Strip dual mode loop resonator for resonating microwave in dual mode and band-pass filter composed of the resonators

Abstract: A strip loop resonator, comprising: a loop-shaped strip line (187, 193, 214, 225, 235) for resonating a microwave in a single mode according to a line impedance thereof; an input strip line (185) for inputting the microwave to an input point of the loop-shaped strip line in electromagnetic coupling; and an output strip line (186) for outputting the microwave resonated in the loop-shaped strip line from an output point of the loop-shaped strip line in electromagnetic coupling, characterized in that the loop-shaped strip line has an electric length shorter than a wavelength of the microwave and comprises: a pair of coupling partial lines (182a; 182b, 192a; 192b, 222a; 222b, 232a; 232b) arranged in parallel to each other to couple the coupling partial lines to each other in electromagnetic coupling, the line impedance of the loop-shaped strip line being dependent on the electromagnetic coupling between the coupling partial lines; a first side strip line of which both ends are connected to first side ends of the coupling partial lines, the input point of the loop-shaped strip line being placed at the first side strip line; and a second side strip line of which both ends are connected to second side ends of the coupling partial lines, the output point of the loop-shaped strip line being placed at the second side strip line, and the output point of the loop-shaped strip line being spaced a half wavelength of the microwave apart from the input point of the loop-shaped strip line.

Description: BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION: The present invention relates to a strip ring resonator utilized to resonate waves in frequency bands ranging from an ultra high frequency (UHF) band to a super high frequency (SHF) band, and relates to a band-pass filter composed of a series of resonators which is utilized as a communication equipment or measuring equipment. 2. DESCRIPTION OF THE RELATED ART: A half-wave length open end type of strip ring resonator has been generally utilized to resonate microwaves ranging from the UHF band to the SHF band. Also, a one-wave length strip ring resonator has been recently known. In the one-wave length strip ring resonator, no open end to reflect the microwaves is required because an electric length of the strip ring resonator is equivalent to one-wave length of the microwaves. Therefore, the microwaves are efficiently resonated because electric energy of the microwaves resonated is not lost in the open end. In addition, in cases where a band-pass filter is composed of a plurality of strip ring resonators arranged in series, a strip dual mode ring resonator functioning as a two-stage filter is required to efficiently filter the microwave in the band-pass filter. 2-1 PREVIOUSLY PROPOSED ART: A first conventional resonator is described. Fig. 1A is a plan view of a one-wave length strip ring resonator in which no open end is provided. Fig. 1B is a sectional view taken generally along the line I-I of Fig. 1A. Each of constitutional elements of the ring resonator shown in Fig. 1A is illustrated in Fig. 1B. As shown in Fig. 1A, a one-wave length strip ring resonator 11 conventionally utilized is provided with an input strip line 12 in which microwaves are transmitted, a closed ring-shaped strip line 13 in which the microwaves transferred from the input strip line 12 are resonated, and an output strip line 14 to which the microwaves resonated in the strip ring 13 are transferred. As shown in Fig. 1B, the input and output strip lines 12, 14 and the ring-shaped strip line 13 respectively consist of a strip conductive plate 15, a dielectric substrate 16 surrounding the strip conductive plate 15, and a pair of conductive substrates 17a, 17b sandwiching the dielectric substrate 16. The ring-shaped strip line 13 has an electric length equivalent to a wavelength of the microwave. The electric length of the ring-shaped strip line 13 is determined by correcting a physical line length of the ring-shaped strip line 13 with a relative dielectric constant ε r of the dielectric substrate 16. The input strip line 12 is arranged at one side of the strip ring 13 and is coupled to the ring-shaped strip line 13 in capacitive coupling. That is, when the microwaves transmit through the input strip line 12, electric field is induced in a gap space between the input strip line 12 and the ring-shaped strip line 13. Therefore, the intensity of electric field in the ring-shaped strip line 13 is also increased at a coupling point P1 adjacent to the input strip line 12 to a maximum value. The output strip line 14 is arranged at an opposite side of the strip ring 13. In other words, the output strip line 14 is spaced 180 degrees (a half-wave length of the microwaves) in the electric length apart from the input strip line 12. In this case, the intensity of the electric field in the ring-shaped strip line 13 is maximized at a coupling point P2 adjacent to the output strip line 14 because the output strip line 14 is spaced 180 degrees in the electric length apart from the input strip line 12. Therefore, the output strip line 14 is electrically coupled to the ring-shaped strip line 13 in capacitive coupling. In the above configuration, when microwaves are transmitted in the input strip line 12, electric field is induced at a gap portion between the input strip line 12 and the ring-shaped strip line 13 by the microwaves. Therefore, the intensity of the electric field in the ring-shaped strip line 13 is maximized at the coupling point P1 adjacent to the input strip line 12. Thereafter, the electric field induced at the coupling point P1 is diffused into the ring-shaped strip line 13 as traveling waves. In other words, the microwaves are transferred from the input strip line 12 to the ring-shaped strip line 13. In this case, a part of the travelling waves are transmitted in a clockwise direction, and a remaining part of the travelling waves are transmitted in a counterclockwise direction. In cases where the wavelength of the microwaves is equivalent to the electric length of the ring-shaped strip line 13, the microwaves are resonated in the ring-shaped strip line 13. Therefore, the intensity of the microwaves in the ring-shaped strip line 13 is amplified. Thereafter, the intensity of the electric field in the ring-shaped strip line 13 is maximized at the coupling point P2 adjacent to the output strip line 14 because the output strip line 14 is spaced 180 degrees in the electric length apart from the input strip line 12. Therefore, the electric field is induced at a gap space between the ring-shaped strip line 13 and the output strip line 14. As a result, the microwave resonated in the ring-shaped strip line 13 is transferred to the output strip line 14. Accordingly, the strip ring resonator 11 functions as a resonator of the microwaves. In this case, the microwaves can be resonated in the strip ring 13 even though the electric length of the ring-shaped strip line 13 is an integral multiple of the wavelength of the microwaves. The strip ring resonator 11 is often utilized to estimate the dielectric substrate 16 because a resonance frequency (or a central frequency) of the microwaves is shifted according to a physical shape of the dielectric substrate 16 and the relative dielectric constant ε r of the dielectric substrate 16. The strip ring resonator 11 is described in detail in the literature "Resonant Microstrip Ring Aid Dielectric Material Testing", Microwaves & RF, page 95-102, April, 1991. 