JP2002076710A - High frequency filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semi-coaxial resonator band-elimination filter that can maintain a miniaturization when QL value is comparatively small. SOLUTION: This filter is a band-elimination filter 1 of which three semi- coaxial resonators 241-243 are combined with an outer conductor 21 at the fixed interval of λo/4, and of which a phase delay arises by the large capacitance. The inductive posts 10 are interposed into almost the half location between the adjacent resonators. A phase lead for the amount corresponding to the phase delay by the large capacitance is carried out by the posts 10, λo/4 can be ensured electrically, and the necessity of increasing the resonator interval to 3λo/4 can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semi-coaxial resonator type high frequency filter used in a microwave radio transmitting / receiving apparatus or the like, and more particularly to a structure for reducing the size of the filter.

[0002]

2. Description of the Related Art As a high-frequency filter used in a microwave transmitting / receiving apparatus or the like, for example, a band rejection filter having a plurality of semi-coaxial resonators is known. FIG. 3 shows that n =
FIG. 3 is a cross-sectional view illustrating a configuration of a conventional band rejection filter of this type, which is an example of a conventional band rejection filter. The band rejection filter 2 has a rectangular coaxial line as a basic structure, and a first coaxial line is provided on the outer wall of the outer conductor 21.
And the second semi-coaxial resonators 241 and 242 are mounted, and the third semi-coaxial resonator 243 is mounted on the outer wall of the other external conductor 21.

Each semi-coaxial resonator 241, 242, 243
Are semi-coaxial resonators in each of which a central conductor and an external conductor are integrated.
A certain amount protrudes from the coupling hole formed in FIG. As a result, coupling between each of the semi-coaxial resonators 241, 242, 243 and the rectangular coaxial line is realized. The outer conductor 21
A concave portion for positioning is provided in a portion near the coupling hole 17.

The mounting portions of the semi-coaxial resonators 241, 242, and 243 are mounted at portions separated by about λo / 4 (where λo is the wavelength of the center frequency fo to be blocked).

[0005] One end of the rectangular coaxial line is a microwave input end and the other is an output end, and connectors 23 are provided respectively. The center conductor 22 is arranged as a rectangular coaxial line between the input terminal and the output terminal.

In the above band rejection filter 2, when the center frequency of the signal component is fo and the 3 dB width is ΔF, the load Q
L is represented by fo / ΔF, and when n = 3, generally QL
Two values are required. The QL value is determined by two types of values depending on the form of the filter characteristics. If n is large, the required QL value increases, while the desired center frequency fo increases (corresponding to a large number of CHs).
Then, the required QL value increases accordingly.

[0007]

When the resonator spacing is about λo / 4 as shown in FIG. 3, the passing frequency fP and the stop frequency fR are close to each other, for example, (Δf / (fR−fP). )) × 100 = 0.08 (Δf
Is the stop band) and the QL value is relatively small (30
), Each semi-coaxial resonator 241, 242, 243
The effect of the fringing capacitance C formed between the tip of the fixed center conductor and the center conductor 22 increases. Also, the resonator interval becomes apparently long, the electromagnetic field near the center frequency fo is disturbed, and the phase state near the center frequency fo is disturbed. That is, as shown in the filter characteristic diagram of FIG. 4, a “crack” occurs in the attenuation characteristic near the center frequency fo,
Where the attenuation should be 30 dB or more is about 15 dB.

For this reason, conventionally, when the QL value becomes small, as shown in FIG.
And the band rejection filter 3 in which the distance between the semi-coaxial resonators 341, 342 and 343 is set to about 3λo / 4 is used. In this way, the attenuation becomes an improved value as shown in the filter characteristic diagram of FIG. However, the band rejection filter 3 having the structure as shown in FIG. 5 has a significantly larger shape than the band rejection filter 2 shown in FIG. When the band rejection filter is large, the manufacturing cost is high, and the size and cost of the transmitting / receiving device and the like, the housing case, and the like are affected.

SUMMARY OF THE INVENTION In view of the above problems, it is a main object of the present invention to provide an improved high-frequency filter capable of maintaining a small size when the QL value is relatively small.

