JP3434982B2 - Band stop 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 mobile communication device, such as an R
The present invention relates to a band elimination filter used in an F stage or the like, and particularly to a band elimination filter having an asymmetric frequency characteristic effective when a transmission frequency and a reception frequency are close to each other.

[0002]

2. Description of the Related Art In an RF stage of a transmitting circuit and a receiving circuit of a mobile communication device such as an analog or digital mobile phone or a wireless telephone, a transmitting frequency is used when the same antenna is shared by the transmitting circuit and the receiving circuit. To separate the band from the reception frequency band, or to attenuate the harmonics generated due to the nonlinearity of the amplifier circuit, to remove unwanted signal waves such as interfering waves and side waves other than the desired signal wave. A band elimination filter (band elimination filter: BEF) or a band pass filter (band pass filter: BPF) is used for the above.

These band stop filters and band pass filters are generally realized and configured as filter circuits having desired band characteristics by connecting a plurality of series resonant circuits or parallel resonant circuits composed of various circuit elements. . As such a resonance circuit, a parallel resonance circuit is easier to realize than a series resonance circuit, and a connection of these circuits is easier to realize in parallel than a series connection. Further, the configuration in which the parallel resonant circuits are connected in cascade is suitable for realizing the band pass filter, but not suitable for realizing the band stop filter.

Therefore, in order to realize a band elimination filter, conventionally, a parallel resonance circuit is additionally connected with a reactance or susceptance to add a series resonance effect, and these are cascade-connected.

In general, as a method of producing a band elimination filter whose frequency characteristic is symmetrical with respect to the center frequency, first, a target standardized high-pass frequency characteristic is given and expressed by a polynomial of s = jω having the characteristic. The circuit function is determined, the standardized high-pass filter is synthesized from the polynomial, the frequency is converted to a band elimination filter having the desired frequency characteristics, and the equivalent circuit conversion is performed to obtain the actual circuit element. The band stop filter circuit according to the present invention has been implemented. With the band-stop filter configured in this way, it is possible to specify the characteristics of the target band-pass filter at the standardization high-pass filter stage with a simple structure, and to use a standard that has been thoroughly researched and designed. Attenuation characteristics of high-pass filter (Butterworth characteristics,
The advantage is that the Chebyshev characteristic, simultaneous Chebyshev characteristic, Thomson characteristic, etc.) can be used as they are for the band elimination filter.

[0006]

However, in the case of the band elimination filter in which the parallel resonance circuits to which the series resonance effect is added are connected in series, the band stop filter is designed by an unreasonable design including unnecessary characteristics, and therefore, it is a matter of know-how. The number of elements is increased by inserting parallel capacitance to obtain the target characteristic or the filter constant is empirically found, and it cannot be said that the circuit configuration is suitable for the target asymmetrical frequency band rejection characteristic. There was a problem.

Further, depending on the circuit configuration similar to that of the band elimination filter whose frequency characteristic is symmetrical with respect to the center frequency, a band elimination filter having an asymmetric frequency characteristic, that is, attenuation of a zero point or a pole with respect to the center frequency of the band is obtained. There is a problem in that a band elimination filter having an asymmetrical order or the like cannot be constructed because the standardized high-pass filter cannot be expressed by an ordinary circuit network function.

As for the band stop filter having the asymmetric frequency characteristic, there are many manufacturing methods based on the empirical design method or the manufacturing method based on the know-how, and the rational manufacturing method as described above for the band stop filter having the symmetrical frequency characteristic. It is practiced to construct a circuit that obtains a target characteristic at a level similar to that of the above. However, in this case, it is not possible to make a suitable circuit with a simple configuration because it depends largely on a large amount of knowledge and a large amount of know-how based on empirical rules. Therefore, there was a problem that the production prospect was not good.

The present invention has been completed as a result of intensive research conducted by the present inventor in view of the above circumstances, and its purpose is to:
It is an object of the present invention to provide a band elimination filter having an asymmetric frequency characteristic, which is suitable for realizing a target band elimination characteristic with a simple circuit configuration and has a good prospect of production.

