JP2020129725A - Band-rejection filter - Google Patents

Abstract

To provide a band-rejection filter that obtains good reflection characteristics over a wide band from a desired wave band to an unnecessary wave band while maintaining low loss in the desired wave and large attenuation characteristics in the unnecessary wave band.SOLUTION: A band-rejection filter is configured to: load two first resistors 1 connected in series between an input terminal and an output terminal; connect a first resonance circuit 6 in parallel to the two first resistors 1 connected in series; connect one end of a second resistor 2 to a connecting portion of the two first resistors; and ground the other end of the second resistor 2 by a second resonance circuit 9. The first resonance circuit 6 includes a parallel circuit of a first inductor 4 and a first capacitor 5, and the second resonance circuit 9 includes a series circuit of a second inductor 7 and a second capacitor 8, and the first resonance circuit resonates in parallel in the unnecessary wave band, and the second resonance circuit resonates in series in the unnecessary wave band.SELECTED DRAWING: Figure 1

Description

The present invention relates to a band elimination filter that allows a desired wave within a band to pass without being attenuated, significantly suppresses an unnecessary wave outside the band, and has a good reflection characteristic over a wide band.

RF (Radio Frequency) equipment such as radar equipment, communication equipment, and observation equipment prevents unwanted waves outside the desired band from entering, or harmonics or intermodulation distortion components generated inside these equipment. A band-stop filter is used to prevent the unwanted waves from leaking out of the equipment.
As such a band elimination filter, there is one that consists of a lumped element consisting of an inductor and a capacitor, and is designed to maintain good reflection characteristics in the desired wave band within the band and to have almost total reflection in the unnecessary wave band outside the band. To be done. Therefore, the desired wave within the band passes without being attenuated, and the unnecessary wave outside the band is significantly suppressed (for example, refer to Patent Document 1).

JP, 2016-163382, A

In order to apply such a band elimination filter to an RF device, a module using an active device such as an FET (Field Effect Transistor) or a HEMT (High Electron Mobility Transistor) may be connected to the input/output unit of the band elimination filter. is there. Usually, the module is designed to have good reflection characteristics in the band, but it is not always good reflection characteristics outside the band, and it is often close to total reflection.

In such a case, there is a problem that large multiple reflection occurs between the band elimination filter and the module in the unnecessary wave band, and the module oscillates or operates in an unstable manner. Further, the attenuation characteristic of the band elimination filter in the unnecessary wave band is also significantly deteriorated, and the RF device is deteriorated due to the high level unnecessary wave entering the RF device, or the unnecessary wave generated in the RF device is transmitted to the outside of the RF device. There was also a leaking issue.

The band stop filter of the present invention is
A parallel circuit of two first resistors and a first resonant circuit connected in series between the input terminal and the output terminal;
A series circuit of a second resistor whose one end is connected to the connecting portion of the two first resistors and a second resonance circuit whose one end is connected to the other end of the second resistor and whose other end is grounded; A band stop filter having
At frequencies in the unwanted band,
The parallel circuit can be regarded as only the first resistor,
The above series circuit can be regarded as only the second resistor,
At the frequency of the desired wave band,
The first resistor is short-circuited by the first resonant circuit,
The other end of the second resistor is opened by the second resonance circuit.

According to the band elimination filter of the present invention, at the frequency of the unnecessary wave band, it can be considered that the T-type attenuator composed of the first resistance and the second resistance is connected between the input terminal and the output terminal. it can. Therefore, it is possible to obtain a good reflection characteristic over a wide band from the desired wave band to the unnecessary wave band while maintaining a low loss in the desired wave band and a large attenuation characteristic determined by the T-type attenuator in the unnecessary wave band. ..

It is a figure which shows the structure of the band stop filter by Embodiment 1 of this invention. It is a figure which shows the simple equivalent circuit of the band stop filter by Embodiment 1 of this invention. It is a figure which shows the design example of the band stop filter by Embodiment 1 of this invention. FIG. 6 is a diagram showing another design example of the band elimination filter according to the first embodiment of the present invention. It is a figure which shows the structure of the other Example of the band stop filter by Embodiment 1 of this invention. It is a figure which shows the structure of the band stop filter by Embodiment 2 of this invention. It is a figure which shows the simple equivalent circuit of the band stop filter by Embodiment 2 of this invention. It is a figure which shows the design example of the band stop filter by Embodiment 2 of this invention. It is a figure which shows the structure of the other Example of the band stop filter by Embodiment 2 of this invention. It is a figure which shows the structure of the band stop filter by Embodiment 3 of this invention. It is a figure which shows the simple equivalent circuit of the band stop filter by Embodiment 3 of this invention. It is a figure which shows the design example of the band stop filter by Embodiment 3 of this invention. It is a figure which shows the example of calculation of the band stop filter by Embodiment 3 of this invention. It is a figure which shows the structure of the other Example of the band stop filter by Embodiment 3 of this invention. It is a figure which shows the structure of the band stop filter by Embodiment 4 of this invention. It is a figure which shows the simple equivalent circuit of the band stop filter by Embodiment 4 of this invention. It is a figure which shows the design example of the band stop filter by Embodiment 4 of this invention. It is a figure which shows the example of calculation of the band stop filter by Embodiment 4 of this invention. It is a figure which shows the structure of the other Example of the band stop filter by Embodiment 4 of this invention.

