JPS59223003A - Coaxial type band-pass filter - Google Patents

Abstract

PURPOSE:To reduce a shift from a theoretical value of self and mutual capacitances even in case of that which has a wide specific band by forming a shape of an input/ output coupling line so that its cross section is flat, and also making this long shaft length larger than a diameter which is given theoretically when only an adjacent resonance electric conductor whose cross section is circular has been taken into consideration. CONSTITUTION:7a is a theoretical value input/output coupling line, has a diameter which is given theoretically when an adjacent resonance elctric conductor 5a whose cross section is circular has been taken into condiseration, its cross section is flat, its long shaft length is longer than a diameter of the theoretical value input/output coupling line 7a, also the long shaft is made horizontal, and this line 7a is provided between a side wall 1b and the resonance electric conductor 5a. However, in case when a shape of an input/output coupling line 7b is made a flat state having the same diameter as that of the theoretical value input/output coupling line 7a, a self-capacitance of the input/output coupling line 7b becomes smaller than the theoretical value, therefore, a necessary electric performance cannot be realized. Accordingly, the long shaft length of the input/output line 7 is made larger than the theoreticl value, by which the self-capacitance can also be brought close to the theoretical value, and the necessary electric performance can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coaxial interdisicle or combline filter used as a bandpass filter in the microwave band.

Conventionally, there have been filters of this type as shown in FIGS. 1 to 3. In the figure, 1 is a metal case forming the outer conductor of the resonator, which consists of a bottom wall 1a and a side wall 1b integrally formed around the periphery of the bottom wall 1a.

2 is a person, a connector attached for output, 3 is a screw for fixing the connector 2, and 5a, 5b.

Resonant conductors 5c, 5b, and 5a are arranged in the metal case 1 on the same plane and parallel to each other.

4 is connected to the inner conductor of the connector 2, and the resonant conductor 5a
This is a coupling line for extracting an output signal by electromagnetically coupling with the metal case 1, and is disposed between the side wall 1b of the metal case 1 and the outermost resonant conductor 5a. 6 is an adjustment screw for adjusting the equivalent electrical length of the resonant conductor 5.

A plurality of the resonant conductors 5 and adjustment screws 6 are arranged in accordance with the required electrical performance, and the figure shows a structure composed of five stages of resonators.

Next, the operation will be explained.

As shown in FIG. 3, the person, output line 4, and resonant conductor 5 placed in the metal case 1 have self-capacitance between them and the wall surface of the metal case 1, and the resonant conductor 5 has a self-capacitance between each other and the person, There is a mutual capacitance between the output coupling line 4 and the resonant conductor 5a, and the resonant conductor 5 resonates at a predetermined center frequency.

At this time, the self-capacitance and mutual capacitance of the output coupling line 4 and the resonant conductor 5 can be calculated theoretically with high accuracy, and the designed values are usually achieved in the actual circuit using a filter whose fractional band is not so wide. As long as this is done, the expected electrical performance as a filter can be obtained with good reproducibility.

However, in conventional filters configured in this way, when designing a filter with a wide fractional band, the mutual capacitance required between each resonant conductor 5 becomes large. At the same time, it is necessary to reduce the diameter of the resonant conductor 5a adjacent to the input/output coupling line 4. As a result, as shown in Fig. 4, the mutual capacitance of the output coupling line 4 is originally sufficiently small, and therefore the resonant conductor 5b, which is one stage away from the output coupling line 4, is not considered in the theoretical calculation.
There was a disadvantage that the mutual capacitance C between the output coupling line 4, the output coupling line 4, and the output coupling line 4 could no longer be ignored, making it impossible to achieve the desired electrical performance.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and the shape of the output coupling line is made flat in cross section, and the long axis length is made circular in cross section. By making the diameter larger than that theoretically given when only the resonant conductor is considered, and thereby ensuring sufficient electromagnetic coupling between the output coupling line and the second resonant conductor, it is possible to create a device with a wide relative band. FIGS. 5 and 6 show an embodiment of the present invention, in which the deviation of the self and mutual capacitances from the theoretical values can be reduced and the required electrical performance can be easily achieved.

In the figure, the same reference numerals as in FIGS. 1 to 3 indicate the same or equivalent parts, and 7a is a theoretical value line, an output coupling line,
This has a diameter theoretically given when only the adjacent resonant conductor 5a is considered as having a circular cross section, and is shown in broken lines in FIG. 6 for convenience of explanation. And 7 is the output coupling line, which has a flat cross section, and its long axis length is based on the above theory.

It is longer than the diameter of the output coupling line 7a, and is disposed between the side wall 1b and the resonant conductor 5a with its long axis horizontal.

The procedure for obtaining the shape of the output coupling line 7 is as follows.

In order to make the mutual capacitance C with the resonant conductor 5b one step apart as shown in FIG. 4 a negligible value,
It is conceivable to make the shape of the output coupling line 7 flat as shown in 7b in FIG. It is possible to make the electromagnetic coupling looser.

However, as shown in FIG.
If the shape of is made into a flat shape having the same diameter as the theoretical output coupling line 7a, the self-capacitance of the output coupling line 7b becomes smaller than the theoretical value, and therefore the required electrical performance cannot be achieved. occurs.

Therefore, as shown in Figure 6, the person was made into a flat shape.

In order to compensate for the self-capacitance of the output coupling line 7,
By making the long axis length of the output coupling line 7 thicker than the above theoretical value, the self-capacitance can be brought closer to the theoretical value, and as a result, the filter-like shape is shown.
The side wall 1b or the bottom wall 1a of the metal case l is shown in Figures 7 and 8.
People as shown in the figure.

A similar effect can be obtained even if the capacitor is placed close to the output coupling line 7, thereby increasing the self-capacitance of the output coupling line 7.

Further, in the above embodiment, a coaxial type interdigitator and filter has been described, but a coaxial type combline filter may also be used, and in this case, the same effects as in the above embodiment can be obtained.

As described above, according to the present invention, the diameter is theoretically given when the output coupling line is made flat in cross section, and its long axis length is circular in cross section, and only the adjacent resonant conductor is considered. Since it is made larger than , even in the case of a filter with a wide fractional band, the required electrical performance can be easily achieved at low cost.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a conventional coaxial interdigital filter, Fig. 2 is a plan view thereof, Fig. 3 is a sectional view taken along line mm of the second diagram, and Fig. 4 explains its drawbacks. 5 is a plan view of a coaxial bandpass filter according to an embodiment of the present invention, FIG. 6 is a sectional view taken along the line VI-VR of FIG. 5, and FIG. 7 is a diagram showing the implementation of the above embodiment. FIGS. 8 and 9 are cross-sectional views for explaining the process, each showing a modification of the above embodiment. 1... Metal case, 5a to 5C... Resonant conductor, 7.
...People, output coupling line. In addition, in the figure, the same reference numerals indicate the same or equivalent oil content. Agent Masuo Oiwa Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] (11 When considering a box-shaped metal case, a plurality of resonant conductors with a circular cross section and arranged on the same plane and parallel to each other in the metal case, and only adjacent resonant conductors with a circular cross section) has a flat cross-sectional shape with a major axis length larger than the theoretical diameter of the metal case, and is arranged between the side wall of the metal case and the outermost resonant conductor so that the plane containing the major axis coincides with the same plane. 1. A coaxial bandpass filter, comprising: an input/output coupling line, and a second resonant conductor extending inwardly from the input/output coupling line, and having a sufficient electromagnetic coupling with a second resonant conductor.