Electromechanical disc filter
United States Patent Irzhavsky et al.  
 [ 51 Apr. 15, 1975 ELECTROMECHANICAL DISC FILTER [76] Inventors: Alexandr Lvovich Irzhavsky,  
 Otkrytoe schosse, 3, korpus l, kv. 31; Petr Samuilovich Stolyar, ulitsa Petrozavodskaya 17, korpus l, kv. 102; Konstantin Alexandrovich Shulgin, ulitsa Bolhaya Mariinskaya l0, kv. 53, all of Moscow, U.S.S.R.  
 [22] Filed: Aug. 2, 1973 [21] Appl. No.: 384,977  
 [52] US. Cl. 333/71; 333/30 M [51] Int. Cl. H03h 9/02; H03h 9/04; H03h 9/30 [58] Field of Search 333/71, 30 M, 72  
 [56] References Cited UNITED STATES PATENTS 2,615,981 10/1952 Doelz 333/71 3,351,875 11/1967 Midgley 333/71 Primary Examiner-James W. Lawrence Assistant Examiner-Marvin Nussbaum [57] ABSTRACT An electromechanical disc filter differing from the hitherto known ones by the structure of its resonator system. 1n the disclosed resonator systems, the longitudinally extending mechanical links are attached to those points of the face surfaces of the discs where, when there is excited in the disc resonator oscillation with nodal circles, the oscillation created in these links is purely bending one. The advantage offered by the disclosed structures is the possibility of manufacturing with the incorporation of these structures small-size disc filters featuring high mechanical strength and improved mono-frequency characteristics.  
 8 Claims, 24 Drawing Figures PMEMEUAPR 1 51975 sumuq g FIE/l ELECTROMECHANICAL DISC FILTER The invention relates to frequency selection apparatus incorporating as their basic selective components high-quality mechanical resonators mechanically connected to one another and. more particularly. to electromechanical filters.  
  Electromechanical filters are characterized by high selectivity and thermal stability. as well as by being fit for incorporation in narrow-band filters.  
  As far as the above parameters are concerned. they are similar to quartz filters. while their manufacture is both less complicated and less costly.  
  Electromechanical filters can be employed in a vast range of radio and electronic apparatus where selection of a frequency signal is needed. Thus. they may be incorporated in communication systems. in radar installations. in measuring circuits. etc.  
  An electromechanical filter per se is an apparatus comprising an input electromechanical transducer and an output electromechanical transducer. such as magnetostriction. piezoelectric and other transducers. and a mechanical resonance system including. depending on the required selectivity. an adequate plurality of mechanical resonators. e.g. metal resonators interconnected with metal links such as wires. bands. cylinders.  
 etc.  
  Among a variety of electromechanical filters. broad application in the medium-high frequency range (60 kHz to 600 kHz) has been found for electromechanical filters with either axial or parallel arrangement of cylinder-shaped resonators operable in a torsional oscillation mode. plate-type electromechanical filters with resonators operable in a longitudinal oscillation mode and linking elements operable either in a longitudinal oscillation mode or in a bending oscillation mode; disc electromechanical filters incorporating disc resonators operable in a bending oscillation mode with either one or two nodal circles and link elements subjected to longitudinal oscillation.  
  All the above types of electromechanical filters feature similar electric ratings. Electromechanical filters with torsional oscillation have found application in a frequency range from 60 to 300 kHz. A modification of these filters with axial arrangement of the resonators has relatively great length. Thus. the length ofa five-to six-resonator filter rated for operating frequencies of about 100 kHz is a great as ISO to 160 mm. Filters of this last type which are relatively narrow-band ones 1 percent) have to have their mechanical strength enhanced by complicated coupling of the resonators. which structurally leads to an even greater length of the filter.  
 Known is a structure of an electromechanical filter with torsional oscillation of axially arranged resonators. the latter being shaped as dumbbells. This makes it possible to reduce the length of the filter 1.5 to 2.0 times. but this reduction is paid for by considerably complicated manufacture of such filters.  
  A torsional oscillation filter with parallel arrangement of the resonators has a considerably smaller longitudinal dimension than the one having axially extending resonators; however. the overall volume of the former does not differ considerably from that of a similar filter with the axial arrangement.  
