JP2002232207A - Band stop filter and communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To construct a small band stop filter which has a broad stop band using a microstrip line and is excellent in an electromagnetic field concentration degree. SOLUTION: A stripline 2 is formed on one plane of a dielectric board 1, and a lower conductive material 3a is formed entirely on a plane facing the one plane to form a microstrip line. In this state, a plurality of stubs 4a to 4d of the same electrical length are formed radially at equal intervals on the plane of the dielectric board 1 on which the stripline 2 is formed and connected to one point of the stripline 2 through a connecting conductor 5 connecting the stubs 4a to 4d.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission circuit used in a high-frequency circuit, and more particularly to a band rejection filter using a microstrip line.

[0002]

2. Description of the Related Art A conventional band rejection filter using a microstrip line will be described with reference to FIG.
FIG. 5A is an external view of a band rejection filter using a radial stub using a strip line, and FIG. 5B is an equivalent circuit diagram thereof.

In FIG. 5A, reference numeral 1 denotes a dielectric substrate,
2 is a microstrip line, 3a is a conductor, and 4 is a radial stub. Ψ is the central angle of the radial stub, and r is its diameter.

[0004] A strip line 2 is formed on one surface of a dielectric substrate 1, and a conductor 3a is formed on the entire other surface opposite to the strip line. Here, a sector-shaped conductor is formed on the surface on which the strip line 2 is formed, and the center portion of the sector-shaped conductor is connected to the strip line 2 in parallel.
Here, by setting the radius r of the sector to be the length of λ / 4 of the design frequency, the sector-shaped conductor functions as a radial stub, and the end corresponding to the circumference of the sector is connected to the open end and the strip line. Acts as a resonator having a short-circuit end. Thus, a band rejection filter having an attenuation band at the design frequency is configured.

Further, from the equivalent circuit of FIG. 5B, the input impedance Zs as viewed from the point a on the stub side is as follows: Zs = −j · Zo · cotθs FIG. 6 shows the frequency characteristics of the input impedance Zs.

FIG. 6 is a frequency characteristic diagram of the input impedance due to a change in the impedance of the stub. As shown in FIG. 6, when the impedance Zo of the stub decreases,
The proportionality constant of the input impedance Zs with respect to the frequency decreases, and the slope of the characteristic curve becomes gentle over a wide frequency range. Here, assuming that an effective reflection characteristic can be obtained when the input impedance Zs is in the range of ± Zn, when the impedance Zo of the stub is low, the slope of the characteristic curve is gentle. Obtainable.

That is, if the area of the stub is increased by increasing the central angle の of the radial stub shown in FIG. 5A, Zo is reduced, and a filter having a wide stop band can be constructed.

[0008]

However, such a conventional band rejection filter using a microstrip line has the following problems to be solved.

In order to reduce the impedance of a microstrip line, if the substrate has the same thickness, it is necessary to increase the line width. In the case of a sector shape, the area needs to be increased.

However, if the line width is increased (the area is increased), the spread of the electromagnetic field on the substrate also increases.

FIG. 7A is a diagram showing the spread of the electromagnetic field of the microstrip line, and FIG. 7B is a diagram showing a dielectric substrate having a thickness of 0.3 mm and a relative dielectric constant of 3.2. Of the relationship between the distance between the upper conductor and the strip line and the rate of change of the impedance when a high frequency of 30 GHz is transmitted on the microstrip line using the above, using the conductor width w of the strip line as a parameter. It is. In FIG. 7A, 1 is a dielectric substrate, 2 is a strip line, 3a is a lower conductor, and 3b is an upper conductor. Also, w is the width of the strip line, d is the thickness of the dielectric substrate 1, and D is the distance between the strip line and the upper conductor. FIG. 7B shows the fluctuation rate when the distance between the upper conductor and the strip line is 1 mm as 100%. In general, the microstrip line shown in FIG. 7A is used as a part of a high-frequency component mounted on a communication device or the like. (Conductor) may also be electromagnetically coupled. For this reason, the microstrip line is less affected by the higher the electromagnetic field concentration, and has excellent characteristics.

From FIG. 7B, as the width of the strip line increases, the rate of change of the impedance increases.
This is because, when the width of the strip line is increased, electromagnetic coupling between the upper conductor and the strip line is likely to occur, and the distance required for preventing the electromagnetic coupling between the upper conductor and the strip line becomes longer. That's why.

As described above, in order to widen the stop band, the area of the stub must be increased. However, the concentration of the electromagnetic field in the microstrip line is reduced, and the coupling with the upper conductor is reduced. As a result, the characteristics are deteriorated. Further, in order to prevent coupling with the upper conductor, the strip line and the upper conductor must be sufficiently separated from each other, and the package cannot be reduced in size.

An object of the present invention is to provide a small band rejection filter using a microstrip line and having a wide stop band and excellent electromagnetic field concentration, and a communication device including the same.

