JP6232797B2 - Bandpass filter - Google Patents

Description

  The present invention relates to a bandpass filter that passes a signal having a frequency within a predetermined frequency band.

  In recent years, communication technologies that handle electromagnetic waves, such as mobile communication systems using mobile phones and smartphones, wireless LANs, and the like have become widespread. An electronic device used in such a communication technique may be provided with a band-pass filter that passes a signal having a frequency within a predetermined frequency band. For example, FIG. 11 of Patent Document 1 describes a band-pass filter in which two input / output electrodes and a resonance electrode are provided on a dielectric block. In the band-pass filter of Patent Document 1, when a signal having a frequency near the resonance frequency of the resonance electrode is input to one input / output electrode, the resonance electrode disposed between the input / output electrodes resonates, A signal is transmitted between the input / output electrodes. On the other hand, when a signal having a frequency away from the resonance frequency of the resonance electrode is input to one of the input / output electrodes, the resonance electrode does not resonate, and thus no signal is transmitted between the input / output electrodes.

JP-A-5-343902

  By the way, in the band-pass filter of the above-mentioned patent document 1, a ground electrode covering the entire bottom surface of the dielectric block is provided in order to release noise other than a desired signal from the input / output electrode. However, such a ground electrode does not have a frequency characteristic like a resonance electrode, and when a signal or noise having a frequency outside a predetermined frequency band is given to the ground electrode, the ground electrode does not generate noise. The bandpass filter disclosed in Patent Document 1 has a problem that noise cannot be effectively removed.

  Therefore, an object of the present invention is to provide a bandpass filter capable of effectively removing noise. Another object of the present invention is to provide a band-pass filter that can reduce the adverse effects of common mode noise that affects both the signal transmission unit and the ground.

  The present invention has been made to solve the above-mentioned problems, and is a bandpass filter that passes a signal having a frequency within a predetermined frequency band, and is provided on the dielectric substrate and the predetermined frequency band. And a signal ground provided on the dielectric substrate and provided around the signal transmission unit. The signal transmission unit includes an input transmission path connected to the signal input terminal, an output transmission path connected to the signal output terminal, and a resonant element disposed next to the input transmission path and the output transmission path. The signal ground has a resonance frequency that is substantially the same as the resonance frequency of the resonance element.

  In the bandpass filter, the signal ground itself has a resonance frequency that is substantially the same as the resonance frequency of the resonance element, so that noise having a frequency outside a predetermined frequency band hardly passes through the ground. For this reason, the bandpass filter can effectively remove noise, and a bandpass filter that is strong against common mode noise can be obtained.

  In the bandpass filter, the signal transmission unit may be disposed on the main surface of the dielectric substrate, and the signal ground may be disposed in the dielectric substrate. According to this configuration, since the signal transmission unit is exposed from the dielectric substrate, it is possible to easily manufacture the bandpass filter itself and to incorporate the bandpass filter into other devices.

  The bandpass filter may further include a frame ground disposed on a surface opposite to the main surface of the dielectric substrate and connected to a signal ground. By providing the frame ground, there is an advantage that it is further strong against noise and common mode noise.

  In the bandpass filter, it is preferable that the signal ground and the frame ground have substantially the same shape and the same size.

In the bandpass filter, the signal ground may include an opening , and the signal transmission unit may be disposed inside the opening . According to this configuration, since the signal ground does not interfere with the electromagnetic field generated in the signal transmission unit, the ground can be disposed at a position close to the signal transmission unit. Thereby, it can reduce that an electromagnetic field leaks from the side surface of a dielectric substrate.

The signal ground opening has a rectangular shape, and may have a long side longer than the length of the resonant element. According to this configuration, since the area of the bandpass filter can be reduced, there is an advantage that mounting is easy.

  In the bandpass filter, the signal transmission unit may include two resonant elements. In this case, it is preferable that the input transmission path and the output transmission path are disposed between the two resonant elements, and the two resonant elements extend along the input transmission path and the output transmission path. According to this configuration, since the electromagnetic field generated around the input transmission path and the output transmission path is shielded by the two resonant elements, the leakage of the electromagnetic field from the side surface of the dielectric substrate can be reduced.