  Plate-type filters are employed for operation at frequencies of about 400 to 600 kHz. These filters, however. being highly promising from the point of view of miniaturization of electromechanical filters. have not conquered the field on account on intensive side pass bands inherent in such filters. owing to the presence of densely located resonances of bending oscillation in the thin plates.  
  Electromechanical disc filters are used with operating frequencies with a 60 to 600 kHz range. The most commonly used structure of an electromechanical disc filter has peripherally arranged longitudinally oscillating linking elements. A major disadvantage offilters of this structure is their relatively great size. Thus. electromechanical disc filters marketed by the Collins Company and rated for 60 to 108 kHz have an overall volume of about 80 cu.cm. As in the case of torsional oscillation electromechanical filters. the disc filters rated for a relative bandpass below 0.5 percent necessitate the incorporation of complicated coupling or linking means between the resonators. which increases the length of these filters.  
  A reduction in the size of electromechanical disc filters with peripheral linking elements is liable to affect both the mono-frequency characteristics of a filter and its mechanical strength. The reason is as follows. With a reduction in the size of disc resonators. there takes place. across their entire surface. including their peripheries. a reduction of the impedance to the main oscillation with nodal circles. as well as to&#39;side oscillations with their nodal diameters. Simultaneously there is a substantial narrowingof the gap between the resonance frequencies of the side modes of oscillation with nodal diameters and the frequencies with nodal circles; To compensate for this reduction of the impedance values of the resonators and thus maintain the desired bandpass. it is necessary to reduce considerably the diameter of the wire linking elements. which affects the mechanical strength of the oscillation system of a filter. The narrowing of the gap between the side resonance frequencies with nodal diameters and the rated frequency of the filter. with simultaneous reduction of the impedance of the disc resonators to oscillation of this kind is liable to result in considerably increased intensity of side pass bands. which is impermissible.  
  In some cases relatively wide-band filters (4 to H) percent) have their electromechanical disc filter devices constructed with central arrangement of the mechanical linking elements. It is relatively simple to make such filters proof against appearance therein of side resonances. but their mechanical strength is inadequate.  
  It is an object of the present invention to eliminate these disadvantages.  
  lt is also an object of the present invention to create such structures of electromechanical filters which should solve the problem of creating miniature monofrequency filters of adequate mechanical strength having various pass bands within a broad range of frequencies.  
  These and other objects are attained in an electromechanical disc filter comprising an input electromechanical transducer. a plurality of disc resonators arranged parallel to one another in spaced relationship and operable in a bending oscillation mode with nodal circles. said disc resonators including at least one intermediate disc and a pair of terminal discs. interconnected with longitudinally extending mechanical links. and an output electromechanical transducer. in which filter. in accordance with the present invention. said mechanical links are attached to the face surfaces of said disc resonators at points placed along a circle having the diameter equal to that of a nodal circle ofsaid disc resonator.  
  It is advisable that an electromechanical filter wherein said disc resonators are operable in a bending oscillation mode with a single nodal circle should have said mechanical links thereof. interconnecting adjacent pairs of said disc resonators. attached to the face surfaces of each said respective disc resonator at points placed along a circle having a diameter equal to about 0.68 of the external diameter of said disc resonator.  
  It is further advisable that an electromechanical filter. wherein said disc resonators are operable in a bending oscillation mode with two nodal circles. should have said mechanical links thereof. interconnecting adjacent pairs of said disc resonators. attached to the face surfaces of each said respective disc resonator at points placed along a circle having a diameter equal to about 0.82 ofthe external diameter of said disc. Furthermore.  
 it is expedient that said mechanical links should be in this case additionally attached to the face surfaces of said disc resonators at points placed along a circle having a diameter equal to about 0.36 of said external diameter of said disc.  
  In accordance with the proposed arrangement of the mechanical links on the face surfaces of the disc resonators along the nodal circles. the present invention also envisages various structures of resonator systems in one of which said disc resonators interconnected with thin mechanical links are arranged in a stepwise fashion. so that said mechanical links of each intermediate one of said resonators are attached to but one face of said intermediate disc resonator. said mechanical links being disposed to one side of said intermediate disc resonator. whereas each said terminal disc resonator has said mechanical links attached to both face su rfaces thereof. connecting it at one side to the intermediate disc resonator and at the other side. to a support member.  