***Definition of terms***
Unwanted wave band = frequency band of unwanted wave. The band you want to stop with the band stop filter.
Desired wave band=frequency band of desired wave. The band that you do not want to block with the band stop filter.
R1, R2 = resistance value L1, L2, L3, L4 = inductance C1, C2, C3, C4 = capacitance

Embodiment 1.
Hereinafter, Embodiment 1 according to this embodiment will be described with reference to the drawings.
FIG. 1 is a diagram showing the configuration of a band elimination filter according to the first embodiment.
This band elimination filter is provided with a parallel circuit 20 between an input terminal 10 and an output terminal 11 and a first resonance circuit 6 connected in parallel to two first resistors 1 connected in series, and a first parallel circuit 20. One end of the second resistor 2 is connected to the connection portion of the resistor 1 and the other end of the second resistor 2 is grounded by the second resonance circuit 9. The second resistor 2 and the second resonance circuit 9 form a series circuit 30.
The first resonance circuit 6 is composed of a parallel circuit of a first inductor 4 and a first capacitor 5, and the second resonance circuit 9 is a series circuit of a second inductor 7 and a second capacitor 8. It consists of: Further, the two first resistors 1 and the one second resistor 2 form a T-type attenuator 3.
Here, the first resistor 1 and the second resistor 2 are selected as R1 and R2, respectively, and the first inductor 4, the first capacitor 5, the second inductor 7 and the second capacitor 8 are respectively Selected as L1, C1, L2 and C2.

FIG. 2 is a simple equivalent circuit of the band elimination filter according to the first embodiment.
When the parallel resonance frequency of the first resonance circuit 6 is selected as the frequency Fr of the unnecessary wave band, the parallel circuit 20 of the first resistor 1 and the first resonance circuit 6 is regarded as only the first resistor 1 in Fr. be able to.
Similarly, when the series resonance frequency of the second resonance circuit 9 is selected as the frequency Fr of the unnecessary wave band, the series circuit 30 of the second resistor 2 and the second resonance circuit 9 is the second resistor 2 at Fr. Can only be considered. Therefore, it can be considered that the T-type attenuator 3 is loaded between the input terminal 10 and the output terminal 11.
On the other hand, at the frequency F0 of the desired wave band sufficiently distant from the unnecessary wave band, the first resonant circuit 6 has a low impedance regardless of whether F0<Fr or F0>Fr, and the first resistor 1 is short-circuited. Moreover, since the second resonance circuit 9 has a high impedance, the other end of the second resistor 2 is open. Therefore, in F0, the area between the input terminal 10 and the output terminal 11 can be regarded as a through.
Hereinafter, a method of calculating R1, R2, L1, C1, L2 and C2 will be described.

Here, the relationship between the R1 and R2 forming the T-type attenuator 3 and the attenuation amount K can be obtained by the mathematical formula 1.

[Formula 1]
R1=Z0*(K-1)/(K+1)
R2=2*K*Z0/(K*K-1)

In this equation, Z0 is a power source impedance or a load impedance, which is usually 50Ω.
By selecting R1 and R2 in this way, a T-type attenuator having an attenuation amount K over a wide band and excellent reflection characteristics can be obtained regardless of the frequency.

Further, the relationship between L1 and C1 of the first resonance circuit 6 and L2 and C2 of the second resonance circuit 9 is obtained by Expression 2. Here, ωr is an angular frequency and has a relationship of ωr=2πFr.

[Formula 2]
ωr*ωr*L1*C1=1
ωr*ωr*L2*C2=1

In this way, by selecting the resonance frequency of the first resonance circuit 6 and the second resonance circuit 9 as the unnecessary wave band, low loss is achieved in the desired wave band which is sufficiently distant from the unnecessary wave band, and T-shaped in the unnecessary wave band. A large amount of attenuation K determined by the attenuator can be obtained, and a band elimination filter having a good reflection characteristic from the desired wave band to the unnecessary wave band can be obtained.

