Distributed-constant filter

Abstract: A quarter-wave distributed-constant dielectric filter or resonator (30) having a ceramic body (32) which typically is composed principally of barium titanate. The ceramic filter body has one or more resonance holes (40) extending therethrough. A conductive covering (42) of silver or the like on the filter body has a portion formed on the surface defining each reso­ nance hole. Mounted in each resonance hole is a prefabricated capacitor (44) having a first terminal (60) extending from within the resonance hole and a second terminal (62) wholly received in the resonance hole. The second terminal is electrically coupled to the conductive covering on the surface of the resonance hole. The capacitance of the capacitor or capacitors can be known before they are mounted to the filter body, so that the filter is readily manufacturable to exact electrical charac­ teristics desired.

Description: BACKGROUND OF THE INVENTION Our invention relates generally to filters or resonators, and more specifically to a distributed-constant filter or resonator of the class having a dielectric ceramic body. The device of our invention lends itself to use in communication equipment such as used for car telephone, citizens' radio service, cordless telephone, etc. Quarter-wave distributed-constant filters find extensive usage in communication equipment. Although a variety of constructions have been suggested for this type of filter, Nishikawa et al. U.S. Pat. No. 4,464,640 represents an example that we believe is most pertinent to our invention. This prior art device is such that a dielectric body of cylindrical shape, with a lead wire extending axially therethrough, is inserted in each of two or more resonance holes formed in a block of dielectric ceramic material. Capacitive coupling is provided between the lead wires and the electroconductive layers on the surfaces of the ceramic block defining the resonance holes. Basically, we favor this prior art filter because of the simplicity of construction. We do, however, object to the unavoidable fluctuations in the performance characteristics of filters actually manufactured on the fundamental construction described previously. Such fluctuations are unavoidable because the dielectric bodies of plastic or ceramic material are not usually fabricated to very close dimensional tolerances. SUMMARY OF THE INVENTION We propose hereby a novel distributed-constant filter or resonator that is readily manufacturable to desired electrical characteristics. Briefly, the distributed-constant filter or resonator of our invention is defined in claim 1. A filter according to the preamble of claim 1 is known from figure 1 of patent document JP-A-62 136 103. The features of claims and other features and advantages of our invention and the manner of realizing them will become more apparent, and the invention itself will best be understood, from a study of the following description and appended claims, with reference had to the attached drawings showing several preferable embodiments of our invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan of a distributed-constant filter; FIG. 2 is an axial section through the FIG. 1 filter, taken along the line II-II in FIG. 1; FIG. 3 is an enlarged, exploded perspective view of the capacitor used in the FIGS. 1 and 2 filter, the capacitor being shown together with the connector connecting the second capacitor terminal to the conductive covering on the filter body; FIG. 4 is a schematic diagram of an electric circuit equivalent to the FIGS. 1 and 2 filter; FIG. 5 is a perspective view of another form of filter; FIG. 6 is a top plan of the FIG. 5 filter; FIG. 7 is a section through the FIGS. 5 and 6 filter, taken along the line VII-VII in FIG. 6; FIG. 8 is a schematic electrical diagram of an electric circuit equivalent to the FIGS. 5-7 filter; FIG. 9 is a top plan of a preferred form of filter of our invention; FIG. 10 is a section through the FIG. 9 filter, taken along the line X-X in FIG. 9; FIG. 11 is also a section through the FIG. 9 filter, taken along the line XI-XI in FIG. 9; FIG. 12 is an enlarged perspective view of the filter body, with the conductive covering formed thereon, of the FIGS. 9-11 filter; FIG. 13 is a top plan of the assembly of the capacitors and metal-made shield of the FIGS. 9-11 filter; FIG. 14 is a section through the FIG. 13 assembly, taken along the line XIV-XIV in FIG. 13; FIG. 15 is an elevation of the shield of the FIGS. 9-11 filter; FIG. 16 is a view similar to FIG. 10 but showing a further preferred form of filter of our invention; FIG. 17 is a top plan of a further preferred form of filter of our invention; FIG. 18 is a section through the FIG. 17 filter, taken along the line XVIII-XVIII in FIG. 17; FIG. 19 is a view similar to FIG. 18 but showing a further preferred form of