US 3801936 A
The invention relates to a miniaturized YIG band-pass filter with first poles for achieving high selectivity in the microwave range, in which the coupling structure consists of, for example, crossed coaxial inner conductors in an external magnet circuit which are semicircularly bent over the YIG elements, the coupling structure for the YIG resonators being arranged in a filter body which is made of, for example, copper or brass, such that the coaxial supply conductors for coupling the YIG resonators are adjacently arranged and are magnetically coupled, i.e., in the case of filters comprising an even number of YIG resonators they are coupled to each other, and in the case of filters comprising an odd number of YIG resonators the first and the last supply conductor are coupled. The magnetic coupling between the supply conductors can be varied by means of a displaceable shutter.
Description (OCR text may contain errors)
HAVING DEFINED DAMPING POLES United States Patent [111 3,801,936
Roschmann Apr. 2, 1974 MINIATURIZED YIG BAND-PASS FILTER Primary ExaminerPaul L. Gensler  Inventor: Peter Roschmann, Hamburg, Attorney, Agent, or Firm-Frank R. Tnfari Germany D  ABSTRACT  ASS'gnee: Philips Corporation New The invention relates to a miniaturized YIG band-pass filter with first poles for achieving high selectivity in  Filed: Aug. 23, 1972 the microwave range, in which the coupling structure consists of, for exam le, crossed coaxial inner conduc-  Appl 283202 tors in an external mggnet circuit which are semicircularly bent over the YIG elements, the coupling struc-  For i n A li ti P i it D m ture for the YlG resonators being arranged in a filter Aug. 26, 1971 Germany 2142748 body which is made for exampiei copper brass such that the coaxial supply conductors for coupling 52 US. Cl. 333/73 0, 333/83 R the YIG resonators e adjaceml arranged and are 51 Int. Cl. H0lp 1/20 magnetically coupiedi in the case of filters  Field of Search 333/24 0, 73 R, 73 c, 73 s Pfising "umber remnators are coupled to each other, and in the case of filters com-  References Cited prising an odd number of YlG resonators the first and UNITED STATES PATENTS the last supply conductor are coupled. The magnetic coupling between the supply conductors can be varied 3,435,385 3/1969 Cohen 333/73 C by means of a displaceable Shutter 3,400,343 9/1968 Carter 333/73 S 3,368,169 2/1968 Carter et a]. 333/73 S 6 Claims, 8 Drawing Figures Siripline a k 8 2 18 2 s 1 F n 3 3.3 i r 1? I i i 'b 3" 2 3 3" YIG spheres PATENTEDAPR 21914 3L80l; 936
sum 2 or a (MHZ) SHEET BF 4 PATENTED APR 2 I974 MINIATURIZED YIG BAND-PASS FILTER HAVING DEFINED DAMPING' POLES The invention relates to a miniaturized YIG bandpass filter, comprising damping poles in order to achieve high selectivity in the microwave range, in which the coupling structure includes crossed coaxial inner conductors in an external magnetic circuit which are semicircularly bent over the YIG element.
Use is made of the ferrimagnetic'resonance in ferrite bodies; use is preferably made of yttrium-iron-garnet or similar YIG monocrystals, for example, substituted with Ga, which have very small resonance line widths and hence high resonance qualities. As in the first instance the resonant frequency of the ferrimagnetic resonance is determined only by the strength of a static or quasi'static magnetizing field, the absolute dimensions of the ferrimagnetic resonator as opposed to conventional microwave filters with line or cavity resonators are of no importance in the first instance; use is preferably made of polished balls having typical diameters of between 0.3 and 1 mm. This property of the YIG resonators can be used to good advantage so as to realize very small filters; in particular, very small permanently tuned or mechanically tunable filters can be manufactured by means of permanent magnets. These properties are particularly'important for the miniaturized microwave circuits in the strip conductor technique (microstrip) which are manufactured by photoetching and which are being applied in increasing numbers. Strip conductor substrates are generally made of ceramic and have a dielectric constant e of between 9 and 16. Consequently, a reduction of i.e., approximately a factor 3 4; moreover, ignoring the substrate thickness of between 0.2 and 0.6 mm, the strip conductor circuits are only two-dimensional. Due to the comparatively high conduction losses in strip conductors, conventional line resonators in this tech-- e is produced,
nique have low, unloaded qualities in the order of magloaded quality, narrow band filters having low losses and high selectivity cannot be realized according to the strip conductor technique. A desired interconnection of known low-loss coaxial circuit filters or cavity filters and strip conductor circuitsis seldom feasible particulariy due to their various dimensions. On the other hand, YIG filters can in principle be realized with structural dimensions which are compatible with the strip conductor technique.
