Filter, duplexer, and communication device

Abstract: A coplanar resonator comprising first center electrodes (2a, 2b) each having open ends and a ground electrode (3) which extends along either side thereof is formed on the upper plane of a dielectric substrate (1), and second center electrodes (4a, 4b) and a perimeter electrode (5) are formed on the lower plane of the dielectric substrate (1), so as to face the above center electrodes (2a, 2b) and ground electrode (3). Thus, a filter, duplexer, and communication device using the same, are provided, wherein the size of the resonator part formed of electrode patterns on a dielectric substrate is reduced, thereby facilitating ease of reduction in size of the overall device, and increasing no-load Q.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coplanar line filter configured with coplanar resonators provided upon a dielectric substrate, a duplexer, and a communication device using the same. 2. Description of the Related Art Figs. 22A through 22C illustrate a configuration example of a coplanar line filter using a conventional coplanar resonator. Fig. 22A is a plan view of the dielectric substrate, Fig. 22B is a bottom view thereof, and Fig. 22C is a side view thereof. Formed on the upper side of the dielectric substrate 1 are center electrodes 2a and 2b having open ends, and a ground electrode 3 following the sides of these center electrodes. In the diagram, the arrows represent the magnetic field distribution. Due to such a structure, the center electrode 2a and the ground electrode 3 serve as one coplanar resonator, and the center electrode 2b and the ground electrode 3 serve as the other coplanar resonator. Further, these two coplanar resonators collectively exhibit electromagnetic field junction, thereby acting as a filter formed of two tiers of resonators. Generally, filters formed of coplanar resonators can comprise the short-circuit portion of resonators on a single plane of a dielectric substrate, so reduction in size can be realized by 1/4 wavelength resonators, but the amount of leakage of the electromagnetic field distribution in the resonating mode out from the dielectric substrate may be relatively great, i.e., the effective dielectric constant tends to be low, so there has been a limit to the extent of reduction in size. Also, as shown in Figs. 22A through 22C, the electric field heads from the center electrodes toward the ground electrode on either side, so the electric field is concentrated at the ends of the center electrodes. Consequently, there has been a problem in that a high no-load Q cannot be obtained. JP-A-09181501 shows a stripline filter. On a first surface of a first dielectric substrate, a stripline resonator and a first ground pattern are formed. On the entire surface of a second surface, a second ground pattern is composed. On a first surface of a second dielectric substrate, a third ground pattern corresponding to the first ground pattern is formed. On the entire surface of an opposite side, a fourth ground pattern is formed. The ground patterns are connected by holes. The two dielectric substrates are connected by soldering and a band pass filter is composed. Since the grid patterns cover the external surfaces of the two dielectric substrates, micro waves are not propagated to the outside. US-A-2,945,195 describes a microwave filter including a resonator assembly supported on a dielectric sheet and sandwiched between two ground plane plates. Two metal framing members or spacers surround and clamp the periphery of the dielectric sheet and space it from the ground plates. The resonator assembly includes two sinuous transmission lines, one on each side of the sheet. The transmission lines may be formed by coating the dielectric sheet on both sides with metal, such as copper, and then etching away the metal to leave an array of parallel m-shaped conductive strips connected end-to-end by bends. For lower frequencies, the resonator elements may become too large to be self-supporting, so that some auxiliary support is necessary, so that an additional dielectric sheet and an additional transmission line is used to increase the stability of the resonator assembly. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a coplanar line filter, duplexer, and communication device using the same, wherein ease of reduction in size of the entire article is facilitated, and no-load Q is increased. To this end, the coplanar line filter according to the present invention comprises: a dielectric substrate having an upper plane and a lower plane; a coplanar resonator provided upon the upper plane of the dielectric substrate, the coplanar resonator comprising a first center electrode wherein on end thereof is an open end, and a ground electrode with a predetermined gap provided from the first center electrode; a second center electrode provided on the lower plane of the dielectric substrate, formed so as to face the first center electrode across the dielectric substrate; and a