  In the proposed structure of the resonator system. said mechanical links interconnecting said disc resonators are arranged so that the respective diametral planes of said discs. including the axes of said respective mechanical links of any adjacent pair of said discs intersect at an angle (1 within a 90 to 180 range.  
  In this structure of the resonator system. one of the face surfaces of each said intermediate disc resonator is unoccupied. Thus. it becomes possible to position. on this unoccupied face surface of at least one of said intermediate disc resonators. a rejector resonator so that the latter should provide an attenuation or suppression pole.  
  In order to obtain an electromechanical filter of high selectivity without affecting the mechanical strength thereof. the present invention further envisages a struc ture of the resonator system. wherein said intermediate disc resonators are arranged coaxially and make up at least two sections. said sections being interconnected by a disc resonator so that said two sections are disposed to one side of said interconnecting disc resona- I01.  
  Furthermore. the present invention envisages a resonator system wherein at least two said disc resonators from the total plurality of said disc resonators. interconnected with said mechanical links attached to the face surfaces of said disc resonators at points corresponding to the nodal circles. have different geometrical dimensions. all said disc resonators being tuned to the same frequency for oscillation with the nodal circles. said resonators with different geometrical dimensions having different frequencies of side oscillation.  
  The present invention will now be explained in greater detail with reference to a description of several embodiments thereof taken in conjunction with the accompanying drawings. wherein:  
  FIG. I shows an electromechanical disc filter. according to the invention;  
 FIG. 2 is a view taken along line llll of FIG. I;  
  FIG. 3 illustrates the resonator system of an electromechanical disc filter. according to the invention;  
  FIG. 4 shows the disc resonator operating in a bending oscillation mode with a single nodal circle;  
  FIG. 4a is a diagram of distribution of the normal component of velocity V,, at the end surface of the resonator along its radius;  
  FIG. 4b shows a diagram of distribution of impedances 2,, at the end surface of the resonator along its radius;  
  FIG. 4c shows a diagram of distribution of the tangential (radial) component of velocity V at the end surface of the resonator along its radius;  
  FIG. 441 shows a diagram of distribution of impedances Z at the end surface of the resonator along its radius;  
  FIG. 5 shows the disc resonator operating in a bending oscillation mode with two nodal circles;  
  FIG. 5a shows a diagram of distribution of the normal component of velocity V,, at the end surface of the resonator along its radius;  
  FIG. 5b shows a diagram of distribution of impedances 2,, at the end surface of the resonator along its radius;  
  FIG. 50 shows a diagram of distribution of the tangential (radial) component of velocity V at the end surface of the resonator along its radius:  
 FIG. 5d shows a diagram of distribution of impedances Z at the end surface of the resonator along its radius;  
  FIG. 6 shows a resonator system comprising two disc resonators interconnected with peripheral mechanical links;  
  FIG. 6a shows the passage of a signal through a system comprising two disc resonators with peripheral mechanical links at the resonance frequencies of oscillation with nodal circles and nodal diameters;  
  FIG. 7 shows a resonator system comprising two disc resonators interconnected with mechanical links in accordance with the present invention;  
  FIG. 7a shows the passage of a signal through a system constructed in accordance with the present invention. at the resonance frequencies of oscillation with nodal circles and nodal diameters.  
  FIG. 8 illustrates another embodiment of the resonator system of an electromechanical disc filter. according to the invention;  
  FIG. 9 is a top view of the system illustrated in FIG. 8;  
  FIG. 10 illustrates still another embodiment of the resonator system of an electromechanical disc filter. according to the invention;  
  FIG. 11 is a top view of the system illustrated in FIG. 10:  
  FIG. 12 illustrates the resonator system shown in FIG. 8. additionally including rejector resonators:  
 FIG. 13 illustrates a resonator system comprising two sections of resonators: y 7  
  FIG. 14 illustrates a resonator system wherein the resonators have different geometrical dimensions.  
  An electromechanical disc filter constructed in accordance with the present invention is illustrated in FIG. I. It comprises a resonator system I which is the major functional part of the structure of the filter. as well as several attachment and fixture items. such as shows absorbing rubber supports 2. spacers 3. a base 4 with leads 5 soldered thereto and a screen 6 the above items being intended for positioning the resonator system l. for damping its vibration. for its hermetization. for supply and output of electric power and for protecting the system from external mechanical influences.  
