JP2010288179A - Band pass filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow attenuation characteristics of low-and high-pass sides to be nearly symmetrical in a band pass filter using a dielectric resonator. <P>SOLUTION: In s BPF 10, n inner conductor S10a of a resonator 10a is connected to an input terminal IN via a capacitance C14, and also connected to an inner conductor S10b of a resonator 10b via an inductance L14. The inner conductor S10b is connected to an inner conductor S10c of a resonator 10c via an inductance L15 and the inner conductor S10c is connected to an output terminal OUT via a capacitance C15. The number of capacitances and the number of inductances are set to be the same in the four coupling elements of the BPF 10, thereby attenuation characteristics on low and high pass sides separated by a pass frequency positioned therebetween are made nearly symmetrical. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a band-pass filter configured by connecting resonators with a connecting element.

  A conventional bandpass filter (hereinafter referred to as “BPF”) using a TEM (Transverse Electro Magnetic) mode resonator is configured by electrically coupling a resonator and an external circuit. In addition, in a BPF in which two or more resonators are provided in multiple stages, the resonators are also electrically coupled. The coupling method between resonators can be broadly classified into capacitance coupling, inductance coupling, and electromagnetic field coupling, but a semi-coaxial BPF using a TEM mode resonator that forms a resonator casing by processing a metal pipe or a metal plate. In many cases, the electromagnetic field coupling that couples the resonators by using a coupling loop or a method of making holes in the partition walls of the resonators is often employed. On the other hand, a dielectric filter using a dielectric resonator has recently been used for movement and transport for the purpose of reducing the size of products. In the dielectric filter, the dielectric resonator is made of coaxial ceramics, and the total length is obtained by multiplying the quarter wavelength near the pass frequency by the shortening rate obtained from the relative dielectric constant determined by the dielectric material. The length is such that one end face is short-circuited and the other end face is open. In this case, when manufacturing the BPF, it is necessary to electrically couple the internal conductor exposed on the open surface and the internal conductors of the input / output terminal or the adjacent dielectric resonator. In this coupling, since it is difficult to employ electromagnetic coupling due to physical restrictions, capacitance coupling or inductance coupling is often used.

  Capacitance and inductance, which are coupling elements in capacitance coupling and inductance coupling, are connected in series to the dielectric resonator. Therefore, HPF (high-pass filter) tends to occur in the case of capacitance coupling due to the similarity of the equivalent circuit. On the contrary, in the case of inductance coupling, the attenuation characteristic tends to be LPF (low-pass filter). That is, in the capacitance coupling, the fall characteristic of the low band side attenuation amount becomes steeper than the pass band, but the fall characteristic of the high band side attenuation amount becomes slow. On the other hand, in the case of inductance coupling, the reverse characteristics are obtained. This tendency becomes remarkable because the number of coupling elements connected in series increases as the number of stages increases.

JP 7-162209 A JP-A-11-27006

Future communication systems are expected to have higher speeds and larger capacities than the present, but the trend is similar in the VHF / UHF band where the advantages of dielectric filters can be utilized. For example, even in the 170 MHz band that is vacant after the transition to terrestrial digital broadcasting, the introduction of the Mobile WiMAX system or LTE (Long Term Evolution) system is planned, and it is expected that a wider occupied frequency bandwidth than the conventional communication system will be required. Is done. In the case of a communication system that requires a wide band, guard bands are set on the low frequency side and the high frequency side of the frequency band in order to avoid mutual interference with broadcasting and communication using the close frequency band. A BPF that allows such a wide frequency band to pass is a BPF having a wide-band pass frequency characteristic having a multi-stage configuration having a steep attenuation characteristic. As described above, the BPF using the dielectric resonator has asymmetrical attenuation characteristics on the low-frequency side and the high-frequency side. In particular, the BPF having a configuration in which the dielectric resonator is connected in multiple stages has a problem that the asymmetry becomes remarkable. There was a point. Thus, when the attenuation characteristic becomes asymmetric, mutual interference is likely to occur between other broadcast / communication frequency bands adjacent via the guard band.
Accordingly, an object of the present invention is to provide a bandpass filter using a dielectric resonator in which the attenuation characteristics on the low-frequency side and the high-frequency side are almost symmetrical.

  The band-pass filter of the present invention is a band-pass filter having at least one stage of a dielectric resonator, and is composed of a dielectric and a conductive film formed on an inner peripheral surface of a through-hole formed in the dielectric. The dielectric resonator having a conductor and an outer conductor made of a conductive film formed on the outer surface of the dielectric, and between the inner conductor and the input terminal of the first-stage dielectric resonator, the final-stage When two or more stages of the dielectric resonator are provided between the inner conductor of the dielectric resonator and the output terminal, the inner conductor of the dielectric resonator and the dielectric resonator of the next stage A coupling element connected between the inner conductor, the coupling element being either a capacitance coupling element or an inductance coupling element, and when the number of coupling elements is an even number, Inductance coupling element : It is the same number, if the coupling element number is an odd number is the most important feature that the difference between the number of capacitance coupling element and the inductive coupling element number is 1.

  According to the present invention, the number of capacitance coupling elements and the number of inductance coupling elements connecting between the resonator and the input / output terminals and between the resonators provided in two or more stages are the same, or the difference between the two is 1. Therefore, the attenuation characteristics on the low frequency side and the high frequency side can be made almost symmetrical.

It is a figure which shows the circuit structure of the band pass filter of the 1 step | paragraph structure for contrasting with the band pass filter of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter shown in FIG. It is a figure which shows the circuit structure of the band pass filter of the other 1 step | paragraph structure for contrasting with the band pass filter of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter shown in FIG. It is a figure which shows the circuit structure of the band pass filter of 1 step | paragraph structure of 1st Example of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter of 1 step | paragraph structure concerning this invention. 6 is a chart showing the electrical characteristics of the band-pass filter having a one-stage configuration shown in FIGS. 1, 3, and 5 in comparison. It is a figure which shows the circuit structure of the band pass filter of 2 steps | paragraphs structure for contrast with the band pass filter of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter shown in FIG. It is a figure which shows the circuit structure of the band pass filter of 2 steps | paragraphs structure for contrast with the band pass filter of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter shown in FIG. It is a figure which shows the circuit structure of the band pass filter of 2 steps | paragraphs structure of 2nd Example of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter of a 2 step | paragraph structure concerning this invention. It is a figure which shows the circuit structure of the other band pass filter of 2 steps | paragraphs structure of 2nd Example of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the other band pass filter of 2 steps | paragraph structure concerning this invention. FIG. 15 is a chart showing the electrical characteristics of the two-stage band-pass filter shown in FIGS. 8, 10, 12 and 14 in comparison. It is a figure which shows the circuit structure of the band pass filter of 3 steps | paragraphs structure for contrast with the band pass filter of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter shown in FIG. It is a figure which shows the circuit structure of the other band pass filter of the 3 step | paragraph structure for contrasting with the band pass filter of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter shown in FIG. It is a figure which shows the circuit structure of the band pass filter of 3 steps | paragraphs structure of 3rd Example of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter of a 3 step | paragraph structure concerning this invention. It is a figure which shows the circuit structure of the other band pass filter of the 3 step | paragraph structure concerning this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the other band pass filter of 3 steps | paragraph structure concerning this invention. It is a figure which shows the circuit structure of the further another band pass filter of the 3 steps | paragraph structure concerning this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of further another band pass filter of the 3 steps | paragraph structure concerning this invention. It is a figure which shows the circuit structure of the further another band pass filter of the 3 steps | paragraph structure concerning this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of further another band pass filter of the 3 steps | paragraph structure concerning this invention. FIG. 28 is a chart showing the electrical characteristics of the three-stage band-pass filter shown in FIGS. 17, 19, 21, 23, 25 and 27 in comparison. It is a figure which shows the circuit structure of the band pass filter of 4 steps | paragraphs structure for contrast with the band pass filter of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter shown in FIG. It is a figure which shows the circuit structure of the other band pass filter of 4 steps | paragraphs structure for contrasting with the band pass filter of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter shown in FIG. It is a figure which shows the circuit structure of the band pass filter of 4 steps | paragraphs structure of 4th Example of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter of 4 steps | paragraph structure concerning this invention. It is a figure which shows the circuit structure of the other band pass filter of 4 steps | paragraph structures concerning this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the other band pass filter of 4 steps | paragraph structure concerning this invention. It is a figure which shows the circuit structure of the further another band pass filter of the 4 steps | paragraph structure concerning this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of further another band pass filter of the 4 steps | paragraph structure concerning this invention. It is a figure which shows the circuit structure of the further another band pass filter of the 4 steps | paragraph structure concerning this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of further another band pass filter of the 4 steps | paragraph structure concerning this invention. FIG. 41 is a chart showing the electrical characteristics of the four-stage band-pass filter shown in FIGS. 30, 32, 34, 36, 38 and 40 in comparison. It is a figure which shows the circuit structure of the band pass filter of a 5 step | paragraph structure for contrast with the band pass filter of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the bandpass filter shown in FIG. It is a figure which shows the circuit structure of the other band pass filter of the 5 step | paragraph structure for contrasting with the band pass filter of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter shown in FIG. It is a figure which shows the circuit structure of the further another band pass filter of the 5-stage structure for contrasting with the band pass filter of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter shown in FIG. It is a figure which shows the circuit structure of the further another band pass filter of the 5-stage structure for contrasting with the band pass filter of this invention. FIG. 50 is a diagram illustrating attenuation characteristics and return loss characteristics of the bandpass filter illustrated in FIG. 49. It is a figure which shows the circuit structure of the further another band pass filter of the 5-stage structure for contrasting with the band pass filter of this invention. FIG. 52 is a diagram illustrating attenuation characteristics and return loss characteristics of the bandpass filter illustrated in FIG. 51. It is a figure which shows the circuit structure of the further another band pass filter of the 5-stage structure for contrasting with the band pass filter of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter shown in FIG. It is a figure which shows the circuit structure of the other band pass filter of 5 steps | paragraphs structure of 5th Example of this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the band pass filter of 5 steps | paragraph structures concerning this invention. It is a figure which shows the circuit structure of the other band pass filter of 4 steps | paragraph structures concerning this invention. It is a figure which shows the attenuation | damping characteristic and return loss characteristic of the other band pass filter of 4 steps | paragraph structure concerning this invention. FIG. 58 is a chart showing the electrical characteristics of the five-stage band-pass filter shown in FIGS. 43, 45, 47, 49, 51, 53, 55, and 57 in comparison.

A band-pass filter according to a first embodiment of the present invention will be described with reference to FIGS. Note that the one-stage band-pass filter (hereinafter referred to as “BPF”) 1 shown in FIG. 1 and the one-stage BPF 2 shown in FIG. 3 are compared with the one-stage BPF 3 of the present invention shown in FIG. The BPF.
The BPF 3 according to the first embodiment of the present invention is a one-stage BPF using one stage of resonators 3a as shown in FIG. The resonator 3a is a dielectric resonator, and is configured by sintering a dielectric ceramic material such as titanium oxide or barium oxide so as to have a cylindrical shape. A through hole is formed in the resonator 3a substantially along the central axis, and an inner conductor S3a made of a conductive film is formed on the inner peripheral surface of the through hole. An outer conductor made of a conductive film is formed on the entire outer surface excluding the upper surface of the resonator 3a. The inner conductor S3a and the outer conductor are short-circuited on the lower surface of the resonator 3a, the lower surface is a short-circuited surface, and the upper surface of the resonator 3a is an open surface without a conductive film formed thereon. The short-circuit plane is grounded. The electrical length of the resonator 3a is about λ / 4 of the wavelength λ at the resonance frequency. That is, the physical length of the resonator 3a is obtained by multiplying approximately λ / 4 by the shortening rate obtained from the relative dielectric constant determined by the material of the dielectric material. The inner conductor S3a exposed on the open surface of the resonator 3a is connected to the input terminal IN via the capacitance C3 and is connected to the output terminal OUT via the inductance L3.