perimeter electrode provided on the lower plane of the dielectric substrate, formed so as to face the ground electrode across the dielectric substrate. As will become apparent from the later-described embodiments, the center electrode patterns on the upper and lower side of the dielectric substrate are mutually electromagnetically linked so as to act as a ring resonator, so resonance frequency decreases. On the other hand, the dimensions of the electrode patterns for obtaining a predetermined resonance frequency and the dimensions of the dielectric substrate are reduced. Further, resonance mode electromagnetic fields facing in the upper and lower plane directions with a dielectric substrate therebetween improves deterioration of no-load Q (hereafter referred to as "Qo") due to the edge effect, thereby obtaining a high Qo. The duplexer according to the present invention comprises: a transmission filter comprising a coplanar line filter according to the present invention; and a reception filter comprising a coplanar line filter according to the present invention. Thus, high Qo and low insertion loss properties are obtained with an overall small size. The communication device according to the present invention comprises the above filters or duplexer as the processing unit for transmission signals or reception signals in a high-frequency circuit part for example, thereby obtaining high electric usage efficiency properties with a small size. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A through 1C are diagrams illustrating the configuration of a filter according to a first embodiment; Figs. 2A through 2C are diagrams illustrating another configuration example of the filter; Figs. 3A through 3C are diagrams illustrating the resonance mode of the filter by electric field distribution; Figs. 4A through 4C are diagrams illustrating the resonance mode of the filter by electric field distribution; Figs. 5A through 5C are configuration diagrams illustrating a filter according to a second embodiment; Figs. 6A through 6C are configuration diagrams illustrating a filter according to a third embodiment; Figs. 7A through 7C are configuration diagrams illustrating a filter according to a fourth embodiment; Figs. 8A through 8C are configuration diagrams illustrating a filter according to a fifth embodiment; Fig. 9 is a partially enlarged diagram of the filter; Fig. 10 is a diagram illustrating pass properties and reflecting properties of the filter; Figs. 11A through 11C are configuration diagrams illustrating a filter according to a sixth embodiment; Figs. 12A through 12C are configuration diagrams illustrating a filter according to a seventh embodiment; Figs. 13A and 13B are diagrams illustrating an example of the dimensions of the parts of the filter and change in properties; Fig. 14 is a diagram illustrating the relation between the length L2 of the line portions and Qe; Fig. 15 is a diagram illustrating a comparative example of pass properties of the filter and a conventional filter; Figs. 16A and 16B are configuration diagrams illustrating a duplexer according to an eighth embodiment; Figs. 17A and 17B are configuration diagrams illustrating a filter according to a ninth embodiment; Fig. 18 is a diagram illustrating an example of properties of the filter; Figs. 19A and 19B are configuration diagrams illustrating a filter according to a tenth embodiment; Fig. 20 is a diagram illustrating an example of properties of the filter; Fig. 21 is a block diagram illustrating the configuration of a communication device relating to the eleventh embodiment; and Figs. 22A through 22C are configuration diagram illustrating a conventional filter. DESCRIPTION OF THE PREFERRED EMBODIMENTS Figs. 1A through 1C illustrate the configuration of a filter according to a first embodiment. Fig. 1A is a plan view of the dielectric substrate, Fig. 1B is a see-through view thereof showing the patterns on the lower side viewed from above, and Fig. 1C is a cross-sectional view thereof of the portion along line A-A'. Formed on the upper side of the dielectric substrate 1 are mutually parallel first center electrodes 2a and 2b with respective line widths of W1 and having open ends, and a ground electrode 3 distanced from these first center electrodes by a predetermined distance. Also formed are input/output electrodes 6a and 6b extending outwards from predetermined portions on the first center electrodes 2a and 2b. The input/output electrodes 6a and 6b and the ground electrode 3 form respective coplanar lines. Formed on the lower side of the dielectric substrate 1 are second center electrodes 4a and 4b and a perimeter electrode 5, at positions facing the first center electrodes 2a and 2b and the ground electrode 3 on the upper plane, respectively. Note, however, that according to the present example, the electrode patterns are formed with the short-circuit end of the first center electrodes 2a and 2b on the upper side of the dielectric substrate 1 and the short-circuit end of the second