High-frequency circuit Number:7,183,888 from the United States Patent and Trademark Office (PTO) owispatent A high-frequency circuit is formed on a multilayered dielectric substrate having at least two conductive circuit layers. The high-frequency circuit includes: a first spiral conductive strip formed in the first conductive circuit layer, the first spiral conductive strip having at least one turn; and a second spiral conductive strip formed in a second conductive circuit layer which is different from the first conductive circuit layer, the second spiral conductive strip having at least one turn and not being in electrical conduction with the first spiral conductive strip. The first spiral conductive strip and the second spiral conductive strip, located at different levels, overlap each other. The first spiral conductive strip has a rotating direction opposite to a rotating direction of the second spiral conductive strip.<H frequency, circuit, High, frequency, , 7183888.html, Patent, pto, 7183888

Title: High-frequency circuit

Abstract: A high-frequency circuit is formed on a multilayered dielectric substrate having at least two conductive circuit layers. The high-frequency circuit includes: a first spiral conductive strip formed in the first conductive circuit layer, the first spiral conductive strip having at least one turn; and a second spiral conductive strip formed in a second conductive circuit layer which is different from the first conductive circuit layer, the second spiral conductive strip having at least one turn and not being in electrical conduction with the first spiral conductive strip. The first spiral conductive strip and the second spiral conductive strip, located at different levels, overlap each other. The first spiral conductive strip has a rotating direction opposite to a rotating direction of the second spiral conductive strip.

Patent Number: 7,183,888 Issued on 02/27/2007 to Kanno, et al.

Inventors: Kanno; Hiroshi (Osaka, JP), Sakiyama; Kazuyuki (Shijonawate, JP), Sangawa; Ushio (Ikoma, JP), Fujishima; Tomoyasu (Neyagawa, JP)
Assignee: Matsushita Electric Industrial Co., Ltd. (Osaka, JP)

Appl. No.: 10/969,096

Filed: October 21, 2004

Foreign Application Priority Data


Apr 24, 2003 [JP]			2003-120024

Current U.S. Class: 336/200

Current International Class: H01F 5/00 (20060101)

Field of Search: 336/65,83,200,205-208,232

References Cited [Referenced By]

U.S. Patent Documents


3833872	September 1974	Marcus et al.
4959631	September 1990	Hasegawa et al.
6198374	March 2001	Abel
7030725	April 2006	Ahn et al.

Foreign Patent Documents


5-14009	Jan., 1993	JP
7-336104	Dec., 1995	JP
11-274416	Oct., 1999	JP
2000-91805	Mar., 2000	JP
2002-9516	Jan., 2002	JP

Other References

Inder Bahl et al., Microwave Solid State Circuit Design 2.sup.nd Edition pp. 275 Wiley-Interscience, 2003, no month. cited by other .
Sutono et al., IEEE Radio Frequency Integrated Circuits Symposium Digest, "Development of Three Dimensional Ceramic-Based MCM Inductors for Hybrid RF/Microwave Applications", pp. 175-178, 1999, no month. cited by other .
Hejazi et al., IEEE Transactions on Applied Superconductivity, "Compact Superconducting Dual-Log Spiral Resonator With High Q-Factor and Low Power Dependence", vol. 12, No. 2, 2002, no month. cited by other .
Sutono et al., IEEE EPEP Digest, "Investigations of Multi-Layer Ceramic-Based MCM Technology", pp. 83-86, 1998, no month. cited by other.

Primary Examiner: Nguyen; Tuyen T.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack, L.L.P.

Parent Case Text

This application is a continuation of International Application PCT/JP04/04759, filed Apr. 1, 2004.

Claims

What is claimed is:

1. A resonator comprising a multilayered dielectric substrate including: a first spiral conductive strip composed of a conductive strip having at least one turn; and a second spiral conductive strip composed of a conductive strip having at least one turn, wherein the first spiral conductive strip is not in electrical conduction with the second spiral conductive strip, the first spiral conductive strip and the second spiral conductive strip are located at different levels and overlap each other, the first spiral conductive strip has a rotating direction opposite to a rotating direction of the second spiral conductive strip, ends of the first spiral conductive strip are open and not connected to a terminal or other device, and ends of the second spiral conductive strip are open and not connected to a terminal or other device.

2. The resonator according to claim 1, wherein, when the first and second spiral conductive strips are stacked so that spiral centers of the first and second spiral conductive strips coincide with each other, outer peripheries of the first and second spiral conductive strips coincide with each other.

3. The resonator according to claim 1, wherein the open ends of outermost strip subportions of the first and second spiral conductive strips are disposed diagonally opposite from each other with respect to spiral centers of the first and second spiral conductive strips.

4. The resonator according to claim 1, further comprising an input/output line coupled to an outermost strip subportion of either one of the first and second spiral conductive strips.

5. The resonator according to claim 1, wherein the multilayered dielectric substrate further includes a third spiral conductive strip composed of a conductive strip having at least one turn, the third spiral conductive strip is not in electrical conduction with the first spiral conductive strip or the second spiral conductive strip, the third spiral conductive strip and each one of the first and second spiral conductive strips are located at different levels and overlap each other, the second spiral conductive strip is interposed between the first spiral conductive strip and the third spiral conductive strip, the second spiral conductive strip has the rotating direction opposite to a rotating direction of the third spiral conductive strip, and ends of the third conductive strip are open.

6. The resonator according to claim 5, wherein, when the first, second, and third spiral conductive strips are stacked so that spiral centers of the first, second, and third spiral conductive strips coincide with each other, outer peripheries of the first, second, and third spiral conductive strips coincide with each other.

7. The resonator according to claim 5, wherein the open ends of outermost strip subportions of the first and second spiral conductive strips are disposed diagonally opposite from each other with respect to spiral centers of the first and second spiral conductive strips, and the open ends of outermost strip subportions of the second and third spiral conductive strips are disposed diagonally opposite from each other with respect to the spiral center of the second spiral conductive strip and a spiral center of the third spiral conductive strip.