It is a perspective view of the band pass filter concerning the embodiment of the present invention. It is a disassembled perspective view of the band pass filter of FIG. It is a top view of the band pass filter of FIG. It is a top view of the signal ground in the band pass filter of FIG. It is a bottom view of the band pass filter of FIG. It is a figure which shows the current distribution of the signal ground which concerns on Example 1 of this invention. It is another figure which shows the current distribution of the signal ground which concerns on Example 1 of this invention. It is a graph which shows the frequency characteristic of the band pass filter which concerns on Example 2 of this invention. It is a graph which shows the frequency characteristic of the band pass filter which concerns on the comparative example 2-1. It is a graph which shows the frequency characteristic of the band pass filter which concerns on the comparative example 2-2. It is a graph which shows the frequency characteristic of the band pass filter which concerns on Comparative Example 2-3.

  Hereinafter, a bandpass filter according to an embodiment of the present invention will be described with reference to the drawings. In addition, about the structure already demonstrated and the structure equivalent to this, the same code | symbol is attached | subjected and the same description is not repeated. For convenience of explanation, in each figure, the direction indicated by the double arrow W is the width direction of each component, the direction indicated by the double arrow D is the depth direction of each component, and the direction indicated by the double arrow H is each It will be referred to as the height direction of the structure.

  The band pass filter 10 according to the present embodiment is for passing a signal having a frequency within a predetermined frequency band (pass band). As shown in FIG. 1, the dielectric substrate 1 and the signal transmission unit 2 are used. And a signal ground 3 and a frame ground 4.

  As shown in FIGS. 1 and 2, the dielectric substrate 1 is formed in a rectangular shape and includes dielectric layers 11 and 12. The dielectric layer 11 is disposed between the signal transmission unit 2 and the signal ground 3 in the height direction H of the dielectric substrate 1. The dielectric layer 12 is disposed between the signal ground 3 and the frame ground 4 in the height direction H of the dielectric substrate 1.

  As shown in FIG. 1, the signal transmission unit 2 is provided on the main surface S of the dielectric substrate 1, that is, on the dielectric layer 11 so as to extend along the width direction W of the dielectric substrate 1. . 2 and 3, the signal transmission unit 2 includes an input transmission path 21 connected to the signal input terminal 25, an output transmission path 22 connected to the signal output terminal 26, an input transmission path 21 and an output. And resonant elements 23 and 24 arranged next to the transmission path 22. The input transmission path 21, the output transmission path 22, and the resonant elements 23 and 24 are not particularly limited, but can be formed of a metal foil such as a copper foil, for example. Moreover, the input transmission path 21 and the output transmission path 22 are formed in a monopole antenna shape, for example.

As shown in FIG. 3, the input transmission path 21 and the output transmission path 22 are disposed between the resonance element 23 and the resonance element 24 in the depth direction D of the signal transmission unit 2. The resonant elements 23 and 24 extend along the input transmission path 21 and the output transmission path 22. The resonant elements 23 and 24 have a resonant frequency (for example, 2.45 GHz) near the center of the pass band of the bandpass filter 10. In addition, λ described below is a wavelength at a resonance frequency, and is a length in consideration of wavelength shortening by a dielectric or the like. The length (dimension in the width direction W) L _{w1 of the} input transmission path 21 and the length (dimension in the width direction W) L _w2 of the output transmission path 22 are each ¼λ. The lengths (dimensions in the width direction W) _Lw3 of the resonant elements 23 and 24 are ½λ.