center electrodes 4a and 4b on the lower side of the dielectric substrate 1 facing in opposite directions, with the length where the first center electrodes 2a and 2b, and second center electrodes 4a and 4b overlap being represented as L1. Also, the ground electrodes on either side of the input/output electrodes 6a and 6b are connected with wires 7a and 7b, but this portion may be connected with air bridges instead. According to such a structure, the ground potential on either side of the input/output electrodes 6a and 6b is equalized, and the input/output electrode portion is operated as a coplanar line in a stable manner. Figs. 2A through 2C illustrate another configuration example, in the example shown in Figs. 1A through 1C, the ground electrode 3 and the perimeter electrode 5 on the dielectric substrate 1 are independent, but a side electrode 9 may be formed on the side of the dielectric substrate 1 so as to connect the ground electrode 3 and the perimeter electrode 5, as shown in Figs. 2A through 2C. Due to this structure, the potential of the perimeter electrode 5 on the lower side of the dielectric substrate becomes equal to the ground potential, and a stable resonant mode can be obtained. Figs. 3A through 4C are diagrams showing examples of electric field distribution of the filters shown in Figs. 1A through 2C. Figs. 3A through 3C show the electric field distribution in the even mode, and Figs. 4A through 4C show the electric field distribution in the odd mode. It can be clearly understood in light of comparison with the filter using the conventional coplanar resonator shown in Figs. 22A through 22C that with conventional coplanar resonators the direction of the electromagnetic field is between the center electrodes and the ground electrode on either side, but with the resonator according to the present invention the direction of the electromagnetic field is primarily between the upper and lower planes of the dielectric substrate. Accordingly, the concentration of electric field at the end portion of the first center electrodes 2a and 2b is alleviated, and deterioration of Qo due to the edge effect is suppressed. Also, the first and second center electrode portions of the upper and lower planes of the dielectric substrate mutually electromagnetically join to serve as a ring resonator, so the resonance frequency is lower than that of an arrangement configured with a conventional coplanar resonator. That is to say, here the two center electrodes on the upper and lower planes adjacent to one another each serve as a half-wavelength resonator. The open ends of the half-wavelength resonators on the upper plane and the lower plane are joined by electric field in the vertical direction, and act just as a ring resonator. Here, the resonance frequency drops, since the effective dielectric constant is higher and the line length is longer than arrangements comprising coplanar lines. Next, the configuration of a filter according to a second embodiment is shown in Figs. 5A through 5C. Fig. 5A is a plan view of the dielectric substrate, Fig. 5B is a lower view thereof, and Fig. 5C is a cross-sectional view thereof of the portion along the line A-A'. With the first embodiment, the short-circuit ends of the first and second center electrodes on the upper and lower sides of the dielectric substrate 1 face in opposite directions, but with the example shown in Figs. 5A through 5C, the short-circuit ends of the first and second center electrodes on the upper and lower sides of the dielectric substrate 1 face in the same direction. In this case as well, the direction of the electric field is vertical across the dielectric substrate, so a high Qo can be obtained. Figs. 6A through 6C are configuration diagrams of a filter according to a third embodiment. In this example, first center electrodes 2a and 2b are provided upon the upper side of a dielectric substrate 1, and a ground electrode 3 is formed extended along one side of the center electrodes. In the same manner, second center electrodes 4a and 4b are provided upon the lower side of the dielectric substrate, and a perimeter electrode 5 is formed extended along one side of these. Even with such a structure, the resonance mode involves the direction of the electric field being vertical across the dielectric substrate. However, there is no ground electrode for between the first center electrodes 2a and 2b arranged in parallel on the plane direction of the dielectric substrate, so the first-tier resonator made up of the first center electrode 2a and second center electrode 4a and the ground electrode 3 and perimeter electrode 5, and the second-tier resonator made up of first center electrode 2b and second center electrode 4b and the ground electrode 3 and perimeter electrode 5 can be joined in an even more intense manner. Figs. 7A through 7C are configuration diagrams of a filter according to a fourth embodiment. With this example, a ground electrode 3 is formed extending along both sides of the first center