JP2015171027A - Filter, multicoupler using the same and antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter having a microstrip-structure capable of reducing passing loss, a multicoupler using the same and an antenna.SOLUTION: The filter includes: a central substrate 4 including a dielectric substrate 2 and a signal conductor 3 which is constituted of strip conductor formed on the dielectric substrate 2 for attenuating a specific frequency band in a passing signal; and two sheets of ground conductors 5 which are disposed while sandwiching the central substrate 4 in a thickness direction being interposed by an air layer. The signal conductor 3 is formed on the surface and the rear face of the dielectric substrate 2 symmetrically with respect to a plane extending in a thickness direction of the dielectric substrate 2.

Description

  The present invention relates to a filter, a duplexer using the filter, and an antenna device.

  2. Description of the Related Art Conventionally, a filter having a microstrip structure in which a signal conductor that attenuates a specific frequency band among signals passing through is formed on one surface of a dielectric substrate and a ground conductor is formed on the other surface is known.

  For example, Patent Document 1 discloses a filter having a structure in which a resonator is formed by a stub and a signal input / output unit and a stub are connected by an input / output line.

JP 2006-253877 A

  However, the conventional microstrip structure filter has a problem that if a dielectric substrate having a low dielectric loss tangent value and a large energy loss is used, the passage loss becomes large.

  The loss due to the dielectric loss tangent of the dielectric substrate is caused by the electric field fluctuation in the dielectric substrate. However, in the conventional filter, the electric field is concentrated in the dielectric substrate due to the structure, and the passage loss becomes large.

  As a method for improving the passage loss, there is a method using an expensive dielectric substrate having a small dielectric loss tangent value. In this case, the cost becomes high.

  As another method of improving the passage loss, a method of forming a triplate structure by forming a signal conductor from a sheet metal without using a dielectric substrate is also conceivable. There was a problem that it was necessary to adjust electrical characteristics later. Further, when the signal conductor is divided, there is a problem that the number of parts is increased and the cost is increased.

  Therefore, an object of the present invention is to provide a microstrip structure filter that solves the above-described problems and reduces a passage loss, a duplexer using the filter, and an antenna device.

  The present invention has been devised to achieve the above object, and comprises a dielectric substrate and a strip conductor formed on the dielectric substrate, and a signal conductor for attenuating a specific frequency band among signals passing therethrough. , And two ground conductors disposed so as to sandwich the central substrate from the thickness direction through an air layer, and the signal conductor is provided on the front and back surfaces of the dielectric substrate. The filter is formed and symmetrical with respect to a plane passing through the center in the thickness direction of the dielectric substrate.

  A hole may be formed along the signal conductor in the dielectric substrate on at least one side of the signal conductor.

  The signal conductor includes an input / output unit for inputting / outputting a signal, a stub constituting a resonator, and an input / output line connecting the input / output unit and the stub, and at least a tip portion of the stub. You may form the said hole so that.

  The signal conductor has an input / output unit for inputting / outputting a signal, a stub constituting a resonator, and an input / output line connecting the input / output unit and the stub, and at least the input / output line You may form the said hole so that it may follow.

  The hole may be a through hole penetrating the dielectric substrate.

  You may provide the through hole which electrically connects the said signal conductor formed in the front and back of the said dielectric substrate.

  Moreover, this invention is a duplexer provided with the said filter.

  Moreover, this invention is an antenna apparatus provided with the said filter.

  You may provide the duplexer which combined the said some filter.

  According to the present invention, it is possible to provide a filter having a microstrip structure with reduced passage loss and an antenna device using the same.

It is a figure which shows the filter which concerns on one Embodiment of this invention, (a) is a top view of a center board | substrate, (b) is sectional drawing which shows a track | line structure. (A) is a graph which shows the pass characteristic of the filter of FIG. 1, (b) is the graph which expanded the vertical axis | shaft in the principal part. It is a figure which shows the filter of a prior art example, (a) is a top view, (b) is sectional drawing which shows a track | line structure. (A) is a graph which shows the pass characteristic of the filter of the prior art example of FIG. 4, (b) is the graph which expanded the vertical axis | shaft in the principal part. It is a top view which shows an example of the duplexer using the filter of this invention. (A) is a graph which shows the pass characteristic of each filter of the duplexer of FIG. 5, (b) is the graph which expanded the vertical axis | shaft in the principal part. It is a figure which shows the filter which concerns on other embodiment of this invention, (a) is a top view of a center board | substrate, (b) is sectional drawing which shows a track | line structure. (A) is a graph which shows the pass characteristic of the filter of FIG. 7, (b) is the graph which expanded the vertical axis | shaft in the principal part. FIG. 8 is a plan view of a central substrate showing a modification of the filter of FIG. 7.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  1A and 1B are views showing a filter according to the present embodiment, in which FIG. 1A is a plan view of a central substrate, and FIG. 1B is a sectional view showing a line structure.