[0010]

A band elimination filter according to a first aspect of the present invention comprises a plurality of rectilinear resonance units using TEM transmission lines and a plurality of reactance elements connected in series to the parallel resonance units. A value of the series reactance element connected in series to the parallel resonance part of each series-parallel resonance circuit, which has a frequency band rejection characteristic asymmetric with respect to the center frequency, in which parallel resonance circuits are connected in series via a series reactance element. Is the value of one series reactance element for the cascade connection adjacent to the series-parallel resonance circuit or the sum of the parallel connections of two series reactance elements of the same sign,
Alternatively, the value is a sum of parallel connections of two series reactance elements having different signs, or a value deviated by a predetermined value determined by contributing to asymmetry with respect to the center frequency, and a sign Is the opposite.

A band stop filter according to claim 2 of the present invention is the band stop filter according to claim 1, wherein
It is characterized in that the TEM transmission line is composed of a quarter-wave type TEM transmission line and has a stop band at a third frequency of the center frequency.

Further, a band elimination filter according to a third aspect of the present invention is the band elimination filter according to the first aspect, wherein the TEM transmission line is a half-wave type TEM transmission line and the center frequency is 2 It is characterized by having a stop band at the following frequencies.

According to the band elimination filter of the present invention, the circuit has a parallel resonance section using a TEM (Transverse Electro-Magnetic) transmission line and a parallel resonance section for realizing an asymmetric frequency band rejection characteristic. A plurality of series-parallel resonant circuits consisting of reactance elements connected in series,
The values of the series reactance elements connected in series to the parallel resonance part of each series-parallel resonance circuit are ones for the series connection adjacent to the series-parallel resonance circuit. Either the value of the series reactance element or the value of the sum of parallel connections of two series reactance elements of the same sign, or the value of the sum of the parallel connection of two series reactance elements of different signs, or with respect to the center frequency Since the values are shifted by a predetermined value that is determined by contributing to the asymmetry, and the signs are opposite, it is possible to realize the target asymmetric frequency band rejection characteristics with a simple circuit configuration. A band stop filter having an asymmetrical frequency characteristic that can be manufactured and has a good manufacturing prospect.

According to the band stop filter of the present invention, since the frequency band stop characteristic which is asymmetrical with respect to the center frequency can be realized, the pass band can be provided in the frequency band immediately above or below the stop band, and the transmission frequency can be set. When the two spectrums of the band and the reception frequency band are adjacent to each other with a small interval, there is an advantage that they can be effectively separated.

According to the band elimination filter of the second aspect of the present invention, the impedance seen from the other side of the TEM transmission line having a short circuit on one side having a length l is Z.
= JZ ₀ × tan (2πlf / v), which is a periodic function of f, so that when the lowest parallel resonance frequency is the resonance frequency, it has a stop band at a frequency of the third order of the center frequency, that is, three times as large. Then, even for frequencies above the third order, odd multiples of the center frequency, that is, fifth order, seventh order,
A stop band is also included in the ninth-order frequencies.

On the other hand, according to the band elimination filter of the third aspect of the present invention, the impedance seen from the other side of the TEM transmission line of one length open (open) having a length l is Z.
= −jZ ₀ × cot (2πlf / v), which is a periodic function of f, so that when the lowest parallel resonance frequency is the resonance frequency, there is a stop band at a frequency that is quadratic of the center frequency, that is, twice the frequency. In addition, even for frequencies above the second order, an even multiple of the center frequency, that is, fourth order, 6
The next, eighth, ... Frequency also has a stop band. Further, by combining with a series-parallel resonant circuit using a λ / 4 type TEM transmission line, a stop band is provided even at integral multiples of the center frequency, that is, third, fourth, fifth ...

Further, in the band elimination filter of the present invention, each of the plurality of series-parallel resonance circuits is connected to the parallel resonance part using the TEM transmission line and the parallel resonance part to realize the asymmetric frequency band rejection characteristic. A reactance element connected in series, that is, a capacitance or an inductance, which is a circuit configuration in which two or more series-parallel resonant circuits are cascade-connected through a series reactance element, that is, an inductance or a capacitance, without a parallel susceptance. There is. Then, the value of the reactance element connected in series to the parallel resonance part using the TEM transmission line of each series-parallel resonance circuit is the value of one series reactance element adjacent to the series-parallel resonance circuit for cascade connection or It is the sum of the parallel connection of two series reactance elements of the same sign, or the sum of the parallel connection of two series reactance elements of different signs, or a frequency band rejection characteristic asymmetric with respect to the center frequency. Is a value deviated by a predetermined value determined by contributing to
And the sign is reversed. With such a circuit configuration, the band stop filter has the advantages that the number of circuit elements is reduced and the adjustment is minimized.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, when designing and implementing a band elimination filter, an actual circuit configuration and circuit elements are configured in consideration of a certain reference potential (ground potential). And, when one of the pair of terminals of a certain circuit element is grounded to ground, the configuration in which both terminals do not have the same potential with respect to ground is called unbalanced, and both terminals are sufficiently separated from ground. When both terminals have the same electric potential with respect to the ground as in the case of being balanced, the unbalanced configuration is generally stable and the balanced configuration is critical.

