RESONATOR AND FILTER USING IT

Abstract: A resonator constituted of an external conductor (1), a dielectric plate (2), a resonating capacitance element, an input terminal (5) and an output terminal (6). The plate (2) is fixed at the upper and lower ends to the upper and lower walls of the conductor (1), respectively. The resonating capacitance element is constituted of electrodes composed of metallic thin layers or metallic plates respectively provided on the front and back of the plate (2). The lower end of one of the electrodes is electrically connected to the lower wall of the conductor (1), and a gap is formed between the upper end of the one electrode and the upper wall of the conductor (1). The upper end of the other electrode is electrically connected to the upper wall of the conductor (1), and a gap is formed between the lower end of the other electrode and the lower wall of the conductor (1).

Description: Technical Field The present invention relates to a resonator that is used for the elimination of noise, the splitting and synthesis of signals, etc., in radio communication devices, broadcast devices, and so on, and also relates to a filter comprising this resonator. BACKGROUND ART Resonators composed of capacitors and coils which are lumped-parameter circuit elements, or helical resonators have been conventionally used in relatively low frequency bands, such as short wave and ultrashort wave bands. Fig. 1 is a vertical cross section of a conventional helical resonator, and Fig. 2 is a horizontal cross section thereof. This helical resonator comprises an external conductor 201; a capacitor electrode 203; insulators 204 1 and 204 2 ; a helical resonance element 202 at one end mechanically fixed to and electrically connected with the inside wall of the external conductor 201 , wound coil-like in its middle portion, attached at the other end to the capacitor electrode 203 , and fixed to the inside wall of the external conductor 201 via the insulators 204 1 and 204 2 ; a movable electrode 205 ; a drive screw 206 to one end of which the movable electrode 205 is attached, and which passes through the external conductor 201 ; a lock nut 207 that is used to fix the drive screw 206 to the external conductor 201 ; and input/output coupling elements and input/output terminals (not shown) With this helical resonance element, the resonance frequency can be finely tuned by rotating the drive screw 206 forward or backward to move the movable electrode 205 ahead or back so that the capacity of the electrode 203 can be varied. The conventional resonator described above has the following drawbacks. Since the helical resonance element 202 is formed by the winding of a metallic wire or a relatively thin rod-shaped conductor in the form of a coil, not only is the heat-radiating surface area of the helical resonance element 202 itself small, but the thermal conductivity into the external conductor 201 is poor, so the heat produced by power loss in the helical resonance element 202 is not effectively radiated from the helical resonance element 202 and the external conductor 201 , and the resonance frequency fluctuates as a result of distortion due to the elevated temperature of the various constituent components of the resonator. The ends of the helical resonance element 202 are directly or indirectly supported by and fixed to the inside wall of the external conductor 201, but the middle portion is not supported by any support, and is instead formed so that it maintains a coiled posture by its own rigidity, so vibration resistance is poor, fabrication is difficult, and the cost is high. When the diameter of the wire or rod that forms the helical resonance element 202 is relatively large, distortion of the helical resonance element 202 itself due to the elevated temperature of the helical resonance element 202 repeatedly applies mechanical strain to the insulators 204 1 and 204 2 through the electrode 203, and in severe cases the insulators 204 1 and 204 2 would be broken. Because of its high impedance, a helical resonance element has inferior withstand voltage characteristics. When a filter is constructed from such a helical resonance element, the various above-mentioned drawbacks encountered with a helical resonance element appears as drawbacks directly in the filter. CH-A-315 733 discloses a resonator comprising an outer cylindrical conductor and an inner cylindrical conductor. A first terminal is connected to the inner conductor, whereas a second terminal is connected to the outer conductor. The end portions of the inner and outer