 but being substantially parallel to a relatively small portion of the line conductor 48 in proximity to the short 52. A cavity 54 is formed in the inner face 18 of the substrate 14 directly beneath the portions of the line conductors 48 and 50 which are adjacent to the short 52. A first and a second YIG resonator element 56 and 58 in the form of a sphere are located in the cavity 54 respectively beneath the line conductor 48 and 50 by means of the dimples 60 and 62 formed therein. Both YIG resonator elements 56 and 58, however, do not contact the respective line conductors but lie beneath the upper face 12 of the substrate 14 by predetermined separation. This separation was illustrated in reference to the first embodiment described with respect to FIGS. 1 and 2(a). Additionally, the ground plane 16 includes a recess 64 beneath the cavity 54 in order to accommodate a portion of the YIG resonator elements 56 and 58. Whereas the embodiment shown in FIGS. 3 and 4 required four RF connectors, the third embodiment requires only two connectors 66 and 68 respectively coupled to the extremities of the line conductors 48 and 50 which appear at the adjacent edges of the substrate 14. When RF signals are applied to line conductors 48 and 50 by means of the RF connectors 66 and 68 and a DC biasing magnetic field H of proper magnitude is applied to the YIG resonator elements 56 and 58, a two pole filter of the bandpass type will be provided and selective coupling between line conductors 48 and 50 will occur due to the resonance phenomenon of the YIG resonator elements.

Referring now to FIGS. 7 and 8 there is illustrated a fourth embodiment of the subject invention which is similar to the embodiment shown in FIG. 5 with the exception that the electrical short 52 on top of the substrate 14 is deleted and the microstrip conductors 48 and 50 are terminated in a short near the YIG spheres 56 and 58 on the upper or inner face 28 of the ground plane 16. This is provided by the holes 49 and 51 completely through the substrate 14. By a suitable metal plating procedure the conductors 48 and 50 are extended into the holes 49 and 51, respectively and an electrical contact made with the ground plane 16. This is shown in greater detail in FIG. 8.

Although up to this point one and two pole YIG filters have been considered, the present invention particularly as regards the last embodiment shown in FIGS. 7 and 8 is adapted to be configured with three or more poles or YIG resonators. For example, FIG. 9 discloses a modification of the embodiment shown in FIG. 7 to include three equally spaced YIG resonators 56, 57, and 58 located in the recess 64 along a row transverse to the line conductors 48 and 50 under the surface 12 of the substrate 14. FIG. 10, on the other hand, illustrates a four pole YIG filter and includes four resonators 56, 58, 59 and 61 arranged in a row transverse to the line conductors 48 and 50;

What has been shown and described, therefore, is an improvement in YIG filter apparatus requiring one substrate, and one ground plane with all of the microstrip line conductor means being located on a common surface or face in a non-overlapping fashion with the YIG resonator element means being located in the substrate beneath the microstrip line conductors.

We claim as our invention:

1. A magnetic tunable microstrip transmission line filter, comprising in combination:

a. dielectric substrate means having inner and outer faces;

b. ground plane means having inner and outer faces, said outer face thereof abutting the inner face of said dielectric substrate means;

c. first and second microstrip transmission line means for transmitting electromagnetic wave energy located on said outer face of said substrate means;

d. ferrimagnetic resonator means positioned to selectively couple said electromagnetic wave energy between said first and second microstrip transmission line means;

e. means for magnetically biasing said ferrimagnetic resonator means; wherein f. said first and second transmission lines include substantially equal parallel line portions and wherein said resonator means comprises at least one yttrium iron garnet sphere located in close proximity to said parallel line portions.

2. The invention as defined by claim 1 wherein said sphere is located between said parallel line portions beneath said outer face of said dielectric substrate means.

3. The invention as defined by claim 1 wherein said first and second transmission line means comprise first and second line conductors, and a short circuit conductor contacting said first and second line conductors, said first and second line conductors and said short circuit conductor being located in substantially a common plane on said outer face of said dielectric substrate means, and wherein said resonator means comprises at least one YIG resonator element located in close proximity to said first and second line conductors.

4. The invention as defined by claim 3 wherein said at least one YlG resonator is located directly beneath at least one line conductor.

5. The invention as defined by claim 1 wherein said first and second transmission line means comprise first and second line conductors, and a short circuit conductor contacting said first and second line conductors, said first and second line conductors and said short circuit conductor being located in substantially a common plane on said outer face of said dielectric substrate means, wherein said resonator means comprises a plurality of YIG resonators located in close proximity to said first and second line conductors.

6. The invention as defined by claim 5 wherein said plurality of YIG resonators are comprised of a first and a second sphere of single crystal yttrium-iron-garnet respectively located beneath said first and second line conductors.

7. The invention as defined by claim 1 wherein said first and second transmission line means comprise first and second line conductors located in substantially a common plane on said outer face of said dielectric substrate and passing through said dielectric means at a point in proximity to said resonator means and respectively terminating in an electrical short circuit on said outer face of said ground plane.

8. The invention as defined by claim 7 wherein said resonator means comprises at least one YIG resonator element located in close proximity to said first and second line conductor and said electrical short circuit.

9. The invention as defined by claim 7 wherein said resonator means comprises a plurality of YIG resonators.

10. The invention as defined by claim 9 wherein said plurality of YIG resonators comprises at least three YIG resonators arranged in a row beneath said outer face of said substrate substantially perpendicular to said first and second line conductor and within a boundary defined by said line conductors.