JP2000252706A - Dual mode filter - Google Patents

Abstract

(57) [Problem] To provide a dual mode filter used in a high-frequency circuit or the like to realize high attenuation in a stop band and low loss in a pass band. SOLUTION: A ring resonator 101 whose electric length is 360 degrees around one circumference, and an arbitrary point on the ring resonator 101 is set as a reference point 1
The capacitive stub 10 connected to the reference point 105 as 05
2 and 13 from 90 degrees clockwise from reference point 105
A first input / output port 103 arranged to generate electric field coupling with the ring resonator 101 up to 5 degrees, and a ring resonator between 90 degrees and 135 degrees counterclockwise from the reference point 105; With the configuration including the first input / output port 101 and the second input / output port 104 arranged to generate electric field coupling, the position of the attenuation pole can be easily adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dual mode filter used for a high frequency circuit or the like.

[0002]

2. Description of the Related Art Conventionally, there is a dual mode ring type filter as one of filters used for devices and circuits in mobile communication. FIG. 4 is a plan view showing the structure of a conventional dual mode ring type filter. This is JA Curtis
"Digest of the IEEE International Conference on Microwave Waves, 1991," pp. 443-446 (1991).
IEEE International Microwow
ave Symposium Digest, pp. 4
43-446).

In FIG. 4, reference numeral 400 denotes a single-wavelength (360 ° electrical length) stripline ring resonator;
02 is an input / output line, 403 and 404 are gap capacitors, and 405 is a strip line stub with an open end.
The electrical length between the input / output lines is 90 °, and the distance between the input / output lines 401 and 402 is 135 ° between the strip line stub 405 and the center of the input / output lines 401 and 402.

[0004] The operation of the dual mode filter using the stripline ring resonator configured as described above will be described below. First, input line 4
The traveling wave propagated from 01 is electric-field-coupled to the ring resonator via the coupling capacitance, and generates a strong electric field near the input line on the ring resonator 400. This electric field propagates in the ring resonator 400 in the clockwise and counterclockwise directions as a traveling wave.

[0005] First, the traveling wave counterclockwise receives a phase change of 90 ° and reaches near the output line. However, since the electric field is minimized here, it is not coupled to the output line 402. As a result, the traveling wave further advances by 135 °, and reaches the position of the strip line stub 405 having an open end. Here, since a discontinuous portion exists in the line, a part thereof becomes a reflected wave, and the rest propagates to the vicinity of the input line 401 and is coupled to the input line 401 via a coupling capacitance.

The reflected wave from the open-end stripline stub 405 recedes by 135 ° and reaches the vicinity of the output line 402, but has a phase difference of 270 ° round trip.
Here, the electric field becomes maximum, electric field coupling occurs, and a traveling wave propagates to the output line 402.

Similarly, as for the traveling wave in the clockwise direction, only the reflected wave from the strip line stub 405 having the open end is coupled to the input line 401 and propagated. When this operation is viewed as a resonator, it can be said that there are two orthogonal modes in the resonator, and the two modes are coupled by the strip line stub 405 to operate as a two-stage filter. This filter has a feature that the radiation loss is small because the resonator has a ring shape and there is no open end. Further, there is a feature that an attenuation pole is provided in the vicinity of the passband, and a feature that a large amount of attenuation can be obtained even with a small number of stages is known.

[0008]

However, in the above-described conventional dual mode filter, the electrical distance between the two input / output ports must be fixed at 90 degrees, and therefore the position of the attenuation pole is controlled. It is difficult to construct a filter that effectively utilizes the attenuation pole.

The present invention provides a dual mode resonator specific
It is an object of the present invention to realize a method of controlling the position of an attenuation pole, thereby realizing a high attenuation in a stop band and a low loss in a pass band.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a ring resonator having an electrical length of 360 degrees around one circumference and an arbitrary point on the ring resonator as a reference point. A connected capacitive stub, a first input / output port arranged to generate electric field coupling with the ring resonator between 90 degrees and 135 degrees clockwise from the reference point, and the reference point And a second input / output port arranged so as to generate electric field coupling with the ring resonator between 90 degrees and 135 degrees in a counterclockwise direction from the first direction.

The present invention also provides a ring resonator having an electrical length of 360 degrees around one circumference, a capacitive stub connected to the reference point using an arbitrary point on the ring resonator as a reference point, A first input / output port arranged to generate electric field coupling with the ring resonator between 135 degrees and 180 degrees clockwise from 135 degrees, and 135 degrees to 180 degrees counterclockwise from the reference point And a second input / output port arranged so as to generate electric field coupling with the ring resonator.

As a result, a highly accurate dual mode filter having a high attenuation characteristic in a stop band and a low loss characteristic in a pass band can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is characterized in that a ring resonator having an electrical length of 360 degrees and one circumference is connected to the reference point using an arbitrary point on the ring resonator as a reference point. A capacitive stub, a first input / output port arranged to generate electric field coupling with the ring resonator in a clockwise direction from 90 degrees to 135 degrees from the reference point, and 135 degrees from 90 degrees counterclockwise
A dual-mode filter having a ring input and a second input / output port arranged so as to generate electric field coupling up to a certain degree, without changing the passband frequency band. This has the effect that the position of the attenuation pole can be adjusted.