filter of our invention; FIG. 20 is a partial section through a further preferred form of filter of our invention; FIG. 21 is a section through the assembly of capacitors and metal-made shield of a further preferred form of filter of our invention; FIG. 22 is a top plan of a further preferred form of filter of our invention; FIG. 23 is a section through a further preferred form of filter of our invention; FIG. 24 is a top plan of one of the capacitor assemblies of the FIG. 23 filter; FIG. 25 is a section through the FIG. 24 capacitor assembly, taken along the line XXV-XXV in FIG. 24; and FIG. 26 is a left hand side elevation of the FIGS. 24 and 25 capacitor assembly. DESCRIPTION OF THE PREFERRED EMBODIMENTS We will now describe in detail the filter 30 of FIGS. 1 and 2. This filter is a quarter-wave distributed-constant dielectric ceramic resonator, having a cylindrical dielectric body 32 of a ceramic material composed principally of barium titanate. The dielectric filter body 32 has a pair of opposite end faces 36 and 38, with a resonance hole 40 extending therebetween in coaxial relation to the filter body. A conductive covering 42 is formed on both inside and outside surfaces, as well as the bottom end face 38, of the tubular filter body 32. Only the top end face 36 of the filter body 32 is left exposed. Typically, the conductive covering 42 may be formed by coating a silver paste on the required surfaces of the filter body 32 and by subsequently baking the coating. Mounted in the resonance hole 40 in the filter body 32 is a prefabricated coupling capacitor 44 illustrated in axial section in FIG. 2. FIG. 3 also shows only the capacitor 44 in enlarged and exploded perspective. It will be noted from these figures that the capacitor 44 has a dielectric ceramic body 46 disposed coaxially with the filter body 32. An electrode 48, in the shape of a tube closed at one end, is fitted over the top end 50, as well as the neighboring part of the surface 52, of the capacitor body 46. Another electrode 54 of similar shape is fitted over the bottom end 56, as well as the neighboring part of the surface 52, of the capacitor body 46. As indicated in FIG. 3, the opposed ends of the two electrodes 48 and 54 have a spacing 58 therebetween. The electrostatic capacitance between the electrodes 48 and 54 is inversely proportional to the spacing 58. We recommend that the electrodes 48 and 54 be formed by plating a suitable metal over the entire surfaces 50, 52 and 56 of the capacitor body 46 and then by grinding off the midportion of the plating to create the spacing 58. The dimension of the spacing 58 parallel to the axis of the capacitor body 46, and therefore the capacitance offered by the electrodes 48 and 54, are readily adjustable by varying the width to which the metal plating on the capacitor body is ground off. The capacitor 44 further comprises a pair of terminals 60 and 62 in electrical contact with the pair of electrodes 48 and 54, respectively. The first or top terminal 60 comprises a metal cap 64 fitted over the top electrode 48, and a lead wire 66 soldered to the metal cap and extending from within the resonance hole 40 beyond the plane of the top end face 36 of the filter body 32. We suggest that the metal cap 64 be both self-biased into firm engagement with the top electrode 48 and soldered thereto. The soldering of the metal cap to the top electrode will be easy by preforming a solder plating on the metal cap and by heating the metal cap, and so melting the solder, after the metal cap has been pressfitted over the top electrode. The second or bottom terminal 62 likewise comprises a metal cap 68 fitted over the bottom electrode 54, and a lead wire 70 welded to the metal cap 68. The bottom terminal metal cap 68 can be coupled to the bottom electrode 54 in the same way as the top terminal metal cap 64 is to the top electrode 48. The bottom terminal lead wire 70 is disposed collinearly with the top terminal lead wire 66 and is short enough to be wholly received in the resonance hole 40. As indicated in FIG. 2, a plastic molding 72 encases all but the leads 66 and 70, and parts of the metal caps 64 and 68, of the capacitor 44. A metal-made connector 74 electrically connects the bottom terminal 62 to the conductive covering 42 on the inside surface of the filter body 32. We have shown the connector 74 of this particular embodiment as a one-piece construction of a relatively small diameter tubular portion 76 and a larger diameter tubular portion 78 in concentric arrangement. The smaller diameter portion 76 is closely fitted over the bottom terminal lead wire 70. Made resilient by having notches 80 cut therein at constant angular spacings, the larger diameter portion 78 is pressfitted in the resonance hole 40 for contact with the conductive covering 42. The connector 74 may further be soldered as at 