8. The resonator according to claim 1, wherein the multilayered dielectric substrate further includes: a third spiral conductive strip composed of a conductive strip having at least one turn, the third spiral conductive strip adjoining the first spiral conductive strip in a lateral direction and having a same rotating direction as that of the first spiral conductive strip; and a fourth spiral conductive strip composed of a conductive strip having at least one turn, the fourth spiral conductive strip adjoining the second spiral conductive strip in a lateral direction and having a same rotating direction as that of the second spiral conductive strip, the third spiral conductive strip is not in electrical conduction with the fourth spiral conductive strip, the third spiral conductive strip and the fourth spiral conductive strip are located at different levels and overlap each other, the third spiral conductive strip has a rotating direction opposite to a rotating direction of the fourth spiral conductive strip, ends of the third spiral conductive strip are open, and ends of the fourth spiral conductive strip are open.

9. The resonator according to claim 8, wherein, when the first and second spiral conductive strips are stacked so that spiral centers of the first and second spiral conductive strips coincide with each other, outer peripheries of the first and second spiral conductive strips coincide with each other, and when the third and fourth spiral conductive strips are stacked so that spiral centers of the third and fourth spiral conductive strips coincide with each other, outer peripheries of the third and fourth spiral conductive strips coincide with each other.

10. The resonator according to claim 8, wherein the open ends of outermost strip subportions of the first and second spiral conductive strips are disposed diagonally opposite from each other with respect to spiral centers of the first and second spiral conductive strips, and the open ends of outermost strip subportions of the third and fourth spiral conductive strips are disposed diagonally opposite from each other with respect to spiral centers of the third and fourth spiral conductive strips.

11. The resonator according to claim 1, wherein a current distribution density at the open ends of the first spiral conductive strip is 0, and a current distribution density at the open ends of the second spiral conductive strip is 0.

12. The resonator according to claim 5, further comprising an input/output line coupled to an outermost strip subportion of any of the first, second, and third spiral conductive strips, wherein the input/output line is connected to a portion other than the open ends of the any of the first, second, and third spiral conductive strips.

13. The resonator according to claim 5, further comprising an input/output line coupled to an outermost strip subportion of any of the first, second, and third spiral conductive strips, wherein the input/output line is separated from and not electrically connected to the first, second, and third spiral conductive strips.

14. The resonator according to claim 8, further comprising a plurality of input/output lines coupled to outermost strip subportions of any of the first, second, third, and fourth spiral conductive strips, wherein the input/output lines are connected to portions other than the open ends of the any of the first, second, third, and fourth spiral conductive strips.

15. The resonator according to claim 8, further comprising a plurality of input/output lines coupled to outermost strip subportions of any of the first, second, third, and fourth spiral conductive strips, wherein the input/output lines are separated from and not electrically connected to the first, second, third, and fourth spiral conductive strips.

16. The resonator according to claim 1, wherein the resonator is operable to inhibit exhibition of resonance at a frequency which is twice as high as a fundamental frequency, and exhibit resonance at a frequency which is a multiple, of an integer equal to or greater than 3, of the fundamental frequency.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high-frequency circuit which is capable of transmitting or radiating a high-frequency signal in the microwave or millimeter range, and more particularly to a high-frequency circuit capable of exhibiting resonance.

2. Description of the Background Art

In recent years, wireless communication devices have made advancements in terms of downsizing and high-functionalization, which have enabled the drastic prevalence of cellular phones. In the years to come, further downsizing, high-functionalization, and cost reduction are expected.

A high-frequency circuit which is mounted in a wireless communication device such as a cellular phone requires a resonator as an element for composing circuits such as filters, an antenna, and the like.

For example, a 1/2 wavelength resonator composed of a transmission line whose both ends are open terminated may be used as a resonator. FIG. 25A is an upper plan view showing a conventional 1/2 wavelength resonator. FIG. 25B is a cross-sectional view of the conventional 1/2 wavelength resonator shown in FIG. 25A.

A 1/2 wavelength resonator which is composed of a transmission line 900 whose both ends are open terminated as shown in FIG. 25A needs to be as long as 7.5 cm in the case where its resonance frequency is 2 GHz. Therefore, in order to reduce the circuit size, it is necessary to somehow reduce the resonator length. It is generally known that using a material with high dielectric constant for the circuit substrate 901 can reduce the length of the open-ended transmission line 900, and hence the size of the resonator composed thereof.

On the other hand, it is also generally known that, when a plurality of resonators composed of transmission lines are electromagnetically coupled, the lowest-order resonance frequency thereof can be reduced. FIG. 26A is an upper plan view showing a conventional resonator in which two resonators are electromagnetically coupled together. FIG. 26B is a cross-sectional view of the conventional resonator shown in FIG. 26A composed of two electromagnetically coupled resonators. As disclosed in Document 1 (Microwave Solid State Circuit Design 2nd Edition pp. 275 Wiley-Interscience 2003), if two resonators are coupled together with a short distance between two parallel coupled-lines 902 and 903 contained therein, resonance will no longer occur at a resonance frequency f0 at which resonance would have occurred in the case where there was only a single resonator. Instead, an even mode resonance at a resonance frequency f1 (where f1<f0) and an odd mode resonance at a resonance frequency f2 (where f2>f0) will occur. The more strongly the two resonators are coupled, the farther away the values of f1 and f2 will shift from the value of f0. Therefore, by realizing a stronger coupling between two resonators which have a resonance frequency of f0, a resonator which resonates at a lower resonance frequency f1 (i.e., with a longer wavelength) can be provided; that is, for a given resonance frequency, a resonator having a shorter resonator length can be realized than in the case of employing a single resonator.

However, substrate materials having high dielectric constant are more expensive than substrate materials having low dielectric constant, e.g., resin. Therefore, the aforementioned technique of downsizing a resonator by using a material with high dielectric constant for the circuit substrate leads to cost problems, regardless of whether the entire circuit is formed by using a substrate of a material with high dielectric constant or only the resonator portion is formed of a material with high dielectric constant.