electrodes 2a and 2b on the upper side of the dielectric substrate 1, and a perimeter electrode 5 is formed extending along one side of each of the second center electrodes 4a and 4b on the lower side thereof. According to this structure, the resonators of the first tier and the second tier can be joined at a degree partway between that shown with the filters according to the first and second embodiments and the third filter shown in Figs. 6A through 6C. Next, the configuration of a filter according to a fifth embodiment will be described with reference to Figs. 8A through 9. As shown in Figs. 8A through 8C, first center electrodes 2a and 2b and a ground electrode 3 are formed on the upper plane of the dielectric substrate 1, and near the end of the first center electrodes 2a and 2b opposite to the open end thereof (other end) the first center electrodes 2a and 2b are connected to the ground electrode 3 via lines 8a and 8b. Fig. 9 is an enlarged view of the line portion thereof. A meandering line 8a with a line width W2 is thus formed between the first center electrode 2a and the ground electrode 3 on either side thereof. This is true for the other line 8b as well. These lines 8a and 8b are capable of making external connection by the inductance of the lines 8a and 8b, and use the ends of the first center electrodes 2a and 2b which are not the open ends as the input/output portions thereof. According to this structure, the wires and air bridges and the like for connecting the non-continuous portions of the ground electrode in the case of so-called tap connections such as shown in Figs. 1A through 1C are unnecessary, and an external connection structure can be made by the electrode pattern on the dielectric substrate along, so ease of manufacturing thereof is facilitated. Fig. 10 illustrates the transmission properties and reflection properties of the filter shown in Figs. 8A through 8C. Thus, even in the event that the center electrodes and ground electrode are connected with lines to make external connection, low-reflection low-insertion-loss properties can be obtained at the pass band. Figs. 11A through 11C are configuration diagram of a filter according to a sixth embodiment. With the example shown in 8A through 8C, input/output of signals is performed from the other end on the upper plane of the dielectric substrate 1, but with the example shown in Figs. 11A through 11C, a line 8a is provided between the first center electrode 2a on the upper side of the dielectric substrate 1 and the ground electrode 3 on either side thereof, and a line 8b is provided between the second center electrode 4b on the lower side of the dielectric substrate and the perimeter electrode 5 on either side. Thus, input and output of signals is performed on the upper and lower planes of the dielectric substrate and in opposing directions, thereby markedly securing isolation between input and output. Fig. 14 illustrates the relation of external Q (Qe) as to the length L2 of the line 8a and 8b portions with the filters shown in Figs. 8A through 8C and Figs. 11A through 11C. Here, the length of the dielectric substrate is W = 5.2 mm, the width is D = 2.5 mm, and the thickness is T = 0.2 mm, the width of the lines of the center electrodes is W1 = 0.3 mm, the width of the lines 8a and 8b is W2 = 0.03 mm, and the length wherein the center electrodes on the upper and lower planes of the dielectric substrate overlap is L1 = 3.5 mm. Thus, Qe can be greatly changed by the length L2 of the lines connecting the center electrodes and the perimeter electrode on either side thereof, so a predetermined external connection can be determined. Figs. 12A through 12C are configuration diagrams of a filter according to a seventh embodiment. this is an example wherein the length of the lines 8a and 8b shown in Figs. 8A through 8C have been shortened to a minimal length. That is to say, lines 8a and 8b are formed between certain positions on the first center electrodes 2a and 2b and the ground electrode 3 on either side thereof at a minimal length. Fig. 13A illustrates the relation between the length L1 wherein the first and second center electrodes on the upper and lower planes of the dielectric substrate overlap and the center frequency Fo. Here, the length of the dielectric substrate is W = 5.2 mm, the width is D = 2.5 mm, and the thickness is T = 0.2 mm, the width of the lines 8a and 8b is W2 = 0.1 mm, the length of the lines 8a and 8b is L2 = 0.1 mm, and the line width of the center electrodes W1 is a parameter. Thus, the center frequency Fo of the filter can be determined by the length L1 wherein the center electrodes on the upper and lower planes of the dielectric substrate each overlap. Fig. 13B illustrates the relation of the joining coefficient K between the resonators as to the width W1 of the center electrodes 2a, 2b, 4a, and 4b. Here, W, D, T, W2, and L2 are the same conditions as with Fig. 13A, and the length L1 wherein the center electrodes on the upper and lower planes of the