The width of the pass band of the bandpass filter 10 can be adjusted by changing the distance L _d1 (FIG. 3) between the input transmission path 21 and the output transmission path 22 and the resonant elements 23 and 24. That is, if the distance L _d1 is reduced, the degree of electromagnetic coupling between the input transmission path 21 and the output transmission path 22 and the resonant elements 23 and 24 increases. In this case, since the signal is transmitted from the input transmission path 21 to the output transmission path 22 even if the resonance of the resonance elements 23 and 24 is small, the width of the pass band of the bandpass filter 10 is widened. On the other hand, if the distance L _d1 is increased, the degree of electromagnetic coupling between the input transmission path 21 and the output transmission path 22 and the resonant elements 23 and 24 decreases. In this case, since the signal is transmitted from the input transmission path 21 to the output transmission path 22 only when the resonance of the resonance elements 23 and 24 is large, the width of the pass band of the bandpass filter 10 is narrowed.

  As shown in FIGS. 1 and 2, the signal ground 3 is disposed in the dielectric substrate 1. Specifically, the signal ground 3 is provided between the dielectric layer 11 and the dielectric layer 12 in the height direction H. The signal ground 3 is not particularly limited, but can be formed of, for example, a metal foil such as a copper foil.

As shown in FIGS. 2 and 4, the signal ground 3 has a rectangular shape. The length (dimension in the width direction W) and width (dimension in the depth direction D) of the signal ground 3 are substantially equal to the length (dimension in the width direction W) and the width (dimension in the depth direction D) of the dielectric substrate 1. . The thickness of the dielectric layer 11 (the dimension in the height direction H), that is, the distance L _h1 (FIG. 2) in the height direction H between the signal ground 3 and the signal transmission unit 2 is the ground in a general bandpass filter. Is preferably smaller than the distance between the signal transmission unit and the signal transmission unit. For example, in a general band pass filter, the distance between the ground and the signal transmission unit is about 1.0 mm to 1.6 mm, whereas the distance L _h1 in the band pass filter 10 of the present embodiment is 0.1 mm. It can be set to ˜0.5 mm, more preferably 0.1 mm to 0.2 mm.

As shown in FIGS. 2 and 4, the signal ground 3 is provided around the signal transmission unit 2. Specifically, the signal ground 3 has an annular shape by having the opening 31. The opening 31 only needs to be provided as a portion that does not conduct with respect to a portion other than the opening 31 that conducts as ground. Inside the opening 31, the input transmission path 21, the output transmission path 22, and the resonance elements 23 and 24 of the signal transmission unit 2 are arranged. The signal input terminal 25 and the signal output terminal 26 are disposed on the dielectric substrate 1 at both ends in the width direction W of the dielectric substrate 1 and outside the opening 31. In other words, signal ground 3 of the present embodiment is defined by a rectangle having a longer long side than the length L _w3 resonator element 23, 24.

The opening 31 of the signal ground 3 of the present embodiment has a rectangular shape. The input transmission path 21 and the output transmission path 22 of the signal transmission unit 2 are provided along the long side of the opening 31, and the signal input terminal 25 and the signal output terminal 26 are positioned at both ends of the long side of the signal ground 3. doing. The opening 31 is formed such that the length of the long side (dimension in the width direction W) L _w4 (FIG. 4) is 1 / 2λ, that is, longer than the length L _w3 of the resonance elements 23 and 24. . For example, in the case of the present embodiment, the length is set to be about 0.4 mm longer, but may be set to be about 0.3 mm to about 0.5 mm longer in consideration of the intersection in manufacturing the substrate. Thereby, the signal ground 3 has a resonance frequency substantially the same as the resonance frequency of the resonance elements 23 and 24. Since the signal ground 3 only needs to be able to resonate with a signal having a frequency within the pass band of the bandpass filter 10, the “resonance frequency substantially the same as the resonance frequency of the resonance elements 23 and 24” of the signal ground 3 is at least the bandpass filter 10. Any frequency included in the passband may be used. However, the resonance frequency of the signal ground 3 is preferably a frequency in the vicinity of the center of the pass band of the bandpass filter 10, similarly to the resonance elements 23 and 24. For example, the resonance frequency of the signal ground 3 can be the resonance frequency ± 100 MHz of the resonance elements 23 and 24, more preferably the resonance frequency ± 50 MHz of the resonance elements 23 and 24.