In the one-stage BPF 3 in the first embodiment of the present invention shown in FIG. 5, when the passing frequency is 150 MHz, the characteristic impedance Z _3a of the resonator _3a is about 16.667Ω, and the resonant frequency f _3a passes. The frequency is about 150.00 MHz, the capacitance C3 is about 4.08 pF, and the inductance L3 is about 275.9 nH. FIG. 6 shows the attenuation characteristic of the BPF 3 and the frequency characteristic of the return loss. Referring to FIG. 6, a return loss of 50 dB or more is obtained at a pass frequency of 150.0 MHz. Also, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 21.7 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 21.6 dB, and the difference between the two attenuations is 0.1 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is approximately 19.7 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is approximately 19.7 dB, and the difference between the two attenuations is 0.0 dB. Furthermore, the attenuation at 135 MHz which is 15 MHz lower than the pass frequency is about 17.2 dB, the attenuation at 165 MHz which is 15 MHz higher than the pass frequency is about 17.1 dB, and the difference between the two attenuations is 0.1 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 13.7 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 13.7 dB, and the difference between the two attenuations is 0.0 dB.

Next, the one-stage BPF 1 shown in FIG. 1 is a one-stage BPF using one stage of the resonator 1a. Since the resonator 1a has the same configuration as that of the resonator 3a, a description thereof is omitted. However, a through hole is formed substantially along the central axis of the resonator 1a, and an inner peripheral surface of the through hole is formed on the inner peripheral surface of the through hole. An inner conductor S1a made of a conductive film is formed. The inner conductor S1a exposed on the open surface of the resonator 1a is connected to the input terminal IN via the capacitance C1 and is connected to the output terminal OUT via the capacitance C2. 1 has a characteristic impedance Z _1a of the resonator _1a of about 16.667Ω and a resonance frequency f _1a of about 162.324 MHz when the passing frequency of the BPF ₁ is 150.0 MHz. The capacitance C1 and the capacitance C2 are about 3.946 pF. FIG. 2 shows the attenuation characteristic of the BPF 1 and the frequency characteristic of the return loss.

  Referring to FIG. 2, the BPF 1 has a return loss of 50 dB or more at a pass frequency of 150.0 MHz. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 25.0 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 18.9 dB, and the difference between the two attenuations is 6.1 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 22.3 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 17.4 dB, and the difference between the two attenuations is 4.9 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 19.1 dB, the attenuation at 165 MHz, which is 15 MHz higher than the pass frequency, is about 15.5 dB, and the difference between the two attenuations is 3.6 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is approximately 14.9 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is approximately 12.6 dB, and the difference between the two attenuations is 2.3 dB.

The one-stage BPF 2 shown in FIG. 3 is a one-stage BPF using one stage of the resonator 2a. Since the resonator 2a has the same configuration as that of the resonator 3a, a description thereof will be omitted. However, a through hole is formed substantially along the central axis of the resonator 2a. An inner conductor S2a made of a conductive film is formed. The inner conductor S2a exposed on the open surface of the resonator 2a is connected to the input terminal IN via the inductance L1, and is connected to the output terminal OUT via the inductance L2. 3 has a characteristic impedance Z _2a of about 16.667Ω and a resonance frequency f _2a of about 138.674 MHz when the passing frequency of the BPF ₂ is 150.0 MHz. The inductance L1 and the inductance L2 are about 263.5 nH. FIG. 4 shows the attenuation characteristics of the BPF 2 and the frequency characteristics of the return loss.

  Referring to FIG. 4, BPF2 has a return loss of 50 dB or more at a frequency of 150.0 MHz. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 18.5 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 24.5 dB, and the difference between the two attenuations is 6.0 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 17.2 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 22.0 dB, and the difference between the two attenuations is 4.8 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 15.4 dB, the attenuation at 165 MHz, which is 15 MHz higher than the pass frequency, is about 18.9 dB, and the difference between the two attenuations is 3.5 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 12.6 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 14.9 dB, and the difference between the two attenuations is 2.3 dB.

  FIG. 7 shows a diagram of the attenuation characteristics of the BPF 1 shown in FIG. 1 and the BPF 2 shown in FIG. 3 configured as a single stage and the BPF 3 shown in FIG. 5 configured as a single stage according to the present invention. Referring to FIG. 7, in the BPF 1 in which the coupling element has only the capacitance of C1 + C2, the sum of the differences is 16.9 dB, and the low frequency side and the high frequency side across the pass frequency of the BPF 1 It can be seen that the attenuation characteristic is asymmetric. In addition, in the BPF2 in which the coupling element is only L1 + L2 inductance, the total difference is 16.6 dB, and the attenuation characteristics of the low band side and the high band side across the pass frequency of the BPF 2 are asymmetric. It turns out that it is. On the other hand, in the BPF 3 of the first embodiment in which the coupling element is a combination of the capacitance and inductance of C3 + L3, the total difference is 0.2 dB, and the passing frequency of the BPF 3 is sandwiched. It can be seen that the attenuation characteristics on the low frequency side and the high frequency side are almost symmetrical. Thus, by combining the same number of capacitances and inductances in the coupling element, the attenuation characteristics of the BPF 3 can be made almost symmetrical.

Next, a band-pass filter according to a second embodiment of the present invention will be described with reference to FIGS. Note that the two-stage BPF 4 shown in FIG. 8 and the two-stage BPF 5 shown in FIG. 10 are BPFs for comparison with the two-stage BPF 6 and BPF 7 of the present invention shown in FIG. 12 and FIG. .
The BPF 6 of the second embodiment of the present invention is a BPF having a two-stage configuration in which two resonators 6a and 6b are connected as shown in FIG. Since the resonator 6a and the resonator 6b have the same configuration as the resonator 3a, a detailed description thereof will be omitted, but a through hole is formed substantially along the central axis of the resonator 6a and the resonator 6b. An inner conductor S6a and an inner conductor S6b made of a conductive film are formed on the inner peripheral surface of the through hole. Further, the inner conductor S6a exposed on the open surface of the resonator 6a is connected to the input terminal IN via the capacitance C7, and is connected to the inner conductor S6b of the resonator 6b via the inductance L7. S6b is connected to the output terminal OUT via a capacitance C8.

The two-stage BPF 6 in the second embodiment of the present invention shown in FIG. 12 has a characteristic impedance Z _6a and a characteristic impedance Z _6b of both the resonator 6a and the resonator 6b of about 16.5 when the pass frequency is 150 MHz. The resonance frequency f _6a and the resonance frequency f _6b are both about 138.17 MHz, the capacitance C7 and the capacitance C8 are both about 6.53 pF, and the inductance L7 is about 584 nH. FIG. 13 shows the attenuation characteristic of the BPF 6 and the frequency characteristic of the return loss. Referring to FIG. 13, the return loss has a bimodal characteristic, a return loss of about 28 dB is obtained at a pass frequency of 150.0 MHz, and a return loss of 50 dB or more at the maximum is obtained. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 34.5 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 31.3 dB, and the difference between the two attenuations is 3.2 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 30.1 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 27.6 dB, and the difference between the two attenuations is 2.5 dB. Furthermore, the attenuation at 135 MHz which is 15 MHz lower than the pass frequency is about 24.6 dB, the attenuation at 165 MHz which is 15 MHz higher than the pass frequency is about 22.8 dB, and the difference between the two attenuations is 1.8 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 17.2 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 16.0 dB, and the difference between the two attenuations is 1.2 dB.

  Next, another BPF 7 configuration of the second embodiment of the present invention is shown in FIG. The BPF 7 is a two-stage BPF in which two resonators 7a and 7b are connected. Since the resonator 7a and the resonator 7b have the same configuration as the resonator 3a, a detailed description thereof will be omitted, but a through hole is formed substantially along the central axis of the resonator 7a and the resonator 7b. An inner conductor S7a and an inner conductor S7b made of a conductive film are formed on the inner peripheral surface of the through hole. Further, the inner conductor S7a exposed on the open surface of the resonator 7a is connected to the input terminal IN via the inductance L8 and is connected to the inner conductor S7b of the resonator 7b via the capacitance C9. S7b is connected to the output terminal OUT via an inductance L9.

Further, the other BPF 7 of the two-stage configuration in the second embodiment of the present invention shown in FIG. 14 has the characteristic impedance Z _7a and characteristic impedance Z _7b of the resonator 7a and the resonator 7b when the passing frequency is 150 MHz. The resonance frequency f _7a and the resonance frequency f _7b are both about 143.98 MHz, the inductance L8 and the inductance L9 are both about 166 nH, and the capacitance C9 is about 2.07 pF. FIG. 15 shows the attenuation characteristic of the BPF 7 and the frequency characteristic of the return loss. Referring to FIG. 15, the return loss has a bimodal characteristic, a return loss of about 28 dB is obtained at a pass frequency of 150.0 MHz, and a maximum return loss of 50 dB or more is obtained. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 31.6 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 34.4 dB, and the difference between the two attenuations is 2.8 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 27.8 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 30.1 dB, and the difference between the two attenuations is 2.3 dB. Furthermore, the attenuation at 135 MHz which is 15 MHz lower than the pass frequency is about 23.0 dB, the attenuation at 165 MHz which is 15 MHz higher than the pass frequency is about 24.7 dB, and the difference between the two attenuations is 1.7 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 16.2 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 17.3 dB, and the difference between the two attenuations is 1.1 dB.

Next, the two-stage BPF 4 shown in FIG. 8 is a two-stage BPF in which the resonator 4a and the resonator 4b are connected in two stages. Since the resonator 4a and the resonator 4b have the same configuration as the resonator 3a, a detailed description thereof is omitted, but a through hole is formed along substantially the central axis of the resonator 4a and the resonator 4b. An inner conductor S4a and an inner conductor S4b made of a conductive film are formed on the inner peripheral surface of the through hole. The inner conductor S4a exposed on the open surface of the resonator 4a is connected to the input terminal IN via the capacitance C4 and is connected to the inner conductor S4b of the resonator 4b via the capacitance C5. S4b is connected to the output terminal OUT via a capacitance C6. The two-stage BPF 4 shown in FIG. 8 has a characteristic impedance Z _4a and a characteristic impedance Z _4b of the resonator 4a and the resonator 4b of about 16.667Ω when the passing frequency of the BPF ₄ is 150.0 MHz. The resonance frequency f _4a and the resonance frequency f _4b are both about 162.70 MHz, the capacitance C4 and the capacitance C6 are both about 6.49 pF, and the capacitance C5 is about 1.90 pF. FIG. 9 shows the attenuation characteristic of the BPF 4 and the frequency characteristic of the return loss.

  Referring to FIG. 9, the return loss has a bimodal characteristic, a return loss of about 28 dB is obtained at a pass frequency of 150.0 MHz, and a return loss of 50 dB or more at the maximum is obtained. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 37.5 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 28.2 dB, and the difference between the two attenuations is 9.3 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 32.4 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 25.1 dB, and the difference between the two attenuations is 7.3 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is approximately 26.3 dB, the attenuation at 165 MHz, which is 15 MHz higher than the pass frequency, is approximately 20.8 dB, and the difference between the two attenuations is 5.5 dB. Furthermore, the amount of attenuation at 140 MHz, which is 10 MHz lower than the passing frequency, is about 18.2 dB, the amount of attenuation at 160 MHz, which is 10 MHz higher than the passing frequency, is about 14.7 dB, and the difference between the two amounts of attenuation is 3.5 dB.