2-2 ANOTHER PREVIOUSLY PROPOSED ART: A second conventional resonator is described. Fig. 2 is a plan view of a strip dual mode ring resonator functioning as a two-stage filter. As shown in Fig. 2, a strip dual mode ring resonator 21 conventionally utilized is provided with an input strip line 22 in which microwaves are transmitted, a one-wave length strip ring 23 electrically coupled to the input strip line 22 in capacitive coupling, and an output strip line 24 electrically coupled to the strip ring 23 in capacitive coupling. The input strip line 22 is coupled to the strip ring 23 through a gap capacitor 25, and the output strip line 24 is coupled to the strip ring 23 through a gap capacitor 26. Also, the output strip line 24 is spaced 90 degrees (or a quarterwave length of the microwaves) in the electric length apart from the input strip line 22. The strip ring 23 has an open end stub 27 in which the microwaves are reflected. The open end stub 27 is spaced 135 degrees (or 3/8-wave length of the microwaves) in the electric length apart from the input and output strip lines 22, 24. In the above configuration, the action of the strip dual mode ring resonator 21 is qualitatively described in a concept of travelling waves. When travelling waves are transmitted in the input strip line 22, electric field is induced in the gap capacitor 25. Therefore, the input strip line 22 is coupled to the strip ring 23 in the capacitive coupling, so that a strong intensity of electric field is induced at a point P3 of the strip ring 23 adjacent to the input strip line 22. That is, the travelling waves are transferred to the coupling point P3 of the strip ring 23. Thereafter, the travelling waves are circulated in the strip ring 23 to diffuse the electric field strongly induced in the strip ring 23. In this case, a part of the travelling waves are transmitted in a clockwise direction and a remaining part of the travelling waves are transmitted in a counterclockwise direction. An action of the travelling waves transmitted in the counterclockwise direction is initially described. When the travelling waves transmitted in the counterclockwise direction reach a coupling point P4 of the strip ring 23 adjacent to the output line 24, the phase of the travelling wave shifts by 90 degrees. Therefore, the intensity of the electric field at the coupling point P4 is minimized. Accordingly, the output strip line 24 is not coupled to the strip ring 23 so that the travelling waves are not transferred to the output strip line 24. Thereafter, when the travelling waves reach the open end stub 27, the phase of the travelling wave further shifts by 135 degrees as compared with the phase of the travelling wave reaching the coupling point P4. Because the open end stub 27 is equivalent to a discontinuous portion of the strip ring 23, a part of the travelling waves are reflected at the open end stub 27 to produce reflected waves, and a remaining part of the travelling waves are not reflected at the open end stub 27 to produce non-reflected waves. The non-reflected waves are transmitted to the coupling point P3. In this case, because the phase of the non-reflected waves transmitted to the coupling point P3 totally shifts by 360 degrees as compared with that of the travelling waves transferred from the input strip line 22 to the coupling point P3, the intensity of the electric field at the coupling point P3 is maximized. Therefore, the input strip line 22 is coupled to the strip ring 23 so that a part of the non-reflected waves are returned to the input strip line 22. A remaining part of the non-reflected waves are again circulated in the counterclockwise direction so that the microwaves transferred to the strip ring 23 are resonated. In contrast, the reflected waves are returned to the coupling point P4. In this case, the phase of the reflected waves at the point P4 further shifts by 135 degrees as compared with that of the reflected wave at the open end stub 27. This is, the phase of the reflected wave at the point P4 totally shifts by 360 degrees as compared with that of the travelling waves transferred from the input strip line 22 to the coupling point P3. Therefore, the intensity of the electric field at the coupling point P4 is maximized, so that the output strip line 24 is coupled to the strip ring 23. As a result, a part of the reflected wave is transferred to the output strip line 24. A remaining part of the reflected wave is again circulated in the clockwise direction so that the microwave transferred to the strip ring 23 is resonated. Next, the travelling waves transmitted in the clockwise direction is described. A part of the travelling waves transmitted in the clockwise direction are reflected at the open end stub 27 to produce reflected waves when the phase of the travelling waves shifts by 135 degrees. Non-reflected waves formed of a remaining part of the travelling waves reach the coupling point P4. The phase of the non-reflected waves totally shifts by 270 degrees so that the intensity of the electric field induced by the non-reflected waves is minimized. Therefore, the non-reflected waves are not transferred to the output strip line 24. That is, a part of the non-reflected waves are transferred from the coupling point P3 to the input strip line 22 in the same manner, and a remaining part of the non-reflected waves are again circulated in the clockwise direction so that the microwave transferred to the strip ring 23 is resonated. In contrast, the reflected waves are returned to the coupling point P3. In this case, because the phase of the reflected waves at the coupling point P3 totally shifts by 270 degrees, the intensity of the electric field