As shown in FIGS. 1 and 5, the frame ground 4 is provided on the surface opposite to the main surface S of the dielectric substrate 1, that is, on the bottom surface of the dielectric layer 12, and covers the entire bottom surface of the dielectric layer 12. Covering. The frame ground 4 has a rectangular shape that is substantially the same shape and size as the signal ground 3. The shapes and dimensions of the signal ground 3 and the frame ground 4 do not need to be exactly the same. For example, when the signal ground 3 and the frame ground 4 are overlapped, the outer edges of both are 0.15 mm to 0.00 mm. It may be displaced by about 2 mm. The frame ground 4 is connected to the signal ground 3. The thickness (dimension in the height direction H) of the dielectric layer 12, that is, the distance L _h2 (FIG. 2) in the height direction H between the frame ground 4 and the signal ground 3 is not particularly limited. For example, the thickness may be 1.0 mm to 3.0 mm, more preferably 1.5 mm to 2.0 mm. The frame ground 4 is formed of a metal foil such as a copper foil, for example.

  Next, the operation of the bandpass filter 10 configured as described above will be described.

<Operation of signal transmission unit>
First, the basic operation of the bandpass filter 10, that is, the operation of the signal transmission unit 2 will be described.

  In the band pass filter 10, when an electromagnetic wave signal having a frequency within the pass band is input to the signal input terminal 25, the signal propagates through the input transmission path 21, and an electromagnetic field is generated around the input transmission path 21. The resonant elements 23 and 24 resonate due to the electromagnetic field around the input transmission path 21, and an electromagnetic field is also generated around the resonant elements 23 and 24. The output transmission path 22 resonates due to the electromagnetic field around the resonant elements 23 and 24, and the input transmission path 21 and the output transmission path 22 are electromagnetically coupled. As a result, the signal input to the signal input terminal 25 propagates from the input transmission path 21 to the output transmission path 22 and is output from the signal output terminal 26.

  Thus, if the frequency of the signal input to the signal input terminal 25 is within the pass band of the bandpass filter 10, this signal is transmitted from the signal input terminal 25 to the signal output terminal 26. However, the closer the frequency of the input signal is to the resonant frequency of the resonant elements 23 and 24, the greater the signal transmission efficiency from the signal input terminal 25 to the signal output terminal 26.

  On the other hand, in the band pass filter 10, when an electromagnetic wave signal having a frequency outside the pass band is input to the signal input terminal 25, an electromagnetic field is generated around the input transmission path 21. However, since the resonant elements 23 and 24 do not resonate due to the electromagnetic field around the input transmission path 21, no electromagnetic coupling occurs between the input transmission path 21 and the output transmission path 22. For this reason, the signal input to the signal input terminal 25 does not propagate to the output transmission path 22 and is not output from the signal output terminal 26.

  Even if the frequency of the signal input to the signal input terminal 25 is outside the pass band, for example, when the frequency is near the boundary of the pass band, the signal input terminal 25 to the signal output terminal 26 are used. A signal may be transmitted to However, even in this case, there is no particular problem because the amount of signal transmission from the signal input terminal 25 to the signal output terminal 26 is negligibly small.

<Ground operation>
Next, the operation of the signal ground 3 will be described.

  The signal ground 3 allows a signal having a frequency within the passband of the bandpass filter 10 to pass when an electromagnetic wave signal is given regardless of a signal input to the signal input terminal 25, but a frequency outside the passband. Limit the passage of signals.

  More specifically, when a signal other than a signal having a frequency in the passband is applied to the signal ground 3, the signal ground 3 having a resonance frequency approximate to the resonance frequency of the resonance elements 23 and 24 resonates. As a result, the signal given to the signal ground 3 propagates through the signal ground 3 and passes through the signal ground 3. On the other hand, when a signal having a frequency outside the passband and noise are applied to the signal ground 3, the signal ground 3 does not resonate. For this reason, the signal and noise given to the signal ground 3 do not propagate through the signal ground 3 and do not pass through the signal ground 3.