With respect to the resonance circuit as a parallel resonance section which is a basic circuit in the band characteristic filter, it is the most stable in the case of the LC resonance circuit when both terminals of L and C are grounded. Corresponds to an unbalanced configuration in which one terminal is grounded with a common potential and parallel resonant circuits are connected in parallel. In an LC resonant circuit having a configuration other than this, only one terminal or no terminal is grounded out of a total of four terminals of L and C, and such a balanced configuration is practically difficult to use.

In addition, the resonator as the parallel resonance section has a TEM.
The conditions are the same when a transmission line is used. Basically, λ / 4 (quarter wavelength) type and λ / 2 (half wavelength) type are used.
It is difficult to use except the unbalanced configuration in which one terminal of the TEM type transmission line is grounded. Further, a configuration in which the end surface of the TEM transmission line is short-circuited rather than open is more stable in characteristics and easier to use.

From the above, in general, a structure in which LC parallel resonators are connected in cascade or a λ / 4 type TE with shorted end faces is used.
The configuration in which the M transmission line resonators are connected in cascade is suitable for a bandpass filter, but is not suitable for a bandstop filter. Therefore, the bandpass filter is LC
Parallel resonator or λ / 4 type TEM with shorted end faces
This can be realized relatively easily based on the configuration in which the parallel connection of the transmission line resonators is connected in series.

On the other hand, since the band elimination filter is difficult to realize as it is, a series resonance effect is added by adding reactance elements such as capacitance and inductance in series to the parallel resonance section of the parallel connection as the parallel resonance section to add the series resonance effect. It is realized on the basis of the configuration in which the above are connected in cascade. However, such a series-parallel resonance circuit includes unnecessary parallel resonance in addition to series resonance, and it cannot be manufactured in a theoretically clean form, and it depends on experience and know-how due to a large manufacturing method. . Further, when the frequency band rejection characteristic is asymmetrical with respect to the center frequency, it is difficult for the conventional circuit configuration to have a good visibility and be easily realized by an actual circuit element.

With respect to the band elimination filter of the present invention, the circuit configuration of the band elimination filter having a desired asymmetric frequency band elimination characteristic may be realized by, for example, the manufacturing procedure described below.

The first example of the embodiment of the band elimination filter of the present invention will be described in detail below in accordance with its manufacturing procedure.

First, the center frequency f ₁ (Hz)> transmission zero frequency f ₂ (Hz) is set, and the basic production policy of the target band stop filter is to realize a band stop filter of f ₁ (Hz). Pass f ₂ and block f ₁ , and n
Assuming that the frequency of f ₁ (Hz) has the characteristic of the band elimination filter, the target band elimination characteristic is set as the frequency characteristic shown in FIG. In FIG. 1, the horizontal axis represents frequency f (Hz) and the vertical axis represents transmission amount | H (f) |
Is represented.

Next, a standardized high-pass filter having an asymmetrical standardized high-pass characteristic including an even function or an even function and an odd function in the real part and an odd function or an odd function and an even function in the imaginary part is provided. Find the network function. By using such a network function as a standardized high-pass filter having an asymmetrical standardized high-pass characteristic at the standardized high-pass stage, frequency conversion and equivalent circuit conversion are performed under the same conditions. A band stop filter having a target asymmetric frequency characteristic can be realized.

In this case, when viewed as a single element, since it is an ideal reactance, it has a combination including an even function in its imaginary part, but the transmission characteristic (transmission amount) of the entire circuit has a form including all the above-mentioned combinations. . In the case of the band elimination filter having the frequency characteristic shown in FIG. 1, the obtained frequency characteristic of the standardized high-pass filter is as shown in FIG.
In FIG. 2, f _p (Hz) represents the transmission zero point frequency.