  As shown in FIGS. 1A and 1B, the filter 1 includes a central substrate 4 having a dielectric substrate 2 and a signal conductor 3 made of a strip conductor formed on the dielectric substrate 2, and a central substrate 4. And two ground conductors 5 disposed so as to be sandwiched from the thickness direction through the air layer. As the ground conductor 5, it is preferable to use a metal plate made of aluminum that is lightweight, low-cost and excellent in weather resistance.

  The signal conductor 3 is configured to attenuate a specific frequency band in the signal passing therethrough. That is, the signal conductor 3 is configured such that a specific frequency band is greatly attenuated and hardly passes, and other specific frequency bands pass almost without attenuation. Here, the case where the filter 1 which passes 2 GHz band and attenuates 1.5 GHz band is comprised is demonstrated.

  Specifically, the signal conductor 3 includes two input / output units 7 that input and output signals, two stubs (open stubs) 6 that form a resonator, and a strip that connects the input / output unit 7 and the stub 6. And an input / output line 8 which is a conductor.

  The input / output line 8 includes two input / output side lines 8a connected to the input / output unit 7, two low impedance lines 8b connected to the input / output side line 8a and wider than the input / output side line 8a, The high-impedance line 8c is narrower than the low-impedance line 8b connecting the two low-impedance lines 8b. The stub 6 is configured to extend from the low impedance line 8b. The configuration of the signal conductor 3 including the input / output line 8 is not limited to this, and can be appropriately changed according to the frequency band to be attenuated.

  Now, in the filter 1 according to the present embodiment, the signal conductor 3 is formed on the front and back surfaces of the dielectric substrate 2 and is formed substantially symmetrically with respect to the plane passing through the center of the dielectric substrate 2 in the thickness direction. ing.

  That is, in the filter 1 according to the present embodiment, the signal conductors 3 having substantially the same pattern are formed on the front and back surfaces of the dielectric substrate 2 so that the signal conductors 3 on the front and back surfaces substantially overlap in plan view. Here, a double-sided copper foil substrate capable of forming strip conductors on both sides of the dielectric substrate 2 was used as the central substrate 4. The signal conductors 3 on the front and back surfaces of the dielectric substrate 2 are formed in the same shape except for a portion where the upper wiring shape is different, such as a connection portion to a connector.

  By using the strip conductors formed on the front and back surfaces of the dielectric substrate 2 as the signal conductors 3, the structure is such that two inverted strip lines are arranged across the dielectric substrate 2, and pass through the dielectric substrate 2. It is possible to reduce the electric field to suppress the influence of the dielectric substrate 2 and to reduce the passage loss due to the influence of the dielectric substrate 2.

  A common signal is supplied to the signal conductors 3 formed on the front and back surfaces of the dielectric substrate 2. In the filter 1, a through-hole 9 that electrically connects the signal conductors 3 on the front and back surfaces is formed so as to compensate for the asymmetry of the signal conductors 3 on the front and back surfaces of the dielectric substrate 2. Here, the through holes 9 are formed in the tip portions of the stubs 6 and the low impedance lines 8b of the input / output lines 8, but the positions where the through holes 9 are formed are not limited thereto. If the signal conductors 3 formed on the front and back surfaces are completely symmetrical, no current flows through the through hole 9 connecting the signal conductors 3 on the front and back surfaces.

  The overall pass characteristics including the attenuation region of the filter 1 are shown in FIG. FIG. 2B is an enlarged view of the passband (near 2 GHz) in FIG. Here, the dielectric substrate 2 is a relatively low-priced and general glass epoxy substrate, the thickness of the dielectric substrate 2 is 0.8 mm, the relative dielectric constant is 4.4, and the dielectric loss tangent is 0.02.

  As shown in FIG. 2A, in the filter 1, it can be seen that the 1.5 GHz band is attenuated and the 2 GHz band is passing. As shown in FIG. 2B, the attenuation at 2 GHz was 0.16 dB.

