Resonator

Abstract: There is provided a resonator which can suppress degradation of the Q factor, adjust the frequency, and reduce the size and profile thereof. A voltage controlled oscillator (10) using a resonator includes a multilayer substrate (12). The multilayer substrate (12) includes a first grounding conductor layer (14), a first dielectric layer (16), a strip line layer (18), a second dielectric layer (22), a second grounding conductor layer (24), and a third dielectric layer (26). A strip line (20) is formed on the strip line layer (18), and a microstrip line (28) is formed on the third dielectric layer (26). The strip line (20) is connected to the microstrip line (28) via a through hole (30) to form the resonator. A portion (32), facing the microstrip line (28), of the second grounding conductor layer (24) is removed.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonator, and more specifically, it relates to a resonator used for a voltage controlled oscillator or the like. 2. Description of the Related Art Fig. 5 is a schematic representation showing an example of a voltage controlled oscillator using a conventional resonator. A voltage controlled oscillator 1 includes a dielectric substrate 2. A grounding conductor layer 3 is formed on the reverse side of the dielectric substrate 2. A microstrip line 4 is formed on the surface of the dielectric substrate 2, and a resonator comprises the dielectric substrate 2, the grounding conductor layer 3 and the microstrip line 4. In addition, a plurality of electronic parts 5 are mounted on the surface of the dielectric substrate 2. The voltage controlled oscillator 1 comprises these electronic parts 5 and the resonator. In such a resonator, the frequency can be adjusted by cutting the microstrip line 4. Further, as shown in Figs. 6 and 7 and according to the disclosure of JP 06013808 (MURATA), JP 05335835 (KYOCERA) or JP 06216614 (CASIO), the resonator can be formed of the grounding conductor layer 3, the dielectric layer 6 and a strip line 7 by including the multilayer substrate formed of two grounding conductor layers 3 and a plurality of dielectric layers 6, and laminating the strip line layer 8 forming the strip line 7 between the two grounding conductor layers 3. In this case, a circuit formed of the electronic parts 5 mounted on the surface of the multilayer substrate is connected to the strip line 7 via a through hole 9. The size and profile of parts and modules, including for example voltage controlled oscillators, used in portable terminals have been reduced, and it has been difficult to ensure sufficiently pattern area of the microstrip line pattern formed on the surface of the substrate with the electronic parts mounted thereon. On the other hand, in the strip line resonator shown in Fig. 6, there are no problems in ensuring the pattern area of the strip line; however, there are structural problems in which the Q factor is low, and the C/N and S/N characteristics are degraded compared with the microstrip line resonator formed on the substrate surface. Further, the technology to cut the strip line formed in an intermediate layer of the multilayer substrate is required to adjust the frequency. Also, if a conductor layer is provided inside the substrate in the microstrip line resonator, the space between the microstrip line and the conductor layer inside the substrate is reduced, and the thickness of the dielectric layer therebetween is also reduced, and thus, the Q factor of the microstrip line resonator is degraded thereby. If the thickness of the inside dielectric layer is increased to prevent such degradation of the Q factor, a problem occurs, the thickness of the substrate will not satisfy the low profile requirement. SUMMARY OF THE INVENTION Accordingly, it is a major object of the present invention to provide a resonator which can suppress the degradation of the Q factor, adjust the frequency, and reduce the size and profile thereof. There is provided in the present invention a resonator comprising a multilayer substrate including at least two conductor layers which include at least two grounding conductor layers and a plurality of dielectric layers with one of the grounding conductor layers formed on a reverse side thereof, a strip line formed between the two grounding conductor layers, a microstrip line formed on the surface of the multilayer substrate, and a through hole formed in the dielectric layer to connect the strip line and the microstrip line, wherein at least a portion, facing the microstrip line, of the conductor layer closest to the microstrip line is removed. In this resonator, the portion of the conductor layer formed inside the multilayer substrate facing the microstrip line may be removed so that the grounding conductor layer formed on the reverse side of the multilayer substrate is facing the microstrip line. The area of the microstrip line on the surface of the multilayer substrate can be reduced by forming the microstrip line on the surface of the multilayer substrate, forming the strip line inside thereof, and connecting these components to each other via the through hole to constitute the resonator. The frequency of the resonator can be adjusted by cutting the microstrip line on the surface of the multilayer substrate. In addition, the space between the microstrip line and the conductor layer can be increased by removing the conductor layer portion inside the multilayer substrate facing the microstrip line, and the degradation of the Q factor due to a reduction in size can be suppressed. The space between the microstrip line and the grounding conductor layer can be maximized by removing a portion of the conductor layer inside the multilayer substrate so that the microstrip line faces the grounding conductor layer on the reverse side of the multilayer substrate, and the Q factor can be improved thereby. The above-described objects, other objects, and features and advantages of the present invention will become apparent from the detailed description of the embodiment of the present invention with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic representation of an example of a voltage controlled oscillator using a resonator in accordance with the present invention. Fig. 2 is an exploded perspective view of a multilayer substrate used in the voltage controlled oscillator shown in Fig. 1. Fig. 3 is a schematic representation showing a removed portion facing a microstrip line of a second grounding conductor layer. Fig. 4 is a schematic representation showing the microstrip line and the second grounding conductor layer facing each other. Fig. 5 is a schematic representation of an example of the voltage controlled oscillator using a conventional resonator. Fig. 6 is a schematic representation of another example of the voltage controlled oscillator using the conventional resonator. Fig. 7 is an exploded perspective view of a multilayer substrate used for the voltage controlled oscillator shown in Fig. 6. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a schematic representation showing an example of a voltage controlled oscillator using a resonator of the present invention. A voltage controlled oscillator 10 includes a multilayer substrate 12. A first grounding conductor layer 14 is formed on a reverse side of the multilayer substrate 12 as shown in Fig. 2. A first dielectric layer 16 is laminated on the first grounding conductor layer 14. In addition, a strip line layer 18 is formed on the first grounding conductor layer 16. A strip line 20 is formed, for example, in a U-shaped manner on the strip line layer 18. In addition, a second dielectric layer 22 is laminated on the strip line layer 18. A second grounding conductor layer 24 is laminated on the second dielectric layer 22. In addition, a third dielectric layer 26 is laminated on the second grounding conductor layer 24. A microstrip line 28 is formed on the third dielectric layer 26. One end of the microstrip line 28 is formed on a part corresponding to one end of the strip line 20. To connect the strip line 20 to the microstrip line 28, a through hole 30 is formed in the second dielectric layer 22, the second grounding conductor layer 24, and the third dielectric layer 26. The strip line 20 is connected to the microstrip line 28 via the through hole 30 to form a resonator. A portion 32 of the second grounding conductor layer 24 facing the microstrip line 28 is removed, and the microstrip line 28 and the first grounding conductor layer 14 are disposed facing each other via the dielectric layers 16, 22, 26. A plurality of electronic parts 34 are mounted on the surface with the microstrip line 28 formed thereon to form a circuit. This circuit is connected to the resonator to constitute the voltage controlled oscillator 10. The multilayer substrate 12 is manufactured by printing an electrode paste on a dielectric ceramic green sheet in the shape of each conductor layer, strip line, and microstrip line, and then laminating and baking the electrode paste. In the electrode paste printed part forming the second grounding conductor layer 24, the portion 32 facing the microstrip line 28 is formed by not printing the electrode paste thereat. The first grounding conductor layer 14, the first dielectric layer 16, the strip line 20 formed on the strip line layer 18, the second dielectric layer 22, and the second grounding conductor layer 24 form a strip line resonator, and the first grounding conductor layer 16, the three dielectric layers 16, 22, 26, and the microstrip line 28 form a microstrip line resonator. A single resonator is formed by connecting the strip line resonator to the microstrip line resonator. In these resonators, one resonator comprises one strip line resonator and one microstrip line resonator, and thus, the area of the microstrip line 28 can be reduced compared with a case where the resonator comprises only microstrip lines. Thus, the multilayer substrate 12 can be reduced in size. Further, the frequency of the resonator can be adjusted by cutting the microstrip line 28 formed on the surface of the multilayer substrate 12. In addition, the portion 32 facing the microstrip line 28 of the second grounding conductor layer 24 inside the multilayer substrate 12 is removed, and thus, the microstrip line 28 and the first grounding conductor layer 14 are facing each other as shown in Fig. 3, and the dielectric layers 16, 22, 26 therebetween are thick. Thus, in this resonator, the Q factor can be improved compared with a case where the microstrip line 28 and the second grounding conductor layer 24 are facing each other as shown in Fig. 4. An experiment was actually made for the case where a portion facing a microstrip line of an intermediate conductor layer was removed and a case where the portion facing the microstrip line was not removed. Here, the C/N characteristic most related to the Q factor was examined. It was proved that the C/N ratio was improved by about 2 dB in a case where an inside conductor layer was removed, and the space between the microstrip line 28 and the first grounding conductor layer 14 facing each other was 0.75 mm compared with a case where the second grounding conductor layer 24 shown in Fig. 1 was not removed, and the space between the microstrip line 28 and the second grounding conductor layer 24 facing each other was 0.15 mm. The structure of the multilayer substrate 12 is not limited to the structure shown in Figs. 1 and 2, and other conductor layer may be formed thereon. Also, in such a case, the space between the microstrip line 28 and the conductor layer facing it can be increased by removing a portion facing the microstrip line of the inside conductor layer. The conductor layer facing the microstrip line 28 is not limited to the first grounding conductor layer 14; however, the microstrip line 28 may face a conductor layer inside the multilayer substrate 12, and the space between the microstrip line 28 and the conductor layer facing it may be determined according to a necessary characteristic. In the present invention, the area of the microstrip line on the surface of the multilayer substrate can be reduced by forming a resonator by connecting the strip line to the microstrip line, and thus the resonator can also be reduced in size. Further, the frequency of the resonator can be easily adjusted by cutting the microstrip line on the surface of the multilayer substrate. In addition, the space between the microstrip line and the conductor layer facing it can be increased by removing the portion, facing the microstrip line, of the conductor layer inside the multilayer substrate and the Q factor can be improved thereby.

Claims: A resonator comprising: a multilayer substrate (12) comprising: at least two conductor layers (14, 24) which include at least two grounding conductor layers (14, 24); and a plurality of dielectric layers (16, 22, 26) with one of said grounding conductor (14) layers formed on a reverse side thereof; a strip line (20) formed between two of the grounding conductor layers (14, 24); a microstrip line (28) formed on a surface of said multilayer substrate (12); and a through hole (30) formed in said dielectric layer (22) to connect said strip line (20) to said microstrip line (28), characterized in that at least a portion (32), facing the microstrip line (28), of said conductor layer (24) closest to said microstrip line (28) is removed. A resonator according to Claim 1, wherein a portion (32) of said conductor layer (24) formed inside said multilayer substrate (12) facing said microstrip line (28) is removed so that said grounding conductor layer (14) formed on a reverse side of said multilayer substrate (12) is facing said microstrip line (28).

Inventors: TAKAHASHI YOSHINORI, TAKAHASHI, YOSHINORI, Takahashi, Yoshinori, Murata Manufact. Co., Ltd.
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 2001
Main classification: H01P7
IPC codes: H05K1, H03B5, H01P7