On the other hand, in order to shift the resonance frequencies by introducing a higher degree of coupling between two parallel coupled-lines contained in two resonators, the distance between the parallel lines must be made very short, which means that a drastic improvement in strip formation precision is necessary. However, given the current demands for reducing costs associated with production processes, it is not realistic to improve strip formation precision just for the sake of realizing an extreme reduction in the distance between parallel lines of a resonator. Thus, it would be unrealistic to provide a resonator having a short resonator length by reducing the distance between parallel coupled-lines.

Therefore, what would be practical is to provide a downsized resonator by using a circuit structure which is applicable to a semiconductor process, a production process for a low-temperature sintered ceramic substrate, a multilayer circuit process for a resin substrate, or the like.

It is possible to obtain a high degree of coupling between parallel coupled-lines by deploying two transmission lines in multiple layers, such that the transmission lines overlap each other in the thickness direction. FIG. 27 is a cross-sectional view showing a conventional resonator having an enhanced coupling degree, in which two transmission lines 904 and 905 are disposed in multiple layers so as to overlap each other in the thickness direction. However, the technique illustrating FIG. 27, where two transmission lines are disposed in multiple layers so as to overlap each other in the thickness direction has the following two problems.

A first problem is that there is a limit to the reduction in resonance frequencies that can be achieved based on the capacitance obtained by the parallel overlapping of the two transmission lines 904 and 905. No matter how strong an electromagnetic coupling is obtained by the above technique, the new resonance frequency f1 will not be much below the fundamental frequency f0. This technique is only effective for causing a resonance in the case where the length of the coupled-lines is 1/2 of the wavelength of the electromagnetic waves. Thus, the length of the coupled-lines is still required to be about 1/2 of the wavelength, which is a limitation to downsizing.

A second problem is that the resonance obtained from parallel coupled-lines cannot provide adequate spurious prevention characteristics. For example, a band-pass filter used in an actual communication device needs to have not only passing characteristics for a desired band and blocking characteristics for frequencies in the immediate neighborhood of the desired band, but also spurious prevention characteristics for removing harmonic components which may have occurred in various active elements in a previous block. A resonator which is based on parallel coupled-lines is not entirely suitable for use in a communications module since it is impossible to control a resonance which occurs at a frequency which is twice the fundamental frequency.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a compact resonator having a simple structure which is much shorter than the wavelength of electromagnetic waves of a transmission band and which does not resonate at a frequency about twice a fundamental resonance frequency, the resonator not requiring additional use of any special material. A further object of the present invention is to provide a compact filter circuit having a blocking function for a frequency which is twice a transmission frequency.

The present invention has the following features to attain the object mentioned above.

The present invention is directed to a high-frequency circuit formed on a multilayered dielectric substrate having at least two conductive circuit layers, comprising: a first spiral conductive strip formed in the first conductive circuit layer, the first spiral conductive strip having at least one turn; and a second spiral conductive strip formed in a second conductive circuit layer which is different from the first conductive circuit layer, the second spiral conductive strip having at least one turn and not being in electrical conduction with the first spiral conductive strip, wherein, the first spiral conductive strip and the second spiral conductive strip, located at different levels, overlap each other, and the first spiral conductive strip has a rotating direction opposite to a rotating direction of the second spiral conductive strip.

In the high-frequency circuit according to the present invention, an overlapping coupling capacitance which couples the first spiral conductive strip and the second spiral conductive strip exists near a portion where the first spiral conductive strip and the second spiral conductive strip, located at different levels, overlap each other. As a result of a first high-frequency current flowing through the first spiral conductive strip being transferred to the second spiral conductive strip via an overlapping coupling capacitance, a second high-frequency current flows through the second spiral conductive strip. When a coupling occurs such that the direction in which the second high-frequency current flows in the same direction as that of the first high-frequency current, the overlapping portion between the first spiral conductive strip and the second spiral conductive strip can be regarded as parallel coupled-lines in which an even mode is induced so that currents will flow in the same direction. The second high-frequency current which flows along the second spiral conductive strip can further move to the first spiral conductive strip via an overlapping coupling capacitance. Thus, the high-frequency circuit according to the present invention can function as a resonator which exhibits resonance for electromagnetic waves of an elongated wavelength beyond its physical size. Since a capacitance circuit in itself functions as a high-pass filter, in order for the high-frequency circuit according to the present invention to exhibit resonance at a lower resonance frequency, an advantageous arrangement would be where a high-frequency current flowing through the high-frequency circuit according to the present invention will travel via an overlapping coupling capacitance by a minimum number of times, so that the first and/or second spiral conductive strips are efficiently utilized for effectively increasing the resonator length. Therefore, by ensuring that the first spiral conductive strip and the second spiral conductive strip have opposite rotating directions, it becomes possible to obtain resonance at a reduced resonance frequency.

With respect to the resonance at the fundamental frequency in the high-frequency circuit, the open ends of the outermost strip subportions of both spiral conductive strips can be considered as open ends of the entire structure. Therefore, a zero current distribution density exists at such open terminating ends. On the other hand, in the high-frequency circuit according to the present invention, currents flowing through the spiral conductive strips mutually transfer via an overlapping coupling capacitance between the spiral conductive strips, so that a zero current distribution density cannot exist near the overlapping portion between the spiral conductive strips. Similarly, in order for a signal having a wavelength corresponding to a frequency which is twice the frequency at which a fundamental mode resonance occurs to exhibit resonance, it is necessary that the open ends of the outermost strip subportions of both spiral conductive strips correspond to the open ends of the entire structure, and also that a zero current distribution density exits near an overlapping portion between the spiral conductive strips. However, since the spiral conductive strips no longer function as individual spiral conductive strips but can only exhibit resonance utilizing a coupling between the spiral conductive strips, the condition that a zero current distribution density should exit near an overlapping portion between the spiral conductive strips cannot be satisfied. It is at a frequency which is three times the fundamental frequency that the resonating conditions are satisfied without a zero current distribution density existing in the neighborhood of the overlapping portion between the two spiral conductive strips when a zero current distribution density exists at the open terminating ends of the outermost strip subportions of the spiral conductive strips. Note that, in order to obtain this effect according to the present invention, the two spiral conductive strips should not be mechanically connected by through-vias or the like.