  In addition to the above resonator system and auxiliary parts and fixtures. the electromechanical filter includes inductance coils 7 and permanent magnets 8 (FIG. 2) which are elements of a functionally complete electromechanical transducer assembly.  
  The present invention and the advantages thereof are connected with the improvements in the structure of the resonator systems of electromechanical disc filters. Therefore. the following disclosure is going to dwell primarily on the features pertaining to the construction of the resonator systems.  
  One of the structures of resonator systems. in accordance with the present invention. is illustrated in FIG. 3. This resonator system 1 includes an array of intermediate disc resonators 9, a pair of terminal disc resonators I0. mechanical links 11 and metal magnetostrictive rods 12.  
  The mechanical links ll serve to attach the terminal disc resonators 10 to the respective support sleeves 13 by means of which the resonator system 1 (FIG. I) is mounted in the shock absorbing supports 2; The sleeves 13 (FIG. 3) receive thereinside the inductance coils 7 (FIG. I). while the permanent magnets 8 are mounted externally of the sleeves 13.  
  Consider now the conditions under which there will be ensured in the mechanical links of the resonator system a practically pure mode of bending oscillation. These conditions are provided for when the disc resonators have excited therein bending oscillation with nodal circles.  
  Illustrated in FIG. 4a is a disc resonator and one of the extreme positions thereof when bending oscillation with a single nodal circle is excited in the disc. The diagrams in FIGS. 4b and 4d show the distribution of the normal component V, and tangential component V, of the velocities of the points on the face surface of the disc resonator along the radius thereof. FIGS. 4(- and 4e illustrate the distribution of the respective components 2,, and Z, of the impedance at the same points of the disc resonator. It is seen from the FIGS. 4a. b. c. d. e that when oscillation with a single nodal circle is excited in the disc. at points a belonging to a circle having a radius R the velocity V,, equals zero. while the impedance Z,, is infinite. A similar picture is observed in the case of oscillation with two nodal circles. Let us view FIGS. 51:, h, c. d. e. In this case. V,, equals zero and Z,, is practically infinite. respectively. at points b and c belonging to the circles with respective radii R and R;; which are the radii of the first and second nodal circles. respectively.  
  It can be readily comprehended that longitudinal mechanical links attached at the points a in FIG. 4a or at the points h and c in FIG. 4b in a resonator system including either two or more such disc resonators will have transmitted therethrough exclusively bending oscillation.  
  Let us further evaluate the advantage offered by electromechnaical disc filters contructed in accordance with the present invention over those of the prior art.  
  It is known that the coupling factor between disc resonators. as well as the band pass of the filter. are proportional to the ratio of the wave resistance of the mechanical links to the impedance values of the disc resonator at points of attachment of the mechanical links.  
  The above fact relates the width of the band pass of an electromechanical disc filter to the mechanical strength of the resonator system thereof. It can be understood that in order to have a relatively narrowbandpass electromechanical disc filter. it is necessary to reduce the wave resistance of its mechanical links. which can be attained by reducing the cross-sectional area of these mechanical links. i.e.. by reducing the mechanical strength of the resonator system. It is this fact that brings about the necessity of introducing additional untuned resonators into the structure of the hitherto known electromechanical disc filters with peripheral arrangement of the mechanical links.  
  It is be seen from FIGS. 4 and 5 that with the mechanical links attached at the points a. h and t. the coupling factor between the resonators is determined exclusively by the impedance values Z, at these points and by the wave resistance of the mechanical links to bending oscillation.  
  The above statement is true due to the fact that at these points the impedance values Z, are infinite. i.e.. the disc resonators exhibit infinite resistance to longitudinal oscillation in the mechanical links. when they oscillate in a mode with nodal circles. It is also seen from FIGS. 4 and 5 that the impedance values Z, at the points a, b. c are considerably greater than the imped ance values 2,, at the periphery of the disc. Besides. the wave resistance of the wire rods of which the mechanical links are made to bending oscillation is considerably lower than their resistance to longitudinal oscillation.  