conductors are short circuited. The other end portions are connected to a capacity. DISCLOSURE OF THE INVENTION It is object of the present invention to provide a resonator in which heat is effectively radiated away from the capacitor element and external conductor, the fluctuation in resonance frequency is extremely small, the vibration resistance is excellent, and the impedance is low, and to provide a filter in which this resonator is used. The resonator according to the present invention comprises: an external conductor; a variable capacitor element comprising a first fixed electrode composed of a metal hollow cylinder whose lower end portion is fixed to the lower wall of the external conductor, a second fixed electrode composed of a metal hollow cylinder that is provided coaxially with the first fixed electrode with a gap on the outside of the first fixed electrode, and whose upper end portion is fixed to the upper wall of the external conductor, and a hollow or solid cylindrical movable electrode that is coaxial with the first and second fixed electrodes and is attached to the upper wall of the external conductor so that the insertion length of the movabe electrode into the first fixed electrode can be varied; an input terminal; an output terminal; and means for connecting the second fixed electrode to the input terminal and the output terminal in a high-frequency fashion. A preferred embodiment of the resonator according to the present invention comprises a hollow cylinder composed of a solid dielectric whose upper and lower end portions face the upper and lower walls respectively, of the external conductor a suitable distance away, a first fixed electrode composed of a metal thin layer that adheres around the inner surface of the hollow cylinder and whose lower end portion is electrically connected to the lower wall of the external conductor, the second fixed electrode being composed of a metal thin layer that adheres around the outer surface of the hollow cylinder and whose upper end portion is electrically connected to the upper wall of the external conductor. In another embodiment of the resonator according to the invention, the means for connecting the fixed electrode to the input terminal and the output terminal in a high-frequency fashion comprises two inductance elements or two capacity elements for the compensation of transmission characteristics connected in series between the input terminal and the output terminal; and the connecting point of the two inductance elements or the two capacity elements being connected to the second fixed electrode in a high-frequency fashion. A filter according to the present invention comprises: a common external conductor; a plurality of variable capacitor elements connected in series in a high-frequency fashion, provided at suitable intervals and means for connecting the second fixed electrode of the top capacitor element of the plurality of capacitor elements to the input terminal in a high-frequency fashion; and means for connecting the second fixed electrode of the last capacitor element of the plurality of capacitor elements to the output terminal in a high-frequency fashion. The resonator according to the present invention has good thermal conductivity between the capacitor element and the external conductor because of the relatively large thermal radiation surface area of the resonance capacity element, so heat is effectively radiated from the capacitor element and the external conductor, and therefore the rise in the temperature of the various resonator components is kept low and there is extremely little fluctuation in resonance frequency caused by distortion of the components as a result of elevated temperature. Furthermore, the structure is extremely simple and mechanically tough, so the product has excellent vibration resistance. The withstand voltage characteristics are also good because of the low impedance of the resonator. These same advantages are realized with a filter that incorporates the resonator according to the present invention. Further, in the case of a resonator formed with variable capacity by means of fixed and movable electrodes, the range over which the capacity can be varied is wider and the resonance frequency can be set over a wider range, so resonators with a greater variety of resonance frequencies can be formed using parts of the same configurations and the same dimensions, and the costs entailed can therefore be lowered. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical cross section of a conventional resonator. Fig. 2 is a horizontal cross section of a conventional resonator. Fig. 3 is a vertical cross section according to the present invention, Fig. 4 is a horizontal cross section of the resonator according to the present invention; Fig. 5 is an equivalent circuit diagram of the resonator shown in Fig. 4 ; Fig. 6 is a diagram illustrating an example in an embodiment in which the input terminal 96 and the fixed electrode 93 are capacitively coupled by the capacity element 102, and the output terminal 97 and the fixed electrode 93 by the capacity element 65; Fig. 7 is a diagram illustrating an example in an embodiment in which probes 104 and 105 are used as the input/output coupling means. Fig. 8 is a diagram illustrating an example in an embodiment in which loops 106 and 107 are used as the input/output coupling means; Fig. 9 is a vertical cross section of the resonator of a further embodiment according to the present invention; Fig. 10 is an equivalent circuit diagram of the resonator shown in Fig. 9 ; Fig. 11 is a diagram illustrating the transmission characteristics of the resonator shown in Fig. 9 ; Fig. 12 is a vertical cross section of the resonator of a further embodiment according to present invention; Fig. 13 is an equivalent circuit diagram of the resonator shown in Fig. 12 ; Fig. 14 is a diagram illustrating the transmission characteristics of the resonator shown in Fig. 12 ; Fig. 15 is a vertical cross section of the resonator in a further embodiment according to the present invention. Fig. 16 is an equivalent circuit diagram of the resonator shown in Fig. 15 ; Fig. 17 is a diagram illustrating the transmission characteristics of the resonator shown in Fig. 15 ; Fig. 18 is a vertical cross section of the resonator of a further embodiment according to the present invention; Fig. 19 is an equivalent circuit diagram of the resonator shown in Fig. 18 ; Fig. 20 is a diagram illustrating the transmission characteristics of the resonator shown in Fig. 18 ; Fig. 21 is a vertical cross section of an embodiment in which the coupling element 110 in the practical example shown in Fig. 10 has been replaced with a probe 104; Fig. 22 is a vertical cross section of an embodiment in which the coupling element 110 in the embodiment shown in Fig. 9 has been replaced with a loop 106; Fig. 23 is a vertical cross section of an embodiment in which the coupling element 110 in the embodiment shown in Fig. 15 has been replaced with a probe 104; Fig. 24 is a vertical cross section of an embodiment in which the coupling element 110 in the embodiment shown in Fig. 15 has been replaced with a loop 106; Fig. 25 is a vertical cross section of a filter constructed using the resonator shown in Fig. 3 ; Fig. 26 is a horizontal cross section of a filter constructed using the resonator shown in Fig. 3 ; Fig. 27 is an equivalent circuit diagram of the filter shown in Figs. 25 and 26 ; Fig. 28 is a converted equivalent circuit diagram of the equivalent circuit diagram shown in Fig. 27 ; Fig. 29 is a diagram illustrating an example of the relation between the interstage magnetic field coupling coefficient and the interval of the centers of adjacent capacitor elements; Fig. 30 is a vertical cross section of a band-pass filter in which the interstage coupling consists of electric field coupling; Fig. 31 is an equivalent circuit diagram of the band-pass filter shown in Fig. 30; Fig. 32 is a converted equivalent circuit diagram of the equivalent circuit, diagram shown in Fig. 31. Fig. 3 is a vertical cross section of the resonator according to the present invention, and Fig. 4 is a horizontal cross section thereof. The resonator in this embodiment comprises a cubic external conductor 91; a solid dielectric hollow cylinder 92 made of ceramic; a variable capacitor element composed of fixed electrodes 93A and 93B, and a movable electrode 94; a fixing member 93C that is used to fix the fixed electrode 93A, a fixing member 93D that is used to fix the fixed electrode 93B, a lock nut 95 that is used to fix the movable electrode 94; an input terminal 96; an output terminal 97; an input coupling wire 98; an output coupling wire 99; a resonance frequency fine-tuning element 100; and a lock nut 101. The external conductor 91 may also be a bottomed cylinder. The upper and lower ends of the hollow cylinder 92 are a suitable distance apart from, and face the upper and lower walls, respectively, of the external conductor 91. The fixed electrode 93A, 93B are made of a metal thin layer such as silver that is bonded around the inside and outside, respectively, of the hollow cylinder 92. The