FIG. 3 is a design example of the band elimination filter according to the first embodiment. Here, the first resonance circuit 6 is selected to have L1=5.2 nH and C1=54 pF so that the first resonance circuit 6 resonates in parallel at the frequency Fr=300 MHz in the unnecessary wave band, and the second resonance circuit 9 resonates in series at 300 MHz. In this case, L2=170 nH and C2=1.65 pF are selected, and further, R1=47Ω and R2=3.2 Ω are selected so that the attenuation amount is 30 dB.

As shown in FIG. 3, in the band elimination filter of this embodiment, the attenuation amount in the desired wave band F0=100 MHz, which is sufficiently lower than Fr, is approximately 0 dB, and the attenuation amount in the unnecessary wave band 300 MHz is the same as that of the T-type attenuator 3. An attenuation amount of about 30 dB is obtained, and a good reflection characteristic (return loss characteristic) of about 25 dB or more is obtained over a wide band of frequencies 0 to 600 MHz.
Further, even if the desired wave band is sufficiently higher than Fr, for example, F0=500 MHz is selected, the amount of attenuation is almost 0 dB.

***Other design examples***
FIG. 4 shows another design example of the band elimination filter according to the first embodiment.
Here, another band stop filter having Fr=400 MHz is cascade-connected to the band stop filter shown in FIG. The band-stop filters connected in cascade are selected to L1=3.2 nH and C1=41 pF so as to resonate in parallel at the frequency Fr=400 MHz of the unnecessary wave band, and the second resonance circuit 9 resonates in series at 400 MHz. , L2=128 nH, C2=1.24 pF, and R1=47Ω and R2=3.2Ω so that the attenuation amount is 30 dB.
As shown in FIG. 4, in the band elimination filter of this embodiment, the attenuation amount in the desired wave band F0=100 MHz, which is sufficiently lower than Fr, is approximately 0 dB, and the attenuation amounts in the unnecessary wave bands 300 MHz and 400 MHz are 30 dB respectively. In addition, a good reflection characteristic of about 24 dB or more can be obtained over a wide frequency band of 0 to 600 MHz.
As described above, even when a plurality of band stop filters are cascade-connected, the reflection characteristics of the individual band stop filters are good, so that the attenuation characteristics of the individual band stop filters are maintained and the desired wave band is maintained. It is possible to suppress a plurality of unnecessary waves at the same time without affecting.

*** Other examples ***
FIG. 5 is a diagram showing the configuration of another example of the band elimination filter according to the first embodiment.
The same or corresponding parts are designated by the same reference numerals.
In this band elimination filter, a first resonance circuit 6 is connected in parallel to each first resistor 1. Even with such a configuration, the equivalent circuit in the desired wave band and the unnecessary wave band is the same as that in FIG. Therefore, even with this band elimination filter, low loss can be achieved in the desired wave band, a large amount of attenuation can be obtained in the unnecessary wave band, and good reflection characteristics can be obtained over a wide band.

***Features of Embodiment 1***
The band elimination filter of this embodiment is loaded with two first resistors connected in series between the input terminal and the output terminal, and each of the first resistors or the two first resistors connected in series is loaded. The first resonance circuit is connected in parallel. Further, one end of the second resistor is connected to the connecting portion of the two first resistors, and the other end of the second resistor is grounded by the second resonance circuit. The first resonant circuit is a parallel circuit of a first inductor and a first capacitor, the second resonant circuit is a series circuit of a second inductor and a second capacitor, and the first resonant circuit is Parallel resonance occurs in the unnecessary wave band, and the second resonance circuit resonates in series in the unnecessary wave band.

***Effects of Embodiment 1***
According to the band elimination filter of this embodiment, when the desired wave band is sufficiently separated from the unnecessary wave band, the first resonant circuit has a low impedance close to a short circuit in the desired wave band, and the second resonant circuit has Since the impedance is close to open, the input terminal and the output terminal can be approximately regarded as through.
On the other hand, in the unnecessary wave band, the first resonance circuit has a high impedance and the second resonance circuit has a low impedance. Therefore, the T-type attenuator including the first resistance and the second resistance serves as an input terminal. It can be regarded as loaded between the output terminals.
Therefore, it is possible to obtain a good reflection characteristic over a wide band from the desired wave band to the unnecessary wave band while maintaining a low loss in the desired wave band and a large attenuation characteristic determined by the T-type attenuator in the unnecessary wave band. ..
When such a band elimination filter is applied to an RF device, it is possible to remarkably suppress a large multiple reflection that occurs between the band elimination filter in the unnecessary wave band and the module, resulting in unstable operation of the module and attenuation of the band elimination filter. It is possible to prevent the quantity from deteriorating.
Therefore, there is an effect that it is possible to prevent the characteristics of the RF device from deteriorating due to the entry of a high-level unwanted wave in the unwanted wave band outside the band, or to prevent the unwanted wave generated in the RF device from leaking outside the RF device.