Next, with respect to the standardized high-pass filter having the frequency characteristics as shown in FIG. 2, -jk is used to obtain an equivalent circuit shown in FIG. 3 by giving an asymmetrical transmission zero point in the pass band in the standardized high band. Introduce. In FIG. 3, a ₁ a ₂
· A ₃ each represents an inductance value or the capacitance value, -jk represents the ideal reactance value.

Next, by performing equivalent circuit conversion for unifying the parallel inductances, a standardized high-pass filter circuit as shown by the equivalent circuit in FIG. 4 is obtained. By performing such equivalent circuit conversion and making the inductance values uniform, the resonant circuits after the frequency conversion can be made into substantially the same resonant circuits (series or parallel), and the circuit is easily realized.

Next, impedance conversion is performed on the equivalent circuit of FIG. 4, and the equivalent circuit including the ideal transformer (transformation ratio n) is converted into an equivalent circuit as shown in FIG. By including the ideal transformer in this way, the inductance values of the respective inductances can be made the same by properly selecting the value of the transformation ratio n, and further, it is possible to make the same resonance circuit after the frequency conversion. Realized easily.

Next, the central j component of the equivalent circuit of FIG. 5 is put together to form an equivalent circuit as shown in FIG.

Next, the inductance of the equivalent circuit of FIG. 6 is converted into capacitance, and the equivalent circuit as shown in FIG. 7 is converted.

Further, regarding the equivalent circuit of FIG. 7, a ₁ = a
_3. Set n so that all capacitance values are equal. Here, the condition that the coefficient j of a series reactance element that cascade-connects a plurality of stages of parallel-parallel resonant circuits is + j, and the coefficient j of the reactance element that is serially connected to the parallel resonant portion of each series-parallel resonant circuit is -j. Is added, an equivalent circuit as shown in FIG. 8 is obtained. Note that in FIG. 8, n = (k
_{+ (A 1 / a 2)} -1/2) is / 2.

Thus, when the equivalent circuit conversion is performed from the standardized high-pass filter having the asymmetrical standardized high-pass characteristic to determine the circuit configuration of the band elimination filter and the value of each circuit element, a plurality of series circuits are originally used. Converting series resonance to parallel resonance by using parallel elements of π-type gyrator for cascade connection of resonance circuits and parallel susceptance that creates asymmetric frequency characteristics, and multiple series-parallel resonance circuits having the same constant have the same reactance. It is possible to configure a band elimination filter circuit having an asymmetrical frequency characteristic, which is cascade-connected via the reactance element having the.

Further, by realizing the series resonance circuit as described above using the parallel resonance circuit, the circuit becomes the most stable in terms of grounding, the number of circuit elements is reduced, and the adjustment is minimized. Have. Furthermore, the degree of freedom in circuit design such as the series reactance for series-to-parallel conversion and the sign of each element of the π-type gyrator can be freely selected, and the degree of freedom in actual circuit elements is also increased. There is also.

Then, frequency conversion is performed on the equivalent circuit of FIG. 8 to realize an asymmetric equivalent band stop filter circuit having a target asymmetric band stop characteristic as shown in FIG. Note that in FIG. 9, l = n ² 2πΔ / {a ₁
(2πf ₁ ) ² }, c = (a ₁ / n ² ) × (1 / 2π
Δ).

Here, the frequency conversion may be performed by the same conversion as that for the standardized high-pass filter in the production of a normal band-elimination filter having a symmetrical frequency characteristic. Can be produced with good visibility as with a band elimination filter having a symmetrical frequency characteristic.

Next, the asymmetric equivalent band stop filter circuit is constructed by performing narrow band approximation in the vicinity of the center frequency f ₁ (Hz) of the target asymmetric frequency characteristic to the asymmetric equivalent band stop filter circuit of FIG. In each of the circuit elements, the ideal reactance or ideal susceptance is equal to the reactance or susceptance at the center frequency f _1, and the inductance or capacitance (+ jn,
-Jn, + jn ² / (-2n-k)), and a plurality of stages of series-parallel resonant circuits having the same constant, which are composed of a parallel resonant section and a capacitance or an inductance connected in series to the parallel resonant section, have the same impedance. Cascaded via the reactance element (-jn) having
A band stop filter having an asymmetric frequency characteristic converted into an actual circuit element is realized. Here, the ideal reactance or ideal susceptance of each circuit element is a constant reactance or susceptance (even function) that does not depend on frequency.
Is the reactance or susceptance (imaginary part) having.