upper end of the fixed electrode 93A is soldered to the inner side of the conductive fixing member 93C, which is in the form of a flanged hollow cylinder, and the flange of the fixing member 93C is fixed by a screw to the upper wall of the external conductor 91. The lower end of the fixed electrode 93B is attached in elastic contact with the upper portion of the conductive fixing member 93D whose upper portion is provided with a plurality of slits to achieve elasticity and which is in the form of a bottomed hollow cylinder. This fixing member 93D is fixed to the lower wall of the external conductor 91 by a screw, using the threaded hole formed in the bottom of itself. The movable electrode 94 made of a solid or hollow cylindrical conductor (such as copper) threaded around its outside, and is screwed into the threaded hole formed in the upper wall of the external conductor 91 coaxially with the fixed electrodes 93A and 93B. The insertion length of the movable electrode 94 into the hollow cylinder 92, and therefore the insertion length of the movable electrode 94 into the fixed electrode 93B can be varied by the rotation of the movable electrode 94 in a forward or reverse direction to move the movable electrode 94 forward or backward. The movable electrode 94 is fixed by the lock nut 95. The input terminal 96 and the output terminal 97 consist, for example, of coaxial plugs, and the external conductor that forms these coaxial plugs is connected to the external conductor 91. The input coupling wire 98 is connected at one end to the internal conductor of the coaxial plug 96, and at the other end to the fixed electrode 93A. The output coupling wire 99 is connected at one end to the internal conductor of the coaxial plug 97, and at the other end to the fixed electrode 93A. The fine-tuning element 100 is made of a metal screw threaded into the wall of the external conductor 91, and is fixed by a lock nut 101. With a resonator constructed in this manner, a parallel resonance circuit whose equivalent circuit is shown in Fig. 5, is formed by the distributed inductance of the external conductor 91 and the capacity of the variable capacitor element composed of the solid dielectric hollow cylinder 92, the fixed electrodes 93A and 93B, and the movable electrode 94. In Fig. 5, the symbol R represents the resonance circuit, the symbol M 6R represents the input magnetic field coupling coefficient, and the symbol M R7 represents the output magnetic field coupling coefficient. When high-frequency power is applied, for example, to the coaxial plug 96, the electromagnetic field distribution in this resonator will be such that the electric field vector is expressed by the solid arrowed line E in Fig. 3, the current by the solid arrowed line I in Fig. 3 , and the magnetic field by the broken line H in Fig. 4. Since inductance is relatively small, and the capacitance is relatively large in this resonator, this resonator is a low impedance type with good withstand voltage characteristics. If a ceramic with a high dielectric constant and a dielectric loss that is nearly zero is used as the hollow cylinder 92 made of a solid dielectric in the variable capacitor element, then the Q (Q u ) of the variable capacitor element consisting of the solid dielectric hollow cylinder 92, the fixed electrodes 93A and 93B, and the movable electrode 94 can be ignored. In addition, the electronic energy that can be accumulated in this resonator will correspond to the volume of the external conductor 91, and the resistance in the metal portion of this resonator can be kept extremely low, so that an extremely large unloaded Q can be obtained. The inventor was able to obtain the following experimental equation (4) for the unloaded Q (Q u ) through the use of prototypes whose external conductor 91, fixed electrodes 93A and 93B, and movable electrode 94 are made of copper, although the magnitude of the unloaded Q (Q u ) will vary with the ratio of the inductance to the capacitance of the resonator. Q u ≒ 20 f 0 ½ • SH where f 0 is the resonance frequency (MHz) and SH is the height (cm) of the external conductor 91 (cm) (see Fig. 3 ). Although Fig. 3 illustrates an example of a case in which tap coupling by the coupling wires 98 and 99 is used as means for coupling in high-frequency fashion the input terminal 96 with the fixed electrode 93A, and the output terminal 97 with the fixed electrode 93A, means for capacitively coupling the input terminal 96 with the fixed electrode 93A via the capacity element 102 and means for capacitively coupling the output terminal 97 with the