Embodiment 2.
In the second embodiment, points different from the above-described embodiments will be described.
FIG. 6 is a diagram showing the configuration of the band elimination filter according to the second embodiment.
The same or corresponding parts are designated by the same reference numerals.
This band elimination filter has a parallel circuit 20 of a first resistor 1 and a first resonant circuit 6 loaded between an input terminal 10 and an output terminal 11, and a second resistor at both ends of the first resonant circuit 6. One end of each of the second resistors 2 is connected, and the other ends of each of the second resistors 2 are collectively grounded by one second resonance circuit 9. The second resistor 2 and the second resonance circuit 9 form a series circuit 30.
The band stop filter of this embodiment uses a π-type attenuator 12 instead of the T-type attenuator 3 shown in FIG. 1, and the first resonance circuit 6 and the second resonance circuit 9 are shown in FIG. It is the same as that of the first embodiment shown in FIG.

FIG. 7 is a simple equivalent circuit of the band elimination filter according to the second embodiment.
Similar to the first embodiment, when the parallel resonance frequency of the first resonance circuit 6 is selected as the frequency Fr of the unnecessary wave band, the parallel circuit 20 of the first resistor 1 and the first resonance circuit 6 is Fr. It can be regarded as only the first resistor 1. When the series resonance frequency of the second resonance circuit 9 is selected as the frequency Fr of the unnecessary wave band, the series circuit 30 of the second resistor 2 and the second resonance circuit 9 is only the second resistor 2 in Fr. Can be considered. Therefore, it can be considered that the π-type attenuator 12 is loaded between the input terminal 10 and the output terminal 11.
On the other hand, since the first resonance circuit 6 has a low impedance at the frequency F0 of the desired wave band sufficiently distant from Fr, the first resistor 1 is short-circuited. Moreover, since the second resonance circuit 9 has a high impedance, the other end of the second resistor 2 is open. Therefore, in F0, the area between the input terminal 10 and the output terminal 11 can be regarded as a through.

Here, the relationship between R1 and R2 forming the π-type attenuator and the attenuation amount K can be obtained by Expression 3.

[Formula 3]
R1=2*Z0*Z0*R2/((R2*R2)-(Z0*Z0))
R2=Z0*(K+1)/(K-1)

Also in this equation, Z0 is a power source impedance or a load impedance, which is usually 50Ω, as in the equation 1. By selecting R1 and R2 in this way, it is possible to obtain a π-type attenuator having an attenuation amount K over a wide band regardless of the frequency and having a good reflection characteristic.

FIG. 8 is a design example of the bandpass filter according to the second embodiment. Here, as in the first embodiment, L1=5.2 nH, C1=54 pF, L2=170 nH, C2=1 so that the resonance frequencies of the first resonance circuit 6 and the second resonance circuit 9 are 300 MHz, respectively. .65 pF, and R1=782Ω and R2=53.3Ω so that the attenuation amount is 30 dB.
As shown in the figure, in the band elimination filter of this embodiment, the attenuation amount in the desired wave band F0=100 MHz, which is sufficiently lower than Fr, is almost 0 dB, and the attenuation amount in the unnecessary wave band 300 MHz is the same as that of the π-type attenuator 12. An attenuation amount of about 30 dB is obtained, and a good reflection characteristic (return loss characteristic) of about 25 dB or more is obtained over a wide band of frequencies 0 to 600 MHz. These characteristics are the same as those of the first embodiment shown in FIG.

Comparing the π-type attenuator 12 used in the band elimination filter of this embodiment with the T-type attenuator 3 of the first embodiment, in order to obtain the same amount of attenuation of 30 dB, the first resistor 1 has a resistance of 47Ω→782Ω, The second resistance 2 is 3.2Ω→53.3Ω, and it can be realized with a high resistance of 10 times or more using the π-type attenuator 12 rather than using the T-type attenuator 3.
Therefore, there is an advantage that the degree of freedom in design is increased by selecting these to configure the band elimination filter.