The invention had for its object to provide, by means of YIG resonators, low-loss, narrow band bandpass filters of small volume which can be readily incorporated in a microstrip circuit without taking in too much space, and having defined damping poles and a very large slope steepness of their characteristic curve.
It must be possible for the filter to be inserted in a strip conductor circuit as a complete structural compo: nent similar to, for example, diodes or transistors.
As is known, the slope steepness of a filter (selectively) increases as the number of resonant circuits used increases. In the case of a given number of resonant circuits, methods are also known how to produce defined damping poles on the filter curve to increase the slope steepness (known methods: Zobel elements, Cauer elements, elliptically coupled filters, n-path filters). The use of this technique reduces the number of resonant circuits required for a given damping of a filter, thus offering substantial savings as regards money and structural dimensions. For example, a two-circuit band-pass filter with two damping poles can have a slope steepness which corresponds to that of a three or four-circuit straight-coupling filter (Tchebyscheff, Butterworth), and the losses in the band-pass range are even smaller. These filters are particularly suitable if the image frequency of the desired intermediate frequency is to be suppressed in an RF mixer the distance between the band-pass centre frequency and the pole frequency must then be equal to twice the intermediate frequency. I
According to the invention a band-pass filter with two well defined damping poles of its characteristic curve is'achieved in that the coupling structure for the YIG resonators in a filter body which is made of, for example, copper or brass, is arranged such that the coaxial supply conductors for coupling the first and for coupling the last YIG resonator are adjacently arranged and are magnetically coupled to each other in filters comprising an even number of YIG resonators or, in the case of filters comprising an odd number of YIG resonators, the coaxial supply conductor for coupling the first YIG resonator is magnetically coupled to the conductor for coupling the last YIG resonator.
The drawing shows some embodiments according to the invention. Therein:
FIG. 1 shows in cross-section a two-stage Y-IG bandpass filter component, i FIG. 2 is a perspective view of the embodiment of FIG. 1 comprising magnets,
FIG. 3 is a diagrammatic plan view of the embodi ment of FIG. I, 1
FIG. 4 shows band-pass filter curves,
FIG. 5 shows a cross-section through a YIG filter with magnetic coupling,
FIG. 6 is a diagrammatic plan view of the embodiment of FIG. 5,
FIG. 7 is a cross-sectional view of a further embodiment, and
FIG. 8 is a diagrammatic view of a tunable embodiment with magnets. J
In accordance with FIG. 1, the coaxial inner conductor 2 for the supply are fed out of the filter block 1 such that they are adjacently arranged, preferably in parallel, at a distance of approximately 0.5 to 1 mm from each other. The filter body which is mounted in a permanent magnet is first built into a measuring adapter and the YIG balls 3 are adjusted according to the frequency wobbling method by means of holders 3'. The filter component thus obtained is connected to the strip conductor circuit supported on a substrate 5 which is provided with a grounded plate 9 and appropriate paspling loops 4, fixing leaf spring 6, and screw 7. FIG. 2 i
is a perspective view of the filter component with magnets, inthis case a permanent magnet circuit, comprising a yoke 10 and permanent magnets 11. The connection of the magnet to the filter body can be effected by screwing, or by bonding or soldering. A method of connecting the filter component in a strip conductor substrate is shown in FIG. 3: the fixing spring 6 is screwed to a projection I5 of the filter body 1 by means of a screw 7, the spring 6 then pressing 6 then pressing on the substrate (FIG. 3), thus producing a counter pressure. The coaxial supply conductors 2 can be connccted in a conductive manner to the strip conductor 8 by soldering or bonding.
To producedamping poles in the filter curve, the supply conductors 2 which are magnetically coupled to the YIG resonators are also coupled to each other. The principle will be described with reference to FIG. 4.
The transmission curve 12 which is denoted by a signal passing through a broken line represents the amplitude behaviour of a straight-coupled band-pass filter, as a function of the frequency; line 13 shows the transmission a introduced by the magnetic coupling of the supply conductors (which can be measured, for example, when the YIG balls are removed from the filter body). Curve 14 is a resulting band-pass filter curve with damping poles. The pole frequencies f and f are situated at the intersections of lines 12 and 13 (interference); at these intersections the signal transmitted by the YIG resonators and the signal (a transmitted by the magnetic coupling of the supply conductors cancel each other. It was experimentally found that the damping poles are situated between 65 dB and 70dB, determined by minor phase errors, so that the condition of equal amplitudes in the case of opposed phase does not occur simultaneously. By changing the level a of the directly coupled signal, the distance from the pole frequenciesf and f to the centre frequency f can be symmetrically shifted; starting from the 3 dB band width (A f dB) of the filter, values (f,, f,) of approximately f m to M B) p n J1 chie e thi h. 92 T? sponcls to a coupling level a of dB to approximately 55 dB.