Thus, there is provided a low-cost but highly-functional resonator which is more compact than conventionally, and which can be constructed based on a simple structure without requiring any special material, such that the high-frequency circuit does not exhibit resonance at a frequency which is twice the fundamental resonance frequency, and structured in a size which is much shorter than the wavelength of electromagnetic waves of a transmission band.

Preferably, the multilayered dielectric substrate has three or more conductive circuit layers, the high-frequency circuit further comprising: at least one third spiral conductive strip formed in a third conductive circuit layer which is different from the first and second conductive circuit layers, the third spiral conductive strip having at least one turn and not being in electrical conduction with the first and second spiral conductive strips,

wherein, the at least one third spiral conductive strip overlaps the first and second spiral conductive strips at respectively different levels, and any adjoining spiral conductive strips among the first to third spiral conductive strips have opposite rotating directions to each other.

According to the above structure, due to a current flowing through the first spiral conductive strip, a magnetic field is generated in a direction which perpendicularly cuts through the center of the first spiral conductive strip. The magnetic field thus generated also cuts perpendicularly through the center of the overlapping second spiral conductive strip. Since a capacitance which couples the first spiral conductive strip and the second spiral conductive strip is generated in an overlapping portion, a current flows through the second spiral conductive strip in the same direction as in the first spiral conductive strip. A magnetic field which lies perpendicularly across the conductive circuit layer in which the second spiral conductive strip is formed also lies across the overlapping third spiral conductive strip. Since a capacitance which couples the second spiral conductive strip and the third spiral conductive strip is generated in an overlapping portion, a current flows through the third spiral conductive strip in the same direction as in the second spiral conductive strip. Thus, a current flows through the third spiral conductive strip in the same direction as in the first spiral conductive strip. This principle also holds true in the case where there are four or more overlapping spiral conductive strips.

In order for a combined structure composed of a plurality of adjoining pairs of spiral conductive strips to function as a resonator having an even longer resonator length, it is necessary that the plurality of adjoining pairs of spiral conductive strips all satisfy the condition for allowing an adjoining pair of overlapping spiral conductive strips to function as a resonator having the longest resonator length. Therefore, the condition for achieving the longest resonator length can be described as the rotating directions being opposite in every adjoining pair of spiral conductive strips.

Thus, according to the present invention, a resonator which is more compact than conventionally can be provided at low cost, based on a simple structure and without requiring any special material.

Preferably, if the first to third spiral conductive strips were to be placed on one another so that a spiral center of each spiral conductive strip coincides, outer peripheries of the first to third spiral conductive strips would coincide with one another.

More preferably, open terminating ends of outermost strip subportions of any two adjoining spiral conductive strips are disposed diagonally opposite from each other with respect to the spiral center of each spiral conductive strip.

In a preferable embodiment, the high-frequency circuit further comprises an input/output line which is directly connected to a portion of an outermost strip subportion of any one of the first to third spiral conductive strips.

Thus, a strong coupling between a compact resonator and an external circuit can be realized by using a simple and compact circuit.

For the sake of simplifying the circuit structure, it is preferable that the spiral conductive strip and the input/output line are formed in the same conductive circuit layer. However, similar effects can also be obtained by disposing the spiral conductive strip and the input/output line in different conductive circuit layers, and electrically connecting the spiral conductive strip and the input/output line via a through-via.

Preferably, the high-frequency circuit further comprises at least one stacked spiral conductive strip resonator formed on the multilayered dielectric substrate, the at least one stacked spiral conductive strip resonator having the same structure as that of a stacked spiral conductive strip resonator composed of the first to third spiral conductive strips, wherein the stacked spiral conductive strip resonators are disposed adjoining one another.

According to the above structure, the two adjoining stacked spiral conductive strip resonators each have a stacked structure, and therefore a spatial capacitance occurs between the stacked spiral conductive strips. In addition, when a current flows through one of the stacked spiral conductive strip resonators, a magnetic field which is generated so as to penetrate through the inside of the stacked spiral conductive strip resonator also closes its magnetic flux on the outside of the stacked spiral conductive strip resonator. Therefore, the magnetic field is in a direction perpendicular to the multilayered dielectric substrate. Consequently, by disposing the other stacked spiral conductive strip resonator so that this ambient magnetic field penetrates through the other stacked spiral conductive strip resonator with a sufficient intensity, a current can also flow through the other stacked spiral conductive strip resonator. Thus, by simply disposing the two stacked spiral conductive strip resonators so as to adjoin each other, a desired inter-resonator coupling can be obtained. Moreover, this advantageous effect of being able to adjust a coupling between the stacked spiral conductive strip resonators based on the distance therebetween can be obtained without requiring any additional processes which may involve the use of a material with high dielectric constant or the like. Therefore, the high-frequency circuit having the above structure can be produced at low cost.

In a preferable embodiment, at least one of the stacked spiral conductive strip resonators includes: a fourth spiral conductive strip formed in the first conductive circuit layer so as to adjoin the first spiral conductive strip, the fourth spiral conductive strip having the same rotating direction as the rotating direction of the first spiral conductive strip and having at least one turn; a fifth spiral conductive strip formed in the second conductive circuit layer so as to adjoin the second spiral conductive strip, the fifth spiral conductive strip having the same rotating direction as the rotating direction of the second spiral conductive strip and having at least one turn; and at least one sixth spiral conductive strip formed in the third conductive circuit layer so as to adjoin the third spiral conductive strip, the at least one sixth spiral conductive strip having the same rotating direction as the rotating direction of the third spiral conductive strip and having at least one turn, wherein the fourth to sixth spiral conductive strips overlap one another at respectively different levels.

Preferably, the high-frequency circuit further comprises a plurality of input/output lines coupled to the respective stacked spiral conductive strip resonators.

