JP3490679B2 - Amplitude deviation compensation bandpass filter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bandpass filter, and more particularly to an amplitude deviation compensation type bandpass filter in which the amplitude deviation of the passband is smaller than in the prior art.

[0002]

2. Description of the Related Art In a mobile communication base station apparatus, a terrestrial digital television backbone station transmitter apparatus, etc., a resonance element (for eliminating noise due to an IM wave (intermodulation wave), etc., and power combining in an antenna duplexer ( For example, a bandpass filter including a coaxial resonance element, a capacitive loading resonance element, a dielectric resonance element, etc. is used. And W-C in mobile communication
In the case of the DMA and the OFDM modulation system of the terrestrial digital television, the amplitude deviation in the pass band of the band pass filter affects the bit rate (BER) characteristic.
A bandpass filter having a small amplitude deviation within the passband is required.

[0003]

As described above, W-CDMA in mobile communication and O in terrestrial digital television.
The band pass filter used in the FDM modulation method has a small amplitude deviation in the pass band, for example, 0.
Those within 2 dB are required. However, conventionally,
In a bandpass filter used for a mobile communication base station device, a terrestrial digital television backbone station transmitter, etc., the amplitude deviation within the passband is generally within 0.5 dB, and is used for the above-mentioned applications. There was a problem that it could not be done. The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is, for example, W-CDMA in mobile communication and OF of terrestrial digital television.
In the band pass filter used for the DM modulation method,
It is an object of the present invention to provide a technique capable of reducing the amplitude deviation in the pass band as compared with the conventional technique. The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0004]

In a lumped constant type bandpass filter, a resistance element for compensation is inserted in a part of a resonance circuit to reduce an amplitude deviation in the bandpass.
For example, it is described in the following document (a). (B) Yazaki Ginsaku, Takebe Miki, "Transmission Circuits and Filters," pp. 361-366, 1972, incorporated association
FIG. 10 issued by the Institute of Electronics and Communication Engineers is a circuit diagram showing a bandpass filter described in FIG. 14.5 of the above-mentioned document (a) in which the amplitude deviation within the bandpass is improved. In the bandpass filter shown in FIG. 10, a compensation resistance element is inserted in a part of the resonance circuit to reduce the amplitude deviation in the passband. However,
In the bandpass filter shown in FIG. 10, a loss resistance is increased by inserting a resistance element for compensation in a part of the resonance circuit. Here, in the bandpass filter shown in FIG. 10, the input impedance (impedance viewed from the input terminal) is 200Ω, and the output impedance (impedance viewed from the output terminal) is 600Ω. Hereinafter, in this specification, the difference between the input impedance and the output impedance is referred to as an impedance slope.

The present inventor has found that even in a distributed constant type band pass filter, the amplitude deviation in the pass band can be reduced by adding the impedance slope described above, and the present invention has been accomplished. The present invention has been made based on the above findings, and the outline of representative ones of the inventions disclosed in the present application will be briefly described as follows. That is, the present invention provides a bandpass filter comprising a plurality of resonant elements connected in cascade between an input terminal and an output terminal, at least one of said input terminals and said output terminal, has an impedance transformer, When the input impedance of the band pass filter is Zin and the output impedance of the band pass filter is Zout, Zin <Zout is satisfied.

In a preferred embodiment of the invention, λo
Where Z1 is the wavelength of the center frequency of the bandpass filter and Z1 is the characteristic impedance of the transmission line connected to one of the impedance transformers, the impedance transformer has a length λo / 4 and a characteristic impedance Zo.
Where Zo = (Z1 × Zin) ^1/2 , or Zo =
It is characterized by being constituted by a coaxial line of (Z1 × Zout) ^1/2 . In a preferred embodiment of the invention, λ
When the tube wavelength of the waveguide when the g-center frequency of the band-pass filter, the characteristic impedance of the transmission line connected to one of the impedance transformer and Z1,
The impedance transformer has a length of λg / 4 and a characteristic impedance Zo of Zo = (Zo × Zin) ^1/2 ,
Alternatively, it is characterized by being constituted by a waveguide that is Zo (Z1 × Zout) ^1/2 .