  Thus, in the bandpass filter 10 of the present embodiment, the signal ground 3 itself has a resonance frequency that is substantially the same as the resonance frequency of the resonance elements 23 and 24. For this reason, high frequency noise outside the pass band hardly passes through the signal ground 3. Therefore, the band pass filter 10 can effectively remove noise. Since the signal transmission unit 2 and the signal ground 3 have substantially the same resonance frequency, it is particularly effective for common mode noise outside the passband.

Further, in the band pass filter 10, since the input transmission path 21 and the output transmission path 22 are arranged between the resonant element 23 and the resonant element 24, the bandpass filter 10 is generated around the input transmission path 21 or the output transmission path 22. The electromagnetic field is shielded by the resonant elements 23 and 24. As a result, leakage of the electromagnetic field from the side surface of the dielectric substrate 1 can be reduced. Furthermore, since the distance L _h1 (FIG. 2) between the signal ground 3 and the signal transmission unit 2 is reduced in the bandpass filter 10, it is possible to more reliably reduce the leakage of the electromagnetic field from the side surface of the dielectric substrate 1. .

Further, the band-pass filter 10, signal ground 3 includes an opening 31, the signal transmission unit 2 is disposed inside the opening 31. Therefore, even when the distance L _h1 (FIG. 2) between the signal ground 3 and the signal transmission unit 2 is small, the electromagnetic field generated around the input transmission path 21 and the output transmission path 22 interferes with the signal ground 3. do not do. As a result, it is possible to prevent the signal transmission efficiency from decreasing while reducing the leakage of the electromagnetic field from the side surface of the dielectric substrate 1.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. In the above embodiment, the signal ground 3 is provided around the signal transmission unit 2 by disposing the signal transmission unit 2 inside the opening 31, but is not particularly limited thereto.

  In the above embodiment, the signal ground 3 is provided below the signal transmission unit 2, but may be provided above the signal transmission unit 2 and provided on the same plane as the signal transmission unit 2. It may be.

  Further, the positions of the signal transmission unit 2 and the signal ground 3 are not particularly limited. The signal ground 3 may be provided on the main surface S of the dielectric substrate 1, or may be provided on the bottom surface (surface opposite to the main surface S) of the dielectric substrate 1. The signal transmission unit 2 may be provided in the dielectric substrate 1, or may be provided on the bottom surface (surface opposite to the main surface S) of the dielectric substrate 1.

  Moreover, in the said embodiment, although the input transmission path 21 and the output transmission path 22 were arrange | positioned between the resonant element 23 and the resonant element 24 in the depth direction D, these arrangement | positioning is not specifically limited. . For example, the resonant elements 23 and 24 may be disposed between the input transmission path 21 and the output transmission path 22 in the depth direction D, or between the input transmission path 21 and the output transmission path 22 in the width direction W. The resonance elements 23 and 24 may be arranged on the front side.

  Moreover, in the said embodiment, although the signal transmission part 2 was provided with the two resonant elements 23 and 24, it should just be provided with the at least 1 resonant element.

  In the above embodiment, a signal is input from the signal input terminal 25 and a signal is output from the signal output terminal 26. However, the signal input terminal 25 and the signal output terminal 26 are terminals that can input and output signals. It may be. That is, not only the signal input to the signal input terminal 25 is output from the signal output terminal 26 but also the signal input to the signal output terminal 26 can be output from the input terminal 25.

Moreover, in the said embodiment, although the signal ground 3 and the frame ground 4 comprised the rectangle, they can be formed in various shapes. The shape of the opening 31 of the signal ground 3 is not necessarily rectangular and can be appropriately changed.

  Moreover, in the said embodiment, although the signal ground 3 and the frame ground 4 became the substantially same shape and the substantially same dimension, the shape and / or dimension of the signal ground 3 and the frame ground 4 may differ.