FIG. 10 shows the band elimination filter of the present invention as an example of the circuit configuration of the band elimination filter obtained in this way, as a circuit in which the parallel resonance part of a plurality of stages of series-parallel resonance circuits is constituted by TEM transmission lines. .

In the band elimination filter circuit of FIG.
The parallel resonant parts of the first-stage and third-stage series-parallel resonant circuits are short stub λ / 4 type TEM transmission lines, and the parallel resonant parts of the second-stage series-parallel resonant circuit are open stub λ / 2 type TE.
The example approximated by the M transmission line is shown.

Here, it is desirable to use a λ / 4 type TEM transmission line for the parallel resonance section, because it is basically easier to make a TEM transmission line having a shorter electrical length and the accuracy of the narrow band approximation is good. However, in the λ / 4 type TEM transmission line, an even multiple of the center frequency, that is, double, double, ... (parallel)
Since resonance cannot be obtained, it is advisable to combine a series-parallel resonance circuit having a parallel resonance part using a minimum number of λ / 2 type TEM transmission lines only for the purpose of obtaining the resonance.

It is needless to say that the band elimination filter of the present invention can be configured by a combination other than the above and a configuration by another circuit element.

Further, in FIG. 10, A ₁ = A ₃ = (1/2
π) × si ⁻¹ {−Δn / (2f ₁ a ₁ )}, Z ₀₁ = Z ₀₃
= N × cot (A ₁ π), l ₁ = l ₃ = (A ₁ v) /
(2f ₁ ), A ₂ = (1 / 2π) × si ⁻¹ {−Δ (2n
_{+ K) / (2f 1 a} 1)}, Z 02 = {- (2n-k) /
n ² } × tan (A ₂ π), l ₂ = (A ₂ v) / (2f
₁ ). However, si (x) = {sin (x)} /
x is the propagation velocity. The frequency characteristic of this band elimination filter is almost the same as the target characteristic shown in FIG.

As a result, the ideal reactance or the ideal susceptance among the circuit elements that contribute to the odd function of the real part and the even function of the imaginary part that constitute the asymmetric equivalent band stop filter circuit is measured at the center frequency f ₁ (Hz). By substituting an inductance or capacitance with the same reactance or the same susceptance,
A plurality of series-parallel resonant circuits having the same constant, which are composed of a parallel resonant section using a TEM transmission line and a reactance element (capacitance or inductance) connected in series to the parallel resonant section, are cascade-connected by reactance elements having the same impedance. The circuit configuration of the asymmetric equivalent band stop filter converted into the circuit element can be realized.

Next, a second example of the embodiment of the band elimination filter of the present invention will be described in the same manner as the three-element one-side zero point band elimination filter.

First, the target asymmetric frequency band rejection characteristic is set as shown in the frequency characteristic of FIG.

Next, a standardized high-pass filter having an asymmetrical standardized high-pass characteristic including an even function or an even function and an odd function in the real part and an odd function or an odd function and an even function in the imaginary part is provided. Find the network function. In the case of the band elimination filter having the frequency characteristic shown in FIG. 11, the frequency characteristic of the standardized high pass filter is as shown in FIG.

Next, first, an equivalent circuit conversion for unifying the circuit elements into parallel capacitances or inductances in the standardized high-pass for the standardized high-pass filter of the frequency characteristics as shown in FIG. Obtain the same standardized high-pass filter circuit as shown by the equivalent circuit in 3.

Next, the equivalent circuit shown in FIG. 13 is obtained by converting capacitance into inductance, introducing n by impedance conversion, and introducing a gyrator in the equivalent circuit shown in FIG.

Next, the parallel susceptance -jn of the π-type gyrator is divided into _two by introducing x ₁ or x ₂ . That is, the susceptance j (1 / n) is replaced by j (1 /
x) and j (1 / n-1 / x), the equivalent circuit shown in FIG. 14 is obtained.

Here, the difference from the first example is that in the first example, when the transformation ratio n that makes all the capacitances the same in the standardized high-pass filter is determined, the cascade connection is correspondingly made. In contrast to the ideal reactance that is uniquely determined, the value of the ideal reactance for cascade connection can be arbitrarily selected by introducing the parallel susceptance in the second example.

Further, the inductance is converted into the capacitance to obtain the equivalent circuit of the asymmetric equivalent band stop filter shown in FIG.