82 to the conductive covering 42 and to the bottom terminal 62. We recommend the coating of a solder paste on the required parts of the connector 74. The solder paste may be fused after mounting the connector 74 in place. We understand that, in use, the filter 30 is enclosed in a grounded metal casing, not shown. This unshown casing is to be electrically connected to the conductive covering 42 on the filter body 32. Typically, the dielectric filter body 32 has an axial dimension of 10.0 millimeters (mm), an outside diameter of 6.0 mm, and an inside diameter of 2.8 mm. FIG. 4 is a diagram of an electric circuit equivalent to the dielectric filter 30. The resonance circuit comprising capacitance C1 and inductance L1 is constituted of the conductive covering 42 on the filter body 32. The coupling capacitance C a at the input stage corresponds to the capacitor 44 in the resonance hole 40. Constructed as in the foregoing, the distributed-constant filter 30 gains the following advantages: 1. The capacitance of the coupling capacitor 44 can be known before it is mounted in place on the filter body 32, the capacitor being prefabricated instead of being fabricated in place on the filter body. Therefore, in the manufacture of filters in accordance with our invention, only those prefabricated capacitors may be employed which have the desired capacitance values. Experiment has proved that the yield of the dielectric filters of the desired capacitance values can be improved to approximately 80% in accordance with our invention. 2. The capacitance of the coupling capacitor 44 is readily adjustable by varying the spacing 58 between the pair of electrodes 48 and 54 on the opposite ends of the capacitor body 46. 3. The coaxial arrangement of the capacitor 44 within the filter body 32 makes it easy to connect the bottom terminal 62 to the conductive covering 42 on the filter body 32 via the connector 74. 4. The resiliency of the connector 74 contributes to the ready and positive connection of the capacitor bottom terminal 62 to the conductive covering 42. 5. The metal caps 64 and 68 of the capacitor terminals 60 and 62 afford firm connection of the capacitor body 46 to the leads 66 and 70. 6. The resonance frequency is readily variable as the coupling capacitor 44 is displaced axially of the filter body 32 within the resonance hole 40. Embodiment of FIGS. 5-8 FIGS. 5-7 illustrate another form of quarter-wave distributed-constant dielectric filter 30 a in accordance with our invention. The filter 30 a has a dielectric body 32 a in the shape of a box having a pair of opposite end faces 36 a and 38 a and four side faces 37 a . A pair of resonance holes 40 a extend between the end faces 36 a and 38 a in parallel spaced relation to each other. Positioned intermediate the two resonance holes 40 a , a coupling hole 39 a also extends between the end faces 36 a and 38 a . A grounded conductive covering 42 a covers all but the top end face 36 a , and the surface bounding the coupling hole 39 a , of the filter body 32 a . Mounted in the respective resonance holes 40 a are a pair of prefabricated coupling capacitors 44 a which are each of the same construction as the coupling capacitor 44 of the FIGS. 1-4 filter 30. Thus each coupling capacitor 44 a comprises a dielectric body 46 a of cylindrical shape, and a pair of electrodes 48 a and 54 a on the opposite ends of the filter body 46 a , a pair of terminals 60 a and 62 a in electrical contact with the respective electrodes 48 a and 54 a , and a molded plastic enclosure 72 a enveloping the required parts of the capacitor. The top terminal 60 a of each coupling capacitor 44 a comprises a metal cap 64 a and a lead wire 66 a . The bottom terminal 62 a comprises a metal cap 68 a and a lead wire 70 a . The top terminal lead 66 a extends outwardly of one associated resonance hole 44 a . Shorter than the top terminal lead 66 a , the bottom terminal lead 70 a is wholly disposed in the resonance hole 44 a . A metal-made connector 74 a connects the bottom terminal 62 a to the conductive covering 42 a via the solder 82 a . Typically, the filter body 32 a is sized 10.0 mm (height) by 13.0 by 6.0. The diameter of each resonance hole 40 a is 2.8 mm, and that of the coupling hole 39 a is 1.3 mm. FIG. 8 represents an electric circuit equivalent to the filter 30 a . The two resonance circuits comprising capacitors C1 and C2 and inductors L1 and L2 are constituted of the dielectric body 32 a and the grounded conductive covering 42 a thereon. An inductive impedance Z1 interconnects the two resonance circuits. The coupling hole 39 a contributes to the creation of the inductive impedance Z1. The pair of capacitors 44 a provide input coupling capacitance C a and output coupling capacitance C b , so that the leads 66 a of these capacitors function not only as such but also as terminals for