induced by the reflected waves are minimized so that the reflected waves are not transferred to the input strip line 22. Thereafter, the reflected waves reach the coupling point P4. In this case, because the phase of the reflected waves at the coupling point P4 totally shifts by 360 degrees, the intensity of the electric field induced by the reflected waves is maximized. Therefore, a part of the reflected waves are transferred to the output strip line 24, and a remaining part of the reflected waves are again circulated in the counterclockwise direction so that the microwaves transferred to the strip ring 23 are resonated. Accordingly, because the microwaves can be resonated in the strip ring 23 on condition that a wavelength of the microwaves equals the electric length of the strip ring 23, the strip dual mode ring resonator 21 functions as a resonator and a filter. Also, the microwaves transferred from the input strip line 22 are initially transmitted in the strip ring resonator 23 as the non-reflected waves, and the microwaves are again transmitted in the strip ring resonator 23 as the reflected waves shifting by 90 degrees as compared with the non-reflected waves. In other words, two orthogonal modes formed of the non-reflected waves and the reflected waves independently coexist in the strip ring resonator 23. Therefore, the strip dual mode filter 21 functions as a dual mode filter. That is, the function of the strip dual mode filter 21 is equivalent to a pair of a single mode filters arranged in series. In addition, a ratio in the intensity of the reflected waves to the non-reflected waves is changed in proportional to the length of the open end stub 27 projected in a radial direction of the strip ring resonator 23. Therefore, the intensity of the reflected microwave transferred to the output strip line 24 can be adjusted by trimming the open end stub 27. The strip dual mode ring resonator 21 is proposed by J.A. Curtis "International Microwave Symposium Digest", IEEE, page 443-446(N-1), 1991. 2-3 PROBLEMS TO BE SOLVED BY THE INVENTION: However, there are many drawbacks in the strip ring resonator 11. That is, it is difficult to manufacture a small-sized strip ring resonator 11 because a central portion surrounded by the ring-shaped strip line 13 is a dead space. Also, the electric length of the ring-shaped strip line 13 cannot be minutely adjusted after the ring-shaped strip line 13 is manufactured according to a photo-etching process or the like. In this case, the resonance frequency of the microwaves depends on the electric length of the ring-shaped strip line 13. Therefore, the resonance frequency of the microwaves cannot be minutely adjusted. In addition, in cases where a plurality of strip ring resonators 11 are arranged in series to compose a band-pass filter, it is difficult to couple the ring-shaped strip lines 13 to each other because the ring-shaped strip lines 13 are curved. Also, there are many drawbacks in the strip ring resonator 21. That is, a central frequency of the microwaves filtered in the strip ring resonator 21 cannot be minutely adjusted because the central frequency of the microwaves depends on the width of the open end stub 27 extending in a circumferential direction of the strip ring 23. Therefore, the central frequency of the microwaves manufactured does not often agree with a designed central frequency. As a result, a yield rate of the strip ring resonator 21 is lowered. Also, because a resonance width (or a full width at half maximum) can be adjusted only by trimming the length of the open end stub 27, the resonance width cannot be enlarged. In other words, in cases where the width of the open end stub 27 in the circumferential direction is widened to enlarge the resonance width, the phase of the reflected waves reaching the output strip line 24 undesirably shifts. As a result, the intensity of the microwaves transferred to the output strip line 24 is lowered at the central frequency of the microwaves resonated. Accordingly, in cases where a plurality of strip ring resonators 21 are arranged in series to compose a band-pass filter, the filter is limited to a narrow passband type of filter. SUMMARY OF THE INVENTION The object is to provide a small-sized strip ring resonator in which the resonance frequency is easily and minutely adjusted and the resonance width is narrow, and to provide a band-pass filter composed of the resonators. The object is achieved by the provision of a strip ring resonators according to claims 1 and 8 and a band-pass filter as specified in claim 10. BRIEF DESCRIPTION OF THE DRAWINGS The objects, features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which: Fig. 1A is a plan view of a conventional one-wave length type of strip ring resonator in which no open end is provided; Fig. 1B is a sectional view taken generally along the line I-I of Fig. 1A; Fig. 2 is a plan view of a conventional strip dual mode ring resonator functioning as a two-stage filter; Fig. 3 is a plan view of a strip dual mode ring resonator according to a first embodiment; Fig. 4 is a plan view of a strip dual mode ring resonator according to a second embodiment; Fig. 5 is a plan view of a strip dual mode ring resonator according to a third embodiment; Fig. 6 is a plan view of a strip dual mode ring resonator according to a fourth embodiment. Fig. 7 is a plan view of a strip dual mode ring resonator according to a fifth embodiment; Fig. 8 is a plan view of a strip dual mode ring resonator according to a sixth embodiment; Fig. 9 is a plan view of a band-pass filter in which two microwave resonators shown in Fig. 18 are arranged in series according to a seventh embodiment; and Fig. 10 is a plan view of a band-pass filter in which the microwave resonators shown in Fig. 18 are arranged in series according to an eighth embodiment . DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a ring resonator and a band-pass filter composed of the resonators according to the present invention are described with reference to drawings. Fig. 3 is a plan view of a strip ring resonator according to a first embodiment. As shown in Fig. 18, a strip ring resonator 181 comprises a pair of parallel coupling line sections 182a, 182b arranged in parallel, a first side connecting line 183 through which first side ends of the parallel coupling lines 182a, 182b are connected, a second side connecting line 184 through which the other side ends of the parallel coupling line sections 182a, 182b are connected, an input tap coupling line 185 coupled to the first side connecting line 183 in inductive coupling, and an output tap coupling line 186 coupled to the second side