Further, in the above relational expression, x ₁ = -n
When y ₁ and x ₂ = −ny ₂ (y ₁ , y ₂ > 1) are set and the condition that the parallel capacitances are the same is added, n is determined as follows. √ (a ₁ / a ₂ ) = (y ₁ / y ₂ ) × |
{(K-2n) × ( -ny 2) -2n 2} / {(- y 1
+1) × n} | = (y ₁ / y ₂ ) × | −ky ₂ + 2n
(Y ₂ −1) | / (y ₁ −1), and n = [ky ₂ /
(Y ₂ −1) + {(y ₁ −1) × y ₂ } / {(y ₂ −
1) × y ₁ } × √ (a ₁ / a ₂ )] / 2. By the way, y
→ If ∞, the conventional band stop filter circuit without a parallel capacitance is provided, and if y = 2, half of the reactance or susceptance is a parallel capacitance.

FIG. 16 shows an equivalent circuit of the asymmetric equivalent band stop filter thus obtained. The circuit shown in FIG. 16 is the same as that shown in FIG. 15, but is expressed in a form easy to see as x = yn and is fixed (limited) to either one of ± n.

In the second example as well, the frequency conversion may be performed in the same manner as that for a standardized high pass filter in the production of a normal band stop filter having a symmetrical frequency characteristic.

Next, narrow band approximation is performed in the vicinity of the center frequency f ₁ (Hz) of the target asymmetric frequency characteristic for the asymmetric equivalent band stop filter circuit of FIG. 15 or 16 to convert it into an actual circuit element. A band elimination filter having asymmetrical frequency characteristics is realized. FIG. 17 shows a circuit configuration example of the band stop filter having the target asymmetric band stop characteristic obtained in this way, and the asymmetric band of the present invention in which a plurality of series-parallel resonant circuits are formed by TEM transmission lines. A circuit configuration example of the blocking filter is shown in FIG.

In these examples, the reactance element connected in series to the parallel resonance part using the TEM transmission line is a capacitance, and the reactance element connecting a plurality of series-parallel resonance circuits in cascade is an inductance. However, this case has an advantage that the number of inductances is smaller than the number of capacitances.

Further, in the band elimination filter circuit of the present invention of FIG. 18, an example is shown in which a short stub λ / 4 type TEM transmission line is used in the parallel resonance part of the series-parallel resonance circuit of each stage. It should be noted that other combinations of configurations and configurations of other circuit elements are possible.

In FIG. 17, the value of each circuit element is as shown in FIG. Further, in FIG. 18, A ₁ = A ₃ = (1
/ 2π) × si ^-1 [Δny ₁ / {2f ₁ (y ₁ -1) a
₁ }], Z ₀₁ = Z ₀₃ = {ny ₁ / (y ₁ -1)} × co
t (A ₁ π), l ₁ = l ₃ = (A ₁ v) / 2f ₁ , A ₂
= (1 / 2π) × si ⁻¹ [(Δ / 2f ₁ ) × y
₁ ² {(2n-k) y ₂ -2n} / {y ₂ (y ₁ -1)
² a ₁ }], Z ₀₂ = [n ² y ₂ / {(2n−k) y ₂ −
2n}] × cot (A ₂ π), l ₂ = (A ₂ v) / 2f
_{Is 1} . However, si (x) = {sin (x)} / x
And v is the propagation velocity. The frequency characteristics of these band elimination filters are the target characteristics shown in FIG.

In the second example as well, similar to the first example, the ideal reactance among the circuit elements that contribute to the odd function of the real part and the even function of the imaginary part that form the asymmetric equivalent band stop filter circuit Alternatively, by replacing the ideal susceptance with an inductance or a capacitance having the same reactance or the same susceptance at the center frequency f ₁ (Hz), the parallel resonance section using the TEM transmission line and the capacitance or the inductance connected in series to the parallel resonance section are used. It is possible to realize the circuit configuration of the asymmetric equivalent band stop filter of the present invention, which is obtained by connecting a plurality of series-parallel resonant circuits having constants in series with the inductance elements having the same reactance and converting them into actual circuit elements.

The above is merely an example of the embodiments of the present invention, and the present invention is not limited to them. Various modifications and improvements may be made without departing from the gist of the present invention. No problem.