The interference required for producing the damping poles can occur symmetrically on both filter flanks only if the signal frequencies f f 2 f0), transmitted by the filter and situated about f0 below and above the pass frequency range, have approximately the same phase or a phase position which is shifted a mult ipl egf 2 11 with respect to each other. In band-pass filters the phase position for signals fgfo generally amounts to a multiple of 1r which is about equal to the number of filter circuits: the above phase condition (multiple of 2 1r is satisfied only if there is an even number of filter circuits; in that case the magnetic coupling a between the filter supply conductors can be effected as described in the foregoing.
In the case of an odd number of filter circuits, the magnetic coupling a must be effected, for example, between the supply conductor for the (external) coupling of the first resonator and the inner coupling conductor 2' for the (inner, related to the filter) coupling of the last resonator.
The magnetic coupling of the supply conductors can be effected through partial opening of the partition between the supply conductors. FIGS. 5 and 6 show an embodiment which results from the omission of the bar 15. The distance a between the filter supply conductors 2 as well as the distance b between the filter bodies and the conductor side of the microstrip substrate influence the level a of the directly coupled signal. FIG. 7 shows the principle of an embodiment which enables continuous adjustment of the coupling level a the two supply conductors being coupled through the slit 16; the coupling can be varied by means of a displaceable shutter 17. Other similar devices utilizing screws are alternatively possible.
FIGS. 6 and 8 show a further method of connecting the filter body to the microstrip substrate. The filter which is arranged below the substrate is secured by means of the screws 18 on the circuit side of the substrate. FIG. 8 shows the required threaded holes 19, for example, in the magnet yoke. FIG. 8 also shows a simple possibility of tuning the centre frequency of the filter by screwing the screw 20, made of a magnetic material, further into or out of the hole so that a magnetic shunt is produced which more or less decreases the field in the range of the filter, and hence the resonant frequency. By means of a coil 21 in the magnetic circuit, an electronic (additional) tuning can also be achieved which is advantageous, for example, for an electronically controlled frequency readjustment. The generation of pole frequencies is not restricted to the special cases described here, but the required measures can also be realized in known electronically tunable YIG filters in accordance with the described embodiments.
Finally, some results will be given which were obtained on an embodiment according to FIG. 6 (and FIG. 8):
Centre frequency f 2,500 MHz Intermediate damping 1.5 dB
3 dB bandwidth 12 MHz Pole frequencies f i 60 MHZ Pole damping 67 dB Coupling level a -47 dB Dimensions of the filter block 12 X6 X 5 mm Mechanical tuning range 2,500 2,000 MI-Iz Temperature-dependency of f,, approximately 20 KHZ! C.
What is claimed is:
l. A miniaturized YIG band-pass filter having defined damping poles comprising: an even number of ferrimagnetic YIGresonators, a filter body of electroconductive non-magnetizable material, a corresponding number of chambersformed in said body for receiving said YIG resonators, respectively, the first and the last chamber being arranged adjacent each other and interconnected by a coupling aperture, two parallel passages leading from said first and last chambers respectively, to an external surface of said body, an input and output coupling structure including coaxial supply conductors passing through said passages and being magnetically coupled to one side of said YIG elements, a crossed inner conductor passing through said coupling aperture and being magnetically coupled to another side of said YIG elements, and an open space formed in said body between predetermined portions of said supply conductor to produce an additional coupling therebetween thereby forming damping poles in the filter curve.
2. A YIG bandpass filter as claimed in claim 1, characterized in that an adjustable magnetic shunt is provided for the external magnetic field for the YIG resonators.
3. A YIG band-pass filter as claimed in claim 1, characterized in that the external magnetic circuit can be electronically adjusted by means of a coil.
6. A band-pass filter according to claim 4, further including an additional chamber with a YlG resonator, and portions of said crossed inner conductor being directed against side opening to introduce coupling between a supply conductor of one YlG resonator and the inner conductor near the other YlG resonator.
UNETED PATENT OFFECE QERTIFECATL OF CGRREC'HGN Patent No. 3,801, 936 Dated April 2, 1974 InventorQ Y ROSCHMANN It is certified that error appears in the above-idntified patent and that said Letters Patent are hereby corrected as shown below:
In the title a e Section  change "2142748" to Signed and sealed this 1st day of October 1974,
Cu MARSHALL DANN Commissioner of Patents MCCOY M. GIBSON JR. Attesting Officer