connecting line 184 in inductive coupling. Each of the parallel coupling line sections 182a, 182b has a wide width W1 and an electric length L1, and the parallel coupling line sections 182a, 182b are spaced a narrow distance S1 apart from each other. Therefore, inside portions of the parallel coupling line sections 182a, 182b are strongly coupled to each other in capacitive coupling in cases where microwaves are transmitted in the parallel coupling line sections 182a, 182b. The first and second side connecting lines 183, 184 have a narrow width W2 and an electric length L2. Both ends of the first side connecting line 183 are connected to outside portions of the parallel coupling lines 182a, 182b at a first side (or a left side in Fig. 18), and both ends of the second side connecting line 184 are connected to the outside portions of the parallel coupling line sections 182a, 182b at a second side (or a right side in Fig. 18). Therefore, a rectangular shape of microwave resonator 187 is formed of the parallel coupling line sections 182a, 182b and the first and second side connecting lines 183, 184. An electric length of the microwave resonator 187 sums up to L E = 2*L1 + 2*L2. Also, both ends of the first side connecting line 183 are not coupled to each other so much in cases where microwaves are transmitted in the first side connecting line 183. Also, both ends of the second side connecting line 184 are not coupled to each other so much in the same manner. In the above configuration, microwaves having various wavelengths around a resonance microwave λ o are transferred from the input tap coupling line 185 to the first side connecting line 183 because the input tap coupling line 185 is coupled to the first side connecting line 183 in the inductive coupling. Thereafter, the microwaves transferred to the line 183 are circulated in the microwave resonator 187 in clockwise and counterclockwise directions, according to the characteristic impedance of the microwave resonator 187. The characteristic impedance of the microwave resonator 187 depends on the electric length L E of the microwave resonator 187, a line impedance of the microwave resonator 187, and the capacitive coupling between the parallel coupling line sections 182a, 182b. Strength of the capacitive coupling between the parallel coupling line sections 182a, 182b depends on the shape of the parallel coupling line sections 182a, 182b such as the width W1 and the distance S1. In cases where the wavelength of the microwaves agrees with the resonance wavelength λ o of the microwaves, the microwaves are resonated in the microwave resonator 187. The resonance wavelength λ o of the microwaves resonated in the microwave resonator 187 is longer than the electric length L E of the microwave resonator 187 because the parallel coupling line sections 182a, 182b are strongly coupled to each other in capacitive coupling. In detail, a resonance frequency ω o relating to the resonance wavelength λ o , an inductance L, and a capacitance C are generally related according to a resonance equation ω o 2 =1/(LC). Also, the capacitive coupling between the parallel coupling line sections 182a, 182b is equivalent to a capacitor having the capacitance C. Therefore, the resonance frequency ω o is lowered in proportion as the capacitive coupling between the parallel coupling line sections 182a, 182b is stronger. As a result, the resonance wavelength λ o of the microwaves is lengthened by the capacitive coupling between the parallel coupling lines 182a, 182b. In addition, an unloaded quality factor Q in a resonance circuit is generally defined according to an equation Q = ω o *C*R, where the symbol R denotes a resistance in the resonance circuit. Therefore, the unloaded quality factor Q is increased in proportion as the capacitive coupling between the parallel coupling line sections 182a, 182b is stronger. In this case, the unloaded quality factor Q is also generally defined according to an equation Q = ω o /(2*Δω), where the symbol 2*Δω denotes a resonance width of the microwaves resonated in the resonance circuit. Therefore, the resonance width is narrowed in proportion as the capacitive coupling between the parallel coupling line sections 182a, 182b is stronger. Thereafter, the microwaves resonated in the microwave resonator 187 are transferred to the output tap coupling line 186 because the microwave resonator 187 is coupled to the line 186 in the inductive coupling. Accordingly, even though the wavelength of the microwaves is longer than the electric length L E of the microwave resonator 187, the microwaves can be resonated in the strip ring resonator 181. In other words, because the microwaves can be resonated even though the wavelength of the microwaves is longer than the electric length L E , the electric length L E of the microwave resonator 187 can be shortened. That is, the strip ring resonator 181 can be minimized regardless of the wavelength of the microwaves. For example, on condition that a relative dielectric constant is ε r =2.2, a thickness of the microwave resonator 187 is H1=10 mm, the electric length of the parallel coupling line sections 182a, 182b is L1=160 degrees, the electric length of the first and second side connecting lines 183, 184 is L2=20 degrees, a resistance of each of the parallel coupling lines 182a, 182b is R1=50 Ω, a resistance of each of the first and second side connecting lines 183, 184 is R2=100 Ω, and a pseudo-resonance frequency of the microwaves is ω p =1.0 GHz, a resonance frequency ω o equals 0.992*ω p in case of a relative distance S1/H1=4. A resonance frequency ω o equals 0.98*ω p in case of a relative distance S1/H1=2. And, a resonance frequency ω o equals 0.96*ω p in case of a relative distance S1/H1=0.2. In cases where the relative dielectric constant ε r is increased, a ratio of the resonance frequency ω o to the pseudo-resonance frequency ω p is furthermore reduced because the strength of the capacitive coupling between the parallel coupling line sections 182a, 182b is increased. Also, the resonance wavelength λ o of the microwaves can be minutely adjusted by changing the width W1 of the parallel coupling line sections 182a, 182b or the distance S1 between the parallel coupling line sections 182a, 182b. The strength of the capacitive coupling between the parallel coupling line sections 182a, 182b can be changed by trimming the parallel coupling line sections 182a, 182b. Also, because the unloaded quality factor Q is increased depending on the strength of the capacitive coupling between the parallel coupling line sections 182a, 182b, the strip loop resonator 181 in which the resonance width