[0062]

As described above, according to the band stop filter of the present invention, the circuit has a parallel resonance part using a TEM transmission line and a parallel resonance part for realizing an asymmetric frequency band stop characteristic. A series parallel-resonance circuit consisting of a reactance element (capacitance or inductance) connected in series with a series connection via a reactance element (inductance or capacitance) connected in series. The value of the series reactance element connected in series to the parallel resonance part of the circuit is the value of one series reactance element adjacent to the series-parallel resonance circuit for cascade connection, or the parallel connection of two series reactance elements of the same sign. Or the value of the sum of parallel connections of two series reactance elements of opposite signs, or The value is deviated by a predetermined value that is determined by contributing to the asymmetry with respect to the center frequency, and the sign is opposite. It was possible to provide a band elimination filter having an asymmetric frequency characteristic, which can realize the characteristics and has a good manufacturing prospect.

Further, according to the band stop filter of the present invention, since the frequency band stop characteristic which is asymmetrical with respect to the center frequency can be realized, the pass band can be provided in the frequency band immediately above or below the stop band, and the transmission frequency can be set. It was possible to provide a band elimination filter having advantages such as being able to effectively separate two spectra of a band and a reception frequency band when they are adjacent to each other with a small interval.

Further, in the band elimination filter of the present invention, each of the plurality of series-parallel resonant circuits is connected to the parallel resonant part using the TEM transmission line and the parallel resonant part in order to realize the asymmetrical frequency band rejection characteristic. A reactance element connected in series, that is, a capacitance or an inductance, which is a circuit configuration in which two or more series-parallel resonant circuits are cascade-connected through a series reactance element, that is, an inductance or a capacitance, without a parallel susceptance. Therefore, the value of the reactance element connected in series to the parallel resonance part of each series-parallel resonance circuit is
The value of one series reactance element or the sum of the parallel connection of two series reactance elements of the same sign for the cascade connection adjacent to the series-parallel resonant circuit, or the parallel connection of two series reactance elements of different signs. The sum of the values or the value deviated by a predetermined value determined by contributing to the asymmetry with respect to the center frequency, and the signs are opposite. Therefore, it is possible to provide a band elimination filter having the advantages that the number of circuit elements is reduced and the adjustment is minimal.

Further, according to the band elimination filter of the present invention, the equivalent circuit conversion is performed from the standardized high pass filter having the asymmetrical standardized high pass characteristic to perform the equivalent circuit conversion and the circuit configuration of the band rejection filter and the constant of each circuit element. To determine the TEM transmission line, the parallel elements of the π-type gyrator for connecting multiple parallel resonant circuits in cascade and the parallel susceptance that creates the asymmetrical frequency characteristic are used to convert the series resonance into parallel resonance. A band-stop filter having an asymmetric frequency characteristic of a circuit configuration in which a plurality of series-parallel resonant circuits having the same constant consisting of a parallel resonant section used and a capacitance or an inductance connected in series to it are cascaded by reactance elements having the same reactance, and Become.

Further, according to the band elimination filter of the present invention, a certain series resonance circuit can be realized by using parallel resonance circuits, and the band elimination filter can be realized by connecting them in series. It has the most stable circuit configuration.

Furthermore, as shown in the first example of the embodiment, according to the present invention, since the number of circuit elements is small, the restriction on the element sensitivity is relaxed, and the adjustment can be minimized. Even if the number of circuit elements is increased as shown in the second example, each can be set to a value that is easy to realize, and the degree of freedom in circuit design and the degree of freedom in actual circuit elements can be increased. It is a band stop filter having.

Further, in the first example of the embodiment of the band elimination filter of the present invention, each of the plurality of series-parallel resonant circuits is connected in series to the parallel resonant section using the TEM transmission line and the parallel resonant section. It has a circuit configuration in which two or more series-parallel resonance circuits are connected in series via a series reactance element without parallel susceptance, and is connected in series to the parallel resonance part of each series-parallel resonance circuit. The value of the connected reactance element is the value of one series reactance element for cascade connection adjacent to the series-parallel resonant circuit, or the value of the sum of parallel connection of two series reactance elements of the same sign, or of different sign. It is a value deviated from the sum value of the parallel connection of two series reactance elements by a predetermined value determined by the relationship between the center frequency and the transmission zero frequency, and There characterized by comprising as those are opposite, in such a circuit configuration, the less number of circuit elements, there is an advantage that adjustment minimal.