connection of the filter 30 a to other circuits. The filter 30 a comprising the two resonators is essentially equivalent in construction to the FIGS. 1-4 filter 30. Thus the filter 30 a gains the same advantages as set forth in connection with the filter 30. Embodiment of the invention of FIGS. 9-15 The distributed-constant filter 30 b shown in FIGS. 9-11 also comprises a dielectric body 32 b with a conductive covering 42 b thereon, and two coupling capacitors 44 b mounted one in each resonance hole 40 b in the filter body. Basically, this filter 30 b is akin in construction and operation to the FIGS. 5-8 filter 30 a . However, in the filter 30 b , the two coupling capacitors 44 b are integrally combined with a metal-made shield 90 via an insulating support 92 which is molded from a thermoplastic. The insulating support 92 may be molded in one piece with the coupling capacitors 44 b and metal shield 90 before the capacitors are mounted to the filter body 32 b . FIGS. 13 and 14 illustrate the one-piece assembly 94 of the coupling capacitors 44 b , metal shield 90 and insulating support 92. As will be understood from FIG. 15, taken together with FIGS. 13 and 14, the metal shield 90 comprises a web 96 overlying the coupling hole 39 b and the neighborhoods of the resonance holes 40 b , a pair of side flanges 98 depending from the opposite sides of the web 96 to be held against those parts of the conductive covering 42 b which are on the longer side faces of the filter body 32 b , and four upstanding lugs 100 for use in mounting the filter 30 b to a circuit board, not shown, and as grounding terminals. The web 96 is secured to the insulating support 92. FIG. 14 best indicates that the insulating support 92 comprises a flat major portion 102 interconnecting the two coupling capacitors 44 b , a pair of depending bosses 104 for determination of the radial positions of the coupling capacitors in the resonance holes 40 b , and a pair of flanges 106 for determination of the axial positions of the coupling capacitors in the resonance holes. The insulating support 92 envelopes all but the leads 66 b and parts of the metal caps 64 b and 68 b of the coupling capacitors 44 b . In assembling the filter 30 b of FIGS. 9-11 the assembly 94 of the coupling capacitors 44 b , metal shield 90 and insulating support 92 may be mounted to the filter body 32 b having the conductive covering 42 b preformed thereon. The depending bosses 104 of the insulating support 92, which envelope the coupling capacitors 44 b , are shaped and sized to fit in the resonance holes 40 b in the filter body 32 b . Therefore, these bosses may be readily inserted in the resonance holes 40 b , to a depth determined by the thickness of the insulating support flanges 106 resting on the top of the filter body 32 b . It is thus seen that the coupling capacitors 44 b can be readily mounted in position on the filter body 32 b . As best illustrated in FIG. 11, the pair of side flanges 98 of the metal shield 90 have the spacing therebetween so determined as to be closely held against those parts of the conductive covering 42 b which are on the longer sides of the filter body 32 b . The mounting of the metal shield 90 is made easier by the fact that the metal shield 90 permits some resilient displacement of the side flanges 98 away from each other when they are being fitted over the filter body 32 b . Preferably, and as indicated at 108 in FIG. 11, the metal shield 90 may be soldered to the conductive covering 42 b for positive mechanical and electrical connection thereto. So mounted to the filter body 32 b , the coupling capacitors 44 b are electrically coupled to the conductive covering 42 b in the same way as in the two foregoing disclosed filters 30 and 30 a . For mounting the thus completed filter 30 b to an un shown circuit board, the lugs 100 of the metal shield 90 may be inserted in associated holes in the circuit board and grounded. The leads 66 b may be connected to the signal lines on the circuit board. The filter 30 b possesses the following advantages, in addition to those set forth in conjunction with the filters 30 and 30 a : 1. The two coupling capacitors 44 b and the shield 90 are combined into the single assembly 94 via the insulating support 92. The assemblage of the filter 30 b is thus made materially easier with the reduction of the number of parts that must be put together. 2. The two coupling capacitors 44 b , as well as the leads 66 b , can be maintained in exact positions relative to each other as the capacitors are supported by the metal shield 90 capable of manufacture to close dimensional tolerances. 3. As the leads 66 b are held with little or no variations in the spacing therebetween, fluctuations in the electrical characteristics of the filter are reduced to a minimum. 