Coaxial resonator and dielectric filter using the same

Abstract: A coaxial resonator according to the present invention has an outer conductor (4) on an outer peripheral surface of a dielectric block (1) having at least four side surfaces and having a through hole (2) provided in its approximately central part and an inner conductor (3) on an inner peripheral surface of the through hole, and one of two end faces perpendicular to the through hole is opened and the other end face (5) is short-circuited. A pair of an input electrode (26) and an output electrode (27) which are not brought into electrical contact with the outer conductor and are independent of each other is provided in a position in proximity to the opened end face on the outer peripheral surface of the dielectric block, and respective portions of both the electrodes are extended to the side surfaces, which are respectively adjacent to the electrodes, of the dielectric block. Consequently, the input electrode and the output electrode are capacitively coupled to each other, and the input electrode and the output electrode are respectively capacitively coupled to the inner conductor. Coupling capacitance can be adjusted by the areas of the electrodes.

Description: The invention relates to a coaxial resonator and a dielectric filter. As microwave remote communication has been put into practice, it has been requested to make a communication equipment more lightweight and smaller in size. This leads to a request to miniaturize a duplexer which is an essential component in such an equipment. Examples of a filter used for a duplexer in a microwave band generally includes a so-called coaxial resonator constituted by an outer conductor provided on an outer peripheral surface of a dielectric member having a through hole provided therein and an inner conductor provided on an inner peripheral surface of a through hole, and a strip-line type resonator using a strip line. As the filters, a quarter-wavelength type filter which resonates at one-fourth a resonance frequency f by producing the filter in one side short-circuited construction has been generally well known. In addition, a coaxial dielectric resonator constructed using a material having a high dielectric constant (εr = 40 to 90) has been widely used as one suitable for miniaturization. Particularly in a portable telephone, a receiving band and a transmission band are used in proximity to each other. Accordingly, a so-called polarized method having an attenuation pole is adopted for a filter for a duplexer. Examples of such a polarized method include a method of obtaining an antiresonance frequency by connecting a capacitor or an inductor in series with a coaxial dielectric resonator (see Japanese Utility Model Laid-Open Gazette No. 4566/1987) and a method of coupling resonators which are not adjacent to each other by jumping (see Japanese Patent Laid-Open Gazette No. 108801/1988). Figs. 24A and 24B illustrate a polarized filter explaining the former method, where Fig. 24A is a perspective view showing the filter, and Fig. 24B is a diagram showing an equivalent circuit thereof. Three coaxial resonators are used to fabricate a polarized bandpass filter. In this polarized band-pass filter, three coaxial resonators 62 are provided on a dielectric substrate 61. Antiresonance capacitances 63a, 63b and 63c are respectively connected to the coaxial resonators 62. In addition, chip capacitors 64a to 64d are provided on the dielectric substrate 61. The two chip capacitors 64b and 64c out of the chip capacitors 64a to 64d are inter-stage coupling capacitors for coupling the coaxial resonators to each other. However, in the above described filter shown in Fig. 24A and 24B, an inter-stage coupling portion is required. Accordingly, the dielectric substrate 61 must be made relatively large so as to form the inter-stage coupling portion, thereby to make it impossible to miniaturize the filter. On the other hand, in the above described method of coupling the resonators which are not adjacent to each other by jumping, a jump coupling substrate is required, thereby to similarly make it impossible to miniaturize the filter. JP-A-59-119901 describes a band stop filter comprising a transmission line formed on a single side of a dielectric block containing an array of holes. JP-A-1053601 describes a miniature band pass filter. EP-A-0401839 describes a dielectric filter formed from a block of ceramic material with holes extending from a top surface toward a bottom surface. The invention has been made in view of the above described circumstances and aims to provide a small-sized dielectric filter and to provide a coaxial resonator used for the small-sized dielectric filter. According to the present invention there is provided a coaxial resonator comprising: a dielectric block having two end faces, plural side faces substantially parallel to an axis between the two end faces, and an inner surface defined by a bore substantially parallel with the axis between the two end faces; and a conductive layer formed on one of the end faces, each of the plural side faces, and the inner surface; and an electrode characterised in that the electrode is formed on both a portion of one of the side faces and a portion of another of the side faces adjacent thereto. In a quarter-wavelength type coaxial resonator in which an outer conductor is formed on an outer peripheral surface of a dielectric block having at least four side surfaces and having a through hole provided in its approximately central part and an inner conductor is formed on an inner peripheral surface of the through hole, and one of two end faces perpendicular to the through hole is opened and the other end face is short-circuited, a coaxial resonator according to an embodiment of the invention has an input electrode and an