dielectric substrate overlap is a parameter. Thus, the joining coefficient between the resonators can be determined by the length L1 wherein the center electrodes on the upper and lower planes of the dielectric substrate overlap and the line width W1 of the center electrodes. With the example in Figs. 13A and 13B, the conditions of L2 = 0.1 are set with external joining set to the weakest, so that effects of external joining can be ignored. Fig. 15 is a diagram illustrating the transmission properties of the filter shown in Figs. 12A through 12C. This figure also shows the properties of a filter as shown in Figs. 12A through 12C with conventional coplanar resonators wherein center electrodes and perimeter electrodes are not provided to the lower plane side of the dielectric substrate. Here, the solid lines represent arrangements according to the embodiment, and the dotted lines represent conventional structures. Also, Table 1 shows the properties of two filters. Type Mode f even, f odd [MHz] Center frequency [MHz] Qo odd Qo even Average Qo Embodiment Odd 2312.76 2479.42 61.06 61.32 Even 2646.07 61.58 Conventional Even 4389.60 4545.50 56.01 46.23 example Odd 4701.39 36.45 As can be seen here, in the event that the length of the center electrodes are the same, the center frequency is far lower than filters using conventional coplanar resonators. At the same time, Qo increases greatly. Accordingly, the line length necessary for obtaining the desired center frequency is shortened, and the overall filter can be reduced in size. Also, increased Qo allows low-loss properties to be obtained. Incidentally, in Fig. 15, the insertion loss is greater for the solid line than for the dotted line, but this is due to effects of external joining, and is not due to Qo. Next, Figs. 16A and 16B illustrate a configuration example of a duplexer according to an eighth embodiment. Fig. 16A is a plan view, and Fig. 16B is a lower view. First center electrodes 2a, 2b, 2c, and 2d, and a ground electrode 3 extending around either side thereof are formed on the upper plane of a dielectric substrate 1. Second center electrodes 4a, 4b, 4c, and 4d, are formed on the lower plane of the dielectric substrate, at positions facing the above first center electrodes 2a, 2b, 2c, and 2d, respectively, and a perimeter electrode 5 is also formed extending around either side thereof. Also, input/output electrodes 6a, 6b, 6c, and 6d vertically extending from predetermined places on the four first center electrodes are formed on the upper plane of the dielectric substrate 1, and the spaces between the ground electrodes on either side of these input/output electrodes are connected with wires. Further, an input/output electrode 10 wherein one end serves as an antenna port ANT and the other end connects to the ground electrode 3 is formed, and the input/output electrodes 6b and 6c are made to conduct to predetermined places on this input/output electrode 10. The two-tier coplanar line resonator made up of the first and second center electrodes 2a, 2b, 4a, and 4b, and the ground electrode 3 and perimeter electrode 5 positioned from the center electrodes by a certain distance, as shown in Figs. 16A and 16B, is used as a transmission filter, and the two-tier coplanar line resonator made up of the first and second center electrodes 2c, 2d, 4c, and 4d, and the ground electrode 3 and perimeter electrode 5 positioned from the center electrodes by a certain distance, is used as a reception filter. Thus, an antenna resonator is configured wherein the input/output electrode 6a serves as the transmission signal input port TX, and wherein the input/output electrode 6d serves as the reception signal output port RX. Incidentally, with the example shown in Figs. 16A and 16B, the perimeter electrodes 5 and 5 on the lower plane side of the dielectric substrate are separated between the transmission filter portion and the reception filter portion, so isolation can be increased for each of the filters. Next, the configuration of a filter according to a ninth embodiment will be described with reference to Figs. 17A and 17B and Fig. 18. With this example, as shown in Figs. 17A and 17B, two mutually parallel first center electrodes 2a and 2b each having open ends, and a ground electrode 3 positioned a certain distance therefrom, are formed on the upper plane of a dielectric substrate 1. Second center electrodes 4a and 4b, and a perimeter electrode 5 are formed on the lower plane of the dielectric substrate 1, at positions facing the upper plane first center electrodes 2a and 2b, and the ground electrode 3. Note however, that the electrode patterns are formed with the short-circuit end of the first center electrodes 2a and 2b on the upper side of the dielectric substrate 1 and the short-circuit end of the second center electrodes 4a and 4b on the lower side thereof facing in opposite directions, with the length of the first center electrodes 2a and 2b on the upper plane as L3 and the length of the second center