According to the above means, at least one of the input terminal and the output terminal of the distributed constant type bandpass filter is provided with an impedance transformer composed of a coaxial line or a waveguide, and is used as an input terminal of the bandpass filter. Since the impedance slope is provided between the output terminal and the output terminal, the amplitude deviation in the pass band of the band pass filter can be reduced to, for example, 0.2 dB or less without increasing the pass loss. Become. As a result, W-CDMA in mobile communication and OF of terrestrial digital television
It becomes possible to provide an effective band pass filter by using the DM modulation method.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described with reference to the drawings.
The embodiment will be described in detail. The embodiment will be described.
In all the figures for
No., and repeated explanations are omitted. [First Embodiment] FIG. 1 shows the amplitude of the first embodiment of the present invention.
FIG. 3 is a diagram showing a schematic configuration of a deviation compensation type bandpass filter.
The same figure (a) is an upper plan view, and the same figure (b) is the same figure (a).
A cross section showing the internal structure of the impedance transformer 20 shown in FIG.
It is a figure. 2 is an amplitude deviation compensation type bandpass shown in FIG.
It is sectional drawing which shows the internal structure of a filter, and the same figure (a).
Is a main part showing a cross section taken along the line A-A 'shown in FIG.
The cross-sectional view and FIG. 1B are taken along the line B-B ′ shown in FIG.
FIG. 3 is a cross-sectional view of a main part showing a different cross section. Amplitude of this embodiment
The deviation compensation type bandpass filter is a bandpass filter of order 6.
1 and 2 in FIGS. 1 and 2.₁~ 1_FourIs TE_01
δMode dielectric resonator element, 2 in shield case, 3 in
Force terminal, 4 is an output terminal, 6₁~ 6_FiveIs the inter-stage coupling adjustment screw,
8 is an input coupling loop element, 9 is an output coupling loop element, 1
0₁, 10₂Is TM_{01 δ}Mode dielectric resonator element, 11₁~
11₂Is a support member, 12 is an internal partition wall, and 24 is an interstage connection.
Hole, 25₁~ 25₆Is the frequency adjustment screw, 26₁~ 26₆Is
It is.

In FIG. 1, reference numeral 20 denotes an impedance transformer, which is a feature of the present invention. The impedance transformer 20 is provided on the output terminal side. As shown in FIG. 1B, the impedance transformer 20 includes an inner conductor 2
01 and an outer conductor 202, which is a coaxial line,
The length (Lout) is Lout = λo / 4 when the wavelength of the center frequency of the bandpass filter is λo. The characteristic impedance (Zo (out)) of the coaxial line forming the impedance transformer 20 is the characteristic impedance of the transmission line connected to one side of the impedance transformer 20 (that is, the transmission line connected to the output terminal 4) by Z1. , Zo (out) = (Z1 ×), where Zout is the output impedance of the bandpass filter (that is, the impedance seen by the bandpass filter from the connection point between the impedance transformer 20 and the bandpass filter).
Zout) ^1/2 value. FIG. 3 is a circuit diagram showing an equivalent circuit of the amplitude deviation compensation type bandpass filter of the present embodiment. In the case shown in FIG. 3, the impedance conversion ratio of the impedance transformer 20 is 2: 1. Therefore, for example, when Z1 = 50Ω and Zout = 100, the characteristic impedance of the coaxial line forming the impedance transformer 20 ( Zo (out) is 70Ω (≈ (50 × 10
0) ^1/2 ≈ 70Ω).

FIG. 11 is a top plan view showing a schematic structure of a conventional bandpass filter. The bandpass filter shown in FIG. 11 is the same as the amplitude deviation compensation type bandpass filter of the present embodiment, except that the impedance transformer 20 on the output terminal side is omitted, and the reference numerals in the drawing are the same as those in FIG. Therefore, detailed description thereof will be omitted. As shown in FIGS. 1 and 11, each of the dielectric resonant elements (10 ₁ , 10 ₂ ,
1 ₁ to 1 ₄ field direction) (E) and as the magnetic field direction (H) coincide, i.e., TE _{01 [delta]} -mode dielectric resonator element (1
₁ to 1 ₄₎ and TM _{01 [delta]} mode dielectric resonator element (10 _1, 1
0 ₂ ) are orthogonal to each other, each dielectric resonance element (10 ₁ ,
10 _2, 1 ₁ the to 1 ₄₎ to place, it is possible to construct a band-pass filter of the multi-stage. 11, each dielectric resonator element (10 _1, 10 _{2, 1} 1 to 1 ₄₎ Since there is a magnetic field coupling, the equivalent circuit FIG. 12 (a), the is as shown in (b).