*** Other examples ***
FIG. 9 is a diagram showing the configuration of another example of the band elimination filter according to the second embodiment.
The same or corresponding parts are designated by the same reference numerals.
This band elimination filter has a second resonance circuit 9 connected in series to the other end of each second resistor 2. Even in the case of such a configuration, the equivalent circuit in the desired wave band and the unnecessary wave band is the same as that in FIG. Therefore, even with this band elimination filter, low loss can be achieved in the desired wave band, a large amount of attenuation can be obtained in the unnecessary wave band, and good reflection characteristics can be obtained over a wide band.

***Features of Embodiment 2***
The band elimination filter of this embodiment has a parallel circuit 20 of a first resistor and a first resonance circuit loaded between an input terminal and an output terminal, and a second circuit is provided at both ends of the first resonance circuit. One end of the resistor is connected and the other end of the second resistor is grounded by the second resonance circuit, respectively, or is grounded collectively by one second resonance circuit. The first resonance circuit is a parallel circuit of the first inductor and the first capacitor, and the second resonance circuit is a series circuit of the second inductor and the second capacitor. The first resonance circuit is unnecessary. The second resonance circuit resonates in parallel in the wave band and resonates in series in the unnecessary wave band.

***Effects of Embodiment 2***
According to the band elimination filter of this embodiment, when the desired wave band is sufficiently separated from the unnecessary wave band, the first resonance circuit has a low impedance close to a short circuit in the desired wave band, and the second resonance circuit High impedance close to open. Therefore, in the desired wave band, the input terminal and the output terminal can be approximately regarded as through.
On the other hand, in the unnecessary wave band, the first resonance circuit has a high impedance and the second resonance circuit has a low impedance. Therefore, the π-type attenuator including the first resistance and the second resistance outputs the input terminal and the output terminal. It can be regarded as loaded between the terminals.
Therefore, it is possible to obtain a good reflection characteristic over a wide band from the desired wave band to the unnecessary wave band while maintaining a low loss in the desired wave and a large attenuation property determined by the π-type attenuator in the unnecessary wave band.
When such a band elimination filter is applied to an RF device, it is possible to remarkably suppress large multiple reflections that occur in an unwanted wave, resulting in unstable operation of the module in the unwanted wave band and deterioration of the attenuation of the band elimination filter. Can be prevented.
Further, the values of the first resistance and the second resistance for obtaining the same amount of attenuation in the unwanted wave band are about 10 times as large as the values of the first resistance and the second resistance constituting the T-type attenuator, By selecting these and configuring the band elimination filter, there is also an effect that the degree of freedom in design is increased.

Embodiment 3.
In the third embodiment, points different from the above-described embodiments will be described.

The first and second embodiments are effective when the desired wave band and the unnecessary wave band in which the influence of the first resonance circuit 6 and the second resonance circuit 9 can be ignored are sufficiently separated. However, in an actual RF device, the desired wave band and the unnecessary wave band may be close to each other. In such a case, the influence of the first resonant circuit 6 and the second resonant circuit 9 cannot be ignored, and the loss in the desired wave band increases.
Below, a band elimination filter that suppresses an increase in loss in the desired wave band and obtains excellent characteristics even when the desired wave band and the unnecessary wave band are close to each other will be described.

FIG. 10 is a diagram showing a configuration of an example of the band elimination filter according to the third embodiment.
The same or corresponding parts are designated by the same reference numerals.
This band stop filter has one first resonance circuit 6 connected in parallel across both ends of two first resistors 1 connected in series, and a second resistor 2 is connected to the connection portion of these first resistors 1. Is connected to one end of the second resistor 2 and the other ends of the two second resistors 2 are collectively terminated with one second resonance circuit 9.
The first resonance circuit 6 is composed of a parallel circuit of the first inductor 4 and the first capacitor 5 and a third capacitor 13 connected in series, and the second resonance circuit 9 is a second inductor. The third inductor 14 is connected in parallel to the series circuit of the second capacitor 8 and the second capacitor 8.
Here, the third capacitor 13 and the third inductor 14 are selected as C3 and L3, respectively.

Here, the angular frequency of the desired waveband is ω0 (=2πF0), the angular frequency of the unwanted waveband is ωr (=2πFr), ω0<ωr, and the first resonance circuit 6 is ω0 in series resonance, ωr The parallel resonance, the second resonance circuit 9 has parallel resonance at ω0, and the relationship between C3 and L1 for series resonance at ωr and the relationship between L3 and C2 can be obtained by Expression 4.

[Formula 4]
C3={1-(ω0/ωr)*(ω0/ωr)}/((ω0*ω0)*L1)
L3={1-(ω0/ωr)*(ω0/ωr)}/((ω0*ω0)*C2)

The relationship between ωr and C1 and L1 and the relationship between ωr and C2 and L2 are shown in Equation 2.