output electrode which are not brought into electrical contact with the outer conductor and are independent of each other is provided in a position in proximity to the opened end face on the outer peripheral surface of the dielectric block, and respective portions of both the electrodes are extended to the side surfaces which are respectively adjacent to the electrodes. The input electrode and the output electrode are capacitively coupled to each other, and the input electrode and the output electrode are respectively capacitively coupled to the inner conductor. Coupling capacitances can be adjusted depending on the areas of the above described electrodes. Coaxial resonators can be connected to each other by electrode portions extended to the above described side surfaces (extended portions). Furthermore, the dielectric filter has a plurality of coaxial resonators as described above are arranged side by side, the above described input and output electrodes formed in the respective coaxial resonators are positioned on the same plane, the opened end faces and the short-circuited end faces in the respective coaxial resonators are arranged in the same direction, and the extended portion of the input electrode and the extended portion of the output electrode respectively formed in the adjacent coaxial resonators are brought into close contact with each other. Consequently, the necessity of using a dielectric substrate for carrying chip capacitors and the like in constructing the dielectric filter as a polarized filter is eliminated, thereby to make it possible to miniaturize the dielectric filter. Furthermore, there will be described in a quarter-wavelength type coaxial resonator in which an outer conductor is formed on an outer peripheral surface of a dielectric block having at least four side surfaces and having a through hole provided in its approximately central part and an inner conductor is formed on an inner peripheral surface of the through hole, and one of two end faces perpendicular to the through hole is opened and the other end face is short-circuited, and capacitance is provided so as not to be brought into electrical contact with the outer conductor in a position in proximity to the opened end face on the outer peripheral surface of the dielectric block, or an independent conductor for induction is provided so as to be brought into electrical contact with the inner conductor through a conductor on the short-circuited end face and so as not to be brought into electrical contact with the outer conductor in a position in proximity to the short-circuited end face on the outer peripheral surface of the dielectric block. The above described coaxial resonator comprises the conductor for capacitance or the conductor for induction on the outer peripheral surface of the dielectric block. The conductor for capacitance or the conductor for induction provides a place where in coupling the coaxial resonators to each other by reactance constituted by a chip component, the chip component is carried. The invention also provides a dielectric filter comprising a plurality of coaxial resonators, at least one of which is in accordance with the resonator defined hereinabove, in which filter the input electrodes and the output electrodes in said respective coaxial resonators are positioned in the same plane, the end faces in said respective coaxial resonators are arranged in the same direction, and the input electrode and output electrode of adjacent coaxial resonators are electrically connected to each other. The invention further provides a dielectric filter comprising a plurality of coaxial resonators provided side by side, at least a first one of said resonators being in accordance with the resonator defined hereinabove, in which filter a second one of said resonators comprises a capacitive conductor formed on one of the side faces in a position in proximity to the end face on which the conductive layer is not formed, wherein the resonators are arranged so that the or each electrode of said first resonator lies in the same plane as the capacitive conductor of said second resonator and the end faces of the plural resonators lie in the same respective planes, the filter further comprising reactance means connecting an electrode (6) of the at least one first resonator with the capacitive conductor of the second resonator. The invention further provides a dielectric filter comprising a plurality of coaxial resonators provided side by side, at least one of said resonators being in accordance with the resonator defined hereinabove, in which filter the electrode defining an inductive conductor formed in a position in proximity to the end face on which the conductive layer is formed, wherein the resonators are arranged so that the one side face and the end faces of the resonators lie in the same respective planes, the filter further comprising reactance means connecting the electrodes of the adjacent resonators to each other. Hereinafter, there will be described a dielectric filter wherein a plurality of coaxial resonators each comprising the above described conductor for capacitance are used, all or a part of the conductors for capacitance formed in the respective coaxial resonators are positioned on the same plane, the opened end faces and the short-circuited end faces in the respective coaxial resonators are arranged in the same direction, and the conductors for capacitance in the adjacent coaxial resonators are coupled to each other by reactance, or a plurality of coaxial resonators comprising the above described conductor for induction are used, all or a part of the conductors for induction formed in the respective coaxial resonators are positioned on the same plane, and the opened end faces and the short-circuited end faces in the respective coaxial resonators are arranged in the same direction, and the conductors for induction in the adjacent coaxial resonators are coupled to each other by reactance. Consequently, in the dielectric filter in which a plurality of coaxial resonators as described above are arranged side by side, chip components constituting the above described reactance are carried on the coaxial resonators to couple the coaxial resonators to each other, the necessity of using a dielectric substrate for carrying chip capacitors and the like in constructing the dielectric filter as a polarized filter as in the conventional example is eliminated, thereby to make it possible to miniaturize the dielectric filter. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. In the drawings: Fig. 1 is a perspective view showing an element structure of a coaxial resonator according to an embodiment of the present invention; Fig. 2 is a diagram showing an equivalent circuit of the coaxial resonator illustrated in Fig. 1; Fig. 3 is a perspective view showing an element structure of a dielectric filter according to an embodiment of the present invention; Figs. 4A and 4B are diagrams showing an equivalent circuit of the filter illustrated in Fig. 3; Fig. 5 is a diagram showing the representative characteristics of the dielectric filter according to an embodiment of the present invention; Fig. 6 in a perspective view showing a coaxial resonator which comprises a conductor for capacitance according to an embodiment of the present invention and is used for input or output; Fig. 7 is a perspective view showing a coaxial resonator which comprises a conductor for capacitance used for purposes other than input or output; Fig. 8 is a diagram showing an equivalent circuit of the coaxial resonator described in Fig. 7; Fig. 9 is a perspective view showing a dielectric filter constructed by arranging three coaxial resonators each comprising the conductor for capacitance according to an embodiment of the present invention side by side and coupling the coaxial resonators to each other by chip capacitors; Fig. 10 is a diagram showing an equivalent circuit of the dielectric filter shown in Fig. 9; Fig. 11 is a diagram showing the representative characteristics of the dielectric filter shown in Fig. 9; Fig. 12 is a perspective view showing a dielectric filter constructed by arranging three coaxial resonators each comprising the conductor for capacitance according to an embodiment of the present invention side by side and coupling the resonators to each other by chip coils; Fig. 13 is a diagram showing an equivalent circuit of the dielectric filter shown in Fig. 12; Fig. 14 is a diagram showing the representative characteristics of the dielectric filter shown in Fig. 12; Fig. 15 is a perspective view showing a coaxial resonator which comprises a conductor for induction according to an embodiment of the present invention and is used for input or output; Fig. 16 is a perspective view showing a coaxial resonator which comprises a conductor for induction used for purposes other than input or output; Fig. 17 is a diagram showing an equivalent circuit of the coaxial resonator comprising the conductor for induction according to an embodiment of the present invention; Fig. 18 is a perspective view showing a dielectric filter constructed by arranging three coaxial resonators each comprising the conductor for induction according to an embodiment of the present invention side by side and coupling the resonators to each other by chip capacitors; Fig. 19 is a diagram showing an equivalent circuit of the dielectric filter shown in Fig. 18; Fig. 20 is a diagram showing the representative characteristics of the dielectric filter shown in Fig. 18; Fig. 21 is a perspective view showing a dielectric filter constructed by arranging three coaxial resonators each comprising the conductor for induction according to an embodiment of the present invention side by side and coupling the resonators to each other by chip coils; Fig. 22 is a diagram showing an equivalent circuit of the dielectric filter shown in Fig. 21; Fig. 23 is a diagram showing the representative characteristics of the dielectric filter shown in Fig. 21; and Fig. 24A is a perspective view showing a conventional dielectric filter, and Fig. 24B is a diagram showing an equivalent circuit thereof. As shown in Fig. 1, a dielectric block 1 is in a rectangular parallelopiped shape, and is constituted by a dielectric member (the dielectric constant is 38) composed of, for example, ceramics of a TiO 2 - SnO 2 - ZrO 2 system. The dielectric block 1 has a through hole 2 provided in the longitudinal direction in its central part. In addition, an inner peripheral surface of the above described through hole 2 is coated with a conductive member such as silver, to form an inner conductor 3. On the other hand, an outer peripheral surface of the dielectric block 1 is similarly coated with a conductive member such as silver, to form an outer conductor 4. One of two end faces perpendicular to the above described through hole 2 is opened, while the other end face is short-circuited. Specifically, a short-circuit electrode 5 is formed on the rear surface of the dielectric block 1 to be a termination of the through hole 2, to short-circuit this coaxial resonator. The outer conductor 4 is removed on the whole on the side of the opened end face of one side surface of the dielectric block 1 and on a part on the side of the opened end face of side surfaces adjacent to the one side surface, and an input electrode 26 and an output electrode 27 are formed with a gap G parallel to the axial direction of the coaxial resonator being provided therebetween in this removed portion on the above described one side surface. Specifically, predetermined spacing is formed between both opposed edges of the input electrode 26 and the output