fixed electrode 93A via the capacity element 103 may also be used, as shown in Fig. 6 , or probes 104 and 105 may be used as the input/output coupling means, as shown in Fig. 7. In addition, loops 106 and 107 may be used as the input/output, coupling means, as shown in Fig. 8. Figs. 6 through 8 correspond to the cross section of Fig. 4 viewed from below, omitting the lower side wall of external conductor 91, and hereinafter the same applies to Fig, 9 similar to Figs. 6 through 8. The structure not discussed in the explanation of Figs. 6 through 8 are the same as in Fig. 3. Fig. 9 is a vertical cross section of the resonator of a further embodiment according to the present invention. In this embodiment, a low-pass filter circuit is formed by inductance elements 108 and 109 for the compensation of transmission characteristics, interposed between the connection terminals 96 and 97 with the external circuit, and a capacity element 110 connected between the fixed electrode 93A that forms the capacitor element and the connection point of the inductance elements 108 and 109. With this resonator, as shown by the transmission characteristics in Fig. 11 where the axis of abscissa represents the frequency and the axis of ordinate represents the amount of attenuation, the slope of the attenuation characteristic curve in the frequency region lower than the resonance frequency f 0 is steep, while the slope of the attenuation characteristic curve in the frequency region higher than the resonance frequency f 0 is gentle, and a transmission inhibition band is formed in the frequency region including the resonance frequency f 0 . Fig. 10 is an equivalent circuit diagram of the resonator shown in Fig. 9. The symbol R represents the resonance circuit composed of the external conductor 91 and the variable capacitor element, and the rest of the symbols are the same as in Fig. 9. The resonance frequency f 0 of the circuit composed of the resonance circuit R and the coupling-use capacity element 112 changes according to the capacitance of the coupling-use capacity element 110, and the fine tuning of the resonance frequency can be performed by the provision of an adjustment element similar to the resonance frequency fine-tuning element 100 shown in Fig. 4. Fig. 12 is a vertical cross section of the resonator of a further embodiment according to the present invention. This embodiment differs from the twelfth embodiment shown in Fig. 9 in that the coupling of the connection point of the inductance elements 108 and 109 with the fixed electrode 93A is performed by tap coupling using an inductance element 111, and in that the resonance frequency f 0 of the circuit composed of the resonance circuit R and the coupling-use inductance element 111 changes according to the inductance of the inductance element 111. The rest of the structure and operation is substantially the same as in the embodiment shown in Fig. 9. Fig. 13 is an equivalent circuit diagram of the resonator shown in Fig. 12. Except for the inductance element 111, all of the symbols are the same as in Fig. 10. Fig. 14 where the axis of abscissa and the axis of ordinate are the same as in Fig. 11, is a diagram illustrating the transmission characteristics of the resonator shown in Fig. 12, which is substantially the same as the characteristics shown in Fig. 11. Fig. 15 is a vertical cross section of the resonator of a further embodiment according to the present invention. This embodiment differs from the twelfth embodiment shown in Fig. 9 in that the inductance elements 108 and 109 used in the embodiment shown in Fig. 9 are replaced with capacity elements 112 and 113. The rest of the structure is the same as in the embodiment shown in Fig. 9. Fig. 16 is an equivalent circuit diagram of the resonator shown in Fig. 15. Except for the capacity elements 112 and 113, all of the symbols are the same as in Fig. 10. Fig. 17 where the axis of abscissa and the axis of ordinate are the same as in Fig. 11 , is a diagram illustrating the transmission characteristics of the resonator shown in Fig. 15. In this embodiment, the slope of the attenuation characteristic curve in the frequency region lower than the resonance frequency f 0 is gentle, while the slope of the attenuation characteristic curve in the frequency region higher than the resonance frequency f 0 is steep, and a transmission inhibition band is formed in the frequency region including the resonance frequency f 0 . Fig. 18 is a vertical cross section of the resonator of a further embodiment according to the present invention. This embodiment, is