JP2011097393A - Band pass filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve attenuation characteristics of a band pass filter on a high frequency side other than a pass band by devising the shield case structure of the band pass filter. <P>SOLUTION: In the band pass filter configured of a substrate 100 configured by disposing resonance elements 150a-150f each formed of a microstrip line at predetermined intervals and a shield case 200 surrounding the substrate 100, the shield case 200 includes: a first space portion 280 which is wider than the area where the plurality of resonance elements 150a-150f are disposed, and has a predetermined height; and a second space portion 290 which is formed continuously above the first spatial portion 280 and has a predetermined cutoff frequency. The input high frequency signal of a pass band is transmitted under a transmission mode by the microstrip line and spatial propagation caused by the waveguide mode of an input high frequency signal of a predetermined frequency or lower is suppressed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a band-pass filter that handles high-frequency signals such as a microwave band and a millimeter wave band, and more particularly to a shield case structure with improved pass characteristics.

  Conventionally, high-frequency devices that handle high-frequency signals are equipped with various high-frequency circuits such as amplifiers, mixers, and filters. Among these, the filter is composed of a substrate on which a plurality of resonant elements formed of microstrip lines are arranged at predetermined intervals, and a shield case surrounding the substrate, and a signal in a predetermined frequency band among input high-frequency signals. There is a band-pass filter that passes. Examples of the band pass filter include a side coupling filter, an interdigital filter, and a hairpin filter.

  By the way, in the bandpass filter, the space between the microstrip line and the shield case acts as a waveguide, and the input high-frequency signal does not transmit only the microstrip line, but propagates between the input and output terminals of the filter. By doing so, it appears as an unnecessary signal component other than the pass band, and the filter characteristics deteriorate.

  Therefore, as a method for preventing the deterioration of the filter characteristics due to such spatial propagation, a shield case structure that accommodates the filter and its peripheral parts has been proposed. As shown in FIG. 4A, the ceiling surface on the filter 2 of the shield case 6 includes a substrate 1 on which the filter 2 and its peripheral components 3 to 5 are mounted, and a shield case 6 surrounding the substrate 1. The height of 6c is lowered as a whole, and the ceiling surface 6c and the filter 2 are close to each other. With this shield case structure, the space between the filter 2 and the shield case 6 can be reduced, and air coupling can be reduced. As shown in FIG. 4B, the filter characteristics are improved from the dotted line A to the solid line. (For example, refer to Patent Document 1).

  However, in the case of a bandpass filter formed of a microstrip line, as described above, if the height of the ceiling surface on the resonance element of the shield case is lowered as a whole and the ceiling surface and the resonance element are too close, The pass characteristic of the band pass filter starts to collapse from the low frequency side, and the overall pass characteristic including the pass band is deteriorated. Conversely, if the height of the ceiling is such that the pass characteristics of the bandpass filter do not deteriorate overall, the spatial propagation between the input and output terminals cannot be sufficiently suppressed, and high frequencies other than the passband of the bandpass filter The pass characteristics (attenuation characteristics) on the side cannot be improved so much.

  In order to solve this problem, not only the height of the ceiling surface of the shield case but also the width between the sides of the shield case is reduced, and the cut-off frequency as the waveguide mode is increased to increase the spatial propagation between the input and output terminals. Can be suppressed and pass characteristics (attenuation characteristics) on the high frequency side other than the pass band of the band pass filter can be improved. However, if both sides of the shield case are too close to the microstrip line, the band pass filter still remains. There was a problem that the overall passage characteristics of the camera deteriorated.

Japanese Patent Application Laid-Open No. 2003-209386 (pages 2 to 3, FIGS. 1 and 9)

  In view of the above problems, an object of the present invention is to provide a bandpass filter that can improve attenuation characteristics on the high frequency side other than the passband as a shield case structure.

  In order to solve the above problems, the present invention provides a bandpass filter comprising a substrate configured by arranging a plurality of resonant elements formed of microstrip lines at predetermined intervals, and a shield case surrounding the substrate. The shield case is formed with a first space portion having a predetermined height which is wider than a region where the plurality of resonance elements are arranged, and is connected to the upper side of the first space portion, and has a predetermined cutoff. A second spatial portion having a frequency, and transmitting an input high-frequency signal in a pass band in a transmission mode using a microstrip line, and suppressing spatial propagation in a waveguide mode of the input high-frequency signal below a predetermined frequency It is the structure characterized by doing.