The above structure realizes a band-pass filter circuit by utilizing a plurality of stacked spiral conductive strip resonators, each resonator having a resonator length longer than that of each component spiral conductive strip. Since each stacked spiral conductive strip resonator occupies less space than does a conventional planar resonator, the resultant band-pass filter circuit also takes less space than does a band-pass filter circuit which is based on a conventional planar resonator structure. A conventional 1/2 wavelength resonator composed of a single layer of a planar circuit exhibits resonance also at a frequency which is twice the fundamental wave, a conventional band-pass filter composed of a 1/2 wavelength resonator would have unwanted passing characteristics in a frequency band which is twice as high as the fundamental frequency. However, in the high-frequency circuit having the above structure, each stacked spiral conductive strip resonator composing the filter circuit in itself has characteristics such that resonance at a frequency which is twice the fundamental wave is suppressed. As a result, there is provided an advantageous effect of inhibiting unwanted passing characteristics in a frequency band which is twice as high as the fundamental frequency. Moreover, the high-frequency circuit having the above structure can be produced at low cost because it can provide advantageous effects such as reduction in the circuit area, and inhibition of unwanted passing characteristics in a frequency band which is twice as high as the fundamental pass band, without requiring any additional processes which may involve the use of a material with high dielectric constant or the like. Therefore, the high-frequency circuit having the above structure can be produced at low cost.

In order to obtain a strong coupling between an external circuit and the stacked spiral conductive strip resonator, it is preferable to obtain a coupling by directly connecting a portion of the spiral conductive strip to a portion of the input/output line.

As a result, not only the efficiency of energy transmission from an external circuit to the stacked spiral conductive strip resonator, or from the stacked spiral conductive strip resonator to an external circuit can be improved, but also broad-band filter characteristics can be obtained.

Preferably, if the first and second spiral conductive strips were to be placed on each other so that a spiral center of each spiral conductive strip coincides, outer peripheries of the first and second spiral conductive strips would coincide with each other.

As a result, the capacitance which couples the first spiral conductive strip and the second spiral conductive strip increases at an overlapping portion between the first spiral conductive strip and the second spiral conductive strip. Therefore, a current transfer via an overlapping coupling capacitance between the spiral conductive strips can occur at an even lower frequency. As a result, a further reduction in the resonance frequency becomes possible, i.e., a more compact resonator can be provided.

More preferably, an open terminating end of an outermost strip subportion of the first spiral conductive strip and an open terminating end of an outermost strip subportion of the second spiral conductive strip are disposed diagonally opposite from each other with respect to the spiral center of the first spiral conductive strip.

Thus, an effective overlapping between the spiral conductive strips can be realized in the outermost strip subportion, which has the longest distance per turn around the spiral center of the spiral conductive strip. Therefore, a current transfer via an overlapping coupling capacitance between the spiral conductive strips can occur at an even lower frequency. As a result, a further reduction in the resonance frequency becomes possible, i.e., a more compact resonator can be provided.

In a preferable embodiment, the high-frequency circuit further comprises an input/output line which is directly connected to a portion of an outermost strip subportion of the first or second spiral conductive strip.

Thus, a strong coupling between a compact resonator and an external circuit can be realized by using a simple and compact circuit.

For the sake of simplifying the circuit structure, it is preferable that the spiral conductive strip and the input/output line are formed in the same conductive circuit layer. However, similar effects can also be obtained by disposing the spiral conductive strip and the input/output line in different conductive circuit layers, and electrically connecting the spiral conductive strip and the input/output line via a through-via.

Preferably, the high-frequency circuit further comprises at least one stacked spiral conductive strip resonator formed on the multilayered dielectric substrate, the at least one stacked spiral conductive strip resonator having the same structure as that of a stacked spiral conductive strip resonator composed of the first and second spiral conductive strips, wherein the stacked spiral conductive strip resonators are disposed adjoining one another.

According to the above structure, the two adjoining stacked spiral conductive strip resonators each have a stacked structure, and therefore a spatial capacitance occurs between the stacked spiral conductive strips. In addition, when a current flows through one of the stacked spiral conductive strip resonators, a magnetic field which is generated so as to penetrate through the inside of the stacked spiral conductive strip resonator also closes its magnetic flux on the outside of the stacked spiral conductive strip resonator. Therefore, the magnetic field is in a direction perpendicular to the multilayered dielectric substrate. Consequently, by disposing the other stacked spiral conductive strip resonator so that this ambient magnetic field penetrates through the other stacked spiral conductive strip resonator with a sufficient intensity, a current can also flow through the other stacked spiral conductive strip resonator. Thus, by simply disposing the two stacked spiral conductive strip resonators so as to adjoin each other, a desired inter-resonator coupling can be obtained. Moreover, this advantageous effect of being able to adjust a coupling between the stacked spiral conductive strip resonators based on the distance therebetween can be obtained without requiring any additional processes which may involve the use of a material with high dielectric constant or the like. Therefore, the high-frequency circuit having the above structure can be produced at low cost.

In a preferable embodiment, at least one of the stacked spiral conductive strip resonators includes: a seventh spiral conductive strip formed in the first conductive circuit layer so as to adjoin the first spiral conductive strip, the seventh spiral conductive strip having the same rotating direction as the rotating direction of the first spiral conductive strip and having at least one turn; and an eighth spiral conductive strip formed in the second conductive circuit layer so as to adjoin the second spiral conductive strip, the eighth spiral conductive strip having the same rotating direction as the rotating direction of the second spiral conductive strip and having at least one turn; wherein the seventh and eighth spiral conductive strips overlap each another at respectively different levels.

Preferably, the high-frequency circuit further comprises a plurality of input/output lines coupled to the respective stacked spiral conductive strip resonators.

