JP2014239350A - Filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance filter having an excellent frequency characteristic with a reduced passing loss caused by an influence of a metal member disposed in the periphery of the filter.SOLUTION: The filter includes a substrate 10, a plurality of resonant elements 21, 22, 23 configured by the juxtaposition of microstrip lines at a predetermined gap on the substrate 10, and a metal case 30 covering the plurality of resonant elements 21, 22, 23. The metal case 30 has an inner size which is specified in a direction orthogonal to a transmission direction Z to which the plurality of resonant elements 21, 22, 23 are juxtaposed, and determined to be a waveguide to cut off a frequency component of a pass band of the plurality of resonant elements 21, 22, 23 or lower. The metal case 30, which is a part of the substrate 10, is a case that covers only the plurality of resonant elements 21, 22, 23.

Description

  The present invention relates to a filter used in a high-frequency signal processing device such as a communication system.

  A filter used in a high-frequency signal processing apparatus such as a communication system that has been used in the past stores a substrate on which a resonant element is formed in a metal casing so that electromagnetic energy is emitted and electromagnetic noise from the outside is reduced. Prevents contamination.

  For example, in Patent Document 1, an internal space of a metal casing is provided by providing an unnecessary high-order mode blocking plate that substantially divides the internal space in the internal space of a metal casing that electromagnetically shields a high-frequency circuit. There is described a high-frequency circuit element that cuts off a high-frequency propagation path that propagates and suppresses excitation and propagation of unnecessary higher-order modes that adversely affect the frequency characteristics of the high-frequency circuit element.

JP 2000-269704 A

  However, if the entire substrate on which the resonant element is formed is housed in a metal casing, the cutoff characteristic on the low frequency side of the filter is destroyed, and the flatness of the passband cannot be ensured, resulting in a high pass loss. It was. That is, the passage loss in the pass band has increased due to the influence of the metal member disposed around the filter, such as the metal housing for housing the substrate described above.

  An object of the present invention is made in view of the above-described problems, and provides a high-performance filter having excellent frequency characteristics by reducing a passage loss due to the influence of a metal member arranged around the filter. For the purpose.

(First aspect)
A filter according to a first aspect of the present invention includes a substrate, a plurality of resonance elements configured by arranging microstrip lines in a signal transmission direction at predetermined intervals on the substrate, and a metal case covering the plurality of resonance elements. The internal dimensions of the metal case that are defined in the direction orthogonal to the signal transmission direction are determined so as to be a waveguide that cuts off frequency components below the passband of the plurality of resonant elements. Features.

  According to the first aspect, the inner dimension of the metal case is determined so as to be a waveguide that cuts off frequency components below the pass band of the plurality of resonant elements. For example, when the cross section inside the metal case is rectangular, the inner dimensions are defined by the width in the direction orthogonal to the signal transmission direction and the height from the substrate. It is determined to be a waveguide that cuts off frequency components below the passband.

  This prevents a frequency component to be cut by the filter device determined by the element characteristics of a plurality of resonant elements, that is, a frequency component equal to or lower than the passband from propagating into a space formed between the metal case and the resonant element. Thus, the cutoff characteristic on the low frequency side of the filter becomes steep, the flatness of the pass band can be ensured, and the pass loss can be reduced.

(Second aspect)
The metal case is a case that is a part of a substrate and covers only a plurality of resonant elements.

  According to the second aspect, by adopting a metal case sized so as to cover only the plurality of resonance elements, the filter is not affected by the overall size of the substrate on which the plurality of resonance elements are formed. The cutoff characteristic on the low frequency side becomes steep, the flatness of the pass band can be ensured, and the pass loss can be reduced.

(Third aspect)
According to the third aspect, the pass band of the plurality of resonant elements is a quasi-millimeter wave or millimeter-wave frequency of 20 GHz or more.

  In the quasi-millimeter wave or millimeter-wave frequency band of 20 GHz or more, the signal passage loss in the pass band becomes high due to the influence of a metal member arranged around the filter, such as a metal housing that houses the substrate. There is a problem.