  According to a second aspect of the present invention, in the bandpass filter according to the first aspect, the first space portion has a wider width and a predetermined height than a region where the plurality of resonant elements are arranged, and the second space. The portion has a structure having a width narrower than the width of the first space portion and a predetermined height.

  According to the present invention, as a shield case structure surrounding a substrate configured by arranging a plurality of resonant elements formed by microstrip lines at predetermined intervals, an input high frequency signal in a passband can be transmitted without disturbing a transmission mode by the microstrip line. Since it includes a first space portion and a second space portion for transmitting and suppressing spatial propagation due to the waveguide mode of a high-frequency signal having an attenuation band not less than a predetermined frequency and not less than a predetermined frequency in the pass band. Thus, it is possible to realize a band pass filter having better attenuation characteristics on the high frequency side than a signal in a predetermined pass band.

It is a figure which shows the bandpass filter by this invention, (A) is a cross-sectional view, (B) is a sectional side view. It is a top view which shows the board | substrate of the bandpass filter by this invention. It is a figure which shows the pass characteristic of the band pass filter by this invention. It is a figure for demonstrating the conventional high frequency filter, (A) is a sectional side view which shows the shielding case structure of a high frequency filter, (B) is a figure which shows attenuation amount deterioration of a high frequency filter.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The band-pass filter according to the present invention allows a signal in a predetermined frequency band to pass, and is used in a high-frequency circuit mounted on a high-frequency device that handles a high-frequency signal such as a microwave band or a millimeter wave band.

  As shown in FIGS. 1 and 2, the bandpass filter includes a substrate 100 in which a plurality of resonant elements 150 a to 150 f formed by microstrip lines are arranged at predetermined intervals, and a box-shaped aluminum die-cast surrounding the substrate 100. And a shield case 200 made of metal.

  The substrate 100 is formed around the dielectric 110, the ground conductor 120 formed on the entire back surface of the dielectric 110, the pattern formation region A on the surface of the dielectric 110, and the ground conductor 120 on the back surface through a plurality of through holes 180. A ground conductor 130 connected to the input line 140, an input line 140 made of a microstrip line formed in the pattern formation region A on the surface of the dielectric 110, six resonant elements 150a to 150f, and an output line 160. . Further, near the corner portion of the substrate 100, four screw holes 170 that penetrate the dielectric 110 and the ground conductor 120 and the ground conductor 130 formed on the front and back surfaces of the dielectric 110 are provided.

  The band-pass filter of this embodiment is a side-coupled filter as shown in FIG. 2, and the pattern of these microstrip lines is formed in the pattern formation region A on the dielectric 110 by etching a metal such as copper foil. Has been. In addition to the side-coupled filter, a microstrip line pattern such as an interdigital filter or a hairpin filter may be formed as the band pass filter.

  The shield case 200 is divided into an upper case 210 and a lower case 220. The lower case 220 has an input terminal 230 connected to an input line 140 formed on the surface of the dielectric 110, and a surface of the dielectric 110. An output terminal 240 connected to the output line 160 formed in the above is arranged, and a high-frequency signal is inputted / outputted by the input terminal 230 and the output terminal 240.

  Four screw holes 250 and four screw holes 260 are penetrated near the corners of the upper case 210 and the lower case 220, respectively. The shield case 200 is connected to the upper case 210 and the lower case by the four screws 270. The substrate 100 is fixed so as to be sandwiched between 220. As a result, the upper case 210, the ground conductor 130, the ground conductor 120, and the lower case 220 surround the microstrip line on the dielectric 110 via the four screws 270 to form the shield case 200.

  Next, the structure of the shield case 200, which is a feature of the bandpass filter of the present invention, will be described. The upper case 210 that is in close contact with the substrate 100 transmits a high-frequency signal in a predetermined passband input from the input terminal 230 without disturbing the transmission mode by the microstrip line, and among the input signals, A first space portion 280 and a second space portion 290 are provided for suppressing the spatial propagation of the high-frequency signal in the attenuation band not less than the predetermined frequency and not more than the predetermined frequency due to the waveguide mode.

  The first space portion 280 is configured by a rectangular shape extending in a rectangular shape from the input terminal 230 toward the output terminal 240, and is a direction orthogonal to the transmission direction of the high-frequency signal input from the input terminal 230 through the input line 140. And a width W1 for transmitting a high-frequency signal in a predetermined passband without disturbing the transmission mode by the microstrip line with a width a greater than or equal to the maximum width a between the open ends of the plurality of resonant elements 150a to 150f in FIG. It can be formed or cut by aluminum die casting or the like, and has a predetermined height H1 for transmission without disturbing the transmission mode by the microstrip line.

