JP2008131130A - Band-pass filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a band-pass filter capable of having better attenuation characteristics through the same number of stages of resonators. <P>SOLUTION: The band-pass filter includes an input terminal 11, a first band-pass filter 12 connected to the input terminal 11 and constituted by connecting a plurality of resonators 17 in parallel, a low-pass filter 13 connected to the first band-pass filter 12, a second band-pass filter 14 connected to the low-pass filter 13 and constituted by connecting a plurality of resonators 17 in parallel, and an output terminal 15 connected to the second band-pass filter 14. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention particularly relates to a band-pass filter used for a microwave, a quasi-microwave communication apparatus, or the like.

  As shown in the circuit diagram of FIG. 5, this type of conventional bandpass filter is a circuit in which a plurality of resonators 4 are connected in parallel via a plurality of capacitive couplings 3 between an input terminal 1 and an output terminal 2. Was configured. Then, harmonics and spurious signals that cannot be removed by this band pass filter are removed by a low pass filter (not shown) provided separately.

  As shown in FIG. 6, this bandpass filter has a structure in which a plurality of dielectric resonators 6 are connected to a coupling substrate 8 through coupling fittings 7 in a metal chassis composed of a bottom plate 5a and a box 5b. It is connected and housed, and is connected to an external circuit (not shown) by the input connector 9a and the output connector 9b. 7, 8 (a), and (b) show transmission characteristics when a conventional bandpass filter is used. FIG. 7 shows attenuation near the passband, and FIG. FIG. 8 (b) shows the attenuation amount on the high frequency side.

As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.
JP-A-2-62101

  However, in the conventional band-pass filter described above, when it is intended to obtain sufficient attenuation characteristics, it is necessary to increase the number of stages of the resonator 4 or to add a circuit element for providing an attenuation pole. Had problems.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a band-pass filter that can obtain better attenuation characteristics by using resonators having the same number of stages.

  In order to achieve the above object, the present invention has the following configuration.

  The invention according to claim 1 of the present invention includes an input terminal, a first band pass filter configured by connecting a plurality of resonators in parallel to the input terminal, and the first band pass filter. A low-pass filter connected to the low-pass filter, a second band-pass filter configured by connecting a plurality of resonators in parallel to the low-pass filter, and an output terminal connected to the second band-pass filter. Therefore, according to this configuration, the first band pass filter configured by connecting a plurality of resonators in parallel, the low pass filter connected to the first band pass filter, and the low pass filter are connected to the first band pass filter. Since the second band-pass filter configured by connecting a plurality of resonators in parallel is provided, the first band-pass filter and the second band-pass filter are provided. By matching the action of the filter and the low pass filter can be generated very due to resonance on both sides of the passband, thereby, those having the effect that it is possible to obtain a greater attenuation near the pass band.

  According to the second aspect of the present invention, in particular, the first band-pass filter is formed of a monoblock dielectric filter having at least two stages of resonators, and the second band-pass filter is formed of at least two stages. A monoblock dielectric filter having a resonator is used, and the resonance frequency of the two-stage resonator in the first band-pass filter is substantially matched with the resonance frequency of the two-stage resonator in the second band-pass filter. Therefore, according to this configuration, the resonance frequency of the two-stage resonator in the first bandpass filter and the resonance frequency of the two-stage resonator in the second bandpass filter are substantially matched. By using two two-stage monoblock dielectric filters having through holes of the same length, it is possible to simplify the production of the dielectric resonator. It is expected to have an effect effect.

  As described above, the band-pass filter of the present invention includes an input terminal, a first band-pass filter configured by connecting a plurality of resonators in parallel to the input terminal, and the first band-pass filter. A low-pass filter connected to the second low-pass filter, a second band-pass filter connected to the low-pass filter and a plurality of resonators connected in parallel, and an output terminal connected to the second band-pass filter. Therefore, it is possible to generate resonance poles on both sides of the passband by the matching action of the first bandpass filter, the second bandpass filter, and the lowpass filter, thereby obtaining a larger attenuation characteristic. It has an excellent effect of being able to.