FIG. 13 is a graph showing the attenuation characteristic of the band pass filter shown in FIG. In the figure,
The horizontal axis is frequency (MHz), the memory interval is 10MHz,
The vertical axis is the amount of attenuation (dB), the memory interval is 5 dB,
The center frequency (fo) is 1951 MHz. 14
Is a graph showing an enlarged attenuation characteristic in the pass band shown in FIG. 13, in which the horizontal axis represents frequency (MHz).
The memory interval is 2.5 MHz, and the vertical axis is the amount of attenuation (dB).
Therefore, the memory interval is 0.5 dB. As shown in FIG. 13, the attenuation characteristic is good, but as shown in FIG. 14, an amplitude deviation within several pass bands (for example, fo ± 10 MH).
The amplitude deviation in z) is greater than 0.2 dB.

In the amplitude deviation compensation type bandpass filter of the present embodiment, the impedance transformer 20 is provided on the output terminal side, so that the equivalent circuit is as shown in FIG. FIG. 4 is a graph showing an attenuation characteristic of an example of the amplitude deviation compensation type bandpass filter according to the present embodiment. In the figure, the horizontal axis represents frequency (MHz) and the memory interval is 10M.
Hz, the vertical axis represents the amount of attenuation (dB), the memory interval is 5 dB, and the center frequency (fo) is 1951 MHz. FIG. 5 is a graph showing the attenuation characteristics in the pass band shown in FIG. 4 in an enlarged manner. In the same figure, the horizontal axis represents frequency (MHz).
The memory interval is 2.5 MHz, and the vertical axis is the amount of attenuation (dB).
Therefore, the memory interval is 0.5 dB. As shown in FIG. 5, the amplitude deviation in the pass band of the amplitude deviation compensation type band pass filter of this embodiment (for example, the amplitude deviation within fo ± 10 MHz) is smaller than that of the conventional band pass filter shown in FIG. Has become.

As described above, the amplitude deviation compensation according to the present embodiment is performed.
Type band pass filter, impedance at the output terminal side
A transformer 20 is provided and the interstage coupling adjustment screw shown in FIG.
(6 ₁~ 6_Five) Between the input terminal 3 and the output terminal 4
In addition, the impedance slope is given. By this
To reduce the amplitude deviation in the pass band as compared to the past.
Is possible. Furthermore, in the above-mentioned document (a), the resonance
Insert a resistance element in a part of the path to measure the amplitude deviation in the pass band.
Compensation, which increases insertion loss.
In the form of, the impedance transformer 20 is provided on the output terminal side.
Since it is provided to compensate for the amplitude deviation in the pass band,
Amplitude deviation, such as that described in (a)
Will not increase.

[Second Embodiment] FIG. 6 is a top plan view showing a schematic configuration of an amplitude deviation compensation type bandpass filter according to a second embodiment of the present invention. The amplitude deviation compensation type bandpass filter according to the present embodiment is also a bandpass filter with an order of 6, and the impedance transformer 21 is provided on the input terminal side as well. Different from a pass filter. Note that the reference numerals shown in FIG. 6 are the same as those in FIG. 1, and detailed description thereof will be omitted. As shown in FIG.
The impedance transformer 21 on the input side is composed of a coaxial line, and its length (Lin) is Lin = λo, like the impedance transformer 20 on the output side, where λo is the wavelength of the center frequency of the bandpass filter. The length is / 4.