According to a second aspect of the present invention, there is provided a ring resonator having an electrical length of 360 degrees around one circumference, a capacitive stub connected to the reference point using an arbitrary point on the ring resonator as a reference point, From 135 degrees clockwise from the reference point to 18
A first input / output port arranged to generate electric field coupling with the ring resonator up to 0 degrees, and the ring resonator extending from 135 degrees to 180 degrees counterclockwise from the reference point; And a second arranged to cause electric field coupling with
The dual-mode filter is characterized by having the following input / output ports, and has the effect that the position of the attenuation pole can be adjusted without changing the frequency band of the pass band.

According to the third aspect of the present invention, the distance from the reference point to the first input / output port in the clockwise direction and the distance from the reference point to the second input / output port in the counterclockwise direction. Preferably, the distance is equal to the dual mode filter according to claim 1 or 2.

According to a fourth aspect of the present invention, the electric field coupling between the ring resonator and the first and second input / output ports is capacitive coupling. And has an effect that the position of the attenuation pole can be adjusted so as to increase the amount of attenuation particularly on the low frequency side of the pass band.

According to a fifth aspect of the present invention, the electric field coupling between the ring resonator and the first and second input / output ports is all inductive coupling. And has an effect that the position of the attenuation pole can be adjusted so as to increase the amount of attenuation particularly on the high frequency side of the passband.

According to a sixth aspect of the present invention, the capacitive stub comprises:
6. A radial stub.
In the dual mode filter according to any one of the above, since the impedance discontinuous region in the ring resonator can be localized, an effect that the design of the filter is improved.

According to a seventh aspect of the present invention, there is provided a high-frequency circuit using the dual mode filter according to any one of the first to sixth aspects, which has an effect of realizing an inexpensive and compact high-frequency circuit. Have.

An eighth aspect of the present invention is a wireless device having the high-frequency circuit according to the seventh aspect, and has an effect of realizing an inexpensive and small-sized wireless device.

Hereinafter, this embodiment will be described with reference to FIGS.

(Embodiment 1) FIG. 1 is a plan view showing a structure of a dual mode filter according to the present embodiment. In FIG. 1, reference numeral 101 denotes a ring resonator, which has a circumference of one wavelength in terms of the wavelength of a traveling wave propagating through a line in a pass frequency band. An arbitrary point on the ring resonator 101 is set as a reference point 105, and a radial stub 102 is connected to the reference point 105 as a capacitive stub. From the reference point 105, a first input / output port 103 is provided in a clockwise direction, and a second input / output port 104 is provided in a counterclockwise direction. At this time, the first and second input / output ports 103 and 104 are formed so as to be coupled to the ring resonator 101 through an electric field. In the present embodiment, capacitive coupling is performed.

First and second input / output ports 103 and 104
The electrical position from the reference point 105 is θ
When it is assumed that 1, θ2, it is determined under the condition represented by (Equation 1).

[0024]

(Equation 1)

Here, when the radial stub 102 is connected, discontinuity occurs in the electromagnetic field at the reference point 105. Therefore, when the stub is not connected, the rectangular stubs exist in the ring resonator and are orthogonal and independent. The degeneration of the resonance mode is released by the connection of the stub, and it is possible to operate as a dual mode filter.

In the conventional dual mode filter shown in FIG. 4, first and second input / output ports 401 and 402 are connected to the point where the strip line stub 405 is connected.
The respective electrical lengths θ1 and θ2 up to are expressed as (Equation 2).

[0027]

(Equation 2)

Here, the dual mode according to the present embodiment is described.
Between the dual-mode filter and the conventional dual-mode filter
FIG. 2 shows a comparison of the transmission characteristics. However, in this embodiment,
Position of input / output port of dual mode filter
Is based on (Equation 1) and is based on the condition of (Equation 3).
is there. In FIG. 2, the horizontal axis represents frequency, and the vertical axis | S _{twenty one}
| Indicates transmission characteristics from input port to output port
You.

[0029]

(Equation 3)

FIG. 2 shows that in the conventional filter based on (Equation 2), the attenuation poles appear at substantially symmetrical positions at both ends of the passband, whereas the attenuation filter according to the present embodiment based on (Equation 1). With the filter, the passband changes little,
It can be seen that the attenuation pole has moved to a higher frequency. Therefore, under the condition of (Equation 1), it becomes possible to make the attenuation pole on the lower frequency side asymptotic to the pass band.

In addition, in the present embodiment, since the coupling between the first and second input / output ports is a capacitive coupling,
It is possible to increase the amount of attenuation on the low frequency side of the pass band, and to obtain a large amount of attenuation on the low frequency side as a whole.