Further, another BPF 5 shown in FIG. 10 is a BPF having a two-stage configuration in which the resonator 5a and the resonator 5b are connected in two stages. Since the resonator 5a and the resonator 5b have the same configuration as the resonator 3a, a detailed description thereof is omitted, but a through hole is formed along substantially the central axis of the resonator 5a and the resonator 5b. An inner conductor S5a and an inner conductor S5b made of a conductive film are formed on the inner peripheral surface of the through hole. Further, the inner conductor S5a exposed on the open surface of the resonator 5a is connected to the input terminal IN via the inductance L4, and is connected to the inner conductor S5b of the resonator 5b via the inductance L5. S5b is connected to the output terminal OUT via an inductance L6. In the two-stage BPF 5 shown in FIG. 10, when the passing frequency of the BPF 5 is 150.0 MHz, the characteristic impedance Z _5a and the characteristic impedance Z _5b of the resonator 5a and the resonator _5b are both about 16.667Ω. The resonance frequency f _5a and the resonance frequency f _5b are both about 138.17 MHz, the inductance L4 and the inductance L6 are both about 159 nH, and the inductance L5 is about 505 nH. FIG. 11 shows the attenuation characteristic of the BPF 5 and the frequency characteristic of the return loss.

  Referring to FIG. 11, the return loss has a bimodal characteristic, a return loss of about 28 dB is obtained at a pass frequency of 150.0 MHz, and a return loss of 50 dB or more at the maximum is obtained. Also, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 27.8 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 37.0 dB, and the difference between the two attenuations is 9.2 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is approximately 24.8 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is approximately 32.1 dB, and the difference between the two attenuations is 7.3 dB. Furthermore, the attenuation at 135 MHz which is 15 MHz lower than the pass frequency is about 20.7 dB, the attenuation at 165 MHz which is 15 MHz higher than the pass frequency is about 26.1 dB, and the difference between the two attenuations is 5.4 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is approximately 14.6 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is approximately 18.1 dB, and the difference between the two attenuations is 3.5 dB.

  FIG. 16 is a diagram showing the attenuation characteristics of the BPF 4 shown in FIG. 8 and the BPF 5 shown in FIG. 10 configured as a two-stage configuration, and the BPF 6 shown in FIG. 12 and the BPF 7 shown in FIG. Show. Referring to FIG. 16, in the BPF 4 in which the coupling element is only the capacitance of C4 + C5 + C6, the total difference is 25.6 dB, and the low frequency side and the high frequency band with the passing frequency of the BPF 4 interposed therebetween It can be seen that the side attenuation characteristics are asymmetric. Further, even in the BPF 5 in which the coupling element is only the inductance of L4 + L5 + L6, the total difference is 25.4 dB, and the attenuation characteristics on the low frequency side and the high frequency side across the pass frequency of the BPF 5 Is asymmetric. On the other hand, in the BPF 6 of the second embodiment in which the coupling element is a combination of the capacitance and inductance of C7 + L7 + C8, the sum of the differences is 8.7 dB, and the low frequency side sandwiching the pass frequency of the BPF 6 It can be seen that the attenuation characteristics on the high frequency side are almost symmetrical. Further, also in the other BPF 7 of the second embodiment in which the coupling element is a combination of the inductance and capacitance of L8 + C9 + L9, the total difference is 7.9 dB, and the low frequency side across the pass frequency of the BPF 6 It can be seen that the attenuation characteristics on the high frequency side are almost symmetrical. Thus, by combining the coupling elements so that the difference between the number of capacitances and the number of inductances is 1, the attenuation characteristics of the BPF 6 and the BPF 7 can be made almost symmetrical. Note that the 3 dB bandwidth of the two-stage BPF6 and BPF7 in the second embodiment of the present invention is about 8.5 MHz, and the passband bandwidth is changed from the one-stage BPF to the two-stage BPF. It can be seen that a wide band can be obtained and a steep attenuation characteristic can be obtained.

Next, a bandpass filter according to a third embodiment of the present invention will be described with reference to FIGS. The three-stage BPF 8 shown in FIG. 17 and the three-stage BPF 9 shown in FIG. 19 are the three-stage BPF 10, BPF 11, BPF 12 according to the present invention shown in FIGS. 21, 23, 25, and 27. The BPF is for comparison with the BPF 13.
The BPF 10 according to the third embodiment of the present invention is a BPF having a three-stage configuration in which a resonator 10a, a resonator 10b, and a resonator 10c are connected in three stages as shown in FIG. Since the resonator 10a, the resonator 10b, and the resonator 10c have the same configuration as that of the resonator 3a, a detailed description thereof will be omitted, but the substantially central axes of the resonator 10a, the resonator 10b, and the resonator 10c are omitted. A through hole is formed along the inner peripheral surface of the through hole, and an inner conductor S10a, an inner conductor S10b, and an inner conductor S10c made of a conductive film are formed on the inner peripheral surface of the through hole. Further, the inner conductor S10a exposed on the open surface of the resonator 10a is connected to the input terminal IN via the capacitance C14, and is connected to the inner conductor S10b of the resonator 10b via the inductance L14. S10b is connected to the inner conductor S10c of the resonator 10c via the inductance L15, and the inner conductor S10c is connected to the output terminal OUT via the capacitance C15.

The BPF 10 having a three-stage configuration in the third embodiment of the present invention shown in FIG. 21 has the characteristic impedances Z _10a , Z _10b, and 10a of the resonator 10a, the resonator 10b, and the resonator 10c when the passing frequency is 150 MHz. , The characteristic impedance Z _10c is about 16.667Ω, the resonance frequency f _10a of the resonator _10a and the resonance frequency f 10c of the resonator _10c are both about 157.89 MHz, and the resonance frequency f _10b of the resonator _10b. Is about 143.72 MHz. Capacitance C14 and capacitance C15 are both about 8.22 pF, and inductance L14 and inductance L15 are both about 492 nH. FIG. 22 shows the attenuation characteristics of the BPF 10 and the frequency characteristics of the return loss. Referring to FIG. 22, the return loss has a three-peak characteristic, and a return loss of 50 dB or more is obtained at a pass frequency of 150.0 MHz. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 45.9 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 45.9 dB, and the difference between the two attenuations is 0.0 dB. Further, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 39.8 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 39.9 dB, and the difference between the two attenuations is 0.1 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 32.1 dB, the attenuation at 165 MHz, 15 MHz higher than the pass frequency, is about 32.1 dB, and the difference between the two attenuations is 0.0 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 21.2 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 21.2 dB, and the difference between the two attenuations is 0.0 dB.

  FIG. 23 shows another BPF 11 configuration according to the third embodiment of the present invention. This BPF 11 is a BPF having a three-stage configuration in which the resonator 11a, the resonator 11b, and the resonator 11c are connected in three stages. Since the resonator 11a, the resonator 11b, and the resonator 11c have the same configuration as that of the resonator 3a, a detailed description thereof will be omitted, but the substantially central axes of the resonator 11a, the resonator 11b, and the resonator 11c are omitted. A through hole is formed along the inner periphery of the through hole, and an inner conductor S11a, an inner conductor S11b, and an inner conductor S11c made of a conductive film are formed on the inner peripheral surface of the through hole. Further, the inner conductor S11a exposed on the open surface of the resonator 11a is connected to the input terminal IN via the inductance L16, and is connected to the inner conductor S11b of the resonator 11b via the capacitance C16. S11b is connected to the inner conductor S11c of the resonator 11c via the capacitance C17, and the inner conductor S11c is connected to the output terminal OUT via the inductance L17.

23 has a characteristic impedance Z _11a and a characteristic impedance Z of the resonator 11a, the resonator 11b, and the resonator 11c when the passing frequency is 150 MHz. _11b and the characteristic impedance Z _11c are both about 16.667Ω, the resonance frequency f _11a of the resonator _11a and the resonance frequency f 11c of the resonator _11c are both about 142.56 MHz, and the resonance frequency f of the resonator 11b is _11b is set to about 156.79 MHz. Both the inductance L16 and the inductance L17 are about 132 nH, and the capacitance C16 and the capacitance C17 are both about 2.25 pF. FIG. 24 shows the attenuation characteristic of the BPF 11 and the frequency characteristic of the return loss. Referring to FIG. 24, the return loss has a three-peak characteristic, and a return loss of 50 dB or more is obtained at a pass frequency of 150.0 MHz. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 47.0 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 46.5 dB, and the difference between the two attenuations is 0.5 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 40.8 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 40.4 dB, and the difference between the two attenuations is 0.4 dB. Furthermore, the attenuation at 135 MHz which is 15 MHz lower than the pass frequency is about 33.0 dB, the attenuation at 165 MHz which is 15 MHz higher than the pass frequency is about 32.7 dB, and the difference between the two attenuations is 0.3 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is approximately 22.0 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is approximately 21.8 dB, and the difference between the two attenuations is 0.2 dB.

  Furthermore, the configuration of still another BPF 12 according to the third embodiment of the present invention is shown in FIG. The BPF 12 is a BPF having a three-stage configuration in which the resonator 12a, the resonator 12b, and the resonator 12c are connected in three stages. Since the resonator 12a, the resonator 12b, and the resonator 12c have the same configuration as that of the resonator 3a, detailed description thereof is omitted, but the substantially central axes of the resonator 12a, the resonator 12b, and the resonator 12c are omitted. A through hole is formed along the inner peripheral surface of the through hole, and an inner conductor S12a, an inner conductor S12b, and an inner conductor S12c made of a conductive film are formed on the inner peripheral surface of the through hole. Further, the inner conductor S12a exposed on the open surface of the resonator 12a is connected to the input terminal IN via the capacitance C18 and is connected to the inner conductor S12b of the resonator 12b via the inductance L18. S12b is connected to the inner conductor S12c of the resonator 12c via the capacitance C19, and the inner conductor S12c is connected to the output terminal OUT via the inductance L19.

Still another BPF 12 having a three-stage configuration in the third embodiment of the present invention shown in FIG. 25 has characteristic impedances Z _12a and characteristic impedances of the resonators 12a, 12b and 12c when the passing frequency is 150 MHz. Z _12b and characteristic impedance Z _12c are both about 16.667Ω, the resonance frequency f _12a of the resonator _12a is about 158.10 MHz, and the resonance frequency f 12b of the resonator _12b is about 150.12 MHz. The resonance frequency f _{12c of 12c} is about 142.55 MHz. Capacitance C18 is about 8.42 pF, inductance L18 is about 490 nH, capacitance C19 is about 2.37 pF, and inductance L19 is about 129 nH. FIG. 26 shows the attenuation characteristic of the BPF 12 and the frequency characteristic of the return loss. Referring to FIG. 26, the return loss has a three-peak characteristic, and a return loss of about 48 dB is obtained at a pass frequency of 150.0 MHz. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 45.6 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 45.3 dB, and the difference between the two attenuations is 0.3 dB. Further, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 39.5 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 39.3 dB, and the difference between the two attenuations is 0.2 dB. Furthermore, the attenuation at 135 MHz which is 15 MHz lower than the pass frequency is about 31.7 dB, the attenuation at 165 MHz which is 15 MHz higher than the pass frequency is about 31.5 dB, and the difference between the two attenuations is 0.2 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 20.8 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 20.7 dB, and the difference between the two attenuations is 0.1 dB.

  Next, FIG. 27 shows still another configuration of the BPF 12 according to the third embodiment of the present invention. The BPF 13 is a BPF having a three-stage configuration in which the resonator 13a, the resonator 13b, and the resonator 13c are connected in three stages. Since the resonator 13a, the resonator 13b, and the resonator 13c have the same configuration as that of the resonator 3a, detailed description thereof is omitted. However, the central axis of the resonator 13a, the resonator 13b, and the resonator 13c is almost the same. A through hole is formed along the inner peripheral surface of the through hole, and an inner conductor S13a, an inner conductor S13b, and an inner conductor S13c made of a conductive film are formed on the inner peripheral surface of the through hole. The inner conductor S13a exposed on the open surface of the resonator 13a is connected to the input terminal IN via the capacitance C20, and is connected to the inner conductor S13b of the resonator 13b via the capacitance C21. S13b is connected to the inner conductor S13c of the resonator 13c via the inductance L20, and the inner conductor S13c is connected to the output terminal OUT via the inductance L21.