electrode 27, and the opposed edges are respectively parallel to the axial direction of the coaxial resonator. An extended portion 28 extended from the input electrode 26 is formed in the removed portion on the side surface adjacent to the one side surface, and an extended portion 29 extended from the output electrode 27 is formed in the removed portion on the other side surface adjacent to the one side surface. As the typical dimensions of the above described coaxial resonator, the length is approximately 4.8 mm, and the respective lengths of sides in cross section are approximately 3 mm. In actually connecting the coaxial resonator to the other element, the coaxial resonator shown in Fig. 1 is mounted thereon upside down. In the coaxial resonator of such construction, capacitive coupling as shown in an equivalent circuit diagram of Fig. 2 is formed. Specifically, a capacitance C 67 is formed between the input electrode 6 and the output electrode 7, and capacitances C 63 and C 73 are respectively formed between the input electrode 6 and the output electrode 7 and the inner conductor 3 in the coaxial resonator 1. The same portions as those shown in Fig. 1 are assigned the same reference numerals in Fig. 2. particularly in the coaxial resonator according to the present invention, capacitance values obtained by the capacitive coupling can be changed into desirable capacitance values by adjusting the areas of the electrodes and the like used in the coaxial resonator. For example, since in the case of a dielectric resonator having a dielectric constant of 38, having sides each having a length of 3 mm, and having an inner diameter of 1 mm, the distance from the outer peripheral surface to the inner conductor is approximately 1 mm, the area of each of the electrodes may be 9 mm 2 so as to obtain a capacitance value of approximately 3 pF as the capacitances C 63 and C 73 . At this time, if the length of the gap between the input and output electrodes is 0.1 mm and the width of each of the electrodes is 2 mm, it is possible to obtain a capacitance value of approximately 5 pF as the capacitance C 67 . A dielectric filter according to an embodiment of the present invention will be described with reference to Fig. 3. Fig. 3 illustrates a dielectric filter (a perspective view) in which a plurality of coaxial resonators as described above are provided side by side. Coaxial resonators 31a, 31b and 31c in Fig. 3 are respectively the above described coaxial resonator according to that shown in Fig. 1, and inner peripheral surfaces of through holes of dielectric blocks are respectively provided with inner conductors 32a, 32b and 32c coated with a conductive member such as silver. Outer peripheral surfaces of the dielectric blocks are respectively provided with outer conductors 33a, 33b and 33c coated with a conductive member such as silver. In addition, input electrodes 34a, 34b and 34c are provided on respective one side surfaces of the coaxial resonators 31a, 31b and 31c, and output electrodes 35a, 35b and 35c are provided on the same side surfaces. The output electrodes 35a, 35b and 35c and the input electrodes 34a, 34b and 34c are respectively opposed to each other with a gap G parallel to the axial direction of each of the coaxial resonators being provided therebetween. The respective input and output electrodes are so formed as to be extended to side surfaces which are respectively adjacent to the input and output electrodes, as in the above described coaxial resonator. Therefore, extended portions of the input electrode 35a and the output electrode 34b are brought into close contact with each other, to realize the electrical connection between the coaxial resonator 31a and the coaxial resonator 31b, which cannot be directly seen in Fig. 3. The same is true for the connection between the coaxial resonator 31b and the coaxial resonator 31c. As a specific method, the coaxial resonators are brought into close contact with each other, for example, by soldering or with adhesives. The input electrode 34a and the output electrode 35c respectively function as input and output electrodes of the coaxial resonators and at the same time, also respectively function as input and output electrodes of the dielectric filter. Furthermore, as described in the embodiment shown in Fig. 1, in a case where the above described capacitance values are adjusted by the areas of the electrodes, it is preferable that the shapes and the areas of both the above described electrodes in close contact with each other in the plurality of coaxial dielectric resonators which are adjacent to each other are made equal to each other. Specifically, when the areas are equal to each other but the shapes are different from each other, both the electrodes cannot be completely brought into contact with each other over the whole areas irrespective of an attempt to bring both the electrodes into contact with each other by providing the dielectric resonators side by side, which causes capacitances and the like to vary to adversely affect the characteristics. Fig. 4 is a diagram showing an equivalent circuit of the above described dielectric filter. Fig. 4A is a diagram based on the three capacitances in the equivalent circuit described in Fig. 2, and Fig. 4B is a diagram obtained by subjecting the equivalent circuit to Y - Δ conversion. 