electrodes 4a and 4b on the lower plane as L3'. Also formed on the upper side of the dielectric substrate 1 are lines 8a and 8b connecting the first center electrodes 2a and 2b with the ground electrode 3 on either side thereof. These lines 8a and 8b are formed as meandering lines over a length L2 which is shorter than L3. According to this structure, external connection is made by the inductance of the lines 8a and 8b, and the ends of the first center electrodes 2a and 2b opposite to the open ends are used as the input/output portions thereof. Multiple via holes 11 for allowing conducting between the perimeter electrodes on the upper and lower plans are provided on the perimeter of the dielectric substrate 1. Also, a via hole 12 for allowing conducting between the ground electrode positioned between the first center electrodes 2a and 2b and the perimeter electrode positioned between the second center electrodes 4a and 4b is formed at the approximate center position of the dielectric substrate. Thus, allowing conducting of the ground electrode and perimeter electrode on the upper and lower planes of the dielectric substrate by the via holes 11 and 12 enables suppressing of spurious response due to the electrode patterns on the upper and lower planes of the dielectric substrate. Particularly, the via hole 12 positioned at the center of the dielectric substrate 1 is effective in suppressing spurious response due to the ground electrode or perimeter electrode at the center portion of the dielectric substrate between the center electrodes. The above via holes are formed by the processes of (1) forming holes in the perimeter of the chip to be cut out as a filter while in the wafer state of the dielectric ceramic substrate, (2) forming electrodes within the holes, and (3) dividing into individual chips by dicing. The above via holes are formed by methods for working the post-baking ceramic substrate with laser tools such as carbon dioxide gas laser or YAG laser or the like, ultrasound tools, etc., or methods for baking following opening holes in the ceramic green sheet. Now, as shown in Figs. 17A and 17B, shortening the length L3 of the first center electrodes 2a and 2b on the upper side of the dielectric substrate and lengthening the length L3' of the second center electrodes 4a and 4b on the lower side thereof enables spurious response having an electromagnetic field distribution similar to λ/4 CPW (a coplanar wave guide which resonates at 1/4 wavelength) which becomes spurious response to be shifted to a sufficiently high frequency, without changing the main frequency of the filter. This is because while the main resonance mode of the filter depends on the electrodes on both sides of the dielectric substrate, the spurious response having an electromagnetic field distribution similar to the λ/4 CPW filter is strongly dependent on only the upper side of the dielectric substrate. Fig. 18 illustrates a comparison in transmission properties and reflection properties between a filter wherein spurious response has been suppressed by the via holes shown in Figs. 17A and 17B and a normal filter without via holes formed. Here, S21 represents transmission properties and S11 represents reflection properties, and (original filter) indicates that the filter is a normal filter without via holes formed and (modified filter) indicates that the filter is a filter wherein spurious response has been suppressed by via holes. It can be understood from this diagram that spurious response properties have been markedly improved. At twice the center frequency F0 of this filter (2F0), the amount of decay is 24.2 dB, and the amount of decay is 29.6 dB at three times (3F0), showing that sufficient spurious response suppression is exhibited. Next, the configuration of a filter according to a tenth embodiment will be described with reference to Figs. 19A and 19B and Fig. 20. With the ninth embodiment, a filter is configured of two tiers of resonators, but three or more tiers of resonators can be used to configure the resonator in the same manner. Generally, decay properties can be improved by increasing the number of tiers of the filter. However, with the transmission properties of a filter made up of three tiers of resonators, the spurious response occurs near the high range side of the filter band, and accordingly decay properties could not be improved. With this tenth embodiment, three tiers of resonators are formed and a spurious response suppression is made, thereby improving decay properties. As shown in Figs. 19A and 19B, formed on the upper side of the dielectric substrate 1 are mutually parallel first center electrodes 2a, 2b, and 2c, having open ends, and a ground electrode 3 following the sides of these first center electrodes. Also, formed on the lower side of the dielectric substrate 1 are second center electrodes 4a, 4b, and 4c, and a perimeter electrode 5, at positions facing the first center electrodes 2a, 2b, and 2c and the ground electrode 3 on the upper