Still another BPF 13 having a three-stage configuration in the third embodiment of the present invention shown in FIG. 27 has the characteristic impedance Z _13a and characteristic impedance of the resonator 13a, the resonator 13b and the resonator 13c when the passing frequency is 150 MHz. Z _13b and characteristic impedance Z _13c are both about 16.667Ω, the resonance frequency f _13a of the resonator _13a is about 165.22 MHz, and the resonance frequency f 13b of the resonator _13b is about 149.55 MHz. The resonance frequency f _{13c of 13c} is about 135.96 MHz. Capacitance C20 is about 8.08 pF, capacitance C21 is about 2.25 pF, inductance L20 is about 444 nH, and inductance L21 is about 119 nH. FIG. 28 shows the attenuation characteristic of the BPF 13 and the frequency characteristic of the return loss. Referring to FIG. 28, the return loss has a three-peak characteristic, a return loss of about 35 dB is obtained at a pass frequency of 150.0 MHz, and a maximum return loss of about 41 dB is obtained. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 45.2 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 45.1 dB, and the difference between the two attenuations is 0.1 dB. Furthermore, the attenuation amount at 130 MHz, which is 20 MHz lower than the pass frequency, is about 39.1 dB, the attenuation amount at 170 MHz, which is 20 MHz higher than the pass frequency, is about 39.0 dB, and the difference between the two attenuation amounts is 0.1 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 31.3 dB, the attenuation at 165 MHz, 15 MHz higher than the pass frequency, is about 31.3 dB, and the difference between the two attenuations is 0.0 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 20.4 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 20.4 dB, and the difference between the two attenuations is 0.0 dB.

Next, the three-stage BPF 8 shown in FIG. 17 is a three-stage BPF in which the resonator 8a, the resonator 8b, and the resonator 8c are connected in three stages. Since the resonator 8a, the resonator 8b, and the resonator 8c have the same configuration as that of the resonator 3a, a detailed description thereof will be omitted, but the substantially central axes of the resonator 8a, the resonator 8b, and the resonator 8c are omitted. A through hole is formed along the inner periphery of the through hole, and an inner conductor S8a, an inner conductor S8b, and an inner conductor S8c made of a conductive film are formed on the inner peripheral surface of the through hole. Further, the inner conductor S8a exposed on the open surface of the resonator 8a is connected to the input terminal IN via the capacitance C10, and is connected to the inner conductor S8b of the resonator 8b via the capacitance C11. S8b is connected to the inner conductor S8c of the resonator 8c via the capacitance C12, and the inner conductor S8c is connected to the output terminal OUT via the capacitance C13. 17 has a characteristic impedance Z _8a , a characteristic impedance Z _8b, and a characteristic impedance Z _8c of the resonator 8a, the resonator 8b, and the resonator 8c when the passing frequency of the BPF 8 is 150.0 MHz. Are approximately 16.667 Ω, the resonance frequency f _8a of the resonator _8a and the resonance frequency f 8c of the resonator _8c are both approximately 165.14 MHz, and the resonance frequency f _8b of the resonator _8b is approximately 156.80 MHz. It is said that. Capacitance C10 and capacitance C13 are both about 8.10 pF, and capacitance C11 and capacitance C12 are both about 2.17 pF. FIG. 18 shows the attenuation characteristic of the BPF 8 and the frequency characteristic of the return loss.

  Referring to FIG. 18, the return loss has a three-peak characteristic, and a return loss of about 48 dB is obtained at a pass frequency of 150.0 MHz. The attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 52.5 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 40.0 dB, and the difference between the two attenuations is 12.5 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 45.0 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 35.1 dB, and the difference between the two attenuations is 9.9 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 35.8 dB, the attenuation at 165 MHz, 15 MHz higher than the pass frequency, is about 28.5 dB, and the difference between the two attenuations is 7.3 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is approximately 23.6 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is approximately 18.9 dB, and the difference between both attenuations is 4.7 dB.

The BPF 9 having a three-stage configuration illustrated in FIG. 19 is a three-stage BPF in which a resonator 9a, a resonator 9b, and a resonator 9c are connected in three stages. Since the resonator 9a, the resonator 9b, and the resonator 9c have the same configuration as that of the resonator 3a, detailed description thereof will be omitted, but the substantially central axes of the resonator 9a, the resonator 9b, and the resonator 9c are omitted. A through hole is formed along the inner peripheral surface of the through hole, and an inner conductor S9a, an inner conductor S9b, and an inner conductor S9c made of a conductive film are formed on the inner peripheral surface of the through hole. Further, the inner conductor S9a exposed on the open surface of the resonator 9a is connected to the input terminal IN via the inductance L10, and is connected to the inner conductor S9b of the resonator 9b via the inductance L11. S9b is connected to the inner conductor S9c of the resonator 9c via the inductance L12, and the inner conductor S9c is connected to the output terminal OUT via the inductance L13. 19 has a characteristic impedance Z _9a , a characteristic impedance Z _9b, and a characteristic impedance Z _9c of the resonator 9a, the resonator 9b, and the resonator 9c when the passing frequency of the BPF 9 is 150.0 MHz. Are approximately 16.667 Ω, the resonance frequency f _9a of the resonator _9a and the resonance frequency f 9c of the resonator _9c are both approximately 136.29 MHz, and the resonance frequency f _9b of the resonator _9b is approximately 142.85 MHz. It is said that. The inductance L10 and the inductance L13 are both about 125 nH, and the inductance L11 and the inductance L12 are both about 451 nH. FIG. 20 shows such attenuation characteristics of BPF 9 and frequency characteristics of return loss.

  Referring to FIG. 20, the return loss has a three-peak characteristic, and a return loss of about 50 dB is obtained at a pass frequency of 150.0 MHz. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 39.5 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 51.8 dB, and the difference between the two attenuations is 12.3 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 34.8 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 44.6 dB, and the difference between the two attenuations is 9.8 dB. Furthermore, the attenuation at 135 MHz which is 15 MHz lower than the pass frequency is about 28.3 dB, the attenuation at 165 MHz which is 15 MHz higher than the pass frequency is about 35.7 dB, and the difference between the two attenuations is 7.4 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is approximately 18.8 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is approximately 23.6 dB, and the difference between the two attenuations is 4.8 dB.

  The BPF 8 shown in FIG. 17 and the BPF 9 shown in FIG. 19 having the three-stage configuration, the BPF 10 shown in FIG. 21 having the three-stage configuration according to the present invention, the BPF 11 shown in FIG. 23, the BPF 12 shown in FIG. FIG. 29 shows a chart of the attenuation characteristics of the BPF 13 shown in FIG. Referring to FIG. 29, in the BPF 8 in which the coupling element is only the capacitance of C10 + C11 + C12 + C13, the sum of the differences is 34.4 dB, and the low frequency side across the pass frequency of the BPF 8 It can be seen that the attenuation characteristic on the high frequency side is asymmetric. In addition, in the BPF 9 in which the coupling element is only the inductance of L10 + L11 + L12 + L13, the sum of the differences is 34.3 dB, and the low frequency side and the high frequency side across the pass frequency of the BPF 9 It can be seen that the attenuation characteristic is asymmetric. On the other hand, in the BPF 10 of the third embodiment in which the coupling element is a combination of the capacitance and inductance of C14 + L14 + L15 + C15, the total difference is 0.1 dB, and the low frequency side sandwiching the pass frequency of the BPF 10 It can be seen that the attenuation characteristics on the high frequency side are almost symmetrical.

  Further, also in the other BPF 11 of the third embodiment in which the coupling element is a combination of the inductance and capacitance of L16 + C16 + C17 + L17, the sum of the differences is 1.4 dB, and the low frequency side across the pass frequency of the BPF 11 It can be seen that the attenuation characteristics on the high frequency side are almost symmetrical. Furthermore, in still another BPF 12 of the third embodiment in which the coupling element is a combination of the inductance and capacitance of C18 + L18 + C19 + L19, the sum of the differences is 0.8 dB, and the low frequency band across the pass frequency of the BPF 12 It can be seen that the attenuation characteristics on the side and the high frequency side are almost symmetrical. Furthermore, in still another BPF 13 of the third embodiment in which the coupling element is a combination of the inductance and capacitance of C20 + C21 + L20 + L21, the sum of the differences is 0.2 dB, and the low frequency band across the pass frequency of the BPF 13 It can be seen that the attenuation characteristics on the side and the high frequency side are almost symmetrical. In this way, by combining the four coupling elements with the same number of capacitors and the same number of inductances, the attenuation characteristics of the BPF 10 to BPF 13 can be made almost symmetrical. In addition, although the attenuation characteristics slightly change depending on the connection order of the connection elements of the capacitance and the inductance, since almost symmetrical attenuation characteristics are obtained in any BPF, the connection order may be any connection order. it can. In the third embodiment of the present invention, the 3-stage BPF 10 to BPF 13 has a 3 dB bandwidth of about 10 MHz, and the pass bandwidth is wider than the 2-stage BPF by using a 3-stage BPF. It can be seen that a steep attenuation characteristic can be obtained.

Next, a bandpass filter according to a fourth embodiment of the present invention will be described with reference to FIGS. Note that the four-stage BPF 14 shown in FIG. 30 and the four-stage BPF 15 shown in FIG. 32 are the four-stage BPF 16, BPF 17, BPF 18 according to the present invention shown in FIG. 34, FIG. 36, FIG. 38 and FIG. The BPF is for comparison with the BPF 19.
As shown in FIG. 34, the BPF 16 of the fourth embodiment of the present invention is a BPF having a four-stage configuration in which a resonator 16a, a resonator 16b, a resonator 16c, and a resonator 16d are connected in four stages. Since the resonator 16a, the resonator 16b, the resonator 16c, and the resonator 16d have the same configuration as that of the resonator 3a, detailed description thereof is omitted, but the resonator 16a, the resonator 16b, and the resonator 16c are omitted. A through hole is formed substantially along the central axis of the resonator 16d, and an inner conductor S16a, an inner conductor S16b, an inner conductor S16c, and an inner conductor S16d made of a conductive film are formed on the inner peripheral surface of the through hole. Yes. Further, the inner conductor S16a exposed on the open surface of the resonator 16a is connected to the input terminal IN via the capacitance C35, and is connected to the inner conductor S16b of the resonator 16b via the inductance L35. S16b is connected to the inner conductor S16c of the resonator 16c via the inductance L36, the inner conductor S16c is connected to the inner conductor S16d of the resonator 16d via the inductance L37, and the inner conductor S16d is connected to the output terminal OUT via the capacitance C36. Connected.