The above structure realizes a band-pass filter circuit by utilizing a plurality of stacked spiral conductive strip resonators, each resonator having a resonator length longer than that of each component spiral conductive strip. Since each stacked spiral conductive strip resonator occupies less space than does a conventional planar resonator, the resultant band-pass filter circuit also takes less space than does a band-pass filter circuit which is based on a conventional planar resonator structure. A conventional 1/2 wavelength resonator composed of a single layer of a planar circuit exhibits resonance also at a frequency which is twice the fundamental wave, a conventional band-pass filter composed of a 1/2 wavelength resonator would have unwanted passing characteristics in a frequency band which is twice as high as the fundamental frequency. However, in the high-frequency circuit having the above structure, each stacked spiral conductive strip resonator composing the filter circuit in itself has characteristics such that resonance at a frequency which is twice the fundamental wave is suppressed. As a result, there is provided an advantageous effect of inhibiting unwanted passing characteristics in a frequency band which is twice as high as the fundamental frequency. Moreover, the high-frequency circuit having the above structure can be produced at low cost because it can provide advantageous effects such as reduction in the circuit area, and inhibition of unwanted passing characteristics in a frequency band which is twice as high as the fundamental pass band, without requiring any additional processes which may involve the use of a material with high dielectric constant or the like. Therefore, the high-frequency circuit having the above structure can be produced at low cost.

Thus, according to the present invention, there is provided a compact resonator having a simple structure which does not resonate at a frequency about twice a fundamental resonance frequency, the resonator not requiring additional use of any special material, and a compact band-pass filter circuit having a blocking function for a frequency which is twice a transmission frequency.

These 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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic cross-sectional view showing a high-frequency circuit according to a first embodiment of the present invention taken along line AB in FIGS. 1B and 1C;

FIG. 1B is an upper plan view showing a pattern of a spiral conductive strip 4 which is formed on an outermost surface 2 of an upper conductive circuit layer in a multilayered dielectric substrate 1;

FIG. 1C is an upper plan view showing a pattern of a spiral conductive strip 5 formed on an interface 3 of a lower conductive circuit layer in the multilayered dielectric substrate 1;

FIG. 2A is a diagram illustrating an even mode for explaining an operation principle of the high-frequency circuit according to the first embodiment;

FIG. 2B is a diagram illustrating an odd mode for explaining an operation principle of the high-frequency circuit according to the first embodiment;

FIG. 3A is a diagram for explaining a structural dependency of coupling degree between parallel coupled-lines, illustrating an arrangement in which transmission lines are aligned so as to be completely parallel to each other;

FIG. 3B is a diagram for explaining a structural dependency of coupling degree between parallel coupled-lines, illustrating an arrangement in which transmission lines are disposed parallel to each other, the transmission lines being shifted by half along the longitudinal dimension thereof;

FIG. 3C is a diagram for explaining a structural dependency of coupling degree between parallel coupled-lines, illustrating an arrangement in which the structure of FIG. 3B is bent into a circular configuration so that an inner signal strip and an outer signal strip are coupled in two positions;

FIG. 4 is a diagram showing various points on spiral conductive strips 4 and 5 for explaining a current flow;

FIG. 5 is a diagram for explaining a principle by which resonance occurs at a fundamental frequency in a high-frequency circuit according to the present invention;

FIG. 6 is an upper plan view showing patterns of spiral conductive strips in the case where two layers of spiral conductive strips are formed in the same rotating direction;

FIG. 7A is an upper plan view showing a pattern of a spiral conductive strip 4 whose outermost contour is circular;

FIG. 7B is an upper plan view showing a pattern of a spiral conductive strip 5 whose outermost contour is circular;

FIG. 8A is an upper plan view showing two spiral conductive strips whose open terminating ends are in the same direction as seen from the center of each spiral conductive strip;

FIG. 8B is a view showing a variant from the arrangement of FIG. 8A where one of the spiral conductive strips has been rotated by 90.degree. within its plane around the center of the spiral conductive strip;

FIG. 8C is a view showing a variant from the arrangement of FIG. 8A where one of the spiral conductive strips has been rotated by 180.degree. within its plane around the center of the spiral conductive strip;

FIG. 8D is a view showing a variant from the arrangement of FIG. 8A where one of the spiral conductive strips has been rotated by 270.degree. within its plane around the center of the spiral conductive strip;

FIG. 9A is a schematic cross-sectional view showing a high-frequency circuit according to a second embodiment of the present invention taken along line CD in FIGS. 9B, 9C, and 9D;

FIG. 9B is an upper plan view showing a pattern of a spiral conductive strip 4 which is formed on an outermost surface 2 of an uppermost conductive circuit layer in a multilayered dielectric substrate 1;

FIG. 9C is an upper plan view showing a pattern of a spiral conductive strip 5 formed on an interface 3 of an intermediate conductive circuit layer in the multilayered dielectric substrate 1;

FIG. 9D is an upper plan view showing a pattern of a spiral conductive strip 9 formed on an interface 8 of a lowermost conductive circuit layer in the multilayered dielectric substrate 1;

FIG. 10A is a schematic cross-sectional view showing a high-frequency circuit according to a third embodiment of the present invention taken along line EF in FIGS. 10B and 10C;

FIG. 10B is an upper plan view showing patterns of a spiral conductive strip 4 and an input/output line 12 which are formed on an outermost surface 2 of an upper conductive circuit layer in a multilayered dielectric substrate 1;

FIG. 10C is an upper plan view showing a pattern of a spiral conductive strip 5 formed on an interface 3 of a lower conductive circuit layer in the multilayered dielectric substrate 1;

FIG. 11A is a schematic cross-sectional view showing a high-frequency circuit according to a fourth embodiment of the present invention taken along line GH in FIGS. 11B and 1C;

FIG. 11B is an upper plan view showing patterns of a spiral conductive strips 4 and 14 which are formed on an outermost surface 2 of an upper conductive circuit layer in a multilayered dielectric substrate 1;

FIG. 11C is an upper plan view showing patterns of spiral conductive strips 5 and 15 which are formed on an interface 3 of a lower conductive circuit layer in the multilayered dielectric substrate 1;

FIG. 12A is a schematic cross-sectional view showing a high-frequency circuit according to a fifth embodiment of the present invention taken along line IJ in FIGS. 12B and 12C;