[0010]

According to the high frequency filter of the present invention, a plurality of semi-coaxial resonators are coupled to an outer wall of a signal waveguide through which a high-frequency signal passes, and at least two semi-coaxial resonators are provided. A high-frequency filter having a large fringing capacity in the signal waveguide depending on the degree of coupling, wherein an inductive member is interposed between the coupling portions of the two semi-coaxial resonators. Since the delay due to the capacitance is canceled by the size of the inductive member, the distance between the adjacent semi-coaxial resonators does not need to be 3λo / 4, and the high-frequency filter can be downsized.

In a preferred embodiment, a plurality of semi-coaxial resonators are alternately coupled at predetermined intervals to predetermined portions of the outer wall facing each other. In this case, the inductive member is interposed in the internal space of the signal waveguide and substantially in the middle between the adjacent semi-coaxial resonators.

In the signal waveguide, for example, the outer wall and the inner conductor have a circular coaxial shape or a rectangular coaxial shape, and an inner conductor through which a signal component passes is disposed on a central axis of the signal waveguide. The size of the inductive member changes depending on the capacitance component (load Q, QL) formed by the gap between the center conductor of each semi-coaxial resonator and the internal conductor.

In consideration of versatility, all the semi-coaxial resonators have conductors that direct the internal space of the signal waveguide from a direction perpendicular to the central axis of the signal waveguide, The distance between conductors of adjacent semi-coaxial resonators is approximately λo
/ 4 (λo is the wavelength of the center frequency to be used). Further, the distance between the inductive member and the center conductor of each semi-coaxial resonator is set to be approximately λo / 8. As a result, the excess fringing component can be effectively canceled.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a band rejection filter used in a microwave band will be described below.

FIG. 1 is a cross-sectional view of the band rejection filter of the present embodiment, and FIG. 2 is a cross-sectional view along the line A in FIG. 1. For convenience, the conventional band rejection filter 2 shown in FIG. Here is an example of the case. The same components as those of the conventional band rejection filter 2 are described with the same reference numerals.

In the band rejection filter 1 of the present embodiment, first and second semi-coaxial resonators 241 and 242 are mounted in recesses of the outer wall of a rectangular coaxial outer conductor 21, and the outer wall of the other outer conductor 21 is A third semi-coaxial resonator 243 is mounted in the depression. On the central axis of the inner central conductor 22, connectors 23 provided at each of the input and output ends are arranged. All the semi-coaxial resonators 241 to 243 each have a fixed central conductor and an outer conductor that are integrated, and the fixed central conductor is separated from the inner wall of the coaxial tube through a coupling hole formed in each outer conductor 21. A certain amount is prominent.

The mounting portions of the semi-coaxial resonators 241, 242, 243 are fixedly determined mainly at intervals of about λo / 4 (about 90 °). When the QL value is relatively small, the tip of the fixed central conductor of each of the semi-coaxial resonators 241 to 243 approaches the central conductor 22, so that each of the semi-coaxial resonators 24
1 to 243 of the fixed center conductor and the inner center conductor 22
A large fringing capacity is generated due to the gap between. This large fringing capacitance acts as a delay for the signal component passing through the inner center conductor 22.
Therefore, the interval between the semi-coaxial resonators 241 to 243 becomes apparently long, and the phase near the center frequency fo is delayed.

Therefore, in this embodiment, the first semi-coaxial resonator 2 is separated from the fixed center conductor of the third semi-coaxial resonator 243.
41, about λo in the direction of the second semi-coaxial resonator 242, respectively.
A pair of inductive posts (rods) 10 were interposed at / 8 distant sites. The inductive post 10 is made of a material that becomes a leading phase with respect to the signal component, for example, a thin metal plate or a metal processed into a round bar shape, and functions as a so-called inverter. Attachment of the inductive post is performed by soldering, screwing, or using a conductive adhesive alone or in combination. As a result, the fringing capacitance is effectively canceled, and the phase lag near the center frequency fo, which occurs in the case of the conventional band rejection filter of the same size, is suppressed. In the actual measurement, an improved resonance characteristic as shown in FIG. 6 was obtained although the distance between the semi-coaxial resonators 241 to 243 was λo / 4 as in the present embodiment.
As described above, FIG. 6 shows the resonance characteristics when the interval between the semi-coaxial resonators 341 to 343 is 3λo / 4. Therefore, by employing the structure of the present embodiment, the size of the band rejection filter can be significantly reduced. Understand.