  Hereinafter, a band-pass filter according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram of a bandpass filter according to an embodiment of the present invention, FIG. 2 is an exploded perspective view of the bandpass filter, and FIGS. 3, 4A and 4B are transmission characteristics of the bandpass filter. FIG.

  As shown in the circuit diagram of FIG. 1, the band-pass filter according to the embodiment of the present invention has one end of the first band-pass filter 12 connected to the input terminal 11 and the first band-pass filter 12. One end of the low-pass filter 13 is connected to the other end, and one end of the second band-pass filter 14 is connected to the other end of the low-pass filter 13 and output to the other end of the second band-pass filter 14. The terminal 15 is connected.

  Each of the first band-pass filter 12 and the second band-pass filter 14 has a resonator 17 connected in parallel via a capacitive coupling 16, and the resonance frequency of each resonator 17 is set to a pass frequency. is doing.

  The low-pass filter 13 is a Chebyshev-type filter circuit that uses three elements of the inductor 18 and two elements of the capacitor 19, and removes harmonics and spurious from the band-pass filter.

  Next, the structure of the bandpass filter in one embodiment of the present invention will be described with reference to FIG.

  The band-pass filter according to the embodiment of the present invention includes a monoblock dielectric filter 22a functioning as the first band-pass filter 12 in a metal case 21 including a bottom plate 21a and a box body 21b, and a second A monoblock dielectric filter 22b functioning as a bandpass filter 14 and a metal fitting 23 constituting the lowpass filter 13 are accommodated, and an input connector 24a for introducing an input and an output connector 24b for deriving an output are attached. is there.

  In the monoblock dielectric filter 22a and the monoblock dielectric filter 22b, two through holes 26 parallel to each other are provided in a substantially rectangular parallelepiped dielectric block 25, and the outer peripheral surface parallel to the through hole 26 and the inside of the through holes 26 are provided. A conductor film is formed on the peripheral surface, and the input fitting 27a or the output fitting 27b is press-fitted into one end portion of one through hole 26 via a resin bush 28 and capacitively coupled, and the other through hole 26 is inserted. One end of a metal fitting 23 constituting the low-pass filter 13 is press-fitted through a resin bush 28 to the opposite end of the low-pass filter 13 for capacitive coupling.

  The metal fitting 23 is provided with alternating narrow portions 23 a that function as inductors 18 and wide portions 23 b that function as electrodes of the capacitors 19. The wide portions 23 b are connected to a ground such as a surrounding metal case 21. A capacitor 19 is formed between them.

  Next, transmission characteristics of the band-pass filter according to the embodiment of the present invention will be described with reference to FIGS. 3, 4A, and 4B. Here, the unit of the vertical axis in FIGS. 3, 4A, and 4B indicates the attenuation amount in dB, and the unit of the horizontal axis indicates the frequency in GHz. 3 shows the attenuation near the passband, FIG. 4 (a) shows the attenuation on the low frequency side, and FIG. 4 (b) shows the attenuation on the high frequency side.

  In the transmission characteristic diagrams of FIGS. 3, 4A, and 4B, the pass band is 2.01 to 2.025 GHz, and the poles are at 1.63 GHz on the low frequency side and 2.4 GHz on the high frequency side. Have. Compared with the transmission characteristic diagrams of the conventional bandpass filters in FIGS. 7, 8 </ b> A and 8 </ b> B, the attenuation is about 2 dB at 1.96 to 1.99 GHz in the vicinity of the low band side of the passband. It can be seen that the attenuation is large by 3 to 4 dB at 2.04 to 2.17 GHz in the vicinity of the high band side of the pass band, and the attenuation characteristics are excellent.

  As described above, the band-pass filter according to the embodiment of the present invention has excellent attenuation characteristics as compared with the conventional band-pass filter. This is due to the fact that a resonance pole is generated on both sides of the pass band due to the matching action of the second band pass filter 14 and the low pass filter 13, thereby making it possible to obtain greater attenuation in the vicinity of the pass band. Further, the position of this pole can be changed by the cut-off frequency and impedance of the low-pass filter 13 and the impedance of the resonator 17, and the attenuation can be optimized by adjusting the position of this pole. It can be done.