  Moreover, in the said embodiment, although the frame ground 4 was provided so that the whole bottom face of the dielectric substrate 1 might be covered, the frame ground 4 does not need to be provided. In this case, for example, it is preferable to prevent the electromagnetic wave signal from leaking to the surroundings by covering the band-pass filter 10 with a case.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

<Frequency characteristics of ground>
Example 1
As shown in FIG. 4, the signal ground 3 in which the opening 31 was formed was created. The length _{L w4} of the long sides of the opening 31 was slightly longer than 1/2 [lambda]. The frequency characteristics of the signal ground 3 were verified.

(Evaluation)
FIG. 6A shows a current distribution of the signal ground 3 when a signal having a frequency (2.45 GHz) at the center of the passband is applied to the signal ground 3. In FIG. 6A, it can be seen that the color in the vicinity of the opening 31 has changed, and current is flowing in the signal ground 3. That is, it can be seen that the signal ground 3 resonates with a signal having the center frequency of the pass band, and this signal has passed through the signal ground 3.

  FIG. 6B shows the current distribution of the signal ground 3 when a signal having a frequency (1.00 GHz) outside the passband is applied to the signal ground 3. In FIG. 6B, it can be seen that there is no change in the color of the signal ground 3 and no current flows through the signal ground 3. That is, it can be seen that the signal ground 3 does not resonate due to a signal having a frequency outside the pass band, and this signal does not pass through the signal ground 3.

  From the above, it was confirmed that the signal ground 3 of Example 1 limited the passage of signals having frequencies outside the passband. Therefore, it has been found that if this signal ground 3 is used, noise having a frequency outside the pass band can be effectively removed in the band pass filter.

<Effect of ground on signal transmission efficiency>
When the ground was brought close to the signal transmission unit, the influence of the ground on the signal transmission efficiency was verified.

(Example 2)
A bandpass filter 10 (FIG. 1) was created using the signal ground 3 of Example 1. The distance L _h1 (FIG. 2) between the signal ground 3 and the signal transmission unit 2 was set to 0.1 mm. The distance L _d1 (FIG. 3) between the input transmission path 21 and the output transmission path 22 and the resonant elements 23 and 24 was set to 0.8 mm.

(Comparative Example 2-1)
The same bandpass filter as the bandpass filter 10 of Example 2 was produced except that a ground where no opening 31 was formed was used instead of the signal ground 3 where the opening 31 was formed.

(Comparative Example 2-2)
The same bandpass filter as the bandpass filter of Comparative Example 2-1 was created except that the distance L _d1 (FIG. 3) between the input transmission path 21 and the output transmission path 22 and the resonant elements 23 and 24 was reduced. In the band pass filter of Comparative Example 2-2, the distance L _d1 was set to 0.4 mm.

(Comparative Example 2-3)
The same bandpass filter as the bandpass filter of Comparative Example 2-2 was created except that the distance in the height direction H between the ground and the signal transmission unit 2 was increased. In the bandpass filter of Comparative Example 2-3, the distance in the height direction H between the ground and the signal transmission unit 2 was 1.5 mm.

(Evaluation)
The transmission characteristics of the bandpass filter 10 of Example 2 and the bandpass filters of Comparative Examples 2-1 to 2-3 were measured. In Figure 7A, showing the reflection coefficient _{S 11} and transmission coefficient _{S 21} of the band-pass filter 10 of the second embodiment. Figure 7B, shows the reflection coefficient of the bandpass filter _{S 11} and transmission coefficient _{S 21} of Comparative Example 2-1. Figure 7C, showing the reflection coefficient of the bandpass filter _{S 11} and transmission coefficient _{S 21} of Comparative Example 2-2. In FIG. 7D, showing the reflection coefficient of the bandpass filter _{S 11} and transmission coefficient _{S 21} of Comparative Example 2-3. Here, S ₁₁ is the voltage ratio of the reflected wave at the signal input terminal 25 to the incident wave at the signal input terminal 25. S ₂₁ is the voltage ratio of the transmission wave at the signal output terminal 26 to the incident wave at the signal input terminal 25.