34 has a characteristic impedance Z _16a and characteristics of the resonator 16a, the resonator 16b, the resonator 16c, and the resonator 16d when the passing frequency is 150 MHz. The impedance Z _16b , the characteristic impedance Z _16c and the characteristic impedance Z _16d are all about 16.667Ω, the resonance frequency f _16a of the resonator _16a and the resonance frequency f 16d of the resonator _16d are both about 158.31 MHz, and the resonance The resonance frequency f _16b of the resonator _16b and the resonance frequency f _16c of the resonator _16c are both about 143.60 MHz. Capacitance C35 and capacitance C36 are both about 9.16 pF, inductance L35 and inductance L37 are both about 425 nH, and inductance L36 is about 563 nH. FIG. 35 shows the attenuation characteristic of the BPF 16 and the frequency characteristic of the return loss. Referring to FIG. 35, the return loss has a four-peak characteristic, a return loss of about 27 dB is obtained at a pass frequency of 150.0 MHz, and a maximum return loss of 50 dB or more is obtained. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 59.4 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 62.7 dB, and the difference between the two attenuations is 3.3 dB. Furthermore, the attenuation amount at 130 MHz, which is 20 MHz lower than the pass frequency, is about 51.6 dB, the attenuation amount at 170 MHz, which is 20 MHz higher than the pass frequency, is about 54.2 dB, and the difference between the two attenuation amounts is 2.6 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 41.6 dB, the attenuation at 165 MHz, 15 MHz higher than the pass frequency, is about 43.5 dB, and the difference between the two attenuations is 1.9 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is approximately 27.1 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is approximately 28.3 dB, and the difference between the two attenuations is 1.2 dB.

  Another BPF 17 according to the fourth embodiment of the present invention is a BPF having a four-stage configuration in which a resonator 17a, a resonator 17b, a resonator 17c, and a resonator 17d are connected in four stages as shown in FIG. Yes. Since the resonator 17a, the resonator 17b, the resonator 17c, and the resonator 17d have the same configuration as that of the resonator 3a, detailed description thereof is omitted, but the resonator 17a, the resonator 17b, and the resonator 17c are omitted. A through hole is formed substantially along the central axis of the resonator 17d, and an inner conductor S17a, an inner conductor S17b, an inner conductor S17c, and an inner conductor S17d made of a conductive film are formed on the inner peripheral surface of the through hole. Yes. Further, the inner conductor S17a exposed on the open surface of the resonator 17a is connected to the input terminal IN via the inductance L38, and is connected to the inner conductor S17b of the resonator 17b via the capacitance C37. S17b is connected to the inner conductor S17c of the resonator 17c via the capacitance C38, the inner conductor S17c is connected to the inner conductor S17d of the resonator 17d via the capacitance C39, and the inner conductor S17d is connected to the output terminal OUT via the inductance L39. Connected.

The four-stage BPF 17 in the fourth embodiment of the present invention shown in FIG. 36 has characteristics impedance Z _17a and characteristics of the resonator 17a, the resonator 17b, the resonator 17c, and the resonator 17d when the passing frequency is 150 MHz. The impedance Z _17b , the characteristic impedance Z _17c, and the characteristic impedance Z _17d are all about 16.667 Ω, and the resonance frequency f _17a of the resonator _17a and the resonance frequency f 17d of the resonator _17d are both about 142.17 MHz. The resonance frequency f _17b of the resonator _17b and the resonance frequency f _17c of the resonator _17c are both about 156.68 MHz. The inductance L38 and the inductance L39 are both about 118 nH, the capacitance C37 and the capacitance C39 are both about 2.63 pF, and the capacitance C38 is about 1.82 pF. FIG. 37 shows the attenuation characteristics of the BPF 17 and the frequency characteristics of the return loss. Referring to FIG. 37, the return loss has a four-peak characteristic, a return loss of about 27 dB is obtained at a pass frequency of 150.0 MHz, and a return loss of 50 dB or more at the maximum is obtained. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 63.8 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 60.1 dB, and the difference between the two attenuations is 3.7 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 55.2 dB, the attenuation at 170 MHz, which is 20 MHz higher than the pass frequency, is about 52.3 dB, and the difference between the two attenuations is 2.9 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 44.3 dB, the attenuation at 165 MHz, which is 15 MHz higher than the pass frequency, is about 42.2 dB, and the difference between the two attenuations is 2.1 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is approximately 29.0 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is approximately 27.7 dB, and the difference between the two attenuations is 1.3 dB.

  Furthermore, another BPF 18 of the fourth embodiment of the present invention is a BPF having a four-stage configuration in which a resonator 18a, a resonator 18b, a resonator 18c, and a resonator 18d are connected in four stages as shown in FIG. ing. Since the resonator 18a, the resonator 18b, the resonator 18c, and the resonator 18d have the same configuration as the resonator 3a, detailed description thereof is omitted, but the resonator 18a, the resonator 18b, and the resonator 18c are omitted. A through hole is formed substantially along the central axis of the resonator 18d, and an inner conductor S18a, an inner conductor S18b, an inner conductor S18c, and an inner conductor S18d made of a conductive film are formed on the inner peripheral surface of the through hole. Yes. Further, the inner conductor S18a exposed on the open surface of the resonator 18a is connected to the input terminal IN via the capacitance C40, and is connected to the inner conductor S18b of the resonator 18b via the inductance L40. S18b is connected to the inner conductor S18c of the resonator 18c via the capacitance C41, the inner conductor S18c is connected to the inner conductor S18d of the resonator 18d via the inductance L41, and the inner conductor S18d is connected to the output terminal OUT via the capacitance C42. Connected.

The four-stage BPF 18 in the fourth embodiment of the present invention shown in FIG. 38 has the characteristic impedance Z _18a and characteristic of the resonator 18a, the resonator 18b, the resonator 18c, and the resonator 18d when the passing frequency is 150 MHz. The impedance Z _18b , the characteristic impedance Z _18c, and the characteristic impedance Z _18d are all about 16.667Ω, and the resonance frequency f _18a of the resonator _18a and the resonance frequency f 18d of the resonator _18d are both about 158.44 MHz. The resonance frequency f _18b of the resonator _18b and the resonance frequency f _18c of the resonator _18c are both about 149.08 MHz. Capacitance C40 and capacitance C42 are both about 9.18 pF, capacitance C41 is about 1.92 pF, and inductance L40 and inductance L41 are both about 433 nH. FIG. 39 shows the attenuation characteristic of the BPF 18 and the frequency characteristic of the return loss. Referring to FIG. 39, the return loss has a four-peak characteristic, a return loss of about 27 dB is obtained at a pass frequency of 150.0 MHz, and a return loss of 50 dB or more at the maximum is obtained. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 62.7 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 59.6 dB, and the difference between the two attenuations is 3.1 dB. Further, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 54.2 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 51.8 dB, and the difference between the two attenuations is 2.4 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 43.4 dB, the attenuation at 165 MHz, which is 15 MHz higher than the pass frequency, is about 41.6 dB, and the difference between the two attenuations is 1.8 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 28.2 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 27.1 dB, and the difference between the two attenuations is 1.1 dB.

  Still another BPF 19 of the fourth embodiment of the present invention includes a BPF having a four-stage configuration in which a resonator 19a, a resonator 19b, a resonator 19c, and a resonator 19d are connected in four stages as shown in FIG. Has been. Since the resonator 19a, the resonator 19b, the resonator 19c, and the resonator 19d have the same configuration as that of the resonator 3a, detailed description thereof is omitted, but the resonator 19a, the resonator 19b, and the resonator 19c are omitted. A through hole is formed substantially along the central axis of the resonator 19d, and an inner conductor S19a, an inner conductor S19b, an inner conductor S19c, and an inner conductor S19d made of a conductive film are formed on the inner peripheral surface of the through hole. Yes. Further, the inner conductor S19a exposed on the open surface of the resonator 19a is connected to the input terminal IN via the inductance L42, and is connected to the inner conductor S19b of the resonator 19b via the capacitance C43. S19b is connected to the inner conductor S19c of the resonator 19c via the inductance L43, the inner conductor S19c is connected to the inner conductor S19d of the resonator 19d via the capacitance C44, and the inner conductor S19d is connected to the output terminal OUT via the inductance L44. Connected.

The four-stage BPF 19 in the fourth embodiment of the present invention shown in FIG. 40 has characteristics impedance Z _19a and characteristics of the resonator 19a, the resonator 19b, the resonator 19c, and the resonator 19d when the pass frequency is 150 MHz. The impedance Z _19b , the characteristic impedance Z _19c and the characteristic impedance Z _19d are all about 16.667 Ω, the resonance frequency f _19a of the resonator _19a and the resonance frequency f 19d of the resonator _19d are both about 142.124 MHz, and the resonance The resonance frequency f _19b of the resonator _19b and the resonance frequency f _19c of the resonator _19c are both about 151.15 MHz. The inductance L42 and the inductance L44 are both about 115 nH, the inductance L43 is about 588 nH, and the capacitance C43 and the capacitance C44 are both about 2.74 pF. FIG. 41 shows the attenuation characteristic of the BPF 19 and the frequency characteristic of the return loss. Referring to FIG. 41, the return loss has a four-peak characteristic, a return loss of about 27 dB is obtained at a pass frequency of 150.0 MHz, and a maximum return loss of 50 dB or more is obtained. Also, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 59.7 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 62.0 dB, and the difference between the two attenuations is 2.3 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 51.8 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 53.6 dB, and the difference between the two attenuations is 1.8 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 41.6 dB, the attenuation at 165 MHz, 15 MHz higher than the pass frequency, is about 42.9 dB, and the difference between the two attenuations is 1.3 dB. Furthermore, the attenuation at 140 MHz which is 10 MHz lower than the pass frequency is about 27.0 dB, the attenuation at 160 MHz which is 10 MHz higher than the pass frequency is about 27.8 dB, and the difference between the two attenuations is 0.8 dB.

  Next, the four-stage BPF 14 shown in FIG. 30 is a four-stage BPF in which a resonator 14a, a resonator 14b, a resonator 14c, and a resonator 14d are connected in four stages. Since the resonator 14a, the resonator 14b, the resonator 14c, and the resonator 14d have the same configuration as the resonator 3a, the detailed description thereof is omitted, but the resonator 14a, the resonator 14b, and the resonator 14c are omitted. A through hole is formed substantially along the central axis of the resonator 14d, and an inner conductor S14a, an inner conductor S14b, an inner conductor S14c, and an inner conductor S14d made of a conductive film are formed on the inner peripheral surface of the through hole. Yes. The inner conductor S14a exposed on the open surface of the resonator 14a is connected to the input terminal IN via the capacitance C30, and is connected to the inner conductor S14b of the resonator 14b via the capacitance C31. S14b is connected to the inner conductor S14c of the resonator 14c via the capacitance C32, the inner conductor S14c is connected to the inner conductor S14d of the resonator 14d via the capacitance C33, and the inner conductor S14d is connected to the output terminal OUT via the capacitance C34. Connected.

30 has a characteristic impedance Z _14a , a characteristic impedance Z _14b , and a characteristic impedance Z _14c of the resonator 14a, the resonator 14b, the resonator 14c, and the resonator 14d when the passing frequency is 150 MHz. And the characteristic impedance Z _14d are both about 16.667Ω, the resonance frequency f _14a of the resonator _14a and the resonance frequency f 14d of the resonator _14d are both about 166.90 MHz, and the resonance frequency f _14b of the resonator _14b. The resonance frequency f 14c of the resonator _14c is about 156.88 MHz. Capacitance C30 and capacitance C34 are both about 9.09 pF, capacitance C31 and capacitance C33 are both about 2.54 pF, and capacitance C32 is about 1.87 pF. FIG. 31 shows the attenuation characteristic of the BPF 14 and the frequency characteristic of the return loss. Referring to FIG. 31, the return loss has a four-peak characteristic, and a return loss of about 27 dB is obtained at a pass frequency of 150.0 MHz, and a return loss of 50 dB or more at maximum is obtained. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 68.8 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 53.2 dB, and the difference between the two attenuations is 15.6 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 58.9 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 46.5 dB, and the difference between the two attenuations is 12.4 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 46.7 dB, the attenuation at 165 MHz, 15 MHz higher than the pass frequency, is about 37.5 dB, and the difference between the two attenuations is 9.2 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 30.1 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 24.2 dB, and the difference between the two attenuations is 5.9 dB.