FIG. 12B is an upper plan view showing patterns of spiral conductive strips 4 and 14 and input/output lines 12 and 17 which are formed on an outermost surface 2 of an upper conductive circuit layer in a multilayered dielectric substrate 1;

FIG. 12C is an upper plan view showing patterns of spiral conductive strips 5 and 15 which are formed on an interface 3 of a lower conductive circuit layer in the multilayered dielectric substrate 1;

FIG. 13A is a schematic cross-sectional view showing a high-frequency circuit for evaluation which was subjected to a measurement;

FIG. 13B is an upper plan view showing patterns of a spiral conductive strip 4 and an input/output line 12 of a high-frequency circuit for evaluation which was subjected to a measurement;

FIG. 13C is an upper plan view showing patterns of a spiral conductive strip 5 of a high-frequency circuit for evaluation which was subjected to a measurement;

FIG. 14 is a graph showing changes in a fundamental resonance frequency with respect to a relative offset distance between upper and lower spiral conductive strips;

FIG. 15 is a graph showing measurement results of properties of several high-frequency circuits in which the orientation of a spiral conductive strip formed on the surface of an additional layer is rotated by 45.degree. each;

FIG. 16 is a graph showing measurement results in the case where each spiral conductive strip has 2.25 turns;

FIG. 17 is a graph showing measurement results in the case where each spiral conductive strip has 2 turns;

FIG. 18 is a graph showing frequency characteristics of the reflection intensity of a high-frequency circuit as an example of the third embodiment in which a spiral conductive strip is directly connected to an input/output line, in the case where power is supplied from the input/output line;

FIG. 19A is a schematic cross-sectional view illustrating a high-frequency circuit in which the orientation of an input/output line 12 is rotated by 90.degree. with respect to an outermost strip of a spiral conductive strip 4 so as to together function as parallel coupled-lines which are 200 microns apart;

FIG. 19B is an upper plan view showing patterns of the spiral conductive strip 4 and the input/output line 12 in the high-frequency circuit shown in FIG. 19A;

FIG. 19C is an upper plan view showing a pattern of a spiral conductive strip 5 in the high-frequency circuit shown in FIG. 19A;

FIG. 20 is a graph showing changes in the coupling degree when the distance between two resonators is changed;

FIG. 21 is a graph showing passing characteristics of a first band-pass filter as an example of the fifth embodiment;

FIG. 22 is a graph showing passing characteristics of the first band-pass filter as an example of the fifth embodiment;

FIG. 23 is a graph showing passing characteristics of a second band-pass filter as an example of the fifth embodiment;

FIG. 24 is a graph showing passing characteristics of a second band-pass filter as an example of the fifth embodiment;

FIG. 25A is an upper plan view showing a conventional 1/2 wavelength resonator;

FIG. 25B is a cross-sectional view showing a conventional 1/2 wavelength resonator shown in FIG. 25A;

FIG. 26A is an upper plan view showing a conventional resonator in which two resonators are electromagnetically coupled together;

FIG. 26B is a cross-sectional view of the conventional resonator shown in FIG. 26A composed of two electromagnetically coupled resonators; and

FIG. 27 is a cross-sectional view showing a conventional resonator having an enhanced coupling degree, in which two transmission lines 904 and 905 are disposed in multiple layers so as to overlap each other in the thickness direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the high-frequency circuit according to the present invention will be described with reference to the figures. It will be appreciated that the present invention is not limited to the following embodiments. Although component elements having similar functions are denoted by the same reference numeral in different figures, this does not indicate that such component elements denoted by the same reference numeral are completely identical.

(First Embodiment)

FIG. 1A is a schematic cross-sectional view showing a high-frequency circuit according to a first embodiment of the present invention taken along line AB in FIGS. 1B and 1C. The high-frequency circuit according to the present embodiment is formed on a multilayered dielectric substrate 1 which has two conductive circuit layers. FIG. 1B is an upper plan view showing a pattern of a spiral conductive strip 4 which is formed on an outermost surface 2 of an upper conductive circuit layer in the multilayered dielectric substrate 1. FIG. 1C is an upper plan view showing a pattern of a spiral conductive strip 5 formed on an interface 3 of a lower conductive circuit layer in the multilayered dielectric substrate 1.

In the high-frequency circuit according to the first embodiment, the spiral conductive strip 4 is formed on the surface of an uppermost conductive circuit layer in the multilayered dielectric substrate 1 and the spiral conductive strip 5 is formed in the lower conductive circuit layer such that, if the outermost surface 2 were to be placed on the interface 3, a spiral center O4 of the spiral conductive strip 4 shown in FIG. 1B would coincide with a spiral center O5 of the spiral conductive strip 5 shown in FIG. 1C, and an outer periphery of the spiral conductive strip 4 would coincide with an outer periphery of the spiral conductive strip 5. The rotating direction of the spiral conductive strip 4 and the rotating direction of the spiral conductive strip 5 are opposite. The spiral conductive strip 4 has a clockwise rotating direction from the outside to the center of the spiral, as seen from above the circuit (in the following description, it is to be understood that any reference to a rotating direction of a spiral indicates a rotating direction from the outside to the center of the spiral, as seen from above the circuit). The spiral conductive strip 5, which is formed inside the multilayered dielectric substrate 1, has a counterclockwise rotating direction. The spiral conductive strips 4 and 5 each has 2.5 turns.

Hereinafter, an operation principle of the high-frequency circuit according to the first embodiment will be described.