Comparing Figure 7A and Figure 7B, towards the transmission coefficient S ₂₁ of the band-pass filter 10 of Example 2 is larger than the transmission coefficient S ₂₁ of the band-pass filter of Comparative Example 2-1. Therefore, it can be seen that by forming the opening 31 in the signal ground 3, the electromagnetic field around the signal transmission unit 2 does not interfere with the signal ground 3 and the signal transmission efficiency is improved.

Comparing FIGS. 7B and 7C, towards the transmission coefficient S ₂₁ of the band-pass filter of Comparative Example 2-2 is greater than the transmission coefficient S ₂₁ of the band-pass filter of Comparative Example 2-1. Therefore, it can be seen that even when the distance L _d1 between the input transmission path 21 and the output transmission path 22 and the resonant elements 23 and 24 is reduced, the signal transmission efficiency is improved.

However, comparing FIG. 7A and FIG 7C, towards the transmission coefficient S ₂₁ of the band-pass filter 10 of Example 2, clearly greater than the transmission coefficient S ₂₁ of the band-pass filter of Comparative Example 2-2. Therefore, it is more effective to form the opening 31 in the signal ground 3 than to reduce the distance L _d1 between the input transmission path 21 and the output transmission path 22 and the resonant elements 23 and 24. It turns out that it is effective for improvement.

When comparing FIG. 7A and FIG. 7D, there is not much difference between the transfer coefficient S ₂₁ of the band-pass filter 10 of Example 2 and the transfer coefficient S ₂₁ of the band-pass filter of Comparative Example 2-3. From this, it is understood that if the distance in the height direction H between the ground and the signal transmission unit 2 is increased, the signal transmission efficiency is improved as in the case where the opening 31 is formed in the signal ground 3. However, when the distance L _h1 is increased, there is a problem that electromagnetic field leakage from the side surface of the dielectric substrate 1 increases. Therefore, in order to improve the signal transmission efficiency while reducing the leakage of the electromagnetic field, after forming the opening 31 in the signal ground 3 as in the bandpass filter 10 of the second embodiment, It is preferable to make the signal transmission unit 2 approach.

DESCRIPTION OF SYMBOLS 10 Band pass filter 1 Dielectric board | substrate S Main surface 2 Signal transmission part 21 Input transmission path 22 Output transmission paths 23 and 24 Resonance element 25 Signal input terminal 26 Signal output terminal 3 Signal ground 31 opening 4 Frame ground

Claims (5)

A bandpass filter that passes a signal having a frequency within a predetermined frequency band,
A dielectric substrate;
A signal transmission unit disposed on a main surface of the dielectric substrate and transmitting a signal having a frequency within the predetermined frequency band;
A signal ground provided on the dielectric substrate and including an opening ;
A frame ground disposed on a surface opposite to the main surface of the dielectric substrate and connected to the signal ground;
With
The signal transmission unit is disposed inside the opening,
The signal transmission unit is
An input transmission line connected to the signal input terminal;
An output transmission line connected to the signal output terminal;
A resonant element disposed next to the input transmission line and the output transmission line;
Including
The signal ground has a resonance frequency that is substantially the same as a resonance frequency of the resonance element. The band-pass filter according to claim 1,
The signal ground is a band-pass filter disposed in the dielectric substrate. The bandpass filter according to claim 1 or 2 ,
The bandpass filter, wherein the signal ground and the frame ground have substantially the same shape and dimensions. The bandpass filter according to any one of claims 1 to 3 ,
The band-pass filter, wherein the opening has a rectangular shape and has a long side longer than the length of the resonant element. The band-pass filter according to any one of claims 1 to 4 ,
The signal transmission unit includes two resonant elements,
The input transmission line and the output transmission line are disposed between the two resonant elements,
The two resonant elements are band pass filters extending along the input transmission line and the output transmission line.