  For comparison, as shown in FIG. 3, as a conventional example, a filter 31 having a signal conductor 33 formed on the front surface of a dielectric substrate 32 and a ground conductor 34 formed on the back surface was prepared, and the pass characteristics were obtained. As the dielectric substrate 32, a glass epoxy substrate having a thickness of 1.6 mm, a relative dielectric constant of 4.4, and a dielectric loss tangent of 0.02 was used. FIG. 4A shows the entire pass characteristic including the attenuation region of the filter 31, and FIG. 4B shows an enlarged view of the pass region (near 2 GHz) in FIG. 4A.

  As shown in FIGS. 4A and 4B, in the filter 31, like the filter 1, the 1.5 GHz band is attenuated and the 2 GHz band passes, but the attenuation at 2 GHz is 0.58 dB. It was big.

  That is, when the filter 1 according to the present embodiment is compared with the filter 31 of the conventional example, the attenuation characteristic in the 1.5 GHz band is not significantly changed, but the passing loss in the 2 GHz band is greatly improved.

  This is because, in the filter 31 of the conventional example, a dielectric substrate 32 having a large dielectric loss tangent exists between the signal conductor 33 and the ground conductor 34 where the electric field is concentrated. It seems that it is getting bigger. In the filter 1 according to the present embodiment, there is only an air layer between the signal conductor 3 and the ground conductor 5 facing the air conductor. Since the air layer has a small dielectric loss tangent, a large loss occurs even when the electric field is concentrated. The pass characteristics are good.

  The duplexer according to the present embodiment includes the filter 1 according to the present embodiment. The duplexer is configured by combining a plurality of filters having different pass characteristics, but at least one of the plurality of filters may be the filter 1 according to the present embodiment.

  Further, the antenna device according to the present embodiment includes the filter 1 according to the present embodiment. You may comprise an antenna apparatus so that the duplexer which combined the some filter 1 may be mounted. The antenna device according to the present embodiment is used as a base station antenna for mobile communication, for example.

  As an example, FIG. 5 shows a duplexer 51 that combines a filter 52 that passes the 2 GHz band and attenuates the 1.5 GHz band, and a filter 53 that passes the 1.5 GHz band and attenuates the 2 GHz band. Further, the pass characteristics of the filters 52 and 53 in the duplexer 51 are shown in FIGS. 5 shows only the front surface side of the dielectric substrate 2, the signal conductor 3 having the same pattern is also formed on the back surface side of the dielectric substrate 2 (not shown).

  As shown in FIGS. 6A and 6B, both the 2 GHz band pass loss in the filter 52 (1.5 GHz filter) and the 1.5 GHz band pass loss in the filter 53 (2 GHz filter) are both 0.2 dB or less. It turns out that it is favorable.

  As described above, in the filter 1 according to the present embodiment, the signal conductor 3 is formed on the front and back surfaces of the dielectric substrate 2 and is symmetric with respect to the plane passing through the center of the dielectric substrate 2 in the thickness direction. Is formed.

  With this configuration, it is possible to reduce the electric field passing through the dielectric substrate 2 and improve the passage loss due to the influence of the dielectric substrate 2. As a result, an inexpensive dielectric substrate 2 can be used, and the cost can be reduced. In addition, since the signal conductor 3 can be formed with higher accuracy than the case where the signal conductor 3 is formed of sheet metal, adjustment after assembly is unnecessary, and the working time can be shortened. Further, in the filter 1, since the number of parts does not increase when the signal conductor 3 is divided unlike the case where the signal conductor 3 is formed of sheet metal, the assembly is easy and the manufacturing cost is also reduced. Reduction is possible.

  Next, another embodiment of the present invention will be described.

  The filter 71 shown in FIG. 7 is obtained by further forming holes (slits, long holes) 72 along the signal conductor 3 in the dielectric substrate 2 on at least one side of the signal conductor 3 in the filter 1 shown in FIG. is there.

  By forming the holes 72, it is possible to further reduce the electric field passing through the dielectric substrate 2 to further suppress the influence of the dielectric substrate 2, and to reduce the passage loss due to the influence of the dielectric substrate 2. Even if the hole 72 is formed only on one side of the signal conductor 3, the effect can be obtained, but it is desirable to form the hole 72 on both sides of the signal conductor 3 in order to maintain the balance of the electric field.