4. The shield 90, being configured to fit over the top and pair of opposite sides of the filter body 32 b , is readily manufacturable as by cutting and bending of sheet metal and is readily mountable to the filter body. Embodiment of FIG. 16 The filter 30 c shown in FIG. 16 is analogous in construction with the FIGS. 9-15 filter 30 b except that in this filter 30 c , the bottom terminals 62 c of the two coupling capacitors 44 c are electrically coupled to the conductive covering 42 c on the filter body 32 c via conductive grains 110 which are typically made of copper. The size of the conductive grains 110 may be determined so as to be filled in the annular spaces around the bottom leads 70 c within the resonance holes 40 c and may normally range from approximately 0.2 to 1.0 mm. For connecting the capacitor bottom terminals 62 c to the conductive covering 42 c via the conductive grains 110, the filter body 32 c may first be placed upside down, and a required number of conductive grains may be charged into the resonance holes 40 c together with a solder paste. Then the solder paste may be heated and allowed to solidify thereby electrically connecting the capacitor bottom terminals 62 c to the conductive covering 42 c via the solder 82 c itself and the conductive grains 110. This filter 30 c has the advantage, in addition to those enumerated in connection with the FIGS. 9-15 filter 30 b , of the ease with which the capacitor bottom terminals 62 c can be electrically coupled to the conductive covering 42 c on the filter body 32 c . The same method of connection by conductive grains is, of course, applicable to the FIGS. 1-4 filter 30 having but one resonance hole 40. Embodiment of FIGS. 17-18 The filter 30 d of FIGS. 17 and 18 is similar in construction to the FIG. 16 filter 30 c except that the filter 30 d additionally comprises an insulating circuit board 112. This circuit board is provided with a pair of spaced-apart conductive layers 114 to provide capacitance between the input and output leads 66 d . The circuit board 112 has formed therein two holes 116 through which extend the leads 66 d . Consequently, the positional relationship between the pair of capacitors 44 d can be determined by the circuit board 112 before they are integrally combined by the insulating support 92 d . The insulating support 92 d envelopes the circuit board 112 and the conductive layers 114 except the space between the conductive layers. The capacitance offered by the space between the conductive layers 114 contributes to the improvement of the frequency selectivity of the filter 30 d . Embodiment of FIG. 19 In FIG. 19 is shown a slight modification of the FIGS. 17-18 filter 30 d . The modified filter 30 e features a capacitive element formed by a pair of electrodes 118 on a dielectric ceramic baseplate 120. The capacitive element is disposed on the metal shield 90 e for capacitively coupling the pair of leads 66 e , and the electrodes 118 are electrically connected to the leads 66 e via sheet-metal connectors 122. Additionally, in this filter 30 e , the top end of each resonance hole 40 e has an annular recess 124, and the outer edges of the top end face of the filter 32 e is also recessed at 126. The conductive covering 42 e is formed also on the surfaces defining the recesses 124 and 126. The creation of the additional conductive covering on parts of the top end face 36 e serves the purpose of increasing the dielectric constant of the dielectric body 32 e and, stated conversely, of decreasing the length of the resonance holes 40 e and, in consequence, the height of the filter body 32 e . The additional conductive covering is formed in this embodiment on the surfaces defining the recesses 124 and 126 because this method makes it possible to accurately determine the areas on which the additional covering is to be formed. The additional conductive covering may first be formed, as by coating or plating, on the entire top end face 36 e of the filter body 32 e or beyond the boundaries of the recesses 124 and 126. Then the top end face 36 e may be ground, leaving the additional conductive covering only on the surfaces defining the recesses 124 and 126. Embodiment of FIG. 20 The filter 30 f of FIG. 20 is analogous in construction with the FIGS. 9-15 filter 30 b except for the absence of the metal-made shield 90. This filter 30 f may therefore be put to use with a separate shield. The filter 30 f also differs from the FIGS. 9-15 embodiment in the method of connecting the capacitor bottom terminals 62 f to the conductive covering 42 f on the filter body 32 f . The bottom terminal leads 70 f of the filter 30 f are bent right-angularly and soldered directly at 82 f to the conductive covering 42 f within the resonance holes 40 f . The capacitor bottom terminals can be connected to the conductive covering no less easily and positively than by the other methods disclosed in the