  Thus, it is clear that. in comparison with the hitherto known resonator system with peripheral mechanical links the proposed structure of the resonator system. makes it possible to increase several times the mechanical strength of filters having the same band pass width. or what amounts to the same thing. makes it possible to have a filter with a substantially narrower band pass with structurally simple coupling of the disc resonators.  
  Another characteristic feature of the proposed structure of resonator systems is that it makes it possible to eliminate practically completely the side bandpasses present at the resonance frequency of bending oscillation with nodal diameters. The resonance frequencies of this type of oscillation of the two adjacent orders are. as a rule. close to the resonance frequency of oscillation with nodal circles (i.e.. the useful oscillation) and. therefore. are the most unwanted.  
  The frequency gap between the resonance frequencies of oscillation with nodal circles and that with nodal diameters is usually small and depends on the ratio of the diameter of the disc resonator to the thickness thereof. With the ratio of the diameter of the disc to its thickness increasing. the gap between the said resonance frequencies narrows.  
  For the advantages offered by the proposed electromechanical disc filter to becomes more apparent as far as the mono-frequency characteristics are concerned. let us draw a comparison between the conditions ofthe passage of signals through a resonator system with peripheral arrangement of the mechanical links and those of the passage of signals through a resonator system wherein the mechanical links are attached at the points of the face surface of the disc resonator. placed along a circle having a diameter equal to that of a nodal circle.  
  In both cases. in the disc resonators there take place at frequencies f, and f (FIGS. 6a. b and FIGS. 7a. h the resonances of oscillation. respectively. with nodal circles and nodal diameters. A signal is applied to the centre of the input resonator and is picked up at the centre of the output resonator. The respective points where a signal is applied and picked up are the points of attachment of the magnetostrictive rods of the respective transducers.  
  In the first case illustrated in FIGS. 6a. I). i. e.. in the case of a resonator system including two discs and peripheral mechanical links. there is excited in the input resonator at the frequency f, oscillation with nodal circles which is transmitted via the longitudinally oscillating mechanical links to the output resonator and then to the output electromechanical transducer. Oscillation with nodal diameters at the frequency f; cannot be directly excited when the resonator is excited at the centre thereof. since the impedance value to this oscillation. i.e.. the input resistance of the disc. at the centre thereof. is infinite. However. at a frequency differing from f, there is likewise excited in the disc oscillation with nodal circles. although the amplitude of this oscillation is many times weaker. However. that oscillation affects through the mechanical links the output resonator. exciting therein intensive oscillation with nodal diameters. Therefore. at the output of this resonator system with longitudinal oscillation in the linking elements there will always be present in the communication system at the frequency f: resonance oscillation of the centre of the resonator. which is transmitted to the magnetostrictive rod (not shown) and produces intensive side bandpasses in the filter.  
  In the second case illustrated in FIGS. 7a. b. i.e.. in the case of a resonator system including two resonators connected with mechanical links. in accordance with the present invention. oscillation with a nodal circle excited at the centre of the input resonator at the frequencyf, is transmitted to the mechanical links by the tangential component of the motion of the respective points on the disc. The bending wave propagates itself along the mechanical links toward the second disc where it excites oscillation with a nodal circle. It may appear at first glance that at the frequency]; oscillation with nodal diameters may be excited in the resonator system. as in the first case. i.e.. through weakened oscillation with nodal circles. However. in this case this does not take place. since the effort applied by the mechanical link to the output disc is directed tangentially. i.e.. in the direction of practically infinite values of the impedance of the disc to oscillation with nodal diameters. Consequently. coupling by this type of oscillation in the presently described case may be but extremely weak.  
 . 8 which ensures very low level of oscillation at the frequency f.&#39; at the output of the resonance system.  
  The above characteristic features of the disclosed structure of a resonator system with linking elements subjected to bending oscillation pave the road to creation of small-size mechanically strong electromagnetic disc filters rated for various operating frequencies and bandpass widths and being practically devoid of side bandpasses.  