plane, respectively. In this example, the length of the first center electrodes 2a, 2b, and 2c is L3, the length of the second center electrodes 4a and 4c on the lower plane is L3', and the length of 4b is L3", so that the overlapping length of the center electrodes on the upper side and lower differs between the first and third tiers and the second tier. Also, meandering lines 8a and 8b are formed on the upper plane of the dielectric substrate 1 so as to connect the first center electrodes 2a and 2c and the ground electrode 3 on either side thereof. Multiple via holes 11 for allowing conducting between the ground electrode and perimeter electrode on the upper and lower planes are provided on the perimeter of the dielectric substrate 1. Thus, allowing conducting of these electrodes on the upper and lower planes of the dielectric substrate by the via holes 11 enables suppressing of spurious response due to the electrode patterns on the upper and lower planes of the dielectric substrate. Incidentally, the external connection of the filter is optimized by the number of switchbacks of the lines 8a and 8b. Fig. 20 illustrates a comparison in transmission properties and reflection properties between a filter wherein spurious response has been suppressed by the via holes shown in Figs. 19A and 19B and a normal filter without via holes formed. Here, S21 represents transmission properties and S11 represents reflection properties, and (original filter) indicates that the filter is a normal filter without via holes formed and (modified filter) indicates that the filter is a filter wherein spurious response has been suppressed by via holes. It can be understood from this diagram that spurious response properties have been markedly improved with the filter having via holes formed therein, in the same manner as with the filter made up of two tiers of resonators. At twice the center frequency F0 of this filter (2F0), the amount of decay is 31.2 dB, and the amount of decay is 38.4 dB at three times (3F0), showing that sufficient spurious response suppression is exhibited. In this way, spurious response properties have been improved regardless that this is a three-tier resonator filter, so various applications are possible with this filter. Next, a configuration example of a communication device according to an eleventh embodiment will be described with reference to the block diagram shown in Fig. 21. In Fig. 21, ANT denotes a transmission/reception antenna, DPX denotes a duplexer, BPFa, BPFb, and BPFc each denote band pass filters, AMPa and AMPb each denotes amplifying circuits, MIXa and MIXb each denote mixers, and DIV denotes a divider (synthesizer). OSC denotes a voltage-control oscillator which modulates oscillation frequencies by signals according to transmission signals (transmission data). The MIXa modulates frequency signals output from the DIV with modulation signals, the BPFa passes only the transmission frequency band, the AMPa subjects this to electric power amplification and transmits from the ANT via the DPX. The AMPb amplifies reception signals output from the DPX. Of the amplified signals, the BPFb passes only the reception frequency bandwidth. The MIXb mixes the frequency signals output from the BPFc with the reception signals, and outputs intermediate frequency signals IF. The duplexer shown as the eighth embodiment is used as the duplexer DPX part shown in Fig. 21. Also, the dielectric filter shows as the first through seventh embodiments is used for the band pass filters BPFa, BPFb, and BPFc. Thus, a compact communication device with excellent high-frequency circuit properties can be obtained by using compact filters or duplexers which pass desired frequency bands with low insertion loss. According to the present invention, the dimensions of the electrode patterns for obtaining a predetermined resonance frequency and the dimensions of the dielectric substrate can be reduced in size, and further, filter properties with low insertion loss can be obtained and no-load Q of the resonator is increased. Also, according to the present invention, the need for connection of the non-continuous portions of the perimeter electrode with wires or air bridges, and parts for taking electrostatic capacity, are done away with, and input/output of signals can be performed with electrode patterns on the upper side of the dielectric substrate alone, thereby facilitating ease of manufacturing. Also, according to the present invention, via holes are formed for conduction between the ground electrode and perimeter electrode on the upper plane and lower plane of the dielectric substrate, so spurious response can be suppressed, and excellent conducting properties and reflecting properties can be obtained. Also, according to the present invention, the above filters or duplexer are used as the processing unit for transmission signals or reception signals in a high-frequency circuit part for example, thereby obtaining high electric usage efficiency properties with a small size.