the same as the fourteenth embodiment shown in Fig. 16 in that the capacity elements 112 and 113 are used as transmission characteristic compensation elements, and is the same as the embodiment shown in Fig. 12 in that tap coupling is performed using the inductance element 111 as a coupling element. The rest of the structure is the same as in the embodiment shown in Fig. 15. Fig. 19 is an equivalent circuit diagram of the resonator shown in Fig. 18. Except for the inductance element 111, all of the symbols are the same as in Fig. 72. Fig. 20 where the axis of abscissa and the axis of ordinate are the same as in Fig. 17, is a diagram illustrating the transmission characteristics of the resonator shown in Fig. 18, which is substantially the same as the characteristics shown in Fig. 17. Figs. 21 through 24 are cross sections illustrating further embodiments of the present invention. The resonator in Fig. 21 has a probe 104 in place of the coupling element 110 shown in Fig. 9 ; the resonator in Fig. 22 has a loop 106 in place of the coupling element 110 shown in Fig. 9; the resonator in Fig. 23 has a probe 104 in place of the coupling element 110 shown in Fig. 15 ; and the resonator in Fig. 80 has a loop 106 in place of the coupling element 110 shown in Fig. 15. The rest of the structure in the respective figs. are the same as the structure in Fig. 9 or 15. Fig. 25 is a vertical cross section of a filter constructed using the resonator shown in Fig. 3, and Fig. 26 is a horizontal cross section thereof. This filter comprises an external conductor 91C; fixed electrodes 93A 1 through 93A 4 and 93B 1 through 93B 4 similar to the fixed electrodes 93A and 93B shown in Fig. 3 ; solid dielectric hollow cylinders 92 1 through 92 4 similar to the solid dielectric hollow cylinder 92 shown in Fig. 3 ; fixing members 93C 1 through 93C 4 that are used to fix the fixed electrodes 93A 1 through 93A 4 ; fixing members 93D 1 through 93D 4 that are used to fix the fixed electrodes 93B 1 through 93B 4 ; variable electrodes 94 1 through 94 4 that make up the variable resonance capacity element along with the fixed electrodes 93A 1 through 93A 4 and 93B 1 through 93B 4 and are similar to the movable electrode 94 shown in Fig. 3 ; lock nuts 95 1 through 95 4 that are used to fix the variable electrodes 94 1 through 94 4 ; an input terminal 96; an output terminal 97; an input coupling wire 98; an output coupling wire 99; resonance frequency fine-tuning elements 100 1 through 100 4 ; and lock nuts 101 1 through 101 4 that are used to fix the fine-tuning elements 100 1 through 100 4 . Fig. 27 is an equivalent circuit diagram of the filter shown in Figs. 25 and 26. Symbols R 1 through R 4 represent resonance circuits, the symbol M 61 represents the input magnetic field coupling coefficient, the symbol M 47 represents the output magnetic field coupling coefficient, and symbols M 12 through M 34 represent the interstage magnetic field coupling coefficients. Fig. 28 is a converted equivalent circuit diagram of the equivalent circuit diagram shown in Fig. 27, and the symbols are the same as in Fig. 27. Although Figs. 25 through 28 illustrate a case in which the input/output coupling elements are made of the tap coupling wires 98 and 99, a capacity coupling element made of the capacitors 102 and 103 or the probes 104 and 105 or a magnetic field coupling element made of the loops 106 and 107 shown in Figs. 5 through 8 may also be used to implement the present invention. Fig. 29 illustrates an example of the relation between the interstage magnetic field coupling coefficient and the center spacing of adjacent resonance capacity elements, obtained as a result of repeated experimentation with prototypes by the inventor. The axis of abscissa represents (d - 0.3C)/W where d is the center spacing of adjacent capacitor elements (see Fig. 25), C is the external diameter of the fixed electrodes 93A 1 through 93A 4 that form the variable capacitor element (see Fig. 25), and W is the width of the external conductor 91C (see Fig. 26). The axis of ordinate represent the interstage magnetic field coupling coefficient M k, k+1. The transmission loss L of the band-pass filter shown in Figs. 25 through 28 is expressed by equation (2). Fig. 30 is a vertical cross section of a band-pass filter in which the interstage coupling consists of capacitive coupling. This filter comprises an external conductor 91C; fixed electrodes 93A 1 through 93A 4 , solid dielectric hollow cylinders 92 1 through 92 4 and fixed electrodes 93B 1 through 93B 4 that are provided concentrically to the