  Indeed. when the dimensions of electromechanical disc filters are reduced due to the reduction of the size of the disc resonators. which is most expedient. the following is observed. as far as those latter are concerned. Firstly. the ratio of the diameter to the thickness is increased. which. as it has been already mentioned. results in the narrowing gap between the resonance frequencies of the main and side oscillation. and secondly. the impedance values diminish across the entire surface of the discs. which makes it necessary to reduce the cross-sectional area of the mechanical links. and therefore. to reduce the mechanical strength of the resonator system.  
  With the mechanical links being attached to the face surface of the discs at points placed along a circle having a diameter equal to the diameter of the nodal circle. there is a possibility of developing structures of resonator systems fundamentally new arrangement of the main components.  
  A characteristic feature of these novel structures is an arrangement of the resonators and their mechanical links. wherein either one or several discs of the resonator system have the mechanical links attached to but one of the face surfaces thereof. One of the embodiments of such a resonator system is illustrated in FIGS. 8 and 9 of the appended drawings.  
  In this structure. the disc resonators l4 and 15 are interconnected with a single mechanical link 16. The support sleeves are connected to the discs IS with mechanical links 18. The same face surface of the discs 15 is associated with the magnetostrictive rods 19 of the.  
 Provided that the mechanical links are attached. in  
 accordance with the invention. at points of a circle equalling a nodal circle. i.e.. the mechanical links transmit exclusively bending oscillation. in the lastmentioned structure the value of the coupling factor between two adjacent resonators depends on the orientation of the said diametral planes of these two adjacent discs relative to each other. i.e.. on the value the angle When 0: equals l the structure is. as shown in FIGS. 8 and 9. When a is less than 180. the coupling factor diminishes with the reduction of this angle a. A case when a equals is impractical because then the coupling factor between the two resonators equals zero. Thus. based on the structure of the resonator system illustrated in FIGS. 10 and 11, there may be created electromechanical disc filters which. although being of the same mechanical strength. would feature different bandpass widths. from very narrow ones to relatively broad ones.  
  The presence of freely accessible unoccupied face surfaces of the discs permits of using these surfaces for mounting of additional support means. so as to step up the rigidity of the resonator. system. as rwell as for mounting of rejector resonators to create specified attenuation or suppression poles-An embodiment of the present invention. incorporating such rejector resonators 20. is illustrated in FIG. 12.  
  FIG. 13 of the appended drawings presents an embodiment of a resonator system. in accordance with the invention. which is preferable to be employed in electromechanical disc filters of particularly high selectivity. In this structure. the resonator system is made up by individual sections wherein in each section the resonators 21 are arranged coaxially and parallel to each other. The mechanical links 22 are attached to both surf-aces of each resonator 21. The two sections are interconnected by a resonator 23 with the help of mechanical links 24 attached to but one face surface of the last-mentioned resonator. The unoccupied face surface of this disc resonator 23 is used to attach it toan additional support 25. Alternatively. this face surface. as well as the unoccupied face surfaces of the discs 21 of the two sections may be used for mounting thereon rejector resonators.  
  FIG. 14 of the appended drawings shows a disc resonator system wherein disc resonators 26 have geometrical dimensions that are different from those of disc resonator 27. all the disc resonators of the system being tuned to the same frequency of the main type of oscillation. i.e.. of oscillation with nodal circles and untuned to the side frequencies.  
  This structure of a resonator system is particularly suitable for incorporation in electromechanical disc filters featuring an increased degree of suppression of side oscillation.  
  The above examples of different structures of resonator systems are meant to convey a sufficiently full impression of the prospects they open up for improving various electrical and operational charateristics of electromechanical filters.  
  These structures of the resonator systems promise substantial improvement in a number of electrical. operational and economical characteristics of electromechanical filters.  
  Thus. a 5 9 resonator system constructed in accordance with the present invention and rated for mean frequency of I kHz bandpass has a volume. respectively. 3.5 cu.cm to 5.0 cu.cm; similar filters rated for mean frequency 500 kHz have respective volumes from L cu.cm to 2.0 cu.cm.  
  Electromechanical filters incorporating the resonator systems herein disclosed have relatively high mechanical strength. They have been found to withstand without altering their parameters. vibration loading within a range of vibration frequency up to 2.000 Hz with acceleration up to g. as well as repeated impacts with g acceleration and single impacts with g acceleration.  