[0015]

SUMMARY OF THE INVENTION According to the present invention, there is provided a method for transmitting a connection in which at least two stubs are connected in parallel by forming a strip line having an open end or a short circuit and having an equal electric length. A band rejection filter is configured by connecting in parallel to the line.

Further, according to the present invention, the band rejection filter is constituted by making all the stubs have the same electrical length.

Further, according to the present invention, a band rejection filter is formed by forming a plurality of stubs at equal intervals.

Further, according to the present invention, a communication apparatus is provided with the band rejection filter.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a band rejection filter according to a first embodiment will be described with reference to FIGS. FIG. 1A is an external perspective view of a band rejection filter, and FIG. 1B is an equivalent circuit diagram thereof. In FIG. 1A, 1 is a dielectric substrate, 2 is a strip line, 3a is a lower conductor, 4a to 4d are stubs, and 5 is a connection conductor.

A strip line 2 is formed on one surface of the dielectric substrate 1, and a lower conductor 3a is formed on the entire surface opposite to this, forming a microstrip line as a whole. . In this state, strip line 2
A plurality of stubs 4a to 4d having the same electric length are radially formed at equal intervals on the surface of the dielectric substrate 1 forming the stubs, and strip lines are formed via connection conductors 5 connecting the stubs 4a to 4d. Two points are connected. As shown in FIG. 1B, a plurality of stubs 4a to 4d each having an impedance of Zs are connected in parallel to a connecting conductor 5, and the connecting conductor 5 is connected in parallel to a microstrip line at a point a. Means that.

Here, the input impedance Zin of the stub group viewed from the point a is a parallel connection of the line of the impedance Zs, so that Zin = (1 / Zs + 1 / Zs + 1 / Zs + 1 / Zs) ^-1
= Zs / 4, and the input impedance Zin is 1/4 of the impedance Zs of the stub alone, so that a low impedance stub can be easily formed.

On the other hand, the electromagnetic field concentration will be described below with reference to FIG. FIGS. 2A and 2B are cross-sectional views of a single strip line and a double strip line, respectively. FIG. FIG. 4 is a diagram showing a rate of change of impedance depending on a distance between a body and a strip line. Here, the microstrip line using two strip lines forms a strip line so that the even mode impedance matches the case using one strip line.

FIG. 2C shows the case where the thickness of the dielectric substrate is set at 0.
The experiment was conducted with the dielectric substrate being 3 mm, the relative permittivity of the dielectric substrate being 3.2, and the frequency of the transmission wave being 30 GHz. Further, the rate of change of the impedance is calculated assuming that the impedance when the distance between the strip line 2 and the upper conductor 3b is 1 mm is 100%. Here, the structure having one strip line shown in (a) is based on w = 0.75 mm. As shown in FIG. 2C, when two coupling lines are used, the rate of change in impedance is smaller and the degree of electromagnetic field concentration is superior to that when one coupling line is used (at the time of reference). Also, when the line spacing is increased, the electromagnetic field concentration is further improved.

As described above, a stub using a plurality of lines and having a large interval is superior to a stub using a single line in electromagnetic field concentration. In other words, the use of a stub in which a plurality of stubs are formed radially with a larger interval is more excellent in electromagnetic field concentration than using one fan-shaped stub.

Therefore, by using a stub in which a plurality of stubs are formed radially with a wide interval, it is possible to easily configure a band rejection filter having a high electromagnetic field concentration and being hardly affected by external influences.

Next, the configuration of the band rejection filter according to the second embodiment will be described with reference to FIG. FIG. 3 is an external perspective view of the band rejection filter. In FIG.
1 is a dielectric substrate, 2 is a strip line, 3a is a lower conductor, 4a to 4d, 6a to 6d are stubs, and 5, 7 are connection conductors.

A strip line 2 is formed on one surface of the dielectric substrate 1, and a lower conductor 3a is formed on the entire surface opposite to the strip line 2 to constitute a microstrip line. In this state, a plurality of stubs 4a to 4d having the same electrical length are radially formed at regular intervals on the surface of the dielectric substrate 1 forming the strip line 2, and the stubs 4a to 4d are connected. It is connected to one point of the strip line 2 via the connection conductor 5. Further, a plurality of stubs 6a to 6d having the same electrical length as the stubs 4a to 4d are formed radially at symmetrical positions with respect to the strip line 2, and the strip lines 2 are connected via connection conductors 7 connecting the stubs 6a to 6d. Connected to With this structure, radial stubs composed of stubs 4a to 4d and stubs 6a to 6d are provided.
A radial stub of 6d is connected in parallel with the microstrip line to form a band reject filter.

With such a structure, radial stubs can be formed on both sides of the strip line, so that stubs can be formed over a wider range than in the case of the first embodiment, and a band rejection having a wide band and excellent electromagnetic field concentration. You can configure filters.

Next, the configuration of the band rejection filter according to the third embodiment will be described with reference to FIG.