foregoing. Embodiment of FIG. 21 FIG. 21 shows a modification 94 g of the FIG. 14 assembly 94 of the coupling capacitors 44 b , metal shield 90 and insulating support 92. The modified assembly 94 g differs from the assembly 94 in having no flat major portion 102 of the insulating support. Thus, in the modified assembly 94 g , the insulating support is divided into two discrete portions 92 g each comprising a boss 104 g and a flange 106 g . The two capacitors 44 g and the discrete insulating supports 92 g are joined in the prescribed relative positions solely by the web 96 g of the metal-made shield 90 g . The capacitor bottom terminal leads 70 g are bent right-angularly for connection to the conductive covering on the filter body as in the FIG. 20 filter 30 f . Embodiment of FIG. 22 The filter 30 h seen in FIG. 22 has three resonance holes 40 h and two coupling holes 39 h formed in a filter body 32 h but is similar in fundamental construction to the FIGS. 5-8 filter 30 a . The three resonance holes 40 h are arranged in a row, and two coupling capacitors 44 h are mounted one in each of the two outer holes 40 h . The filter 30 h with the three resonator stages offers the same advantages as set forth in reference to the foregoing embodiments. Embodiment of FIGS. 23-26 The filter 30 i of FIGS. 23-26 is essentially a combination of two filters 130 and 130′, each constructed like the FIG. 20 filter 30 f , in side-by-side arrangement. The output capacitor 44 i of the first filter 130 and the input capacitor 44 i ′ of the second filter 130′ have no top leads. Also, the output capacitor 44 i of the first filter 130 and the input capacitor 44 i ′ of the second filter 130′ are interconnected by a conductive layer 132 on a ceramic baseplate 134 by having their metal caps 64 i and 64 i ′ soldered at 136 and 136′ to the conductive layer 132. The metal-made shield 90 i of the filter 30 i is secured to the insulating baseplate 134 instead of being formed in one piece with the insulating supports 92 i and 92 i ′. The insulating baseplate 134 has formed therein two holes 138 and 138′ for the insertion of the input leads 66 i and 66 i ′. In assembling the filter 30 i there may first be prepared an assembly 140, FIGS. 24-26, of the two coupling capacitors 44 i of the first filter 130 integrally combined with the insulating support 92 i . Another similar assembly, not shown, may also be prepared in which the two coupling capacitors 44 i ′ of the second filter 130′ are combined with the insulating support 92 i ′. Then the two assemblies may be mounted to the common metal shield 90 i via the insulating baseplate 134. The two filters 130 and 130′ may also be secured to each other as by an adhesive, not shown. The filter 30 i gains the same advantages as the foregoing disclosed filters 30-30 h . Possible Modifications Despite the foregoing detailed disclosure we do not wish our invention to be limited by the exact details of the illustrated embodiments. The following is a brief list of possible modifications or alterations of the foregoing embodiments which we believe all fall within the scope of our invention: 1. In connecting the bottom terminals of the capacitors to the conductive covering on the filter body as in the FIG. 16 filter 30 c , the conductive grains may be charged into the resonance holes together with a solder paste attached thereto, instead of separately charging the conductive grains and the solder paste. 2. The conductive grains of the FIG. 16 filter 30 c may be replaced by much smaller particles, with an average size of 10 microns or so, of copper or like conductive material. Other possible substitutes for the conductive grains are particles of the same ceramic material as the dielectric filter body with platings of copper or the like thereon, and particles, grains or pieces of iron or other metals. 3. Particles or other pieces of solder may be employed in place of solder paste for soldering the terminal connectors conductive grains, etc. 4. The inventive concepts may be applied to half-wave distributed-constant filters in which the conductive covering is absent from the bottom end face of the filter body. 5. The pair of leads of each capacitor may be coupled to the electrodes via various means other than the metal caps. 6. The bottom lead of each capacitor may be dispensed with if the bottom metal cap is soldered to the conductive covering on the filter body via the connector, conductive grains, etc. 7. In the FIGS. 17 and 18 filter 30 d , instead of obtaining capacitance by the conductive layers 114 on the circuit board 112, a pair of sheet metal pieces may be embedded in the insulating support 92 d with a gap therebetween and may be connected to the top leads 66 d . 8.The conductive grains and solder paste of the FIG. 16 filter 30 c may be replaced by conductive grains with solder plating layer.