  A BPF 15 having a four-stage configuration shown in FIG. 32 is a four-stage BPF in which a resonator 15a, a resonator 15b, a resonator 15c, and a resonator 15d are connected in four stages. Since the resonator 15a, the resonator 15b, the resonator 15c, and the resonator 15d have the same configuration as the resonator 3a, detailed description thereof is omitted, but the resonator 15a, the resonator 15b, and the resonator 15c are omitted. A through hole is formed substantially along the central axis of the resonator 15d, and an inner conductor S15a, an inner conductor S15b, an inner conductor S15c, and an inner conductor S15d made of a conductive film are formed on the inner peripheral surface of the through hole. Yes. The inner conductor S15a exposed on the open surface of the resonator 15a is connected to the input terminal IN via the inductance L30, and is connected to the inner conductor S15b of the resonator 15b via the inductance L31. S15b is connected to the inner conductor S15c of the resonator 15c via the inductance L32, the inner conductor S15c is connected to the inner conductor S15d of the resonator 15d via the inductance L33, and the inner conductor S15d is connected to the output terminal OUT via the inductance L34. Connected.

32 has a characteristic impedance Z _15a , characteristic impedance Z _15b , characteristic impedance Z _15c of the resonator 15a, the resonator 15b, the resonator 15c and the resonator 15d when the passing frequency is 150 MHz. And the characteristic impedance Z _15d are both about 16.667Ω, the resonance frequency f _15a of the resonator _15a and the resonance frequency f 15d of the resonator _15d are both about 134.92 MHz, and the resonance frequency f _15b of the resonator _15b. The resonance frequency f 15c of the resonator _15c is about 142.87 MHz. The inductance L30 and the inductance L34 are both about 109 nH, the inductance L31 and the inductance L33 are both about 380 nH, and the inductance L32 is about 546 nH. FIG. 33 shows the attenuation characteristic of the BPF 15 and the frequency characteristic of the return loss. Referring to FIG. 33, the return loss has a four-peak characteristic, a return loss of about 27 dB is obtained at a pass frequency of 150.0 MHz, and a return loss of 50 dB or more at maximum is obtained. Also, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 52.4 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 67.7 dB, and the difference between the two attenuations is 15.3 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is approximately 46.0 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is approximately 58.1 dB, and the difference between the two attenuations is 12.1 dB. Furthermore, the attenuation at 135 MHz which is 15 MHz lower than the pass frequency is about 37.2 dB, the attenuation at 165 MHz which is 15 MHz higher than the pass frequency is about 46.2 dB, and the difference between the two attenuations is 9.0 dB. Furthermore, the attenuation at 140 MHz which is 10 MHz lower than the pass frequency is about 24.0 dB, the attenuation at 160 MHz which is 10 MHz higher than the pass frequency is about 29.8 dB, and the difference between the two attenuations is 5.8 dB.

  30 and BPF 15 shown in FIG. 32, and the BPF 16 shown in FIG. 34, BPF 17 shown in FIG. 36, BPF 18 shown in FIG. 38, and FIG. FIG. 42 shows a chart of the attenuation characteristics of the BPF 19 shown in FIG. Referring to FIG. 42, in the BPF 14 in which the coupling element is only the capacitance of C30 + C31 + C32 + C33 + C34, the sum of the differences is 43.1 dB, and the low frequency band across the pass frequency of the BPF 14 It can be seen that the attenuation characteristics on the side and the high frequency side are asymmetric. Also, in the BPF 15 in which the coupling element is only the inductance of L30 + L31 + L32 + L33 + L34, the total difference is 42.2 dB, and the low frequency side and the high frequency side across the pass frequency of the BPF 15 It can be seen that the attenuation characteristic is asymmetric. On the other hand, in the BPF 16 of the fourth embodiment in which the coupling element is a combination of the capacitance and inductance of C35 + L35 + L36 + L37 + C36, the sum of the differences is 9.0 dB, and the low frequency side sandwiching the pass frequency of the BPF 16 It can be seen that the attenuation characteristics on the high frequency side are almost symmetrical.

  Further, in the other BPF 17 of the fourth embodiment in which the coupling element is a combination of the inductance and capacitance of L38 + C37 + C38 + C39 + L39, the sum of the differences is 10.0 dB, and the low frequency side sandwiching the pass frequency of the BPF 17 It can be seen that the attenuation characteristics on the high frequency side are almost symmetrical. In addition, in the other BPF 18 of the fourth embodiment in which the coupling element is a combination of the inductance and capacitance of C40 + L40 + C41 + L41 + C42, the total difference is 8.4 dB, and the low frequency band across the pass frequency of the BPF 18 It can be seen that the attenuation characteristics on the side and the high frequency side are almost symmetrical. Furthermore, in still another BPF 19 of the fourth embodiment in which the coupling element is a combination of the inductance and capacitance of L42 + C43 + L43 + C44 + L44, the sum of the differences is 6.2 dB, and the low frequency band across the pass frequency of the BPF 19 It can be seen that the attenuation characteristics on the side and the high frequency side are almost symmetrical. In this way, by combining the coupling elements so that the difference between the number of capacitances and the number of inductances becomes 1, the attenuation characteristics of the BPF 16 to BPF 19 can be made almost symmetrical. In addition, although the attenuation characteristics slightly change depending on the connection order of the connection elements of the capacitance and the inductance, since almost symmetrical attenuation characteristics are obtained in any BPF, the connection order may be any connection order. it can. In the fourth embodiment of the present invention, the 4-stage BPF 16 to BPF 19 have a 3 dB bandwidth of about 11 MHz, and the 3-stage BPF has a 4-stage BPF so that the passband is wider. It can be seen that a steep attenuation characteristic can be obtained.

Next, a bandpass filter according to a fifth embodiment of the present invention will be described with reference to FIGS. 43, FIG. 45, FIG. 47, FIG. 49, FIG. 51, and FIG. 53, the five-stage BPF 20 to the five-stage BPF 25 are shown in FIG. 55 and FIG. And BPF for comparison with BPF27.
As shown in FIG. 55, the BPF 26 of the fifth embodiment of the present invention is a BPF having a five-stage configuration in which five resonators 26a, 26b, 26c, 26d, and 26e are connected. . Since the resonator 26a, the resonator 26b, the resonator 26c, the resonator 26d, and the resonator 26e have the same configuration as the resonator 3a, a detailed description thereof is omitted, but the resonator 26a and the resonator 26b are omitted. A through hole is formed along substantially the central axis of the resonator 26c, the resonator 26d, and the resonator 26e, and an inner conductor S26a, an inner conductor S26b, and an inner conductor S26c made of a conductive film are formed on the inner peripheral surface of the through hole. , Inner conductor S26d and inner conductor S26e are formed. The inner conductor S26a exposed on the open surface of the resonator 26a is connected to the input terminal IN via the capacitance C68, and is connected to the inner conductor S26b of the resonator 26b via the inductance L68. S26b is connected to the inner conductor S26c of the resonator 26c via the capacitance C69, the inner conductor S26c is connected to the inner conductor S26d of the resonator 26d via the inductance L69, and the inner conductor S26d is connected to the resonator 26e via the capacitance C70. The inner conductor S26e is connected to the output terminal OUT via an inductance L70.

55 has a characteristic impedance of the resonator 26a, the resonator 26b, the resonator 26c, the resonator 26d, and the resonator 26e when the passing frequency is 150 MHz. Z _26a , characteristic impedance Z _26b , characteristic impedance Z _26c , characteristic impedance Z _26d and characteristic impedance Z _26e are all set to about 16.667Ω, and the resonance frequency f _26a of the resonator _26a is set to about 158.61 MHz. The resonance frequency f _26b of the resonator _26c is approximately 148.80 MHz, the resonance frequency f _26c of the resonator _26c is approximately 150.02 MHz, and the resonance frequency f _26d of the resonator _26d is approximately 151.45 MHz. The resonance frequency f _{26e of 26e} is about 141.88 MHz. Capacitance C68 is about 9.64 pF, inductance L68 is about 401 nH, capacitance C69 is about 1.94 pF, inductance L69 is about 585 nH, capacitance C70 is about 2.95 pF, and inductance L70 is about 108 nH. FIG. 56 shows the attenuation characteristic of the BPF 26 and the frequency characteristic of the return loss. Referring to FIG. 56, the return loss has a five-peak characteristic, and a return loss of about 41 dB is obtained at a pass frequency of 150.0 MHz, and a maximum return loss of 46 dB is obtained. The attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 78.2 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 77.8 dB, and the difference between the two attenuations is 0.4 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 68.0 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 67.6 dB, and the difference between the two attenuations is 0.4 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 54.8 dB, the attenuation at 165 MHz, which is 15 MHz higher than the pass frequency, is about 54.6 dB, and the difference between the two attenuations is 0.2 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 35.9 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 35.8 dB, and the difference between the two attenuations is 0.1 dB.

  As shown in FIG. 57, another BPF 27 of the fifth embodiment of the present invention is a BPF having a five-stage configuration in which a resonator 27a, a resonator 27b, a resonator 27c, a resonator 27d, and a resonator 27e are connected in five stages. It is said that. Since the resonator 27a, the resonator 27b, the resonator 27c, the resonator 27d, and the resonator 27e have the same configuration as the resonator 3a, a detailed description thereof is omitted, but the resonator 27a and the resonator 27b are omitted. A through hole is formed along substantially the central axis of the resonator 27c, the resonator 27d, and the resonator 27e, and an inner conductor S27a, an inner conductor S27b, and an inner conductor S27c made of a conductive film are formed on the inner peripheral surface of the through hole. , Inner conductor S27d and inner conductor S27e are formed. Further, the inner conductor S27a exposed on the open surface of the resonator 27a is connected to the input terminal IN via the capacitance C71 and is connected to the inner conductor S27b of the resonator 27b via the capacitance C72. S27b is connected to the inner conductor S27c of the resonator 27c via the capacitance C73, the inner conductor S27c is connected to the inner conductor S27d of the resonator 27d via the inductance L71, and the inner conductor S27d is connected to the resonator 27e via the inductance L72. The inner conductor S27e is connected to the output terminal OUT via an inductance L73.

57 has a characteristic impedance of the resonator 27a, the resonator 27b, the resonator 27c, the resonator 27d, and the resonator 27e when the passing frequency is 150 MHz. Z _27a , characteristic impedance Z _27b , characteristic impedance Z _27c , characteristic impedance Z _27d and characteristic impedance Z _27e are all set to about 16.667Ω, and the resonance frequency f _27a of the resonator _27a is set to about 167.83 MHz. The resonance frequency f _27b of the resonator _27c is approximately 157.18 MHz, the resonance frequency f _27c of the resonator _27c is approximately 149.86 MHz, and the resonance frequency f _27d of the resonator _27d is approximately 142.77 MHz. The resonance frequency f _{27e of 27e} is about 134.46 MHz. Capacitance C71 is about 9.63 pF, capacitance C72 is about 2.73 pF, capacitance C73 is about 1.92 pF, inductance L71 is about 561 nH, inductance L72 is about 357 nH, and inductance L73 is about 105 nH. FIG. 56 shows the attenuation characteristic of the BPF 26 and the frequency characteristic of the return loss. Referring to FIG. 58, the return loss has a five-peak characteristic, a return loss of about 38 dB is obtained at a pass frequency of 150.0 MHz, and a maximum return loss of 40 dB is obtained. Also, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 77.8 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 77.7 dB, and the difference between the two attenuations is 0.1 dB. Furthermore, the attenuation amount at 130 MHz, which is 20 MHz lower than the pass frequency, is about 67.6 dB, the attenuation amount at 170 MHz, which is 20 MHz higher than the pass frequency, is about 67.5 dB, and the difference between the two attenuation amounts is 0.1 dB. Furthermore, the attenuation at 135 MHz which is 15 MHz lower than the pass frequency is about 54.4 dB, the attenuation at 165 MHz which is 15 MHz higher than the pass frequency is about 54.3 dB, and the difference between the two attenuations is 0.1 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 35.5 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 35.4 dB, and the difference between the two attenuations is 0.1 dB.