A λ / 4 type TE is used as a TEM transmission line.
When the M transmission line is used, it has a stop band at the third-order frequency of the center frequency, and is an odd multiple, that is, fifth-order, seventh-order
The band stop filter has a stop band even at the 9th-order frequency, and the electrical length is short, so that it is easy to make and the accuracy of the narrow band approximation is good.

Furthermore, as a TEM transmission line, λ / 2 is used.
When a type TEM transmission line is used, it has a stop band in the second-order frequency of the center frequency, and is an even multiple, that is, fourth-order,
A band-stop filter having a stop band for 6th, 8th, ... frequencies, and a series-parallel resonant circuit using a minimum number of λ / 2-type TEM transmission lines is used for λ / 4-type TEM transmission lines. By using it in combination with the serial-parallel resonant circuit,
The band stop filter has a stop band at frequencies that are integral multiples of the center frequency, that is, second, third, fourth, fifth, ...

[Brief description of drawings]

FIG. 1 is a diagram showing a target band stop characteristic in a first example of an embodiment of the present invention.

FIG. 2 is a diagram showing frequency characteristics of a standardized high pass filter according to a first example of an embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram showing a normalized high pass filter circuit according to a first example of an embodiment of the present invention.

FIG. 4 is an equivalent circuit diagram showing a normalized high pass filter circuit according to a first example of an embodiment of the present invention.

FIG. 5 is an equivalent circuit diagram showing a standardized high-pass filter circuit according to a first example of an embodiment of the present invention.

FIG. 6 is an equivalent circuit diagram showing a normalized high pass filter circuit according to a first example of an embodiment of the present invention.

FIG. 7 is an equivalent circuit diagram showing a normalized high pass filter circuit according to a first example of an embodiment of the present invention.

FIG. 8 is an equivalent circuit diagram showing a normalized high pass filter circuit according to a first example of an embodiment of the present invention.

FIG. 9 is an equivalent circuit diagram showing an asymmetric equivalent band stop filter circuit in the first example of the embodiment of the present invention.

FIG. 10 is a circuit diagram showing a circuit configuration example of a band elimination filter in the first example of the embodiment of the present invention.

FIG. 11 is a diagram showing a target band stop characteristic in the second example of the embodiment of the present invention.

FIG. 12 is a diagram showing a frequency characteristic of a normalized high pass filter according to a second example of an embodiment of the present invention.

FIG. 13 is an equivalent circuit diagram showing a normalized high pass filter circuit according to a second example of the embodiment of the present invention.

FIG. 14 is an equivalent circuit diagram showing a standardized high-pass filter circuit according to a second example of the embodiment of the present invention.

FIG. 15 is an equivalent circuit diagram showing an asymmetric equivalent band stop filter circuit according to a second example of the embodiment of the present invention.

FIG. 16 is an equivalent circuit diagram showing an asymmetric equivalent band stop filter circuit according to a second example of the embodiment of the present invention.

FIG. 17 is a circuit diagram showing a circuit configuration example of a band elimination filter in the second example of the embodiment of the present invention.

FIG. 18 is a circuit diagram showing a circuit configuration example of a band elimination filter in the second example of the embodiment of the present invention.

[Explanation of symbols]

f ₁ ···· center frequency -jk ··· ideal reactance or ideal susceptance

Claims (3)

(57) [Claims] 1. A center frequency in which a plurality of series-parallel resonant circuits each including a parallel resonant section using a TEM transmission line and a reactance element connected in series to the parallel resonant section are cascade-connected via a series reactance element. The series-parallel resonant circuits having asymmetrical band-stop characteristics are opposed to each other.
Value of the series reactance element connected in series to the vibration section
For connecting in series adjacent to the series-parallel resonant circuit
Value of one series reactance element or two with the same sign
Value of the parallel connection of the series reactance elements of
Value of the sum of parallel connection of two series reactance elements of the sign
Or is asymmetric with respect to the center frequency
Deviation by a predetermined value determined by contributing to
And the signs are opposite.
Band-stop filter that. 2. The TEM transmission line is a quarter wavelength type T
2. The band elimination filter according to claim 1, comprising an EM transmission line and having a stop band at a third-order frequency of the center frequency. 3. The TEM transmission line is a half wavelength type T
2. The band elimination filter according to claim 1, comprising an EM transmission line, and having a stop band at a second-order frequency of the center frequency.