FIGS. 2A and 2B are diagrams for explaining an operation principle of the high-frequency circuit according to the first embodiment. When a high-frequency current I4 flows through the spiral conductive strip 4, a charge transfer occurs in a region of the spiral conductive strip 5 which overlaps with a portion of the spiral conductive strip 4, via an overlapping coupling capacitance. As used herein, such an "overlap" exists between different levels within the high-frequency circuit, i.e., at the level of the spiral conductive strip 4 and at the level of the spiral conductive strip 5. As a result, a high-frequency current I5 flows through the spiral conductive strip 5. Each such overlapping region can be regarded as containing two parallel coupled-lines of an arbitrary length. If the high-frequency current 14 flows through the spiral conductive strip 4, two modes will be induced: a mode as shown in FIG. 2A, in which the high-frequency current I4 flowing through the spiral conductive strip 4 and the high-frequency current I5 flowing through the spiral conductive strip 5 are in the same direction; and a mode as shown in FIG. 2B, in which the high-frequency current I4 flowing through the spiral conductive strip 4 and the high-frequency current I5 flowing through the spiral conductive strip 5 are in opposite directions. When regarding the overlapping region as parallel coupled-lines, the former mode is considered as an even mode, and the latter an odd mode.

FIGS. 3A to 3C are diagrams for explaining structural dependencies of coupling degree between parallel coupled-lines. In FIGS. 3A to 3C, a ground conductor for each transmission line is omitted, and only the signal strips are shown. In an arrangement as shown in FIG. 3A, where the transmission lines are aligned so as to be completely parallel to each other, a high coupling degree cannot be obtained. The reason is that, if currents flow through both conductors in the same direction, and if both open terminating ends of each conductor satisfies the open condition, electrical charges of the same sign will be present at the open terminating ends of the two adjoining conductors, and will repel each other rather than coupling.

On the other hand, in an arrangement as shown in FIG. 3B, where the transmission lines are disposed parallel to each other so as to be shifted by half along the longitudinal dimension thereof, the coupling degree can be enhanced.

Furthermore, in an arrangement as shown in FIG. 3C, where the structure of FIG. 3B has been bent into a circular configuration so that an inner signal strip and an outer signal strip are coupled in two positions, the coupling degree between the two strips is maximized, and the resonance frequency is minimized. In this resonance mode, a current flows through both signal strips in the same direction, such that the current continues to flow from the outer signal strip to the inner signal strip, and further from the inner signal strip to the outer signal strip, via a capacitance between the strips. As a result, the high-frequency circuit shown in FIG. 3C can exhibit resonance with respect to electromagnetic waves which are far longer than the physical size that is occupied by the circuit structure. However, with the structure of FIG. 3C, how long wavelengths of electromagnetic waves the structure can function with depends solely on how much transfer of a high-frequency current can occur between the two lines. Therefore, the high-frequency circuit according to the present invention takes steps forward from the compact resonator structure shown in FIG. 3C, which escapes the constraints concerning the wavelength of electromagnetic waves, to realize a most compact resonator, by defining strip shapes for each line structure.

As has been explained with reference to FIG. 3C, according to the principle of the present invention, opposite rotating directions are prescribed for two spiral conductive strips which are formed one above the other in a high-frequency circuit, whereby an advantageous effect of achieving an increased resonator length and hence a more compact resonator can be efficiently realized.

FIG. 4 is a diagram showing various points on spiral conductive strips 4 and 5 for explaining a current flow. Due to a distributive capacitance which exists at an overlapping portion between the two spiral conductive strips, a current component flowing through point B4 on the spiral conductive strip 4 is coupled to point C5 on the spiral conductive strip 5. As a result, a current flows from one point to another, in the order of F4.fwdarw.E4.fwdarw.D4.fwdarw.C4.fwdarw.B4.fwdarw.C5.fwdarw.D5.fwdarw.- E5.fwdarw.F5. The resonator length Lcp-even in this case is much longer than a resonator length Lind of a single spiral conductive strip resonator which resonates due to a current flowing through the spiral conductive strip 4 in the order of F4.fwdarw.E4.fwdarw.D4.fwdarw.C4.fwdarw.B4.fwdarw.A4. Thus, the resonance frequency of a resonance which is obtained by providing such two spiral conductive strips 4 and 5 one above the other is lower than the lowest resonance frequency which can be realized by each of the spiral conductive strips 4 and 5 alone.

FIG. 5 is a diagram for explaining a principle by which resonance occurs at a fundamental frequency in the high-frequency circuit according to the present invention. Hereinafter, with reference to FIG. 5, the reason why resonance occurs at a fundamental frequency in the high-frequency circuit according to the present invention will be described. When open terminating ends 4o and 5o of outermost turns (hereinafter referred to as "outermost strip subportions") of the respective spiral conductive strips 4 and 5 are considered as open ends of the overall structure, a zero current distribution density exists at the open terminating ends 4o and 5o. Herein, the condition for obtaining a fundamental resonance at the lowest frequency is that a current distribution density of a current which is transferred between the spiral conductive strips is increased due to an overlapping coupling capacitance 7 at an overlapping portion 6 between the spiral conductive strips 4 and 5. In the high-frequency circuit according to the present invention, the spiral conductive strips 4 and 5 are coupled via the overlapping coupling capacitance 7 at the overlapping portion 6, so that the current distribution density is non-zero in the neighborhood of the overlapping portion 6 between the spiral conductive strips. Thus, it will be appreciated that the high-frequency circuit according to the present invention does not satisfy the conditions for being able to resonate at a frequency which is twice the fundamental resonance frequency: i.e., that the open terminating ends 4o and 5o of the outermost strip subportions of the two spiral conductive strips correspond to the open terminating ends of the resonance structure itself; and that a zero current distribution density exists in the neighborhood of the overlapping portion 6 between the spiral conductive strips. In other words, the high-frequency circuit according to the present invention has a resonance structure for suppressing resonance at a frequency which is twice the fundamental resonance frequency. Note that, in order to obtain this effect in the high-frequency circuit according to the present invention, any mechanical means such as through-vias should not be used to provide electrical conduction between the two spiral conductive strips.

Note that it is at a frequency which is three times the fundamental frequency that the resonating conditions are satisfied without a zero current density existing in the neighborhood of the overlapping portion between the two spiral conductive strips when a zero current distribution density exists at the open terminating ends of the outermost strip subportions of the spiral conductive strips.

A high-frequency circuit having a similar but different structure to the high-frequency circuit according to the present invention might be a high-frequency circuit which includes two layers of spiral conductive strip having