31a, 31b and 31c in Fig. 4A are illustrated to respectively correspond to the coaxial resonators 31a, 31b and 31c shown in Fig. 3. Furthermore, in, for example, the coaxial resonator 31a, the capacitance value of the capacitance C 67 in Fig. 2 is 3.9 pF, and the capacitance values of the capacitances C 63 and C 73 are respectively 2.6 pF and 1.1 pF. Meanwhile, numerical values in the equivalent circuit are examples in a polarized filter for receiving with respect to a portable telephone in a 1.5 GHz band. Although a large capacitance value of approximately 15 pF can be equivalently obtained in respective capacitances of an input and an output in Fig. 4 (b), it is difficult to obtain such large capacitance values in the conventional dielectric filter comprising coaxial resonators. Fig. 5 is a diagram showing the frequency characteristics of a filter obtained by polarizing the above described dielectric filter in a low frequency band. In Fig. 5, a graph (a) shows the propagation characteristics of the filter, and a graph (b) shows the reflection loss. As shown in Fig. 5, an attenuation pole is formed in a suppressed band having a frequency which is made lower than the center frequency 1.507 GHz of a pass band by 36 MHz, to obtain a suppression level of not less than - 30 dB. It is possible to confirm the effectiveness of the dielectric filter according to the present invention. Furthermore, also in the dielectric filter according to an embodiment of the present invention, in connecting the dielectric filter to the other element, the dielectric filter shown in Fig. 3 is mounted thereon upside down, as described in the coaxial dielectric resonator shown in Fig. 1. A second embodiment will be described with reference to Figs. 6 to 14. As shown in Figs. 6 and 7, a dielectric block 1 is in a rectangular parallelopiped shape having dimensions of approximately 3 mm long x 3 mm wide x 7 mm deep, and is constituted by a dielectric member (the dielectric constant is 38) composed of, for example, ceramics of a TiO 2 - SnO 2 - ZrO 2 system. The dielectric block 1 has a through hole 2 having a diameter of 1 mm provided in the longitudinal direction in its central part. In addition, an inner peripheral surface of the above described through hole 2 is coated with a conductive member such as silver, to form an inner conductor 3. On the other hand, an outer peripheral surface of the dielectric block 1 is similarly coated with a conductive member such as silver, to form an outer conductor 4. One of two end faces perpendicular to the above described through hole 2 is opened, while the other end face is short-circuited. Specifically, a short-circuit electrode 5 is formed on the rear surface of the dielectric block 1 to be a termination of the through hole 2, to short-circuit this coaxial resonator. An independent conductor for capacitance 6 which is composed of a conductive member such as silver and is spaced apart from the above described outer conductor 4 by a distance of 0.2 mm so as not to be brought into electrical contact with the outer conductor 4 is formed in a position in proximity to the above described opened end face on the outer peripheral surface of the dielectric block 1. The coaxial resonator shown in Fig. 6 is for input or output, and the conductor for capacitance 6 is formed over two surfaces, that is, the upper surface and the side surface. On the other hand, the coaxial resonator shown in Fig. 7 is for purposes other than input or output, and the conductor for capacitance 6a is formed only on the upper surface. In the present embodiment, the conductor for capacitance 6 on the above described side surface in the coaxial resonator for input or output shown in Fig. 6 is extended to the lower end of the side surface, and a notch X1 indicated by a dotted line in Fig. 6 is formed on the bottom surface of the coaxial resonator so that the outer conductor 4 formed on the bottom surface is not brought into electrical contact with the conductor for capacitance 6 formed on the above described side surface. The conductor for capacitance 6 is thus extended to the lower end of the side surface, thereby to make it easy to connect the coaxial resonator and the other element to each other on a substrate. Fig. 8 is a diagram showing an equivalent circuit of the above described coaxial resonator. In Fig. 8, C 1 is a capacitance produced between the conductor for capacitance 6 and the inner conductor 3. Specifically, since the conductor for capacitance 6 is formed on the side of the opened end face, an electric field is dominant, so that the conductor for capacitance 6 can be regarded as substantial capacitive coupling. In addition, C 2 and L 1 are an equivalent representation of the characteristics of a coaxial transmission line whose one side is short-circuited and which is constituted by the inner conductor 3 and the outer conductor 4 by a parallel circuit of a capacitance and an inductance. Fig. 9 is a perspective view showing a dielectric filter constituted by three coaxial resonators, where the coaxial resonators 7 and 9 on both sides are coaxial resonators for input or output and of construction shown in Fig. 6, and the coaxial resonator 8 in the center is a coaxial resonator of construction shown in Fig. 7. Each of the coaxial resonators comprises a conductor for capacitance 6 on its upper surface. The conductors for capacitance 6 are respectively extended as electrodes for input or output on the side surfaces in the coaxial resonators 7 and 9 on both sides. The coaxial resonators 7, 8 and 9 are so arranged that all or a part of the conductors for capacitance 6 in the respective coaxial resonators exist on the above described upper surfaces, the opened end faces and the short-circuited end faces in the respective coaxial resonators are arranged in the same direction, and the outer conductor 4 on the side surface in at least one of the coaxial resonators is brought into contact with the outer conductor on the side surface in the adjacent coaxial resonator. A chip capacitor 10 is carried between the conductor for capacitance 6 in the coaxial resonator 7 and the conductor for capacitance 6 in the coaxial resonator 8, and a chip capacitor 11 is carried between the conductor for capacitance 6 in the coaxial resonator 8 and the conductor for capacitance 6 in