FIG. 11 is a simple equivalent circuit of the band elimination filter according to the third embodiment. Similar to the first embodiment, when the resonance frequency of the first resonance circuit 6 is selected to be F0 for series resonance and Fr for parallel resonance, the first resistor 1 is short-circuited with F0 and the first resistor 1 is connected with Fr. It can be considered that the second resistor 2 is loaded, and the other end of the second resistor 2 is open at F0, and the second resistor 2 is loaded at Fr.
Therefore, it can be considered that the input terminal F0 is loaded with the through between the input terminal 10 and the output terminal 11, and the Fr is loaded with the T-type attenuator 3.

FIG. 12 is a design example of the characteristics of the bandpass filter according to the third embodiment.
FIG. 13 is a calculation example of the band elimination filter according to the third embodiment.
Here, the circuit constants of the first resonance circuit 6 are set to L1=5.2 nH, C1=54 pF, C3=67.7 pF and the second resonance circuit 9 so that F0=200 MHz and Fr=300 MHz. The circuit constants are L2=170 nH, C2=1.65 pF, L3=213 nH, and R1=47Ω and R2=3.2 Ω so that the attenuation amount is 30 dB.
As shown in FIG. 12, the band elimination filter of this embodiment has an attenuation of about 0 dB at 200 MHz in the desired wave band, and an attenuation of about 30 dB at 300 MHz in the unwanted wave band, which is the same as the attenuation of the T-type attenuator. In addition, good reflection characteristics (return loss characteristics) of about 25 dB or more can be obtained over a wide frequency band of 0 to 600 MHz.

In this way, the desired wave band is close to the unwanted wave band, and even if the desired wave band is lower than the unwanted wave band, the desired wave is passed through without being attenuated, and the unwanted wave is significantly suppressed, A band elimination filter having good reflection characteristics over a wide band can be realized. For this reason, there is an effect that it is possible to prevent characteristic deterioration of the RF device due to entry of a high-level unwanted wave outside the band and leakage of the unwanted wave generated in the RF device to the outside of the RF device.

*** Other examples ***
FIG. 14 is a diagram showing the configuration of another example of the band elimination filter according to the third embodiment.
The same or corresponding parts are designated by the same reference numerals.
This band elimination filter is a case where a π-type attenuator 12 is used instead of the T-type attenuator 3 shown in FIG. Even when the π-type attenuator 12 is used in this way, the same characteristics as those of FIG. 10 can be obtained as described in the second embodiment.

***Features of Embodiment 3***
In the band elimination filter of this embodiment, the first resonance circuit is composed of a parallel circuit of a first inductor and a first capacitor, and a third capacitor connected in series to this parallel circuit. The second resonance circuit is composed of a series circuit of the second inductor and the second capacitor, and a third inductor connected in parallel to the series circuit.
The first resonance circuit performs series resonance in the desired wave band, parallel resonance in the unnecessary wave band, and the second resonance circuit performs parallel resonance in the desired wave band and series resonance in the unnecessary wave band.

***Effects of Embodiment 3***
According to the band elimination filter of this embodiment, when the desired wave band is close to the unnecessary wave band and the desired wave band is lower than the unnecessary wave band, the first resonance circuit has a low impedance close to a short circuit in the desired wave. , In the unnecessary wave band, the impedance becomes high, which is close to open. On the contrary, the second resonant circuit has a high impedance close to an open circuit in the desired wave band and a low impedance close to a short circuit in the unnecessary wave band.
Therefore, in the desired wave band, the input terminal and the output terminal can be approximately regarded as through. On the other hand, in the unnecessary wave band, it can be considered that the T-type attenuator or the π-type attenuator including the first resistance and the second resistance is loaded between the input terminal and the output terminal.
Therefore, while maintaining a large loss characteristic in the desired wave and a large attenuation characteristic determined by the T-type attenuator or the π-type attenuator in the unnecessary wave band, a good reflection characteristic is obtained over a wide band from the desired wave band to the unnecessary wave band. Obtainable.
When such a band elimination filter is applied to an RF device, it is possible to remarkably suppress large multiple reflections that occur in an unwanted wave, resulting in unstable operation of the module in the unwanted wave band and deterioration of the attenuation of the band elimination filter. Can be prevented.