  Practical implementation and manufacture of the proposed structures of electromechanical disc filters do not present any difficulties. since the techniques of making resonator systems using the methods of singlepoint and multiple-point electrostatic V pulse buttwelding have been already thoroughly developed and realized in practice by :numerous manufacturers.  
  What is claimed is: .l.-An electromechanical disc filter comprising: an inputelectromechanical transducer; a plurality of disc resonators arranged parallel to one another in spaced relationship and operable in a bending oscillation mode &#34;with nodal circles. said plurality including at least one intermediate disc resonator and a pair of terminal disc resonators; longitudinally extending mechanical links interconnecting said disc resonators. said mechanical links being attached to the face surfaces of the respective ones of said disc resonators at points along a &#39;circle having a diameter equal to the diameter of a nodal circle of said disc resonator; support elements for mounting said terminal disc resonators; an output electromechanical transducer said disc resonators being arranged in a stepwise fashion; those of said mechanical links that are associated with each said intermediate disc resonator being attached to but one face surface thereof. said mechanical links being situated to one side of said intermediate disc resonator: each said terminal disc resonator having said mechanical links attached to both face surfaces thereof. said last-mentioned mechanical links at one side of said terminal disc resonator connecting it with the adjacent one of said intermediate disc resonators and at the other side thereof connecting it to the respective one of said support elements.  
  2. An electromechanical disc filter as claimed in claim 1. wherein said mechanical links interconnecting said intermediate disc resonator and terminal disc resonators are parallel to one another and are so arranged that the diametral planes of said discs including the axes of the respective ones of said mechanical links of any two adjacent ones of said discs of said resonatory system intersect at an angle a within a range from 90to 3. An electromechanical disc filter as claimed in claim I, wherein at least one of said disc resonators has attached to the unoccupied face surface thereof a rejector resonator so that said rejector resonator creates an attenuation pole.  
  4. An electromechanical filter as claimed in claim I. wherein two sections are attached by means of links to at least one of said intermediate resonators to one of its face surfaces. each of said sections comprising a plurality of coaxial disc resonators disposed parallel to one another in a spaced relationship.  
  5. An electromechanical disc filter comprising: an input electromechanical transducer; a plurality of disc resonators operable in a bending oscillation mode with nodal circles. said plurality including at least one intermediate disc resonator and a pair of terminal disc resonators; mechanical links interconnecting said disc resonators; an output electromechanical transducer; said mechanical links being attached to the face surfaces of the respective ones of said disc resonators at points thereof along a circle having a diameter equal to the diameter of a nodal circle of said disc resonator: at least two of said plurality of disc resonators having different geometrical dimensions; all said disc resonators being tuned to the same frequency of oscillation withnodal circles; said disc resonators having different geometrical dimensions being tuned to different frequencies of side oscillation.  
  6. An electromechanical disc filter comprising: an input electromechanical transducer: a plurality of disc resonators arranged parallel to one another in spaced relationship and operable in a bending oscillation mode with a single nodal circle. said plurality including at least one intermediate disc resonator and a pair of terminal disc resonators: longitudinally extending mechanical links interconnecting said disc resonators. said mechanical links being attached to the face surfaces of said disc resonators at points making only tangentialradial and angular motion and disposed along a circle having a diameter equal to 0.68 of the external diameter of said disc resonator.  
  7. An electromechanical disc resonator comprising: an input electromechanical transducer: a plurality of disc resonators arranged parallel to one another and operable in a bending oscillation mode with two nodal circles. said plurality comprising at least one intermediate disc resonator and a pair of terminal disc resonators: longitudinally extending mechanical links interconnecting said disc resonators. said mechanical links being attached to the face surfaces of said disc resonators at points making only tangential-radial and angular motion and disposed along a circle having a diameter equal to 0.82 of the external diameter of said disc reso nator.  
  8. An electromechanical disc filter. comprising: an input electromechanical transducer: a plurality of disc resonators arranged parallel to one another and operable in a bending oscillation mode with two nodal circles. said plurality comprising at least one intermediate disc resonator and a pair of terminal disc resonators; longitudinally extending mechanical links interconnecting said disc resonators. said mechanical links being attached to the face surfaces of disc resonators at points making only tangential-radial and angular motion and disposed along a circle having a diameter equal to 0.36 of the external diameter of said disc reso-