Claims: A coplanar line filter, comprising: a dielectric substrate (1) having an upper plane and a lower plane; a coplanar resonator (2a, 2b, 3; 4a, 4b, 5) provided upon the upper plane of said dielectric substrate (1), said coplanar resonator comprising a first center electrode (2a, 2b) wherein one end thereof is an open end, input/output electrodes (6a,6b) extending outward from predetermined portions of the first center electrode (2a, 2b), and a ground electrode (3) with a predetermined gap provided from said first center electrode (2a, 2b); characterized by a second center electrode (4a, 4b) provided on the lower plane of said dielectric substrate, formed so as to face said first center electrode (2a, 2b) across said dielectric substrate; and a perimeter electrode (5) provided on the lower plane of said dielectric substrate, formed so as to face said ground electrode (3) and said input/output electrodes (6a,6b) across said dielectric substrate (1), wherein one end of the second center electrode (4a, 4b) is an open end, and wherein the open end of the first center electrode (2a, 2b) and the open end of the second center electrode (4a, 4b) face in opposite directions. A coplanar line filter according to Claim 1, wherein a plurality of said coplanar resonators (2a, 2b, 3; 4a, 4b, 5) are arranged on the upper plane of said dielectric substrate (1) in a parallel manner with regard to the resonating directions thereof. A coplanar line filter according to Claim 2, wherein ground conducting members connected to said first ground electrode (3) are provided between said plurality of coplanar resonators. A coplanar line filter according to one of Claims 1 to 3, wherein said ground electrode (3) of the upper plane and said perimeter electrode (5) of the lower plane are mutually connected. A coplanar line filter according to Claim 4, wherein said ground electrode (3) and said perimeter electrode (5) are connected by via holes (11; 12) passing through the upper plane and lower plane of said dielectric substrate (1). A coplanar line filter according to one of Claims 1 to 5, wherein said first center electrode (2a, 2b) of the upper plane and said second center electrode (4a, 4b) of the lower plane are mutually joined electromagnetically. A coplanar line filter according to one of Claims 1 to 6, wherein said first center electrode (2a, 2b) and said ground electrode (3) are connected near the end at the opposite side from said open end of said first center electrode. A coplanar line filter according to Claim 7, wherein said first center electrode (2a, 2b) and said ground electrode (3) are connected by a meandering line (8a, 8b). A duplexer (DPX) comprising: a transmission filter (2a, 2b, 3; 4a, 4b, 5) comprising a coplanar line filter according to any one of the Claims 1 through 8; and a reception filter (2c, 2d, 3; 4c, 4d, 5) comprising a coplanar line filter according to any one of the Claims 1 through 8. A communication device (ANT, DPX, BPFa, BPFb, BPFc, AMPa, AMPb, MIXa, MIXb, OSC, DIV) comprising a coplanar line filter according to any one of the Claims 1 through 8. A communication device comprising a duplexer according to Claim 9.

Inventors: TSUJIGUCHI TATSUYA, TSUJIGUCHI, TATSUYA
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 2001
Main classification: H01P1
IPC codes: H01P1, H01P7