is narrowed can be manufactured. Also, in cases where the strip ring resonator 181 is utilized as a resonator in an oscillating circuit, an output signal of the oscillating circuit can stably have an oscillated band of which a frequency range is narrowed. Therefore, superior phase-noise characteristics can be obtained in the oscillated circuit in which the strip ring resonator 181 is utilized. Also, because the strip ring resonator 181 is in rectangular shape, a plurality of resonators 181 can be closely arranged in series. Next, a second embodiment according to the present invention is described. Fig. 4 is a plan view of a strip ring resonator according to a second embodiment. As shown in Fig. 4, a strip ring resonator 191 comprises a pair of parallel coupling line sections 192a, 192b arranged in parallel, the first side connecting line 183 through which first side ends of the parallel coupling line sections 192a, 192b are connected, the second side connecting line 184 through which the other side ends of the parallel coupling line sections 192a, 192b are connected, the input tap coupling line 184, and the output tap coupling line 186. The parallel coupling lines 192a, 192b respectively have a curved inside surface, and the curved inside surfaces of the lines 192a, 192b face each other at the distance S1. Therefore, inside portions of the parallel coupling line sections 192a, 192b are strongly coupled to each other in capacitive coupling in cases where microwaves are transmitted in the parallel coupling lines 192a, 192b. Furthermore, the capacitive coupling between the parallel coupling line sections 192a, 192b is stronger than that between the parallel coupling line sections 182a, 182b because a curved inside surface area of each of the lines 192a, 192b is wider than a straight inside surface area of each of the lines 182a, 182b. The parallel coupling line sections 192a, 192b respectively have the electric length L1 in an outside portion. Therefore, a rectangular shape of microwave resonator 193 is formed of the parallel coupling line sections 192a, 192b and the first and second side connecting lines 183, 184. An electric length of the microwave resonator 193 sums up to L E = 2*L1 + 2*L2. In the above configuration, microwaves having various wavelength around a resonance wavelength λ o are transferred from the input tap coupling line 185 to the first side connecting line 183 in the same manner as in the strip ring resonator 181. Thereafter, the microwaves transferred to the line 183 are circulated in the microwave resonator 193 in clockwise and counterclockwise directions, according to the characteristic impedance of the microwave resonator 193. The characteristic impedance of the microwave resonator 193 depends on the electric length L E of the microwave resonator 193, a line impedance of the microwave resonator 193, and the capacitive coupling between the parallel coupling lines 192a, 192b. Strength of the capacitive coupling between the parallel coupling lines 192a, 192b depends on the shape of the parallel coupling lines 192a, 192b such as the distance S1 and the curved inside surfaces of the lines 192a, 192b. In cases where the wavelength of the microwaves agrees with the resonance wavelength λ o of the microwaves, the microwaves are resonated in the microwave resonator 192. The resonance wavelength λ o of the microwaves resonated in the microwave resonator 192 is longer than the electric length L E of the microwave resonator 187, in the same reason as in the strip ring resonator 181. Also, a resonance width of the microwaves is narrowed in proportion as the capacitive coupling between the parallel coupling line sections 192a, 192b is stronger, in the same reason as in the strip ring resonator 181. Thereafter, the microwaves resonated in the microwave resonator 193 are transferred to the output tap coupling line 186. Accordingly, because the capacitive coupling between the parallel coupling line sections 192a, 192b is stronger than that between the parallel coupling line sections 182a, 182b, the strip ring resonator 191 can be greatly minimized regardless of the wavelength of the microwaves as compared with the strip ring resonator 181. Also, the resonance wavelength λ o of the microwaves can be minutely adjusted by changing the shape of the curved inside surfaces of the parallel coupling line sections 192a, 192b or the distance S1 between the parallel coupling lines 192a, 192b. Also, the strip ring resonator 191 in which the resonance width is narrowed can be manufactured in the same reason as in the strip ring resonator 181. Also, in cases where the strip ring resonator 191 is utilized as a resonator in an oscillating circuit, superior phase-noise characteristics can be obtained in the oscillated circuit in which the strip ring resonator 191 is utilized. Also, because the strip ring resonator 191 is in rectangular shape, a plurality of resonators 181 can be closely arranged in series. Next, a third embodiment according to the present invention is described. Fig. 5 is a plan view of a strip ring resonator according to a third embodiment. As shown in Fig. 5, a strip ring resonator 201 comprises the parallel coupling lines 182a, 182b, the first side connecting line 183, the second side connecting line 184, the input tap coupling line 184, the output tap coupling line 185, and a line-to-line coupling capacitor 202 arranged between the parallel coupling line sections 182a, 182b. The line-to-line coupling capacitor 202 is formed of a plate capacitor or a chip capacitor, and has a lumped capacitance Cw. In the above configuration, because the line-to-line coupling capacitor 202 is arranged between the parallel coupling line sections 182a, 182b, a characteristic impedance in the strip ring resonator 201 is additionally changed by the capacitor 202 as compared with that in the strip ring resonator 181. Accordingly, the strip ring resonator 201 can be greatly minimized regardless of a wavelength of microwaves as compared with the strip ring resonator 181. Also, a resonance wavelength λ o of the microwaves can be minutely adjusted by changing the lumped capacitance Cw of the capacitor 202. The lumped capacitance Cw of the capacitor 202 is, for example, changed by trimming both plates of the capacitor 202 after the strip ring resonator 191 is manufactured. In the third embodiment, the capacitor 202 is additionally provided to the resonator 181. However, it is preferred that the capacitor 202 be additionally provided to the resonator 191. In this case, the strip ring resonator 201 can be greatly minimized as compared with the strip ring resonator 191. Also, the capacitor 