  With respect to such a problem, according to the third aspect, it is possible to reduce the passage loss particularly in a filter applied to a quasi-millimeter wave or millimeter-wave frequency band of 20 GHz or higher.

  ADVANTAGE OF THE INVENTION According to this invention, the passage loss resulting from the influence of the metal member arrange | positioned around the filter can be reduced, and the high performance filter excellent in the frequency characteristic can be provided.

It is a figure for demonstrating the filter to which this invention was applied. It is a figure for demonstrating the internal dimension of a metal case. It is a figure for demonstrating the frequency characteristic of the filter which concerns on this embodiment, and the filter which concerns on a comparative example. It is a figure for demonstrating the frequency characteristic of the filter which concerns on this embodiment, and the filter which concerns on a comparative example. It is a figure for demonstrating the frequency characteristic of the filter which concerns on the other example of this embodiment, and the filter which concerns on a comparative example.

  A mode for carrying out the present invention (hereinafter referred to as the present embodiment) will be described with a specific example. The present embodiment relates to a filter used in a high-frequency signal processing device such as a communication system. As a first specific example of such a filter, the configuration of the filter 1 as shown in FIG. 1 will be described.

(1) Overall Configuration FIG. 1A is a perspective view showing an outline of the filter 1. As shown in FIG. 1A, the filter 1 covers the substrate 10 on which the microstrip line is formed, the resonant elements 21 to 23 formed on the substrate 10, and the resonant elements 21 to 23 formed on the substrate. A metal case 30.

  In the substrate 10, a metal layer 11 that functions as a ground electrode is formed on the bottom surface, a signal line 13 is formed on the top surface, and a dielectric layer 12 is laminated between the metal layer 11 and the signal line 13. . Specifically, as shown in FIG. 1B, the signal line 13 on the upper surface of the substrate 10 is referred to as a total of three resonant elements 21, 22, and 23 (collectively referred to as the resonant element 20) by strip conductive patterns. ) And input / output lines 24 and 25 are formed. The plurality of resonant elements 20 are arranged in the signal transmission direction Z at predetermined intervals, and are configured to transmit signals in a predetermined frequency band by coupling adjacent resonant elements 20 together. That is, the plurality of resonant elements 20 function as a three-stage band pass filter. The filter according to the present invention is not limited to a three-stage bandpass filter, and can be applied to a filter having a predetermined number of stages.

  The metal case 30 is a case that covers the resonant element 20 formed on the substrate 10. Preferably, the metal case 30 is a case that is a part of the substrate 10 and covers only the resonant element 20. In addition, the metal case 30 has an inner dimension of the case that is defined in a direction orthogonal to the signal transmission direction Z so that the width of the waveguide that cuts off a frequency component equal to or lower than the passband of the resonant element 20 is obtained. Is set. It is determined to be a waveguide that cuts off frequency components below the passband of a plurality of resonant elements.

  For example, as shown in FIG. 2, when the cross section inside the metal case 30 is rectangular, the internal dimensions of the metal case 30 can be expressed by the width in the direction orthogonal to the signal transmission direction and the height from the substrate 10. it can. For this reason, in this embodiment, the width of the metal case 30 surrounding the resonant element 20 when viewed from a cross section orthogonal to the signal transmission direction Z is a [m], and the height of the metal case 30 is Let b [m]. The waveguide cutoff frequency, that is, the cut-off frequency fc, of the waveguide whose tube shape is defined by such width a and height b can be derived from the following equation (1).

Here, C ₀ is the signal propagation speed, and m and n are the number of modes.

  As a specific example, the signal frequency propagating between the resonant elements 20 is 41 to 42 GHz, and the metal case 30 is a waveguide that cuts off 43 GHz or less. Here, the metal case 30 may be a waveguide that cuts off a frequency component equal to or lower than the pass band of the resonant element 20 in a state of being attached to the substrate 10.