the coaxial resonator 9. Fig. 10 is a diagram showing an equivalent circuit of the above described dielectric filter. In Fig. 10, C 3 and C 4 respectively indicate capacitances of the chip capacitors 10 and 11. In addition, Fig. 11 is a diagram showing the frequency characteristics of the above described dielectric filter. A graph (a) shows the propagation characteristics of the filter, and a graph (b) shows the reflection loss. As can be seen from Fig. 10, an attenuation pole is formed in a 1.46 GHz band, to obtain a suppression level of approximately - 75 dB, so that the dielectric filter has a function of a polarized band-pass filter. In the dielectric filter exhibiting the above described characteristics, used as the above described chip capacitors 10 and 11 are ones respectively having capacitances C 3 and C 4 of 2 pF. In addition, the area of each of the conductors for capacitance 6 in the coaxial resonators 7 and 9 for input or output is taken as 20 mm 2 so that C 1 ' = 2 pF, C 2 ' = 7 pF, and L 1 ' = 1.6 nH. On the other hand, the area of the conductor for capacitance 6 in the coaxial resonator for purposes other than input or output is taken as 10 mm 2 so that C 1 = 1 pF, C 2 = 7 pF, and L 1 = 1.6 nH. Fig. 12 is a perspective view showing a dielectric filter using chip coils 12 and 13 as reactance. Specifically, the chip coil 12 is carried between the conductor for capacitance 6 in the coaxial resonator 7 and the conductor for capacitance 6 in the coaxial resonator 8, and the chip coil 13 is carried between the conductor for capacitance 6 in the coaxial resonator 8 and the conductor for capacitance 6 in the coaxial resonator 9. Fig. 13 is a diagram showing an equivalent circuit of the dielectric filter comprising the above described chip coils 12 and 13. In Fig. 13, L 2 and L 3 respectively indicate inductances of the chip coils 12 and 13. In addition, Fig. 14 is a diagram showing the frequency characteristics of the above described dielectric filter. A graph (a) shows the propagation characteristics of the filter, and a graph (b) shows the reflection loss. As can be seen from Fig. 13, the dielectric filter has a function of a band preventing filter. In the dielectric filter exhibiting the above described characteristics, used as the above described chip coils 12 and 13 are ones respectively having inductances L 2 and L 3 of 10 nH. In addition, the area of each of the conductors for capacitance 6 in the coaxial resonators 7 and 9 for input or output is taken as 20 mm 2 so that C 1 ' = 2 pF, C 2 ' = 7 pF, and L 1 ' = 1.6 nH. The area of the conductor for capacitance 6 in the coaxial resonator 8 for purposes other than input-or output is taken as 10 mm 2 so that C 1 = 1 pF, C 2 = 7 pF, and L 1 = 1.6 nH. As described in the foregoing, the above described coaxial resonator comprises the conductor for capacitance 6 on the outer peripheral surface of the dielectric block 1, and this conductor for capacitance 6 provides a place where in coupling the coaxial resonators to each other by the chip capacitor 10 or 11 or the chip coil 12 or 13, the chip component is carried. Consequently, in the dielectric filter in which a plurality of coaxial resonators as described above are provided side by side, and the above described chip capacitors 10 and 11 or the chip coils 12 and 13 are carried on the coaxial resonators to couple the coaxial resonators to each other, the necessity of using a dielectric substrate for carrying the chip capacitors in constructing the dielectric filter as a polarized filter as in the conventional example is eliminated, thereby to make it possible to miniaturize the dielectric filter. For example, the conventional dielectric filter shown in Fig. 24 is 9 mm wide x 10 mm deep x 3 mm high. On the other hand, the dielectric filter according to the present embodiment is 9 mm wide x 7 mm deep x 3 mm high. This proves that in the present embodiment, the depth is decreased and the volume is decreased by approximately 30 %. (Embodiment 3) A third embodiment will be described with reference to Figs. 15 to 23. As in the above described embodiment, a dielectric block 1 is in a rectangular parallelopiped shape having dimensions of approximately 3 mm long x 3 mm wide x 7 mm deep, and is constituted by a dielectric member (the dielectric constant is 38) composed of, for example, ceramics of a TiO 2 - SnO 2 - ZrO 2 system. The dielectric block 1 has a through hole 2 having a diameter of 1 mm provided in the longitudinal direction in its central part. In addition, an inner peripheral surface of the above described through hole 2 is coated with a conductive member such as silver, to form an inner conductor 3. On the other hand, an outer peripheral surface of the dielectric block 1 is similarly coated with a conductive member such as silver, to form an outer conductor 4. One of two end faces perpendicular to the above described through hole 2 is opened, while the other end face is short-circuited. As shown in Figs. 15 and 16, an independent conductor for induction 15 which is composed of a conductive member such as silver, and is brought into electrical contact with the above described inner conductor 3 through a conductor on the above described short-circuited end face and spaced apart from the above described outer conductor 4 by a distance of 0.2 mm so as not to be brought into electrical contact with the conductor 4 is formed in a position in proximity to the above described opened end face on the outer peripheral surface of the dielectric block 1. The width of the conductor for induction 15 is set to 0.2 mm. The coaxial resonator shown in Fig. 15 is for input or output, and the conductor for induction 15 is formed over two surfaces, that is, the upper surface and the side surface. On the other hand, the coaxial resonator shown in Fig. 16 is for purposes