202 is positioned in the center of each of the parallel coupling line sections 182a, 182b. However, the position of the capacitor 202 is not limited to the center of each of the parallel coupling line sections 182a, 182b. For example, it is preferred that the capacitor 202 be positioned adjacent to the first side connecting line 183 or be positioned adjacent to the second side connecting lint 184. Next, a fourth embodiment according to the present invention is described. Fig. 6 is a plan view of a strip ring resonator according to a fourth embodiment. As shown in Fig. 6, a strip ring resonator 211 comprises the parallel coupling line sections 182a, 182b, a first side connecting line 212 through which first side ends of the parallel coupling line sections 182a, 182b are connected, a second side connecting line 213 through which the other side ends of the parallel coupling line sections 182a, 182b are connected, the input tap coupling line 184, and the output tap coupling line 185. The first and second side connecting lines 212, 213 have the narrow width W2 and an electric length L3. Both ends of the first side connecting line 212 are connected to the inside portions of the parallel coupling line sections 182a, 182b at the first side, and both ends of the second side connecting line 213 are connected to the inside portions of the parallel coupling line sections 182a, 182b at the second side. Therefore, a microwave resonator 214 is formed of the parallel coupling line sections 182a, 182b and the first and second side connecting lines 212, 213. An electric length of the microwave resonator 214 sums up to L E = 2*L1 + 2*L3. Because the both ends of the first side connecting line 212 are approached to each other, and because the first side connecting line 212 has the narrow width W2, both ends of the first side connecting line 212 are coupled to each other in inductive coupling. Also, both ends of the second side connecting line 213 are coupled to each other in inductive coupling in the same reason. In the above configuration, a characteristic impedance in the strip ring resonator 211 is additionally changed by the first and second side connecting lines 212, 213 as compared with that in the strip ring resonator 181. Accordingly, the strip ring resonator 211 can be greatly minimized regardless of a wavelength of microwaves as compared with the strip ring resonator 181. Next, a fifth embodiment according to the present invention is described. Fig. 7 is a plan view of a strip ring resonator according to a fifth embodiment. As shown in Fig. 7, a strip ring resonator 221 comprises a pair of parallel coupling line sections 222a, 222b, a C-shaped first side connecting line 223 through which first side ends of the parallel coupling line sections 222a, 222b are connected, a C-shaped second side connecting line 224 through which the other side ends of the parallel coupling line sections 222a, 222b are connected, the input tap coupling line 184, and the output tap coupling line 185. Each of the parallel coupling line sections 222a, 222b has a narrow width W3 and an electric length L1, and the parallel coupling line sections 222a, 222b are spaced a narrow distance S1 apart. Therefore, the parallel coupling line sections 222a, 222b are coupled to each other in inductive coupling in cases where microwaves are transmitted in the parallel coupling line sections 222a, 222b. The first and second side connecting lines 223, 224 have the narrow width W3 and an electric length L2. Both ends of the first side connecting line 223 are connected to the parallel coupling line sections 222a, 222b at a first side (or a left side in Fig. 22), and both ends of the second side connecting line 224 are connected to the parallel coupling line sections 222a, 222b at a second side (or a right side in Fig. 22). Therefore, a microwave resonator 225 is formed of the parallel coupling line sections 222a, 222b and the first and second side connecting lines 223, 224. An electric length of the microwave resonator 225 sums up to L E = 2*L1 + 2*L2. Also, both ends of the first side connecting line 223 are not coupled to each other so much in cases where microwaves are transmitted in the first side connecting line 223. Also, both ends of the second side connecting line 224 are not coupled to each other so much in the same manner. In the above configuration, a characteristic impedance in the strip loop resonator 221 is determined according to the electric length L E of the microwave resonator 225 and the inductive coupling between the parallel coupling line sections 222a, 222b. Accordingly, the strip loop resonator 221 can be minimized even though the electric length L E of the microwave resonator 225 is smaller than a wavelength of the microwaves. Next, a sixth embodiment according to the present invention is described. Fig. 8 is a plan view of a strip ring resonator according to a sixth embodiment. As shown in Fig. 8, a strip ring resonator 231 comprises a pair of parallel coupling line sections 232a, 232b, a C-shaped first side connecting line 233 through which first side ends of the parallel coupling line sections 232a, 232b are connected, a C-shaped second side connecting line 234 through which the other side ends of the parallel coupling line sections 232a, 232b are connected, the input tap coupling line 184, and the output tap coupling line 185. The parallel coupling line sections 232a, 232b and the first and second side connecting lines 233, 234 respectively have a narrow width W4, so that a microwave resonator 235 having the narrow width W4 is formed of the lines 232a, 232b, 233, and 234. An electric length of the microwave resonator 235 is the same as that of the microwave resonator 225. The narrow width W4 is narrower than the width W3 of the microwave resonator 225. Therefore, the inductive coupling between the parallel coupling line sections 232a, 232b is stronger than that between the parallel coupling line sections 222a, 222b shown in Fig. 7. In contrast, capacitive coupling between the parallel coupling line sections 232a, 232b is weaker than that between the parallel coupling line sections 222a, 222b shown in Fig. 7. In the above configuration, a characteristic impedance in the strip ring resonator 231 is determined according to the electric length L E of the microwave resonator 235 and the inductive coupling between the parallel coupling line sections 232a, 232b, in the same manner as in the resonator 221. Accordingly, the strip ring resonator 231 can be minimized in the same manner as the resonator 221 shown in Fig. 7. In the fifth to sixth embodiments, it is preferred that the line-to-line capacitor 