  Next, the five-stage BPF 20 shown in FIG. 43 is a five-stage BPF in which the resonator 20a, the resonator 20b, the resonator 20c, the resonator 20d, and the resonator 20e are connected in five stages. Since the resonator 20a, the resonator 20b, the resonator 20c, the resonator 20d, and the resonator 20e have the same configuration as the resonator 3a, a detailed description thereof will be omitted, but the resonator 20a and the resonator 20b. A through hole is formed along substantially the central axis of the resonator 20c, the resonator 20d, and the resonator 20e, and an inner conductor S20a, an inner conductor S20b, and an inner conductor S20c made of a conductive film are formed on the inner peripheral surface of the through hole. , Inner conductor S20d and inner conductor S20e are formed. Further, the inner conductor S20a exposed on the open surface of the resonator 20a is connected to the input terminal IN via the capacitance C50, and is connected to the inner conductor S20b of the resonator 20b via the capacitance C51. S20b is connected to the inner conductor S20c of the resonator 20c via the capacitance C52, the inner conductor S20c is connected to the inner conductor S20d of the resonator 20d via the capacitance C53, and the inner conductor S20d is connected to the resonator 20e via the capacitance C54. The inner conductor S20e is connected to the output terminal OUT via a capacitance C55.

43 has a characteristic impedance Z _20a , a characteristic impedance Z _20b , a characteristic impedance Z _20b of the resonator 20a, the resonator 20b, the resonator 20c, the resonator 20d, and the resonator 20e when the passing frequency is 150 MHz. The characteristic impedance Z _20c , the characteristic impedance Z _20d, and the characteristic impedance Z _20e are all about 16.667 Ω, and the resonance frequency f _20a of the resonator _20a and the resonance frequency f _20e of the resonator _20e are both about 167.73 MHz. The resonance frequency f _20b of the resonator _20b and the resonance frequency f 20d of the resonator _20d are about 157.16 MHz, and the resonance frequency f 20c of the resonator _20c is about 155.75 MHz. Capacitance C50 and capacitance C55 are both about 9.62 pF, capacitance C51 and capacitance C54 are both about 2.73 pF, and capacitance C52 and capacitance C53 are both about 1.88 pF. FIG. 44 shows the attenuation characteristic of the BPF 20 and the frequency characteristic of the return loss. Referring to FIG. 44, the return loss has five peak characteristics, and a return loss of 50 dB or more is obtained at a pass frequency of 150.0 MHz. The attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 87.4 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 68.8 dB, and the difference between the two attenuations is 18.6 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is approximately 75.0 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is approximately 60.3 dB, and the difference between the two attenuations is 14.7 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 59.8 dB, the attenuation at 165 MHz, which is 15 MHz higher than the pass frequency, is about 48.9 dB, and the difference between the two attenuations is 10.9 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is approximately 38.8 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is approximately 32.0 dB, and the difference between the two attenuations is 6.8 dB.

  The BPF 21 having a five-stage configuration shown in FIG. 45 is a five-stage BPF in which the resonator 21a, the resonator 21b, the resonator 21c, the resonator 21d, and the resonator 21e are connected in five stages. Since the resonator 21a, the resonator 21b, the resonator 21c, the resonator 21d, and the resonator 21e have the same configuration as the resonator 3a, the detailed description thereof is omitted, but the resonator 21a and the resonator 21b are omitted. A through hole is formed along substantially the central axis of the resonator 21c, the resonator 21d, and the resonator 21e, and an inner conductor S21a, an inner conductor S21b, and an inner conductor S21c made of a conductive film are formed on the inner peripheral surface of the through hole. , Inner conductor S21d and inner conductor S21e are formed. Further, the inner conductor S21a exposed on the open surface of the resonator 21a is connected to the input terminal IN via the inductance L50, and is connected to the inner conductor S21b of the resonator 21b via the inductance L51. S21b is connected to the inner conductor S21c of the resonator 21c via the inductance L52, the inner conductor S21c is connected to the inner conductor S21d of the resonator 21d via the inductance L53, and the inner conductor S21d is connected to the resonator 21e via the inductance L54. The inner conductor S21e is connected to the output terminal OUT via an inductance L55.

45 has a characteristic impedance Z _21a , a characteristic impedance Z _21b , a characteristic impedance Z _21b of the resonator 21a, the resonator 21b, the resonator 21c, the resonator 21d, and the resonator 21e when the passing frequency is 150 MHz. The characteristic impedance Z _21c , the characteristic impedance Z _21d, and the characteristic impedance Z _21e are all about 16.667Ω, and the resonance frequency f _21a of the resonator _21a and the resonance frequency f _21e of the resonator _21e are both about 134.37 MHz. The resonance frequency f _21b of the resonator _21b and the resonance frequency f 21d of the resonator _21d are about 142.63 MHz, and the resonance frequency f 21c of the resonator _21c is about 144.19 MHz. The inductance L50 and the inductance L55 are both about 103.2 nH, the inductance L51 and the inductance L54 are both about 355 nH, and the inductance L52 and the inductance L53 are both about 550 nH. FIG. 46 shows the attenuation characteristic of the BPF 21 and the frequency characteristic of the return loss. Referring to FIG. 46, the return loss has five peak characteristics, and a return loss of 50 dB or more is obtained at a pass frequency of 150.0 MHz. Also, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 68.1 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 86.5 dB, and the difference between the two attenuations is 18.4 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 60.0 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 74.5 dB, and the difference between the two attenuations is 14.5 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 48.9 dB, the attenuation at 165 MHz, 15 MHz higher than the pass frequency, is about 59.6 dB, and the difference between the two attenuations is 10.7 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 32.0 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 38.9 dB, and the difference between the two attenuations is 6.9 dB.

  Further, the BPF 22 having a five-stage configuration shown in FIG. 47 is a BPF having a five-stage configuration in which the resonator 22a, the resonator 22b, the resonator 22c, the resonator 22d, and the resonator 22e are connected in five stages. Since the resonator 22a, the resonator 22b, the resonator 22c, the resonator 22d, and the resonator 22e have the same configuration as the resonator 3a, a detailed description thereof is omitted, but the resonator 22a and the resonator 22b are omitted. Through holes are formed along substantially the central axis of the resonator 22c, the resonator 22d, and the resonator 22e, and an inner conductor S22a, an inner conductor S22b, and an inner conductor S22c made of a conductive film are formed on the inner peripheral surface of the through hole. , Inner conductor S22d and inner conductor S22e are formed. Further, the inner conductor S22a exposed on the open surface of the resonator 22a is connected to the input terminal IN via the capacitance C56, and is connected to the inner conductor S22b of the resonator 22b via the inductance L56. S22b is connected to the inner conductor S22c of the resonator 22c via the inductance L57, the inner conductor S22c is connected to the inner conductor S22d of the resonator 22d via the inductance L58, and the inner conductor S22d is connected to the resonator 22e via the inductance L59. The inner conductor S22e is connected to the output terminal OUT via the capacitance C57.

47 has a characteristic impedance Z _22a , a characteristic impedance Z _22b , a characteristic impedance Z _22b of the resonator 22a, the resonator 22b, the resonator 22c, the resonator 22d, and the resonator 22e when the passing frequency is 150 MHz. The characteristic impedance Z _22c , the characteristic impedance Z _22d and the characteristic impedance Z _22e are all about 16.667Ω, and the resonance frequency f _22a of the resonator _22a and the resonance frequency f _22e of the resonator _22e are both about 156.39 MHz. The resonance frequency f _22b of the resonator _22b and the resonance frequency f 22d of the resonator _22d are about 143.41 MHz, and the resonance frequency f 22c of the resonator _22c is about 144.42 MHz. Capacitance C56 and capacitance C57 are both about 9.49 pF, inductance L56 and inductance L59 are both about 401 nH, and inductance L57 and inductance L58 are both about 564 nH. FIG. 48 shows the attenuation characteristic of the BPF 22 and the frequency characteristic of the return loss. Referring to FIG. 48, the return loss has a five-peak characteristic, and a return loss of about 50 dB is obtained at a pass frequency of 150.0 MHz. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 75.5 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 81.9 dB, and the difference between the two attenuations is 6.4 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 66.0 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 71.1 dB, and the difference between the two attenuations is 5.1 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 53.6 dB, the attenuation at 165 MHz, which is 15 MHz higher than the pass frequency, is about 57.4 dB, and the difference between the two attenuations is 3.8 dB. Furthermore, the amount of attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 35.5 dB, the amount of attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 37.9 dB, and the difference between the two amounts of attenuation is 2.4 dB.

  Further, the five-stage BPF 23 shown in FIG. 49 is a five-stage BPF in which the resonator 23a, the resonator 23b, the resonator 23c, the resonator 23d, and the resonator 23e are connected in five stages. Since the resonator 23a, the resonator 23b, the resonator 23c, the resonator 23d, and the resonator 23e have the same configuration as the resonator 3a, the detailed description thereof is omitted, but the resonator 23a, the resonator 23b, A through hole is formed along substantially the central axis of the resonator 23c, the resonator 23d, and the resonator 23e, and an inner conductor S23a, an inner conductor S23b, an inner conductor S23c, Inner conductor S23d and inner conductor S23e are formed. Further, the inner conductor S23a exposed on the open surface of the resonator 23a is connected to the input terminal IN via the inductance L60, and is connected to the inner conductor S23b of the resonator 23b via the capacitance C58. S23b is connected to the inner conductor S23c of the resonator 23c via the capacitance C59, the inner conductor S23c is connected to the inner conductor S23d of the resonator 23d via the capacitance C60, and the inner conductor S23d is connected to the resonator 23e via the capacitance C61. The inner conductor S23e is connected to the output terminal OUT via the inductance L61.

49 has a characteristic impedance Z _23a , a characteristic impedance Z _23b , a characteristic impedance Z _23b of the resonator 23a, the resonator 23b, the resonator 23c, the resonator 23d, and the resonator 23e when the passing frequency is 150 MHz. The characteristic impedance Z _23c , the characteristic impedance Z _23d, and the characteristic impedance Z _23e are all about 16.667Ω, and the resonance frequency f _23a of the resonator _23a and the resonance frequency f _23e of the resonator _23e are both about 141.98 MHz. The resonance frequency f _23b of the resonator _23b and the resonance frequency f 23d of the resonator _23d are about 157.08 MHz, and the resonance frequency f 23c of the resonator _23c is about 155.58 MHz. The inductance L60 and the inductance L61 are both about 110.6 nH, the capacitance C58 and the capacitance C61 are both about 2.85 pF, and the capacitance C59 and the capacitance C60 are both about 1.85 pF. FIG. 50 shows the attenuation characteristic of the BPF 23 and the frequency characteristic of the return loss. Referring to FIG. 50, the return loss has a five-peak characteristic, and a return loss of about 47 dB is obtained at a pass frequency of 150.0 MHz, and a return loss of 50 dB or more at the maximum is obtained. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 82.4 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 75.4 dB, and the difference between the two attenuations is 7.0 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is approximately 71.4 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is approximately 65.8 dB, and the difference between the two attenuations is 5.6 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is about 57.4 dB, the attenuation at 165 MHz, which is 15 MHz higher than the pass frequency, is about 53.3 dB, and the difference between the two attenuations is 4.1 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 37.8 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 35.1 dB, and the difference between the two attenuations is 2.7 dB.