  In the present embodiment, the maximum width a is a width between the lower edge of the resonance element 150a and the upper edge of the resonance element 150f in FIG. The width W1 is a width between the left side surface 282 and the right side surface 283, and is a width that is symmetrically separated from the alternate long and short dash line that is the center line of the group of the plurality of resonance elements 150a to 150f. Further, the width W1 is equal to the width b of the pattern formation region A of the dielectric 110 in FIG. The height H <b> 1 is a height from the surface of the pattern formation region A of the dielectric 110 to the ceiling surface 281 of the first space 280.

  Similarly to the first space portion 280, the second space portion 290 is configured by a rectangular body extending in a rectangular shape from the input terminal 230 toward the output terminal 240, and the first space is located above the first space portion 280. Formed as a space continuous with the portion 280, and is larger than the maximum width a between the edges of the open ends of the plurality of resonance elements 150a to 150f (hereinafter referred to as the width a of the group of the plurality of resonance elements 150a to 150f), In addition, the input signal is smaller than the width W1 of the first space 280 for transmitting a high-frequency signal in a predetermined pass band without disturbing the transmission mode by the microstrip line. And a width W2 for suppressing the spatial propagation of the high-frequency signal having an attenuation band equal to or lower than the predetermined frequency by the waveguide mode, and a height H2 for transmitting the transmission mode by the microstrip line without disturbing it. It is formed from.

  The width W2 is a width between the left side surface 292 and the right side surface 293, and is symmetrically separated from the one-dot chain line that is the center line of the plurality of resonance elements 150a to 150f, similarly to the first space portion 280. Width. Further, the width W2 is obtained by dividing the light velocity c by twice the width W2 when the second space 290 is assumed to be a rectangular waveguide in order to suppress the waveguide mode spatial propagation. It is set in consideration of the cut-off frequency fc. The height H <b> 2 is a height from the ceiling surface 281 to the ceiling surface 291 of the first space portion 280.

  Specific design values of the plurality of resonance elements 150a to 150f on the dielectric 110 and the upper case 210 of the shield case 200 described above are, for example, the relative permittivity of the substrate 100 having a thickness T of 0.6 mm. Is 2.6 band-pass filter that passes a signal in a frequency band of 30 GHz to 31 GHz from a high-frequency signal input to the input terminal 230 and outputs the signal from the output terminal 240, a plurality of resonant elements 150a. The width a of the ~ 150f group is approximately 2.4 mm. In addition, as the minimum dimensions for transmitting a high frequency signal in the passband without disturbing the transmission mode by the microstrip line, each dimension forming the first space portion 280 has a width W1 of 4 mm and a height H1 of 1 mm. The dimensions forming the second space 290 are a width W2 of 3 mm and a height H2 of 3 mm. At this time, the cut-off frequency fc of the second space 290 is approximately 50 GHz.

  FIG. 3 shows the pass characteristics of the bandpass filter. The solid line pass characteristic is the pass characteristic of the bandpass filter of the present invention according to the above-described design value, and the pass characteristic such as the dotted line and the alternate long and short dash line simply forms a box-like space as described in the background art section. In this case, the height of the ceiling surface and the width between the side surfaces of the shield case are set. When the shield case width is 5 mm and the height is 4 mm, the dashed line pass characteristic is when the shield case width is 4 mm and when the height is 4 mm. This is a case where the width of the case is 4 mm and the height is 3 mm. As described in the background art, the pass characteristic (attenuation characteristic) on the high frequency side other than the pass band of the band pass filter cannot be sufficiently improved only by reducing the width and height of the shield case.

  On the other hand, in the present embodiment, as the structure of the shield case 200, an input high frequency signal in the pass band is transmitted without disturbing the transmission mode by the microstrip line, and the frequency is higher than the input pass band and equal to or lower than the predetermined frequency. Since the first space portion 280 and the second space portion 290 for suppressing the spatial propagation of the high-frequency signal in the attenuation band due to the waveguide mode are formed, the high frequency side of the signal in the passband frequency of 30 GHz to 31 GHz is formed. As a result, the attenuation characteristic can be improved by setting the attenuation amount to approximately 30 dB or less at a frequency of 32.5 to 39.5 GHz. Further, according to the present invention, the attenuation characteristic can be improved compared to the conventional case even on the low frequency side of the signal having a passband frequency of 30 GHz to 31 GHz.