The characteristic impedance (Zo (in)) of the coaxial line forming the impedance transformer 21 is a characteristic of the transmission line connected to one of the impedance transformers 21 (that is, the transmission line connected to the input terminal 3). Let Z1 be the impedance and Zin be the input impedance of the bandpass filter (that is, the impedance seen by the bandpass filter from the connection point between the impedance transformer 21 and the bandpass filter), Zo (in) = (Z1 × Zi
n) The value is ^1/2 . FIG. 7 is a circuit diagram showing an equivalent circuit of the amplitude deviation compensation type bandpass filter of the present embodiment. In the case shown in FIG. 7, the impedance conversion ratio of the impedance transformer 21 is 2: 1.
When Z1 = 50Ω and Zin = 25, the characteristic impedance of the coaxial line forming the impedance transformer 21 (Z
o (in) is 35Ω (≈ (50 × 25) ^1/2 ≈35
Ω).

FIG. 8 is a graph showing an attenuation characteristic of an example of the amplitude deviation compensation type bandpass filter according to the present embodiment.
In the figure, the horizontal axis represents frequency (MHz), the memory interval is 10 MHz, the vertical axis represents attenuation (dB), the memory interval is 5 dB, and the center frequency (fo) is 1951 MHz. 9 is an enlarged graph showing the attenuation characteristic in the pass band shown in FIG. 8, in which the horizontal axis represents frequency (MHz), the memory interval is 2.5 MHz, and the vertical axis represents the amount of attenuation (dB). ), The memory interval is 0.5 dB. As shown in FIG. 9, the amplitude deviation in the number of pass bands of the amplitude deviation compensation type band pass filter of this embodiment is smaller than that of the amplitude deviation compensation type band pass filter of the above embodiment shown in FIG. There is.

As described above, in the amplitude deviation compensation type bandpass filter of the present embodiment, the impedance transformer 21 is provided on the input terminal side and the impedance transformer 20 is provided on the output terminal side, and the stage shown in FIG. Inter-coupling adjustment screw (6
_{Through 65)} was adjusted to between an input terminal 3 and an output terminal 4,
Impedance slope is added. This allows
It is possible to further reduce the amplitude deviation in the pass band as compared with the conventional case. Further, in the above-mentioned document (a), a resistance element is inserted in a part of the resonance circuit to compensate for the amplitude deviation in the pass band, and therefore the insertion loss increases, but in the present embodiment, the output loss is increased. Impedance transformer 2 on the terminal side
Since 0 is set to compensate for the amplitude deviation in the pass band,
Unlike the one described in the above-mentioned document (a), the amplitude deviation does not increase.

Although the impedance transformers (20, 21) are constructed by the coaxial lines in the above-mentioned respective embodiments, the impedance transformers (20, 2) are described.
1) can also be configured with a waveguide. However, in this case, the length of the waveguide, the tube wavelength of the waveguide at a center frequency of the bandpass filter shown in the following equation (1) (lambda
It is necessary to set λg / 4 of g).

## EQU1 ## λg = λo / (1- (λo / λc) ^1/2 ) where λo is the wavelength at the center frequency of the bandpass filter, and λc is the cutoff wavelength of the waveguide. Further, in each of the above-described embodiments, the present invention is applied to the input terminal 3 and the TM _{01.
Between the δ-} mode dielectric resonance element 10 ₁ and the output terminal 4 and T
The case where the present invention is applied to the bandpass filter in which the magnetic field coupling with the M _{01 δ-} mode dielectric resonance element 10 ₂ is magnetically coupled by the coupling loop element (8, 9) has been described, but the present invention is not limited to this. Instead, between the input terminal 3 and the TM _{01 δ-} mode dielectric resonant element 10 ₁ , the output terminal 4 and the TM ₀₁
between the _δ-mode dielectric resonator element 10 ₂ is also applicable to a band pass filter that is capacitively coupled by capacitor element.