  Further, since the cutoff frequency fc is the value of the lowest mode of the long side, if a> b, m = 1, n = 0, and the width a at fc = 43 GHz is calculated from the equation (1), a ≦ By satisfying the condition of 3.49 mm, the metal case 30 becomes a waveguide that suppresses the progress of radio waves of 43 GHz or less in a space formed between the metal case 30 and the resonant element 20.

  Therefore, when the signal frequency of the filter 1 is 41 to 42 GHz, the metal case 30 covers only the resonant element 20 so that the width thereof is a ≦ 3.49 mm, as will be apparent from the following evaluation result. Passage loss can be reduced.

  Next, the value of the width a of the filter 1 is set to 3.0 [mm], the value of the height b of the filter 1 is set to 2.0 [mm], and the characteristics of the filter 1 and a comparative example without a metal case The characteristics of the filter according to the above are evaluated with reference to FIGS. 3 (A) and 3 (B).

  That is, FIG. 3A is a diagram showing the frequency characteristics of the filter when the metal case 30 is not provided as a comparative example, and the values obtained from the circuit design values and simulation results of the frequency characteristics of the S (1,1) parameter. Are indicated by lines 111a and 111b, respectively, and the circuit design value of the frequency characteristic of the S (2,1) parameter and the value obtained from the simulation result are indicated by lines 121a and 121b, respectively.

  FIG. 3B is a diagram illustrating the frequency characteristics of the filter 1 according to the present embodiment, and the circuit design value and the value obtained from the simulation result of the frequency characteristics of the S (1,1) parameter are respectively expressed as lines 211a, The circuit design value of the frequency characteristic of the S (2,1) parameter and the value obtained from the simulation result are indicated by lines 221a and 221b, respectively.

  FIG. 4 is a view showing the frequency characteristics of the S (2,1) parameter of the comparative example and this embodiment side by side. Here, in FIG. 4, the frequency characteristic of the filter 1 according to the present embodiment is indicated by a solid line, and the frequency characteristic of the filter according to the comparative example is indicated by a broken line.

  First, as apparent from FIG. 3, the filter 1 according to the present embodiment has a lower passband region indicated by the arrows 31 and 32 than the filter without the metal case 30 as in the comparative example. The frequency characteristics are different. As is clear from FIG. 4, the filter 1 according to this embodiment has a radio wave progression of 43 GHz or less as shown by an arrow S <b> 1 in FIG. 4, as compared with the case where the metal case 30 is not provided as in the comparative example. And the cutoff characteristic on the low frequency side of the filter can be made steep. Further, the filter 1 according to the present embodiment can ensure the flatness of the pass band indicated by the arrow S2 in FIG. 4 compared to the case where the metal case 30 is not provided. Furthermore, the filter 1 according to the present embodiment can reduce the passage loss as shown by the arrow S3 in FIG. 4 compared to the case where the metal case 30 is not provided.

  In particular, when the pass band is as short as the 42 GHz band, the distance between the input and output lines is about 5 mm, and the coupling between the metal case and the resonant element becomes strong through the space. For this reason, the ideal cutoff characteristic cannot be obtained with the filter according to the comparative example. On the other hand, the filter 1 according to the present embodiment has the width a and the height b of the metal case 30 so as to be a waveguide that cuts off frequency components below the passband of the resonant element 20. Therefore, it is possible to suppress the progression of radio waves of 43 GHz or less in the space formed between the metal case 30 and the resonant element 20, and as a result, it is possible to reduce the passage loss between the resonant elements 20.

  Further, as shown in FIG. 1B, the filter 1 according to the present embodiment has the widths of the end portions 31 and 32 of the metal case 30 in the input / output lines 24 and 25 larger than the width a inside the metal case 30. It may be further narrowed. Thus, by making the widths of the end portions 31 and 32 narrower than the width a inside the metal case 30, it becomes possible to further reduce the passage loss while suppressing the emission of electromagnetic waves to the outside of the metal case 30. .

(2) Other Examples Further, as another specific example, an example in which the signal frequency propagating between the resonant elements 20 is 24 to 24.25 GHz and the metal case 30 is a waveguide that cuts off 25 GHz or less is shown. This frequency band of 24 to 24.25 GHz is called an ISM (Industry-Science-Medical) band.