interiors of the fixed electrodes 93A 1 through 93A 4 , although not shown in the Fig. 30 ; fixing members 93C 1 through 93C 4 ; fixing members 93D 1 through 93D 4 ; lock nuts 95 1 through 95 4 ; an input terminal 96; an output terminal 97 ; an input coupling capacity element 114 61 ; interstage coupling capacity elements 114 12 through 114 34 ; and an output coupling capacity element 114 47 . Fig. 31 is an equivalent circuit diagram of the band-pass filter shown in Fig. 30 . Symbols R 1 through R 4 represent resonance circuits, the reference numeral 114 61 is the input coupling capacity, reference numeral 114 12 through 114 34 represent the interstage coupling capacity, and the reference numerals 114 47 represent the output coupling capacity. Fig. 32 is a converted equivalent circuit diagram of the equivalent circuit diagram shown in Fig. 31, and the symbols are the same as in Fig. 31. Although Fig. 30 illustrates an example of a case in which the input/output coupling elements consist of capacity elements, tap coupling wires, probes, loops, or other such high-frequency coupling means may also be used. In the embodiments show in Figs. 3 through 32, the fixed electrodes 93A and 93B can be constructed from a hollow cylinder made of a metal conductor that has been strengthened by making the walls thicker, and an air layer can be used instead of the hollow cylinder 92 made of a solid dielectric.

Claims: A resonator comprising: an external conductor (91); a variable capacitor element comprising a first fixed electrode (93B) composed of a metal hollow cylinder whose lower end portion is fixed to the lower wall of said external conductor (91), and a hollow or solid cylindrical moveable electrode (94) that is coaxial with said first fixed electrode (93B), and is attached to the upper wall of said external conductor (91) so that the insertion length of said moveable electrode (94) into said first fixed electrode (93B) can be varied; and an input terminal (96) and an output terminal (97); characterized in that a second fixed electrode (93A, 93A 1 -93A 4 ) composed of a metal hollow cylinder is provided coaxially with said first fixed electrode (93B) with a gap on the outside of said first fixed electrode (93B), and whose upper end portion is fixed to the upper wall of said external conductor (91), and that means (98,99) for connecting said second fixed electrode (93A, 93A 1 -93A 4 ) to said input terminal (96) and said output terminal (97) in a high-frequency fashion are provided. A resonator according to claim 1, wherein a hollow cylinder (92) composed of a solid dielectric is provided whose upper and lower end portions face the upper and lower walls, respectively, of said external conductor (91) a suitable distance away, said first fixed electrode (93B) being composed of a metal thin layer that adheres around the inner surface of said hollow cylinder (92) and whose lower end portion is electrically connected to the lower wall of said external conductor (91), said second fixed electrode (93A, 93A 1 -93A 4 ) being composed of a metal thin layer that adheres around the outer surface of said hollow cylinder (92) and whose upper end portion is electrically connected to the upper wall of said external conductor (91). A resonator according to claim 1 or 2, wherein said means for connecting said fixed electrode to said input terminal and said output terminal in a high-frequency fashion comprises two inductance elements (108,109) or two capacity elements (112,113) for the compensation of transmission characteristics connected in series between said input terminal (96) and said output terminal (97), the connection point of said two inductance elements or said two capacity elements being connected to said second fixed electrode (93A) in a high frequency fashion. A filter comprising: an external conductor (91C); a plurality of variable capacitor elements (114) according to one of claims 1 or 2 connected in series in a high-frequency fashion, provided at suitable intervals; and means (114 61 ) for connecting said second fixed electrode (93) of the top capacitor element of said plurality of capacitor elements to said input terminal (96) in a high frequency fashion, and means (114 47 ) for connecting said second fixed electrode (93) of the last capacitor element of said plurality of capacitor elements to said output terminal (97) in a high frequency fashion.

Inventors: HATANAKA HIROSHI, HATANAKA, HIROSHI
Applicants: NIPPON DENGYO KOSAKU KK, NIHON DENGYO KOSAKU CO. LTD.
Application year: 1995
Main classification: H01P1
IPC codes: H01P1, H01P7