  In the present embodiment, the width W2 of the second space 290 is larger than the width a of the plurality of resonance elements 150a to 150f, and the width W1 for transmitting without disturbing the transmission mode by the microstrip line. However, the present invention is not limited to this, and by forming the first space portion 280, the left side surface 292 and the right side surface 293 of the second space portion 290 and a plurality of microstrip lines are provided. Since the resonance elements 150a to 150f are not too close to each other, the second space portion 290 has a range that does not affect the suppression effect of the space propagation by the waveguide mode and the deterioration of the passband pass characteristic. The width W2 may be equal to or smaller than the width a of the plurality of resonance elements 150a to 150f. In the present embodiment, the width W1 of the first space portion 280 is equal to the width b of the pattern formation region A. However, the present invention is not limited to this, and suppression of spatial propagation by the waveguide mode is performed. The width b of the pattern formation region A may be larger or smaller than the width W1 of the first space 280 as long as the range does not affect the effect and the deterioration of the pass characteristics of the passband. Furthermore, although the present embodiment has been described as a band pass filter, the present invention is not limited to this and may be a high pass filter. Further, in the present embodiment, the shape of the second space portion 290 is a rectangular body having a rectangular cross section, but the present invention is not limited to this, and may be a shape obtained by extending an arc-shaped cross section.

  According to the bandpass filter according to the present invention described above, the shield case 200 (upper case 210) is wider than the region where the plurality of resonant elements 150a to 150f are arranged and has a predetermined height. 280 and a second space part 290 formed above the first space part 280 and having a predetermined cut-off frequency, and transmits an input high-frequency signal in the pass band in a transmission mode using a microstrip line. At the same time, it is characterized in that the spatial propagation due to the waveguide mode of the input high frequency signal below a predetermined frequency is suppressed. The first space portion 280 has a width W1 wider than a region where the plurality of resonant elements 150a to 150f are arranged and a predetermined height H1, and the second space portion 290 has a width W1 of the first space portion 280. It has a narrower width W2 and a predetermined height H2.

  Thus, as a shield case structure surrounding a substrate configured by arranging a plurality of resonant elements formed by microstrip lines at predetermined intervals, an input passband high frequency signal is transmitted without disturbing the transmission mode by the microstrip line. Since the first space portion and the second space portion for suppressing the spatial propagation by the waveguide mode of the high-frequency signal having the attenuation band not less than the predetermined frequency and not less than the predetermined passband frequency are provided, In the shield case formed in a space, it is possible to realize a band-pass filter having better attenuation characteristics on the high-frequency side than a signal in a predetermined pass band that is limited.

DESCRIPTION OF SYMBOLS 100 Board | substrate 110 Dielectric 120 Ground conductor 130 Ground conductor 140 Input line 150a-150f Resonant element 160 Output line 170 Screw hole 180 Through hole 200 Shield case 210 Upper case 220 Lower case 230 Input terminal 240 Output terminal 250 Screw hole 260 Screw hole 270 Screw 280 First space 281 Ceiling surface 282 Left side 283 Right side 290 Second space 291 Ceiling surface 292 Left side 293 Right side W1 Width of first space H1 Height of first space W2 W2 of second space Width H2 Height of second space A Pattern formation region a Maximum width between edges of open ends of a plurality of resonant elements in a direction orthogonal to the transmission direction of the high frequency signal b Width of pattern formation region T Thickness of dielectric

Claims (2)

  In a bandpass filter comprising a substrate configured by arranging a plurality of resonant elements formed of microstrip lines at predetermined intervals and a shield case surrounding the substrate, the shield case is wider than a region where the plurality of resonant elements are arranged. And a first space portion having a predetermined height, and a second space portion formed continuously above the first space portion and having a predetermined cut-off frequency. A band-pass filter that transmits a signal in a transmission mode using a microstrip line and suppresses spatial propagation in a waveguide mode of an input high-frequency signal having a frequency equal to or lower than a predetermined frequency.   The first space portion has a width and a predetermined height wider than a region where the plurality of resonant elements are arranged, and the second space portion has a width and a predetermined height narrower than the width of the first space portion. The bandpass filter according to claim 1, comprising:

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