  Since the cut-off frequency fc of the waveguide is the value of the lowest mode of the long side, if a> b, m = 1, n = 0, and the width a at fc = 25 GHz is calculated from the equation (1), a By satisfying the condition of ≦ 6.0 mm, the metal case 30 becomes a waveguide that suppresses the progression of radio waves of 25 GHz or less in a space formed between the metal case 30 and the resonant element 20.

  Therefore, when the signal frequency of the filter 1 is 24 to 24.25 GHz, the metal case 30 passes only in the resonant element 20 so that the width thereof is a ≦ 6.0 mm, thereby passing the same as in the above example. Loss can be reduced.

  FIG. 5A is a diagram showing the frequency characteristics of the filter when the metal case 30 is not provided as a comparative example, and the values obtained from the circuit design values and simulation results of the frequency characteristics of the S (1,1) parameter are shown as lines. Reference numeral 311 indicates a circuit design value of the frequency characteristic of the S (2,1) parameter and a value obtained from the simulation result, respectively, by a line 321.

  FIG. 5B is a diagram illustrating the frequency characteristics of the filter 1 according to the present example. A circuit design value of the frequency characteristics of the S (1,1) parameter and a value obtained from the simulation result are indicated by a line 411, and S A circuit design value of the frequency characteristics of the (2, 1) parameter and a value obtained from the simulation result are indicated by a line 421. The simulation result shown in FIG. 5B is a result when a is set to 5.3 mm.

  Thus, also in FIGS. 5 (A) and 5 (B), as in the case of FIGS. 3 (A), 3 (B), and 4 described above, the passage loss is reduced and the cutoff characteristic on the low frequency side is reduced. It has been shown to be excellent.

(3) Effect As described above, the filter 1 according to the present embodiment determines the inner dimension of the metal case so as to be a waveguide that cuts off frequency components below the passband of the plurality of resonant elements. The cutoff characteristic on the low frequency side of the filter becomes steep, the flatness of the pass band can be ensured, and the pass loss can be reduced. That is, the filters 1 and 50a can realize excellent frequency characteristics without increasing the pass loss in the pass band due to the influence of the metal members arranged around the filter.

  Preferably, the filter 1 according to the present embodiment employs a metal case 30 that is a part of the substrate and covers only the resonant element, thereby covering the entire substrate with the case. Without being affected by the overall size of the substrate on which the resonant element is formed, the cutoff characteristic on the low band side of the filter becomes steep, the flatness of the pass band can be ensured, and the pass loss can be reduced.

  The filter 1 according to the present embodiment is not limited to the above-described frequency band, and the filter 1 according to the present embodiment has an internal dimension of the metal case 30 and frequency components equal to or lower than the pass bands of a plurality of resonance elements according to application examples. By setting the predetermined value so as to be a waveguide to be cut off, the passage loss can be reduced. Here, at a quasi-millimeter wave or millimeter-wave frequency of 20 GHz or more, the passage loss in the pass band is high due to the influence of a metal member arranged around the filter, such as a metal housing that houses the substrate. There is a problem of becoming. For this reason, the filter 1 according to the present embodiment can reduce the passage loss particularly in a filter applied to a quasi-millimeter wave or millimeter-wave frequency of 20 GHz or more.

1 Filter 10 Substrate 20, 21, 22, 23 Resonant element 30 Metal case

Claims (3)

A substrate,
A plurality of resonant elements configured by arranging microstrip lines in the signal transmission direction at predetermined intervals on the substrate;
A metal case that covers the plurality of resonant elements,
The metal case has an inner dimension that is defined in a direction orthogonal to the signal transmission direction so as to be a waveguide that cuts off frequency components below the passband of the plurality of resonant elements. A filter characterized by   The filter according to claim 1, wherein the metal case is a part of the substrate and covers only the plurality of resonant elements.   2. The filter according to claim 1, wherein a pass band of the plurality of resonant elements is a quasi-millimeter wave or millimeter-wave frequency of 20 GHz or more.