Fourth Embodiment
In the fourth embodiment, points different from the above-described embodiments will be described.
FIG. 15 is a diagram showing a configuration of an example of the band elimination filter according to the fourth embodiment.
The same or corresponding parts are designated by the same reference numerals.
This band stop filter has one first resonance circuit 6 connected in parallel across both ends of two first resistors 1 connected in series, and a second resistor 2 is connected to the connection portion of these first resistors 1. Is connected to one end of the second resistor 2 and the other end of the second resistor 2 is grounded by the second resonance circuit 9.
The first resonance circuit 6 is composed of a parallel circuit of the first inductor 4 and the first capacitor 5, and a fourth inductor 15 connected in series to the parallel circuit, and the second resonance circuit 9 is also provided. Is composed of a series circuit of the second inductor 7 and the second capacitor 8 and a fourth capacitor 16 connected in parallel to the series circuit.
Here, the fourth inductor 15 and the fourth capacitor 16 are selected as L4 and C4, respectively.

Here, the angular frequency of the desired waveband is ω0 (=2πF0), the angular frequency of the unnecessary waveband is ωr (=2πFr), ω0>ωr, and the first resonance circuit 6 is ω0 in series resonance, ωr The parallel resonance, the second resonance circuit 9 has the parallel resonance at ω0, the series resonance at ωr, the relationship between L4 and L1 and the relationship between C4 and C2 can be obtained by Expression 5.

[Formula 5]
L4=L1/{(ω0/ωr)*(ω0/ωr)-1}
C4=C2/{(ω0/ωr)*(ω0/ωr)-1}

Similarly, the relationship between ωr and C1 and L1 and the relationship between ωr and C2 and L2 are shown in Equation 2.

FIG. 16 is a simple equivalent circuit of the band elimination filter according to the fourth embodiment. As in the third embodiment, when the resonance frequency of the first resonance circuit 6 is selected to be F0 for series resonance and Fr for parallel resonance, the first resistor 1 is short-circuited with F0 and the first resistor 1 is connected with Fr. Can be considered loaded. It can be considered that the other end of the second resistor 2 is open at F0 and the second resistor 2 is loaded at Fr.
Therefore, it can be considered that the input terminal F0 is loaded with the through between the input terminal 10 and the output terminal 11, and the Fr is loaded with the T-type attenuator 3. That is, it becomes equal to that of FIG.

FIG. 17 is a design example of the characteristics of the bandpass filter according to the fourth embodiment.
FIG. 18 is a calculation example of the band elimination filter according to the fourth embodiment.
Here, the circuit constants of the first resonance circuit 6 are set to L1=5.2 nH, C1=54 pF, L4=6.7 nH so that F0=400 MHz and Fr=300 MHz, and the second resonance circuit 9 has the same circuit constant. The circuit constants are selected to L2=170 nH, C2=1.65 pF, C4=2.1 pF, and R1=47Ω and R2=3.2Ω so that the attenuation amount is 30 dB.
As shown in FIG. 17, in the band elimination filter of this embodiment, the attenuation amount at 400 MHz in the desired wave band is about 0 dB, and the attenuation amount at 300 MHz in the unnecessary wave band is about 30 dB, which is the same as the attenuation amount of the T-type attenuator. In addition, good reflection characteristics (return loss characteristics) of about 25 dB or more can be obtained over a wide frequency band of 0 to 600 MHz.

In this way, the desired wave band is close to the unwanted wave band, and even if the desired wave band is higher than the unwanted wave band, the desired wave is passed through without being attenuated, and the unwanted wave is significantly suppressed, A band elimination filter having good reflection characteristics over a wide band can be realized. Therefore, there is an effect that it is possible to prevent characteristic deterioration of the RF device due to entry of a high level unnecessary wave out of the band and leakage of the unnecessary wave generated in the RF device to the outside of the RF device.

*** Other examples ***
FIG. 19 is a diagram showing the configuration of another example of the band elimination filter according to the fourth embodiment. The same or corresponding parts are designated by the same reference numerals.
This band elimination filter is a case where a π-type attenuator 12 is used instead of the T-type attenuator 3 shown in FIG. Even when the π-type attenuator 12 is used in this way, the same characteristics as those of FIG. 17 are obtained.

***Features of Embodiment 4***
In the band elimination filter according to the present embodiment, the first resonance circuit is configured by a parallel circuit including a first inductor and a first capacitor, and a fourth inductor connected in series to the parallel circuit, and a second resonance circuit is formed. The resonance circuit is composed of a series circuit of a second inductor and a second capacitor, and a fourth capacitor connected in parallel.
The first resonance circuit performs series resonance in the desired wave band, parallel resonance in the unnecessary wave band, and the second resonance circuit performs parallel resonance in the desired wave band and series resonance in the unnecessary wave band.

