JP2008060900A - Low pass filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a spuriousness on the high-band side is generated because a shape is enlarged and a resonance on the cross direction is generated in an open stub section in a conventional low-pass filter. <P>SOLUTION: The low-pass filter is constituted by inserting a part obtained by cutting a metal plate and alternately configuring capacitors 12 and inductors 13 into a shielding case 11 having a cylindrical internal space. In the low-pass filter, since the capacitors 12 are bent in a circular shape, both ends are joined mutually by a soldering, and the central sections of the inductors 13 are bent so as to be brought near the central section of the internal space of the case; a miniaturization is enabled, and the low-pass filter having excellent frequency characteristics can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention particularly relates to a low-pass filter used in a microwave, quasi-microwave communication apparatus, or the like.

  Conventionally, such a low-pass filter has an open stub portion pattern 2 functioning as a capacitor and a line pattern 3 functioning as a coil alternately arranged in a hollow shield case 1 as shown in FIG. Was configured.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
JP-A-9-232805

  However, in such a configuration, there is a problem that the shape becomes large, and resonance in the width direction occurs in the open stub portion, thereby generating spurious on the high frequency side.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described conventional problems, and to provide a low-pass filter that can be reduced in size and has excellent frequency characteristics with reduced spurious generation.

  In order to solve the above-described conventional problems, the present invention is a low-pass configuration in which a metal plate is cut and a capacitor portion and an inductor portion are alternately arranged and inserted into a cylindrical metal body. It is a filter, the capacitor part is bent in a circle and both ends thereof are joined by brazing, and the central part of the inductor part seems to be bent so as to be near the central part inside the metal body It is a thing.

  The low-pass filter of the present invention can be miniaturized and can provide a low-pass filter having excellent frequency characteristics.

(Embodiment 1)
Hereinafter, the present invention will be described using the first embodiment.

  1 is a cross-sectional view of a low-pass filter according to Embodiment 1, FIG. 1 (a) is a cross-sectional view seen from above, and FIG. 1 (b) is a cross-sectional view seen from a side.

  Inside the cylindrical shield case 11, internal conductors 14 in which patterns to be the capacitor portions 12 and the inductor portions 13 are alternately arranged are inserted. At this time, the inner conductor 14 is formed by punching a copper plate having a thickness of about 0.5 mm so that the capacitor portion 12 has a length of about 8 mm, a width of about 12 mm, and the inductor portion 13 has a length of about 13 mm and a width of about 1 mm. Form. Here, the capacitor portion 12 is bent into a circular shape, and both end portions thereof are joined as silver joints by silver solder. The distance between the capacitor part 12 deformed in this way and the inside of the shield case 11 is set to about 0.5 mm, and a capacitance is formed therebetween. Further, the inductor portion 13 is deformed so that the center portion thereof is about the center of the capacitor portion 12 that has been deformed into a circular shape. FIG. 2 is a perspective view of the inner conductor 14 modified as described above.

  In this way, a low-pass filter having a pass band near 2 GHz and attenuating above 6 GHz is obtained.

  If an electrostatic capacity is to be formed with an open stub type pattern as in the prior art, for example, if the shape is as in Embodiment 1 of the present invention, resonance will occur near 12.5 GHz and spurious will occur near that. become. On the other hand, in the present invention, since both ends are joined to form a circle, resonance in the width direction does not occur and spurious does not occur.

  If a flat inner conductor is used as in the prior art, electrostatic capacity is also generated between the coil pattern and the shield case, which deteriorates the frequency characteristics of the low-pass filter. On the other hand, in the present invention, the inductor portion 13 is deformed so that the center portion thereof is about the center of the capacitor portion 12 that has been deformed into a circular shape. Since the capacity is reduced, the deterioration of the frequency characteristics is also reduced. That is, by deforming the inductor section 13 as described above, the shape in the length direction can be reduced and the frequency characteristics can be improved.

  In addition to the copper plate, the material of the internal conductor may be any material that has a low surface electrical resistance, such as a brass plate or a plated steel plate. As a brazing material, it is not necessary to simply join, but it is desirable that the electric resistance is equal to or smaller than the material of the surface of the inner conductor. In this respect, it is preferable to use silver brazing.

  In the first embodiment, the space between the capacitor portion 12 and the inner wall of the shield case 11 is a space, but a structure in which a dielectric is sandwiched therebetween may be used. In this way, the capacitor unit 12 can be further reduced in size.

  The low-pass filter according to the present invention has an effect that a low-pass filter that can be downsized and has excellent frequency characteristics can be obtained, and is useful for a low-pass filter such as a microwave or a quasi-microwave communication device.

Sectional drawing of the low-pass filter in Embodiment 1 of this invention The perspective view of the internal conductor used for the low-pass filter in Embodiment 1 of this invention Sectional view of a conventional low-pass filter

Explanation of symbols

11 Shield Case 12 Capacitor Part 13 Inductor Part 14 Inner Conductor 15 Joint Part

Claims (2)

A low pass filter configured by cutting a metal plate and alternately forming a capacitor portion and an inductor portion into a cylindrical shielding case with an internal space, the capacitor portion being bent in a circle A low-pass filter in which both ends thereof are joined by brazing, and the central portion of the inductor portion is bent so as to be near the central portion of the inner space of the shield case. The low-pass filter according to claim 1, wherein the brazing material uses a material having an electric resistance equal to or smaller than a surface material of the metal plate.

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