  Furthermore, the BPF 24 having the five-stage configuration shown in FIG. 51 is a five-stage BPF in which the resonator 24a, the resonator 24b, the resonator 24c, the resonator 24d, and the resonator 24e are connected in five stages. Since the resonator 24a, the resonator 24b, the resonator 24c, the resonator 24d, and the resonator 24e have the same configuration as the resonator 3a, the detailed description thereof is omitted, but the resonator 24a, the resonator 24b, Through holes are formed along substantially the central axis of the resonator 24c, the resonator 24d, and the resonator 24e, and an inner conductor S24a, an inner conductor S24b, an inner conductor S24c, Inner conductor S24d and inner conductor S24e are formed. Further, the inner conductor S24a exposed on the open surface of the resonator 24a is connected to the input terminal IN via the capacitance C62, and is connected to the inner conductor S24b of the resonator 24b via the inductance L62. S24b is connected to the inner conductor S24c of the resonator 24c via the capacitance C63, the inner conductor S24c is connected to the inner conductor S24d of the resonator 24d via the capacitance C64, and the inner conductor S24d is connected to the resonator 24e via the inductance L63. The inner conductor S24e is connected to the output terminal OUT via the capacitance C65.

51 has a characteristic impedance Z _24a , a characteristic impedance Z _24b , a characteristic impedance Z _24b of the resonator 24a, the resonator 24b, the resonator 24c, the resonator 24d, and the resonator 24e when the passing frequency is 150 MHz. The characteristic impedance Z _24c , the characteristic impedance Z _24d, and the characteristic impedance Z _24e are all about 16.667Ω, and the resonance frequency f _24a of the resonator _24a and the resonance frequency f _24e of the resonator _24e are both about 158.63 MHz. The resonance frequency f _24b of the resonator _24b and the resonance frequency f 24d of the resonator _24d are about 148.78 MHz, and the resonance frequency f 24c of the resonator _24c is about 155.76 MHz. Capacitance C62 and capacitance C65 are both about 9.68 pF, inductance L62 and inductance L63 are both about 401 nH, and capacitance C63 and capacitance C64 are both about 1.91 pF. FIG. 52 shows the attenuation characteristic of the BPF 24 and the frequency characteristic of the return loss. Referring to FIG. 52, the return loss has a five-peak characteristic, and a return loss of about 48 dB is obtained at a pass frequency of 150.0 MHz, and a maximum return loss of 50 dB is obtained. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 81.3 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 75.2 dB, and the difference between the two attenuations is 6.1 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 70.3 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 65.5 dB, and the difference between the two attenuations is 4.8 dB. Furthermore, the attenuation at 135 MHz which is 15 MHz lower than the pass frequency is about 56.5 dB, the attenuation at 165 MHz which is 15 MHz higher than the pass frequency is about 53.0 dB, and the difference between the two attenuations is 3.5 dB. Furthermore, the amount of attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 37.0 dB, the amount of attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 34.7 dB, and the difference between the two amounts of attenuation is 2.3 dB.

  Further, the five-stage BPF 25 shown in FIG. 53 is a five-stage BPF in which the resonator 25a, the resonator 25b, the resonator 25c, the resonator 25d, and the resonator 25e are connected in five stages. Since the resonator 25a, the resonator 25b, the resonator 25c, the resonator 25d, and the resonator 25e have the same configuration as the resonator 3a, the detailed description thereof is omitted, but the resonator 25a, the resonator 25b, A through hole is formed along substantially the central axis of the resonator 25c, the resonator 25d, and the resonator 25e, and an inner conductor S25a, an inner conductor S25b, an inner conductor S25c, Inner conductor S25d and inner conductor S25e are formed. The inner conductor S25a exposed on the open surface of the resonator 25a is connected to the input terminal IN via the inductance L64 and is connected to the inner conductor S25b of the resonator 25b via the capacitance C66. S25b is connected to the inner conductor S25c of the resonator 25c via the inductance L65, the inner conductor S25c is connected to the inner conductor S25d of the resonator 25d via the inductance L66, and the inner conductor S25d is connected to the resonator 25e via the capacitance C67. The inner conductor S25e is connected to the output terminal OUT via an inductance L67.

53 has a characteristic impedance Z _25a , a characteristic impedance Z _25b , a characteristic impedance Z _25b of the resonator 25a, the resonator 25b, the resonator 25c, the resonator 25d, and the resonator 25e when the passing frequency is 150 MHz. The characteristic impedance Z _25c , the characteristic impedance Z _25d, and the characteristic impedance Z _25e are all about 16.667Ω, and the resonance frequency f _25a of the resonator _25a and the resonance frequency f _25e of the resonator _25e are both about 141.97 MHz. The resonance frequency f _25b of the resonator _25b and the resonance frequency f 25d of the resonator _25d are about 151.36 MHz, and the resonance frequency f 25c of the resonator _25c is about 144.48 MHz. The inductance L64 and the inductance L67 are both about 109 nH, the capacitance C66 and the capacitance C67 are both about 2.95 pF, and the inductance L65 and the inductance L66 are both about 570 nH. FIG. 54 shows the attenuation characteristic of the BPF 25 and the frequency characteristic of the return loss. Referring to FIG. 54, the return loss has a five-peak characteristic, and a return loss of about 48 dB is obtained at a pass frequency of 150.0 MHz, and a maximum return loss of 50 dB is obtained. Further, the attenuation at 125 MHz, which is 25 MHz lower than the pass frequency, is about 75.1 dB, the attenuation at 175 MHz, which is 25 MHz higher than the pass frequency, is about 80.4 dB, and the difference between the two attenuations is 5.3 dB. Furthermore, the attenuation at 130 MHz, which is 20 MHz lower than the pass frequency, is about 65.5 dB, the attenuation at 170 MHz, 20 MHz higher than the pass frequency, is about 69.7 dB, and the difference between the two attenuations is 4.2 dB. Furthermore, the attenuation at 135 MHz, which is 15 MHz lower than the pass frequency, is approximately 53.0 dB, the attenuation at 165 MHz, 15 MHz higher than the pass frequency, is approximately 56.0 dB, and the difference between the two attenuations is 3.0 dB. Furthermore, the attenuation at 140 MHz, which is 10 MHz lower than the pass frequency, is about 34.7 dB, the attenuation at 160 MHz, which is 10 MHz higher than the pass frequency, is about 36.6 dB, and the difference between the two attenuations is 1.9 dB.

  43, BPF 21 shown in FIG. 45, BPF 22 shown in FIG. 47, BPF 23 shown in FIG. 49, BPF 24 shown in FIG. 51 and BPF 25 shown in FIG. 53, and BPF 25 shown in FIG. FIG. 59 shows a chart of the attenuation characteristics of the BPF 26 shown in FIG. 55 and the BPF 27 shown in FIG. Referring to FIG. 59, in the BPF 20 in which the coupling element is only the capacitance of C50 + C51 + C52 + C53 + C54 + C55, the sum of the differences is 51.0 dB, and the low frequency band across the pass frequency of the BPF 20 It can be seen that the attenuation characteristics on the side and the high frequency side are asymmetric. In addition, in the BPF 21 in which the coupling element is only the inductance of L50 + L51 + L52 + L53 + L54 + L55, the sum of the differences is 50.5 dB, and the low frequency side and the high frequency side across the pass frequency of the BPF 21 It can be seen that the attenuation characteristic is asymmetric. Further, in the BPF 227 in which the coupling element is a combination of the capacitance and inductance of C56 + L56 + L57 + L58 + L59 + C57, the total difference is reduced to 17.7 dB, but the attenuation on the low-frequency side and the high-frequency side sandwiching the pass frequency of the BPF 22 It can be seen that the characteristics are somewhat asymmetric. Furthermore, in the BPF 23 in which the coupling element is a combination of inductance and capacitance of L60 + C58 + C59 + C60 + C61 + L61, the total difference is reduced to 19.4 dB, but the low frequency side and the high frequency side across the pass frequency of the BPF 23 are reduced. It can be seen that the attenuation characteristic is slightly asymmetric. Furthermore, in the BPF 24 in which the coupling element is a combination of the inductance and capacitance of C62 + L62 + C63 + C64 + L63 + C65, the total difference is reduced to 16.7 dB, but the low frequency side and the high frequency side across the pass frequency of the BPF 24 are reduced. It can be seen that the attenuation characteristic is slightly asymmetric. Furthermore, in the BPF 24 in which the coupling element is a combination of the inductance and capacitance of L64 + C66 + L65 + L66 + C67 + L67, the total difference is reduced to 14.4 dB, but the low frequency side and the high frequency side across the pass frequency of the BPF 24 It can be seen that the attenuation characteristic is slightly asymmetric.

  On the other hand, in the BPF 26 of the fifth embodiment in which the coupling element is a combination of the capacitance and inductance of C68 + L68 + C69 + L69 + C70 + L70, the total difference is 1.1 dB, and the low frequency side sandwiching the pass frequency of the BPF 26 It can be seen that the attenuation characteristics on the high frequency side are almost symmetrical. Further, in the other BPF 27 of the fourth embodiment in which the coupling element is a combination of the inductance and capacitance of C718 + C72 + C73 + L71 + L72 + L73, the sum of the differences is 0.4 dB, and the low frequency side sandwiching the pass frequency of the BPF 27 It can be seen that the attenuation characteristics on the high frequency side are almost symmetrical. Thus, by combining the coupling elements with the same number of capacitances and inductances, the attenuation characteristics of the BPF 26 and the BPF 27 can be made almost symmetrical. In addition, when the coupling elements are combined so that the difference between the number of capacitances and the number of inductances is 2, the attenuation characteristics of the BPF 22 to BPF 25 can be made closer to symmetry, but cannot be made almost symmetrical. In the fifth embodiment of the present invention, the 5 dB BPF 26 and the BPF 27 have a 3 dB bandwidth of about 11 MHz, and a steep attenuation characteristic can be obtained with a 5-stage BPF compared to a 4-stage BPF. I understand.

  In the band-pass filter of the present invention described above, the resonator is a band-pass filter having one to five stages. However, the present invention is not limited to this, and a band-pass filter having six or more resonators is used. be able to. In this case, the coupling element is a combination of inductance and capacitance, and the number of coupling elements of inductance and the number of coupling elements of capacitance are combined so that the same number or the difference between the two is 1. However, the connection order of the coupling elements of inductance and capacitance can be any connection order. In addition, the above-described pass bandwidth in the band-pass filter of the present invention is an example. By changing the resonance frequency of the resonators connected in multiple stages and the value of the connection element, the pass band width is within a predetermined range. It becomes possible to change the bandwidth. Further, in the band-pass filter of the present invention, the resonator is formed in a cylindrical shape by sintering a dielectric ceramic material. However, the present invention is not limited to this, and the resonator is formed in a prismatic shape or the like. Also good.

1-27 BPF, 1a-27a resonator, 4b-27b resonator, 8c-27c resonator, 14d-27d resonator, 20e-27e resonator, S1a-S27a inner conductor, S4b-S27b inner conductor, S8c-S27c Inner conductor, S14d to S27d Inner conductor, S20e to S27e Inner conductor, IN input terminal, OUT output terminal

Claims (1)

A bandpass filter comprising at least one stage of dielectric resonator,
The dielectric having a dielectric, an inner conductor made of a conductive film formed on an inner peripheral surface of a through-hole formed in the dielectric, and an outer conductor made of a conductive film formed on the outer surface of the dielectric A resonator,
Two or more stages of the dielectric resonator are provided between the inner conductor of the first stage dielectric resonator and the input terminal and between the inner conductor of the last stage dielectric resonator and the output terminal. And a coupling element that connects between the inner conductor of the dielectric resonator and the inner conductor of the dielectric resonator of the next stage,
The coupling element is either a capacitance coupling element or an inductance coupling element. When the number of coupling elements is an even number, the number of capacitance coupling elements and the number of inductance coupling elements are the same, and the number of coupling elements is an odd number. The band-pass filter is characterized in that the difference between the number of capacitance coupling elements and the number of inductance coupling elements is 1.

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