202 be additionally provided to the resonator 221 or 222 to strengthen the capacitive coupling between the parallel coupling line sections 222a, 222b, or the parallel coupling line sections 232a, 232b. Also, it is preferred that a pair of curved coupling lines be provided in place of the straight coupling lines on condition that the curved coupling lines are spaced the distance S1 apart. In the first to sixth embodiments the input and output tap coupling lines 183, 186 are respectively coupled to the first and second side connecting lines in the inductive coupling. However, it is preferred that the input and output tap coupling lines 183, 186 be coupled to the first and second side connecting lines in capacitive coupling. Also, it is preferred that the input and output tap coupling lines 183, 186 be coupled to the parallel coupling line sections 182a, 182b, to 232a, 232b. Next, a seventh embodiment according to the present invention is described. Fig. 9 is a plan view of a band-pass filter in which two microwave resonators 187 shown in Fig. 3 are arranged in series according to a seventh embodiment concept. As shown in Fig. 9, a band-pass filter 241 according to the seventh embodiment comprises an input strip line 242 in which microwaves are transmitted, the microwave resonator 187 arranged in a first stage, the microwave resonator 187 arranged in a second stage, an input coupling capacitor 243 for coupling the input strip line 242 to the first-stage microwave resonator 187 in capacitive coupling, an output strip line 244 in which the microwaves resonated in the microwave resonators 187 are transmitted, an output coupling capacitor 245 for coupling the output strip line 242 to the second-stage microwave resonator 187 in capacitive coupling. The second side connecting line 184 of the first-stage microwave resonator 187 is coupled to the first side connecting line 183 of the second-stage microwave resonator 187 in inductive coupling. Because the width W2 of the first and second connecting lines 183, 184 is narrow, a type of the electromagnetic coupling between the first and second connecting lines 183, 184 is the inductive coupling. In the above configuration, when microwaves are circulated in the first-stage microwave resonator 187, a magnetic field is strongly induced around the second connecting line 184 of the first-stage microwave resonator 187 so that microwaves are induced by the magnetic field in the first connecting line 183 of the second-stage microwave resonator 187. Thereafter, the microwaves are circulated in the second-stage microwave resonator 187, and the microwaves are transferred to the output strip line 244. In this case, each of the microwave resonators 187 functions as a resonator and filter. Therefore, the band-pass filter 241 functions as a four-stage filter. Accordingly, because the microwave resonators 187 are in rectangular shape, the microwave resonators 187 can be closely coupled to each other. Also, because a large number of rectangle-shaped microwave resonators 187 can be orderly arranged, the band-pass filter 241 can be minimized even though a large number of rectangle-shaped microwave resonators 187 are arranged in series. Also, a resonance width of the microwaves in a low band is generally narrowed in cases where the microwaves are transferred in the capacitive coupling, and a resonance width of the microwaves in a high band is generally narrowed in cases where the microwaves are transferred in the inductive coupling. In the band-pass filter 241, the input and output strip lines 242, 244 are coupled to the microwave resonators 187 in the capacitive coupling, and the microwave resonators 187 are coupled to each other in the inductive coupling. Therefore, the resonance width of the microwaves can be narrowed regardless of the frequency of the microwaves. In the seventh embodiment , the microwave resonators 187 are arranged in series. However, the seventh embodiment is not limited to the microwave resonators 187. That is, it is preferred that the microwave resonators 193, 213, 225, or 235 be arranged in series. Next, an eighth embodiment according to the present invention is described. Fig. 10 is a plan view of a band-pass filter in which two microwave resonators 187 shown in Fig. 3 are arranged in series according to an eighth embodiment. As shown in Fig. 10, a band-pass filter 251 according to the seventh embodiment comprises the input tap coupling line 185, the microwave resonator 187 arranged in a first stage, the microwave resonator 187 arranged in a second stage, and the output strip line 186 The parallel coupling line sections 182b of the first-stage microwave resonator 187 is coupled to the parallel coupling line section 182a of the second-stage microwave resonator 187 in capacitive coupling. Because the width W1 of the parallel coupling lines 182a, 182b is wide, a type of the electromagnetic coupling between the parallel coupling line sections 182a, 182b is the capacitive coupling. In the above configuration, when microwaves are circulated in the first-stage microwave resonator 187, electric field is strongly induced around the parallel coupling line section 182b of the first-stage microwave resonator 187 so that microwaves are induced by the electric field in the parallel coupling line section 182a of the second-stage microwave resonator 187. Thereafter, the microwaves are circulated in the second-stage microwave resonator 187, and the microwaves are transferred to the output tap coupling line 186. In this case, each of the microwave resonators 187 functions as a resonator and filter. Therefore, the band-pass filter 251 functions as a four-stage filter. Accordingly, because the microwave resonators 187 are in rectangular shape, the microwave resonators 187 can be closely coupled to each other. Also, because a large number of rectangle-shaped microwave resonators 187 can be orderly arranged, the band-pass filter 251 can be minimized even though a large number of rectangle-shaped microwave resonators 187 are arranged in series. Also, the input and output tap coupling lines 185, 186 are coupled to the microwave resonators 187 in the inductive coupling, and the microwave resonators 187 are coupled to each other in the capacitive coupling. Therefore, a resonance width of the microwaves can be narrowed regardless of the frequency of the microwaves in the band-pass filter 251. In the eighth embodiment, the microwave resonators 187 are arranged in series. However, the eighth embodiment is not limited to the microwave resonators 187. That is, it is preferred that the microwave resonators 193, 213, 225, or 235 be arranged in series.