The positions of the first and second input / output ports are
By adjusting in the range of (Equation 1), the position of the attenuation pole can be adjusted. This is effective when the band where high attenuation characteristics are required is present on the lower side and near the pass band. is there.

Further, by using a radial stub as the stub as in the present embodiment, the coupling region of the stub to the ring resonator can be reduced, so that the impedance change on the ring resonator can be reduced to one point. In addition, it is possible to obtain an effect that unnecessary mode coupling hardly occurs and the design is excellent.

Further, in the present embodiment, the positions θ1 and θ2 of the first and second input / output ports are set to the same angle, but need not necessarily be the same, and 360 ° − (θ1 + θ2).
Is constant, the same operation and effect as those obtained when the port positions θ1 and θ2 are set to the same angle can be obtained without setting them to the same angle. The reason is that a path from the first input / output port 103 to the second input / output port 104 in a counterclockwise direction;
This is because if the path difference from the first port to the second port in the clockwise direction is the same, an attenuation pole is generated in substantially the same frequency band.

Although the stub is arranged outside the ring resonator 101 in the present embodiment, it can be arranged inside.

(Embodiment 2) FIG. 3 is a plan view showing a structure of a dual mode filter according to the present embodiment. In FIG. 3, reference numeral 203 denotes a first input / output port;
Reference numeral 4 denotes a second input / output port, and other configurations are the same as those in FIG. The difference from the configuration of FIG. 1 is that the first and second input / output ports 203 and 204 are electromagnetically connected to the ring resonator 101 by inductive coupling using taps. , First and second input / output ports 20
3, 204 is determined under the condition represented by (Equation 4).

[0037]

(Equation 4)

As shown in (Embodiment 1), (Equation 2)
In the conventional filter based on, the attenuation poles appear at almost symmetrical positions at both ends of the pass band, whereas in the filter according to the present embodiment based on (Equation 4), the pass band hardly changes, The attenuation pole moves to a lower frequency.
Therefore, under the condition of (Equation 4), it becomes possible to make the attenuation pole on the lower frequency side asymptotic to the pass band.

In addition, in this embodiment, since the coupling between the first and second input / output ports 203 and 204 is inductive coupling, the attenuation on the high frequency side of the passband can be increased. As a whole, a large amount of attenuation on the high frequency side can be obtained.

The positions of the first and second input / output ports are
By adjusting within the range of (Equation 4), it is possible to adjust the position of the attenuation pole. This is effective when the band requiring high attenuation characteristics is on the high frequency side and near the passband. It is.

[0041]

As described above, according to the present invention, the appearance frequency of the attenuation pole can be easily controlled only by adjusting the positions of the two input / output ports to the ring resonator. And an advantageous effect that a highly accurate dual mode filter having a low loss characteristic in a pass band can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view showing a structure of a dual mode filter according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a comparison of transmission pass characteristics between a dual mode filter according to an embodiment of the present invention and a conventional dual mode filter.

FIG. 3 is a plan view showing a structure of a dual mode filter according to one embodiment of the present invention.

FIG. 4 is a plan view showing the structure of a conventional dual mode filter.

[Explanation of symbols]

 Reference Signs List 101 ring resonator 102 radial stub 103 first input / output port 104 second input / output port 105 reference point 203 first input / output port 204 second input / output port 400 stripline ring resonator 401 input line 402 output line 403,404 Gap capacitor 405 Strip line stub

Claims (8)

[Claims] 1. A ring resonator having an electrical length of 360 degrees around a circumference, a capacitive stub connected to the reference point using an arbitrary point on the ring resonator as a reference point, and a clockwise direction from the reference point. A first input / output port arranged to generate electric field coupling with the ring resonator between 90 degrees and 135 degrees, and between 90 degrees and 135 degrees counterclockwise from the reference point. A dual mode filter comprising the ring resonator and a second input / output port arranged to generate electric field coupling. 2. A ring resonator having an electrical length of 360 degrees around the circumference, a capacitive stub connected to the reference point using an arbitrary point on the ring resonator as a reference point, and a clockwise direction from the reference point. A first input / output port arranged to generate electric field coupling with the ring resonator between 135 degrees and 180 degrees, and 135 degrees counterclockwise from the reference point.
A dual mode filter comprising: the ring resonator and a second input / output port arranged to generate electric field coupling between degrees and 180 degrees. 3. A distance from a reference point to a first input / output port in a clockwise direction is equal to a distance from the reference point to a second input / output port in a counterclockwise direction. The dual mode filter according to claim 1. 4. The dual mode filter according to claim 1, wherein electric field coupling between the ring resonator and the first and second input / output ports is capacitive coupling. . 5. The dual mode filter according to claim 1, wherein the electric field coupling between the ring resonator and the first and second input / output ports is inductive coupling. . 6. The dual mode filter according to claim 1, wherein the capacitive stub is a radial stub. 7. A high-frequency circuit using the dual mode filter according to claim 1. 8. A wireless device comprising the high-frequency circuit according to claim 7.