Although the present invention has been described with reference to n = 3, in the case of a filter in which a large fringing capacitance occurs in the signal waveguide due to the presence of at least one semi-coaxial resonator, one semi-coaxial resonator is used. An inductive member is interposed between the coupling part and the coupling part of another semi-coaxial resonator, and the main point is that a phase delay due to a large capacitance is advanced by the inductive member to electrically secure λ / 4. Therefore, the number of semi-coaxial resonators, the size, and the number of inductive posts are not limited to the example of the above-described embodiment.

In this embodiment, an example in which a rectangular coaxial is used as the signal waveguide has been described. However, the present invention is similarly applied to a case where the outer wall of the outer conductor and the inner conductor have a circular coaxial shape. Applicable. Even in the case of a circular coaxial shape, a plurality of semi-coaxial resonators are alternately coupled to portions opposed to each other at a fixed interval, and an inductive member is interposed at a substantially intermediate portion between adjacent semi-coaxial resonators.

[0021]

As is apparent from the above description, according to the high frequency filter of the present invention, it is possible to provide a high frequency rejection filter capable of maintaining a small size when the QL value is relatively small.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a band rejection filter according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line A in FIG. 1;

FIG. 3 is a cross-sectional view showing a configuration of a conventional band rejection filter in which semi-coaxial resonators are mounted at an interval of λo / 4.

FIG. 4 is a filter characteristic diagram of a conventional band rejection filter in which semi-coaxial resonators are mounted at intervals of λo / 4.

FIG. 5 is a sectional view showing a configuration of a conventional band rejection filter in which semi-coaxial resonators are mounted at intervals of 3λo / 4.

FIG. 6 is a filter characteristic diagram of a conventional band rejection filter in which semi-coaxial resonators are mounted at an interval of 3λo / 4, and λo /
FIG. 4 is a characteristic diagram of the band rejection filter of the present invention in which inductive posts are provided between semi-coaxial resonators at intervals of 4.

[Explanation of symbols]

 1, 2, 3 Band stop filter 10 Inductive post 21, 31 Outer conductor 22, 32 Inner central conductor 23, 33 arranged on central axis Connector 241, 243, 341, 343 Semi-coaxial resonator

Claims (7)

[Claims] A plurality of semi-coaxial resonators are coupled to an outer wall of a signal waveguide through which a high-frequency signal passes, and a high-frequency component in which a capacitance change occurs in the signal waveguide depending on a coupling degree of at least two semi-coaxial resonators. A high-frequency filter, wherein an inductive member is interposed between coupling portions of the two semi-coaxial resonators. 2. The plurality of semi-coaxial resonators are alternately coupled to predetermined portions of the outer wall facing each other at a fixed interval, and the inductive member is adjacent to an inner space of the signal waveguide in an adjacent space. The high-frequency filter according to claim 1, wherein the high-frequency filter is provided at a substantially intermediate portion between the matching semi-coaxial resonators. 3. All of the semi-coaxial resonators have a central conductor pointing in an internal space of the signal waveguide from a direction perpendicular to a central axis of the signal waveguide. The distance between the center conductors of the semi-coaxial resonator is approximately λo
The high-frequency filter according to claim 2, wherein the ratio is / 4. 4. The high frequency filter according to claim 3, wherein a distance between the inductive member and a center conductor of each semi-coaxial resonator is approximately λo / 8. 5. An inner conductor through which a signal component passes on a central axis of the signal waveguide, is disposed coaxially with the outer wall, and
A structure in which the capacitance component formed by the gap between the center conductor of each semi-coaxial resonator and the internal conductor changes depending on the distance between the center conductors of adjacent semi-coaxial resonators and the amount of attenuation for the signal component. The high frequency filter according to any one of claims 1 to 4, wherein the high frequency filter has: 6. The high frequency filter according to claim 5, wherein the outer wall and the inner conductor are circular coaxial. 7. The high frequency filter according to claim 5, wherein the outer wall and the inner conductor are rectangular coaxial.