other than input or output, and the conductor for induction 15a is formed only on the upper surface. In the present embodiment, the conductor for induction 15 on the above described side surface in the coaxial resonator for input or output shown in Fig. 15 is extended to the lower end of the side surface, and a notch X2 indicated by a dotted line in Fig. 15 is formed on the bottom surface of the coaxial resonator so that the outer conductor 4 formed on the bottom surface is not brought into electrical contact with the conductor for induction 15 formed on the above described side surface. The conductor for induction 15 is thus extended to the lower end of the side surface, thereby to make it easy to connect the coaxial resonator and the other element to each other on a substrate. Fig. 17 is a diagram showing an equivalent circuit of the above described coaxial resonator. In Fig. 17, M is a mutual inductance produced between a self-inductance L 1 ,L 4 produced by the conductor for induction 15 and the inner conductor 3. Specifically, since the conductor for induction 15 is formed on the side of the short-circuited end face, a magnetic field is dominant, so that the conductor for induction 15 can be regarded as substantial inductive coupling. A portion parallel to the inner conductor 3 in the conductor for induction 15 contributes to the inductive coupling, and a portion perpendicular to the inner conductor 3 in the conductor for induction 15 does not contribute to the inductive coupling because magnetic fields in the inner conductor 3 and the perpendicular portion are orthogonal to each other. Such a perpendicular portion is provided so as to couple the coaxial resonators to each other by chip components, as described later. Fig. 18 is a perspective view showing a dielectric filter constituted by three coaxial resonators, where the coaxial resonators 16 and 18 on both sides are coaxial resonators for input or output and of construction shown in Fig. 15, and the coaxial resonator 17 in the center is a coaxial resonator of construction shown in Fig. 16. Each of the coaxial resonators comprises a conductor for induction 15 on its upper surface. The conductors for induction 15 are respectively extended as electrodes for input or output on the side surfaces of the coaxial resonators 16 and 18 on both sides. A chip capacitor 10 is carried between the conductor for induction 15 in the coaxial resonator 16 and the conductor for induction 15 in the coaxial resonator 17, and a chip capacitor 11 is carried between the conductor for induction 15 in the coaxial resonator 17 and the conductor for induction 15 in the coaxial resonator 15. Fig. 19 is a diagram showing an equivalent circuit of the above described dielectric filter. In Fig. 19, C 3 and C 4 respectively indicate capacitances of the chip capacitors 10 and 11. In addition, Fig. 20 is a diagram showing the frequency characteristics of the above described dielectric filter. A graph (a) shows the propagation characteristics of the filter, and a graph (b) shows the reflection loss. As can be seen from Fig. 20, the dielectric filter has a function of a polarized band-pass filter. In the dielectric filter exhibiting the above described characteristics, used as the above described chip capacitors 10 and 11 are ones respectively having capacitances C 3 and C 4 of 2 pF. In addition, the length of each of portions, which are parallel to the axial direction in the coaxial resonators 16 and 18 for input or output (hereinafter referred to as parallel portions), of the conductors for induction 15 in the coaxial resonators 16 and 18 is taken as 3.5 mm so that L 1 ' = 0.3 nH, L 4 ' = 1 nH, and C 2 ' = 7 pF. The length of a parallel portion of the conductor for induction 15 in the coaxial resonator 17 for purposes other than input or output is taken as 3.5 mm so that L 1 = 1.6 nH, L 4 = 1 nH, and C 2 = 7 pF. Fig. 21 is a perspective view showing a dielectric filter using chip coils 12 and 13 as reactance. Specifically, the chip coil 12 is carried between the conductor for induction 15 in the coaxial resonator 16 and the conductor for induction 15 in the coaxial resonator 17, and the chip coil 13 is carried between the conductor for induction 15 in the coaxial resonator 17 and the conductor for induction 15 in the coaxial resonator 18. Fig. 22 is a diagram showing an equivalent circuit of the dielectric filter comprising the above described chip coils 12 and 13. In Fig. 22, L 2 and L 3 respectively indicate inductances of the chip coils 12 and 13. In addition, Fig. 23 is a diagram showing the frequency characteristics of the above described dielectric filter. A graph (a) shows the propagation characteristics of the filter, and a graph (b) shows the reflection loss. As can be seen from Fig. 22, the dielectric filter has a function of a polarized band-pass filter. In the dielectric filter exhibiting the above described characteristics, used as the above described chip coils 12 and 13 are ones respectively having inductances L 2 and L 3 of 10 nH. In addition, the length of each of parallel portions of the conductors for induction 15 in the coaxial resonators 16 and 18 for input or output is taken as 3.5 mm so that L 1 ' = 1.6 nH, L 4 ' = 1.0 nH, and C 2 ' = 7 pF. The length of a parallel portion of the conductor for induction 15 in the coaxial resonator 17 for purposes other than input or output is taken as 3.5 mm so that L 1 = 1.6 nH, L 4 = 1 nH, and C 2 = 7 pF. As described in the foregoing, the coaxial resonator according to the embodiments of the present invention comprises the conductor for capacitance or the conductor for induction on the outer peripheral surface of the dielectric block, and this conductor provides a place where in coupling the coaxial resonators to each other by a chip component, the chip component is