***Effects of Embodiment 4***
According to the band elimination filter of this embodiment, when the desired wave band is close to the unnecessary wave band and the desired wave band is higher than the unnecessary wave band, the first resonance circuit has a low impedance close to a short circuit in the desired wave. , In the unnecessary wave band, the impedance becomes high, which is close to open. On the contrary, the second resonant circuit has a high impedance close to an open circuit in the desired wave band and a low impedance close to a short circuit in the unnecessary wave band.
Therefore, in the desired wave band, the input terminal and the output terminal can be approximately regarded as through. On the other hand, in the unnecessary wave band, it can be considered that the T-type attenuator or the π-type attenuator including the first resistance and the second resistance is loaded between the input terminal and the output terminal.
Therefore, while maintaining a large loss characteristic in the desired wave and a large attenuation characteristic determined by the T-type attenuator or the π-type attenuator in the unnecessary wave band, a good reflection characteristic is obtained over a wide band from the desired wave band to the unnecessary wave band Obtainable.
When such a band elimination filter is applied to an RF device, it is possible to remarkably suppress large multiple reflections that occur in an unwanted wave, resulting in unstable operation of the module in the unwanted wave band and deterioration of the attenuation of the band elimination filter. Can be prevented.

***Other Embodiments***
All or part of the above-described embodiments may be combined with other embodiments.
The bandpass filter according to the above-described embodiments may be applied to radar equipment, communication equipment, observation equipment, and the like, and may also be applied to microwave equipment such as telemetry transmitters and beacon transmitters.

1 1st resistance, 2 2nd resistance, 3 T type attenuator, 4 1st inductor, 5 1st capacitor, 6 1st resonance circuit, 7 2nd inductor, 8 2nd capacitor, 9 Second resonance circuit, 10 input terminal, 11 output terminal, 12 π-type attenuator, 13 third capacitor, 14 third inductor, 15 fourth inductor, 16 fourth capacitor, 20 parallel circuit, 30 series circuit.

Claims (8)

A parallel circuit of two first resistors and a first resonant circuit connected in series between the input terminal and the output terminal;
A series circuit of a second resistor whose one end is connected to the connecting portion of the two first resistors and a second resonance circuit whose one end is connected to the other end of the second resistor and whose other end is grounded; A band stop filter having
At frequencies in the unwanted band,
The parallel circuit can be regarded as only the first resistor,
The above series circuit can be regarded as only the second resistor,
At the frequency of the desired wave band,
The first resistor is short-circuited by the first resonant circuit,
A band elimination filter in which the other end of the second resistor is opened by the second resonance circuit. The band elimination filter according to claim 1, wherein at the frequency of the unwanted wave band, a T-type attenuator composed of the first resistor and the second resistor can be regarded as being connected between the input terminal and the output terminal. .. The first resonance circuit is one first resonance circuit connected in parallel with the two first resistors, or two first resonance circuits connected in parallel with the two first resistors, respectively. The band stop filter according to claim 1 or 2, further comprising: A parallel circuit of a first resistor and a first resonant circuit connected between the input terminal and the output terminal,
A series circuit including two second resistors having one ends connected to both ends of the parallel circuit and a second resonance circuit having one end connected to the other end of the second resistor and the other end grounded A band stop filter,
At frequencies in the unwanted band,
The parallel circuit can be regarded as only the first resistor,
The above series circuit can be regarded as only the second resistor,
At the frequency of the desired wave band,
The first resistor is short-circuited by the first resonant circuit,
A band elimination filter in which the other end of the second resistor is opened by the second resonance circuit. The band elimination filter according to claim 4, wherein at the frequency of the unwanted wave band, it is possible to consider that the π-type attenuator composed of the first resistance and the second resistance is connected between the input terminal and the output terminal. .. The second resonance circuit may be one second resonance circuit that grounds the other ends of the two second resistors, or two second resonance circuits that ground the other ends of the two second resistors, respectively. The band elimination filter according to claim 4 or 5 having a resonance circuit. The first resonant circuit includes a parallel circuit of an inductor and a capacitor, and a capacitor serially connected to the parallel circuit of the inductor and the capacitor.
7. The band elimination filter according to claim 1, wherein the second resonance circuit includes a series circuit of an inductor and a capacitor, and an inductor connected in parallel to the series circuit of the inductor and the capacitor. .. The first resonance circuit has a parallel circuit of an inductor and a capacitor, and an inductor serially connected to the parallel circuit of the inductor and the capacitor,
7. The band elimination filter according to claim 1, wherein the second resonance circuit includes a series circuit of an inductor and a capacitor, and a capacitor connected in parallel to the series circuit of the inductor and the capacitor. ..

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