FIG. 4 is an external perspective view of the band rejection filter. In FIG. 4, 1 is a dielectric substrate, 2 is a strip line, 3a is a lower conductor, 4a to 4d, 8a to 8d are stubs, and 5, 7 are connection conductors.

A strip line 2 is formed on one surface of the dielectric substrate 1, and a lower conductor 3a is formed on the entire surface opposite to the strip line 2 to form a microstrip line. In this state, a plurality of stubs 4a to 4d having the same electrical length are radially formed at regular intervals on the surface of the dielectric substrate 1 forming the strip line 2, and the stubs 4a to 4d are connected. It is connected to one point of the strip line 2 via the connection conductor 5. In addition, a plurality of stubs 8 a to 8, which are different from the stubs 4 a to 4 d and have the same electrical length, are provided at symmetric positions with respect to the strip line 2.
d is formed radially and is connected to the strip line 2 via the connection conductor 7 connecting the stubs 8a to 8d. With this structure, a radial stub including the stubs 4a to 4d and a radial stub including the stubs 8a to 8d are connected in parallel to the microstrip line to form a band rejection filter.

With such a structure, radial stubs can be formed on both sides of the strip line, so that stubs can be formed over a wider range than in the case of the first embodiment. You can configure filters. In addition, by setting the stubs 4a to 4d and the stubs 8a to 8d to have different electrical lengths, a plurality of impedance values are combined, the range of the combined impedance of the entire stub can be increased, and a desired impedance can be easily obtained. Can be formed.

Next, the configuration of the communication device according to the fourth embodiment will be described. The stub described in the above embodiment can be used for an oscillator having a microstrip circuit disclosed in, for example, JP-A-11-003967. That is, elements such as an FET, a varactor diode, and an inductance are connected to a microstrip line, and a resonator is provided. One of the two strip lines, which are part of the resonator, is used as a main line and the other is used as a sub-line. One end of the main line is resistance-terminated, an FET is connected to the other, and a varactor diode is connected to the end of the sub-line. Connected to form a band reflection type oscillator. The above-mentioned stub is used as a band rejection filter near the drain of the FET in the bias circuit composed of a microstrip line connecting the drain of the FET and the bias voltage input electrode in this oscillator. As a result, the band can be rejected in a wide band, and an oscillator having excellent characteristics can be configured. A similar effect can be obtained not only in the oscillator but also in a communication device including a stub using a microstrip circuit.

[0034]

According to the present invention, a connection part in which at least two stubs are connected in parallel with at least two stubs, which are formed by strip lines having the same electrical length and having the terminal part opened or short-circuited, is connected to the transmission line. By connecting in parallel, it is possible to easily configure a wideband and small band rejection filter that is excellent in electromagnetic field concentration and hardly affected by external influences.

Further, according to the present invention, by making all the stubs have the same electrical length, impedance design becomes easy, and a band rejection filter having desired frequency characteristics can be easily formed. In addition, since all the stubs can have substantially the same shape, pattern design and manufacturing can be easily performed.

Further, according to the present invention, since a plurality of stubs are formed at equal intervals, the interval between adjacent stubs cannot be irregularly narrowed, so that the effect of improving the electromagnetic field concentration can be enhanced. Further, since all the stubs have substantially the same shape and the distance between adjacent stubs is substantially the same, pattern design and manufacturing can be easily performed.

Further, according to the present invention, by providing the stub, a communication device having excellent communication characteristics can be configured.

[Brief description of the drawings]

FIG. 1 is an external perspective view and an equivalent circuit diagram of a band rejection filter according to a first embodiment.

FIG. 2 is a cross-sectional view of a microstrip line and a relationship diagram of a stub input impedance variation rate depending on a distance between the microstrip line and an upper conductor.

FIG. 3 is an external perspective view of a band rejection filter according to a second embodiment.

FIG. 4 is an external perspective view of a band rejection filter according to a third embodiment.

FIG. 5 is an external perspective view and an equivalent circuit diagram of a conventional band rejection filter.

FIG. 6 is a frequency characteristic diagram of an input impedance due to a change in impedance of a stub.

FIG. 7 is a diagram showing the spread of the electromagnetic field of the microstrip line, and a diagram showing the relationship between the distance between the upper conductor and the strip line and the rate of change in impedance, using the conductor width w as a parameter.

[Explanation of symbols]

 Reference Signs List 1-dielectric substrate 2-strip line 3a-lower conductor 3b-upper conductor 4-radial stub 4a-4d, 6a-6d, 8a-8d-stub 5,7-connection conductor g-line spacing w-line width

Claims (4)

[Claims] 1. A band rejection filter using a transmission line, comprising: a connection portion in which at least two stubs having an equal electrical length and having a termination portion opened or short-circuited are connected in parallel to the transmission line. filter. 2. The band rejection filter according to claim 1, wherein all of the plurality of stubs have the same electrical length. 3. The band rejection filter according to claim 1, wherein the plurality of stubs are arranged at equal intervals. 4. A communication device comprising the band rejection filter according to claim 1.