carried. Consequently, in the dielectric filter in which a plurality of coaxial resonators as described above are provided side by side, and the above described chip components are carried on the coaxial resonators to couple the coaxial resonators to each other, the necessity of using a dielectric substrate for carrying the chip components in constructing the dielectric filter as a polarized filter as in the conventional example is eliminated, thereby to make it possible to miniaturize the dielectric filter. Although the embodiments of the invention have been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims: A coaxial resonator comprising: a dielectric block (1) having two end faces, plural side faces substantially parallel to an axis between the two end faces, and an inner surface defined by a bore (2) substantially parallel with the axis between the two end faces; and a conductive layer formed on one of the end faces (5), each of the plural side faces (4), and the inner surface (3); and an electrode (6, 15, 26, 27) characterised in that the electrode (6, 15, 26, 27) is formed on both a portion of one of the side faces and a portion of another of the side faces adjacent thereto. A coaxial resonator as claimed in claim 1, wherein the portion of the adjacent side face extends across the width of the adjacent side face and the electrode (6, 15) is formed across substantially the whole width of the portion. A coaxial resonator as claimed in claim 1, further comprising: another electrode formed on a different portion of said one of the side faces and on a portion of a different other side face adjacent said one side face, and wherein said one electrode serves as an input electrode (26) and said other electrode serves as an output electrode (27). A resonator as claimed in claim 1, 2 or 3, wherein the or each of the electrodes (6, 15, 26, 27) are formed in a position in proximity to one of said end faces. A coaxial resonator as claimed in claim 3 or 4, wherein said electrodes (26, 27) cooperate to form a capacitive reactance therebetween. A coaxial resonator as claimed in any preceding claim, wherein the or each of the electrodes (6, 26, 27) cooperate with said conductive layer on the inner surface (3) to form a capacitive reactance having a magnitude depending on the areas of the electrodes. A coaxial resonator as claimed in claim 1, wherein said electrode (15) cooperates with said conductive layer on the inner surface (3) to form an inductive reactance therebetween. A resonator as claimed in claim 3, wherein the or each electrodes (15) is formed in proximity to the end face on which the conductive layer (5) is formed. A resonator as claimed in claim 3, wherein the conductive layer is not formed on the other of the end faces and the or each electrode (6, 26, 27) is formed in proximity to the end face. A resonator according to any preceding claim, wherein said dielectric block is composed of ceramics of a TiO 2 - SnO 2 - ZrO 2 system. A resonator according to any preceding claim, wherein said conductive layer is composed of silver. A dielectric filter comprising a plurality of coaxial resonators, at least one of which is in accordance with the resonator as claimed in claim 3 or any of claims 4 to 11 as dependent thereon, wherein the input electrodes (26) and the output electrodes (27) in said respective coaxial resonators are positioned in the same plane, the end faces in said respective coaxial resonators are arranged in the same direction, and the input electrode (26) and output electrode (27) of adjacent coaxial resonators are electrically connected to each other. A dielectric filter according to claim 12, wherein the input (26) and output electrodes (27) are electrically connected to each other by causing the portions of the electrodes formed on said other side faces of adjacent resonators to be brought into physical contact with each other. A dielectric filter comprising a plurality of coaxial resonators provided side by side, at least a first one of said resonators being in accordance with the resonator as claimed in any of claims 1 to 11, and a second one of said resonators comprises a capacitive conductor (6) formed on one of the side faces in a position in proximity to the end face on which the conductive layer is not formed, wherein the resonators are arranged so that the or each electrode (6) of said first resonator lies in the same plane as the capacitive conductor of said second resonator and the end faces of the plural resonators lie in the same respective planes, the filter further comprising reactance means (10, 12) connecting an electrode (6) of the at least one first resonator with the capacitive conductor of the second resonator. A dielectric filter comprising a plurality of coaxial resonators provided side by side, at least one of said resonators being in accordance with the resonator as claimed in any of claims 1 to 11, the electrode (15) defining an inductive conductor (15) formed in a position in proximity to the end face on which the conductive layer is formed, wherein the resonators are arranged so that the one side face and the end faces of the resonators lie in the same respective planes, the filter further comprising reactance means (10, 12) connecting the electrodes (15) of the adjacent resonators to each other. A dielectric filter according to claim 14 or 15, wherein said reactance means is capacitive reactance (10). A dielectric filter according to claim 14 or 15, wherein said reactance means is inductive reactance (12).

Inventors: HIRAO YASUHIRO, KOBAYASHI YASUMI, KUROKI KAZUHIRO, SIBATA KENICHI, TAKEUCHI KOUSUKE, HIRAO, YASUHIRO, KOBAYASHI, YASUMI, KUROKI, KAZUHIRO, SIBATA, KENICHI, TAKEUCHI, KOUSUKE
Applicants: SANYO ELECTRIC CO, SANYO ELECTRIC CO., LTD.
Application year: 1993
Main classification: H01P1
IPC codes: H01P7, H01P1