Further, in each of the above-described embodiments, the present invention is applied to a plurality of TM ₀₁ 's between the input terminal 3 and the output terminal 4.
_{The case where the δ-} mode dielectric resonant element and the TE _{01 δ-} mode dielectric resonant element are applied to the band-pass filter connected in series has been described, but the present invention is not limited to this, and a general distributed constant type It is also applicable to bandpass filters. That is, the plurality of resonant elements connected in cascade between the input terminal 3 and the output terminal 4 may be, for example, a coaxial resonant element, a capacitive loading resonant element, or the like. The main coupling circuit between the resonant elements connected to the terminal 4 may be capacitive coupling. Although the invention made by the present inventor has been specifically described based on the above-described embodiment, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. Of course,

[0020]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows. ADVANTAGE OF THE INVENTION According to this invention, the amplitude deviation of a pass band can be made smaller than before, and W-CDMA in a mobile communication, and an effective band pass filter are used for the OFDM modulation system of a terrestrial digital television. Is possible.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an amplitude deviation compensation type bandpass filter according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the internal structure of the amplitude deviation compensation type bandpass filter shown in FIG.

FIG. 3 is a circuit diagram showing an equivalent circuit of the amplitude deviation compensation type bandpass filter shown in FIG.

FIG. 4 is a graph showing an attenuation characteristic of an example of the amplitude deviation compensation type bandpass filter shown in FIG. 1.

5 is an enlarged graph showing attenuation characteristics in the pass band shown in FIG. 4. FIG.

FIG. 6 is an upper plan view showing a schematic configuration of an amplitude deviation compensation type bandpass filter according to a second embodiment of the present invention.

7 is a circuit diagram showing an equivalent circuit of the amplitude deviation compensation type bandpass filter shown in FIG.

8 is a graph showing an attenuation characteristic of an example of the amplitude deviation compensation type bandpass filter shown in FIG.

9 is an enlarged graph showing attenuation characteristics in the pass band shown in FIG. 8. FIG.

FIG. 10 is a circuit diagram showing a conventional bandpass filter with improved amplitude deviation within the bandpass.

FIG. 11 is an upper plan view showing a schematic configuration of a conventional bandpass filter.

12 is a circuit diagram showing an equivalent circuit of the bandpass filter shown in FIG.

13 is a graph showing an attenuation characteristic of an example of the bandpass filter shown in FIG.

FIG. 14 is an enlarged graph showing attenuation characteristics in the pass band shown in FIG.

[Explanation of symbols]

₁ 1 ~1 ₄ ... TE ₀₁ δ-mode dielectric resonator element, 2 ... shield case, 3 ... input (or output) terminal, 4 ... output (or input) terminal, 6 _{through 65} ... interstage coupling adjusting screw, 8 ... input (or output) coupling loop element, 9 ... output (or input) coupling loop _{elements, 10 1, 10 2 ... TM} 01 δ -mode dielectric resonator element, 11 ₁ to 11 ₂ ... support member, 12 ... inner partition , 20, 21 ... Impedance transformer, 5 ... Coaxial plug, 24 ... Interstage coupling hole, 25 _{1 to} 25 ₆ ... Frequency adjusting screw, 26 _{1 to} 26 ₆ ... Nut, 201 ... Inner conductor, 202 ...
Outer conductor.

Claims (3)

(57) [Claims] 1. A cascade connection between an input terminal and an output terminal.
In a bandpass filter with multiple resonant elements
And at least one of the input terminal and the output terminal,
An impedance transformer, and the input impedance of the bandpass filter is Zin,
The output impedance of the band pass filter is Zout
That time, Zin <Features and <br /> be that the amplitude deviation compensation bandpass filter satisfies the Zout. 2. When λo is a wavelength of a center frequency of the band pass filter and Z1 is a characteristic impedance of a transmission line connected to one of the impedance transformers, the impedance transformer has a length of λo / 4. in the amplitude of claim 1 characteristic impedance Zo is, the Zo = (Z1 × Zin) ^1/2 or, characterized in that it is constituted by Zo = (Z1 × Zout) coaxial line is ^1/2 Deviation compensation type bandpass filter. Wherein when the tube within the wavelength of the waveguide at a center frequency of the bandpass filter lambda] g, the characteristic impedance of the transmission line connected to one of the impedance transformer and Z1, the impedance transformer Has a length of λg / 4 and a characteristic impedance Zo is Zo = (Z1
× Zin) ^1/2 , or Zo = (Z1 × Zout)
Claim 1 characterized by being composed of a waveguide that is ^1/2
1. An amplitude deviation compensation type bandpass filter according to item 1 .