Claims: A strip ring resonator (181) in which a microwave is resonated, comprising: a rectangle-shaped ring strip line having an electric length shorter than a wavelength of the microwave for resonating the microwave circulated therein in two different directions according to a line impedance thereof, the rectangle-shaped strip line comprising a pair of parallel coupling line sections (182a,b) respectively having a wide width which are capacitively coupled to each other to change a characteristic impedance of the strip line, a first side strip line through which first side ends of the parallel line sections (182a,b) are connected, the first side strip line having a narrow width narrower than the wide width of the parallel coupling line sections (182a,b), and a second side strip line through which second side ends of the parallel line sections (182a,b) are connected, the second side strip line having another narrow width narrower than the wide width of the parallel coupling lines, an input strip line coupled to the rectangle-shaped ring strip line in electromagnetic coupling, the microwave being transferred from the input strip line to the rectangle-shaped ring strip line; and an output strip line coupled to the rectangle-shaped ring strip line in electromagnetic coupling, the microwave being transferred from the rectangle-shaped strip line to the output strip line. A resonator according to claim 1 in which the parallel coupling line sections of the rectangle-shaped ring strip line have curved inside surfaces facing each other to strengthen the capacitive coupling between the parallel coupling lines, the curved inside surfaces being spaced a narrow distance apart. A resonator according to claim 1 in which a line-to-line capacitor (Cw) having a lumped capacitance is arranged between the parallel coupling line sections of the rectangle-shaped strip line to change a characteristic impedance of the rectangle-shaped ring strip line. A resonator according to claim 3 in which one end of the line-to-line capacitor (Cw) being connected to a central portion of one of the parallel coupling lines, and another end of the line-to-line capacitor being connected to a central portion of the other parallel coupling line. A resonator according to claim 1 in which both ends of the first and second side strip lines are connected to inside portions of the parallel coupling line sections of the rectangle-shaped ring strip line, the inside portions of the parallel coupling lines facing each other. A resonator according to claim 1 in which the input strip line is coupled to the first side strip line in conductive coupling, and the output strip line is coupled to the second side strip line in the conductive coupling. A resonator according to claim 1 in which the input strip line is coupled to the first side strip line in inductive coupling, and the output strip line is coupled to the second side strip line in the inductive coupling. A strip ring resonator (221) in which a microwave is resonated, comprising: a loop-shaped strip line having an electric length shorter than a wavelength of the microwave for resonating the microwave circulated therein in two different directions according to a line impedance thereof, the loop-shaped strip line comprising a pair of parallel coupling line sections (222a, 222b) respectively having a narrow width which are arranged in parallel to each other and are coupled to each other in inductive coupling to change a characteristic impedance of the loop-shaped strip line, a first side strip line (223) through which first side ends of the parallel line sections (222a,b) are connected, the first side strip line having the narrow width, and a second side strip line (224) through which second side ends of the parallel lines are connected, the second side strip line having the narrow width, an input strip line coupled to the loop-shaped strip line in electromagnetic coupling, the microwave being transferred from the input strip line to the loop-shaped strip line; and an output strip line coupled to the loop-shaped strip line in electromagnetic coupling, the microwave being transferred from the loop-shaped strip line to the output strip line. A resonator according to claim 8 in which the parallel coupling lines of the loop-shaped strip line are curved to face each other at a narrow distance to strengthen the inductive coupling between the parallel coupling lines. A band-pass filter (241) for filtering a microwave, comprising: a plurality of rectangle-shaped ring strip lines (187) coupled in series which each comprise a pair of parallel coupling line sections respectively having a wide width which are arranged in parallel to each other and are coupled to each other in capacitive coupling to change a characteristic impedance of the rectangle-shaped ring strip line, a first side strip line having a narrow width through which first side ends of the parallel lines are connected, and a second side strip line having another narrow width through which second side ends of the parallel lines are connected, each of the rectangle-shaped ring strip lines having an electric length shorter than a wavelength of the microwave to resonate the microwave circulated therein in two different directions according to a line impedance thereof; an input strip line (242) coupled to the rectangle-shaped strip line in a first stage, the microwave being transferred from the input strip line to the rectangle-shaped strip line in the first stage; and an output strip line coupled to the rectangle-shaped strip line in a final stage, the microwave being transferred from the rectangle-shaped strip line in the final stage to the output strip line. A filter according to claim 10 in which one of the parallel coupling line sections of the rectangle-shaped ring strip line in an upper stage is coupled to one of the parallel coupling line sections of the rectangle-shaped ring strip line in a lower stage in capacitive coupling. A filter according to claim 11 in which the input and output strip lines are coupled to the rectangle-shaped strip lines in inductive coupling. A filter according to claim 10 in which the second side strip line of the rectangle-shaped strip line in an upper stage is coupled to the first side strip line of the rectangle-shaped strip line in a lower stage in inductive coupling. A filter according to claim 13 in which the input and output strip lines are coupled to the rectangle-shaped strip lines in capacitive coupling. A filter according to claim 10 in which the parallel coupling lines of each of the rectangle-shaped strip lines have curved inside surfaces facing each other to strengthen the capacitive coupling between the parallel coupling lines, the curved inside surfaces being spaced a narrow distance apart. A resonator according to claim 10 in which a line-to-line capacitor having a lumped capacitance is arranged between the parallel coupling line section of each of the rectangle-shaped ring strip lines to change a characteristic impedance of the rectangle-shaped strip lines.

Inventors: FUJIMURA MUNENORI, HASEGAWA MAKOTO, MAKIMOTO MITSUO, TAKAHASHI KAZUAKI, FUJIMURA, MUNENORI, HASEGAWA, MAKOTO, MAKIMOTO, MITSUO, TAKAHASHI, KAZUAKI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: H01P1
IPC codes: H01P1, H01P7