Claims: A distributed-constant filter of the type having a dielectric filter body (32b or 32c or 32e or 32f or 32h or 32i) having a pair of opposite end faces, with at least two resonance holes (40b or 40c or 40e or 40f or 40h) extending through the filter body between the pair of end faces, a conductive covering (42b or 42c or 42e or 42f) on the filter body including an inner portion formed on the surface of the filter body defining each resonance hole, and at least two capacitors (44b or 44c or 44d or 44g or 44h or 44i) electrically connected to the inner portion of the conductive covering, characterized in that each capacitor (44b or 44c or 44d or 44g or 44h or 44i) is at least partly disposed in the resonance hole in the filter body, that the distributed-constant filter further comprises holding means (90, 92 or 92d or 90e or 92g, 96g or 92i) for mechanically interconnecting the capacitors (44b or 44c or 44d or 44g or 44h or 44i) for holding them in prescribed positions relative to each other and to the filter body. The distributed-constant filter of claim 1 further comprising a metal-made shield (90 or 90e) mounted to the filter body. The distributed-constant filter of claim 1 wherein the holding means for mechanically interconnecting the capacitors comprises: (a) an insulating support (92 or 92d or 92g or 92i) mechanically interconnecting the capacitors and mounted to the filter body for holding the capacitors in prescribed positions relative to each other and to the filter body, and (b) a metal-made shield (90 or 90e) integrally combined with the insulating support. The distributed-constant filter of claim 3 wherein the insulating support (92 or 92d or 92g or 92i) is formed to include portions enveloping the capacitors and received in the resonance holes in the filter body. The distributed-constant filter of claim 3 wherein the filter body is boxlike in shape, having two pairs of opposite side faces in addition to the pair of opposite end faces, and wherein the metal-made shield (90) comprises: (a) a web (96) overlying one of the opposite end faces of the filter body; and (b) a pair of side flanges (98) extending in parallel spaced relation to each other from opposite sides of the web and held against one pair of opposite side faces of the filter body. The distributed-constant filter of claim 5 wherein the conductive covering includes outer portions formed on the side faces of the filter body and electrically connected to the metal-made shield. The distributed-constant filter of claim 3 further comprising two circuit boards (112) as the insulating support.

Inventors: AKIYAMA ISAO, IGARASHI MASAO, IGUCHI YOSHIAKI TAIYOSO, KAZAMA SATOSHI, KUMAGAI KAZUHIRO, TAKEDA YOSHINOBU, YAMAKI MAMORU, AKIYAMA, ISAO, IGARASHI, MASAO, IGUCHI, YOSHIAKI TAIYOSO, KAZAMA, SATOSHI, KUMAGAI, KAZUHIRO, TAKEDA, YOSHINOBU, YAMAKI, MAMORU
Applicants: TAIYO YUDEN KK, TAIYO YUDEN CO., LTD.
Application year: 1989
Main classification: H01P1
IPC codes: H01P1