  In the present embodiment, the hole 72 is a through hole that penetrates the dielectric substrate 2. The hole 72 may not penetrate the dielectric substrate 2, but when the dielectric substrate 2 is thin, it is affected by the dielectric substrate 2 left without being penetrated and is difficult to process. Therefore, the hole 72 is preferably a through hole.

  In the filter 71, the passage loss can be more effectively reduced by forming the hole 72 so as to be along the portion where the electric field distribution of the signal conductor 3 becomes strong. In the filter 71, in particular, since the electric field distribution becomes strong at the tip portion which is the open end of the stub 6 and the input / output line 8 having a large passing power, the hole 72 is formed at least along the tip portion of the stub 6. At the same time, it is desirable to form the hole 72 along the input / output line 8.

  If the holes 72 are continuously formed, it may be considered that the dielectric substrate 2 in the portion where the signal conductor 3 is formed is in a floating state and vibrations are generated. Therefore, the holes 72 are formed at predetermined intervals along the signal conductor 3, and the dielectric substrate 2 immediately below the signal conductor 3 and the surrounding dielectric substrate 2 are left between the adjacent holes 72. The dielectric substrate 2 is connected by a slice 73. The interval between the holes 72 (the length of the segment 73) and the length of the hole 72 (the interval between the segments 73) may be appropriately set in consideration of the wiring layout and the like. The length) and the length of the hole 72 (interval of the sections 73) need not be constant.

  It is desirable that the distance between the signal conductor 3 and the hole 72, that is, the amount of protrusion of the dielectric substrate 2 protruding laterally from the signal conductor 3 is as small as possible, so that the signal conductor 3 does not get caught during processing. It should be set in consideration of the accuracy of the opening process. Here, the distance between the signal conductor 3 and the hole 72 is 0.5 mm.

  Further, the larger the width of the hole 72, the greater the effect of reducing the loss. However, if the width of the hole 72 is too large, the entire filter 71 is enlarged. Good. Here, the width of the hole 72 was 3 mm.

  The pass characteristics of the filter 71 are shown in FIGS.

  As shown in FIGS. 8A and 8B, the passing loss at 2 GHz is 0.10 dB, which indicates that the passing loss in the 2 GHz band is further improved as compared with the filter 1 in FIG.

  In the filter 71, the hole 72 is rectangular (rectangular), but the shape of the hole 72 is not particularly limited. For example, a circular hole 92 is formed as in the filter 91 shown in FIG. You may make it do.

  The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

  For example, in the above embodiment, a double-sided copper foil substrate is used as the central substrate 4, but the present invention is not limited to this, and a multilayer substrate may be used as the central substrate 4 and the signal conductor 3 may be formed on the front and back surfaces.

  In the above embodiment, an air layer is formed between the central substrate 4 and the ground conductor 5, but a low dielectric loss material may be interposed between the central substrate 4 and the ground conductor 5.

1 Filter 2 Dielectric Substrate 3 Signal Conductor 4 Center Substrate 5 Ground Conductor 6 Stub 7 Input / Output Unit 8 Input / Output Line 9 Through Hole

Claims (9)

A central substrate comprising a dielectric substrate and a signal conductor made of a strip conductor formed on the dielectric substrate and attenuating a specific frequency band of signals passing therethrough,
Two ground conductors arranged so as to sandwich the central substrate from the thickness direction through an air layer,
The signal conductor is formed on the front and back surfaces of the dielectric substrate, and is formed symmetrically with respect to a plane passing through the center in the thickness direction of the dielectric substrate. The filter according to claim 1, wherein a hole is formed along the signal conductor in the dielectric substrate on at least one side of the signal conductor. The signal conductor has an input / output unit for inputting / outputting a signal, a stub constituting a resonator, and an input / output line connecting the input / output unit and the stub,
The filter according to claim 2, wherein the hole is formed at least along the tip of the stub. The signal conductor has an input / output unit for inputting / outputting a signal, a stub constituting a resonator, and an input / output line connecting the input / output unit and the stub,
The filter according to claim 2 or 3, wherein the hole is formed at least along the input / output line. The filter according to claim 2, wherein the hole is a through-hole penetrating the dielectric substrate. The filter according to any one of claims 1 to 5, further comprising a through hole that electrically connects the signal conductors formed on the front and back surfaces of the dielectric substrate.   A duplexer comprising the filter according to claim 1.   An antenna device comprising the filter according to claim 1. The antenna device according to claim 8, further comprising a duplexer combining a plurality of the filters.