  In addition, since the band-pass filter according to the embodiment of the present invention has a built-in low-pass filter 13 for removing harmonics and spurious, it is not necessary to provide a separate low-pass filter unlike a conventional band-pass filter. It has the characteristics.

  In addition, the bandpass filter according to the embodiment of the present invention increases the attenuation amount by incorporating a low-pass filter provided outside the conventional bandpass filter. Therefore, there is no need to add a circuit element such as a notch circuit.

  Furthermore, in the band-pass filter according to the embodiment of the present invention, both the first band-pass filter 12 and the second band-pass filter 14 are constituted by two-stage resonators, and the first band-pass filter 12 is used. Since the low-pass filter 13 is disposed between the second band-pass filter 14 and the second band-pass filter 14, the resonance frequency of each resonator 17 can be made to coincide with the pass frequency, thereby resonating like a conventional band-pass filter. It is not necessary to use resonators having different frequencies in a predetermined arrangement, and it is only necessary to prepare a plurality of the same resonators, so that manufacturing can be simplified.

  Furthermore, when the first band-pass filter 12 and the second band-pass filter 14 including the two-stage resonator 17 are configured by the monoblock dielectric filters 22a and 22b, the dielectric block 25 has the same length. Since the two-stage resonator 17 can be configured by providing two holes 26, the manufacturing of the resonator 17 can be simplified, and the first band-pass filter 12 and the second band-pass filter 14 have the same structure. Since it can be constituted by a dielectric filter, the manufacturing can be further simplified.

  As described above, the band-pass filter according to the embodiment of the present invention is provided with an additional circuit element or the like because the low-pass filter existing outside the conventional band-pass filter is arranged in the band-pass filter. In this case, poles can be generated on the low-frequency side and the high-frequency side of the passband, respectively, thereby improving the attenuation characteristics of the bandpass filter.

  In the embodiment of the present invention, the bottom plate 21a is made of metal constituting the metal case 21, and the low-pass filter 13 is configured using the metal fitting 23 having the narrow portion 23a and the wide portion 23b. However, a circuit board may be used instead of the metal bottom plate 21a. In that case, the low-pass filter 13 may be formed by a circuit board pattern.

  Further, in the band-pass filter of the present invention, the low-pass filter 13 is disposed between the first band-pass filter 12 and the second band-pass filter 14 regardless of the device structure of the embodiment of the present invention described above. The circuit configuration has an effect that the attenuation characteristic can be improved.

  The band-pass filter according to the present invention can generate resonance poles on both sides of the pass band by the matching action of the first band-pass filter, the second band-pass filter, and the low-pass filter. It has the effect that attenuation characteristics can be obtained, and is particularly useful when used in microwave and quasi-microwave communication devices.

The circuit diagram of the band pass filter in one embodiment of the present invention Exploded perspective view of the same bandpass filter Transmission characteristics of the same bandpass filter Transmission characteristics of the same bandpass filter Circuit diagram of a conventional bandpass filter Perspective view of the same bandpass filter Transmission characteristics of the same bandpass filter Transmission characteristics of the same bandpass filter

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Input terminal 12 1st band pass filter 13 Low pass filter 14 2nd band pass filter 15 Output terminal 16 Capacitive coupling 17 Resonator 18 Inductor 19 Capacitor 22a Monoblock dielectric filter 22b Monoblock dielectric filter 23 Hardware 24a Input connector 24b Output connector

Claims (2)

An input terminal, a first band-pass filter configured by connecting a plurality of resonators in parallel to the input terminal, a low-pass filter connected to the first band-pass filter, and a connection to the low-pass filter And a second band-pass filter configured by connecting a plurality of resonators in parallel and an output terminal connected to the second band-pass filter. The first bandpass filter is constituted by a monoblock dielectric filter having at least two stages of resonators, and the second bandpass filter is constituted by a monoblock dielectric filter having at least two stages of resonators, The band-pass filter according to claim 1, wherein the resonance frequency of the two-stage resonator in the first band-pass filter and the resonance frequency of the two-stage resonator in the second band-pass filter are substantially matched.

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