JP2006311469A - Method for connecting small-sized antenna and microstrip line with cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna for a mobile body having coaxial cable fixing means by which a coaxial cable can be easily stored in an antenna container box in an actual utility environment of the mobile body, and to provide a method for connection with a coaxial cable suitable for the antenna. <P>SOLUTION: The principal of the antenna itself comprises a circuit board 10, a ground conductor 11, a dielectric material 12, a radiation element 13, a microstrip line 15, a power feeding pin 17, and a fixing bracket 31. The fixing bracket 31 holds an outer conductor 22 of a coaxial cable 20 so that the coaxial cable 20 can be extended in a horizontal direction or in an approximately horizontal direction while directing the surface of the radiation element 13 toward the direction of an electromagnetic wave. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a small antenna, and more particularly to a small antenna suitable for a case where there is no room for mounting space.
The present invention also relates to a method of connecting a microstrip line and a cable for connecting a small antenna to an external device.

    In recent years, for example, GPS (Satellite Positioning System; Global Positioning System), VICS (Road Traffic Information Communication System; Vehicle) that informs traffic conditions and construction information of major roads, etc. Car navigation devices using the Information and Communication System) have become widespread. Recently, an automatic fee payment system using an ETC (Automatic Toll Collection System) on a toll road has been developed. Furthermore, an emergency communication system that automatically transmits a disaster rescue signal in the event of an accident using an in-vehicle telephone system and GPS has been put into practical use.

The antennas included in these in-vehicle information devices are used by integrating a plurality of planar antennas having different frequency bands because of the limitation of being in-vehicle.
As an example of this, for example, the antenna elements for GPS and VICS are arranged side by side on a single dielectric substrate, and the feed pins of these antenna elements are connected to one transmission line. There is a thing which aims at compactness by this (for example, refer patent document 1).

  In addition to the GPS antenna and the VICS antenna, an ETC antenna is integrated to realize a compact size. (For example, refer to Patent Document 2).

  By the way, for these antennas, antennas having a radiation electrode arranged on a dielectric substrate may be used because of the advantage of being easily miniaturized. In particular, a GPS antenna or an ETC antenna transmits and receives circularly polarized radio waves, and thus a flat patch antenna having a planar radiation electrode disposed on a dielectric substrate is often used. In consideration of miniaturization, a VICS antenna may be a planar patch antenna in which planar radiation electrodes are arranged on a dielectric substrate.

Conventionally, a structure as shown in FIG. 3 is often used as a structure of a planar patch antenna in which planar radiation electrodes are arranged on a dielectric substrate.
FIG. 3 is a cross-sectional view showing a structure of a conventional planar patch antenna as viewed from the side.

  The planar patch antenna shown in FIG. 3 includes, as a single antenna, a circuit board 110, a ground conductor 111 formed on the surface of the circuit board 110, and a dielectric 112 laminated on the surface of the ground conductor 111. A radiating element 113 formed on the surface of the dielectric 112, a through hole 114 vertically penetrating the dielectric 112, a microstrip line 115 formed in a part of the circuit board 110 immediately below the through hole 114, A power supply pin 117 that electrically connects the radiation element 113 and the microstrip line 115 is provided.

In addition, a coaxial cable 120 is connected as a transmission cable.
In a small antenna used at a high frequency, a connection that does not adversely affect the high frequency characteristics of the small antenna when the microstrip line 115 serving as a signal line of the small antenna is connected to the coaxial cable 120 for connection to another device. It is necessary to adopt a method.

    The coaxial cable 120 includes a center conductor 121 electrically connected to the microstrip line 115, an outer conductor 122 (shield wire) electrically connected to the ground conductor 111, and a covering 123 that covers the outer conductor 122. . A ground conductor 118 electrically connected to the ground conductor 111 is provided on the same surface as the microstrip line 115 of the circuit board 110, and this and the outer conductor 122 are fixed via a soldering portion 129, whereby the ground conductor 111 and Impedance between the outer conductors 122 is suppressed as much as possible.

As described above, the connection between the small antenna and the coaxial cable is generally performed by soldering the central conductor of the coaxial cable on the microstrip line. In this case, the central conductor is completely covered with solder. With this, accurate high frequency connection can be realized.
JP-A-9-139625 JP 2002-314331 A

By the way, the conventional small antenna described in the background art has a problem that it is not easy to be housed in a compact storage box intended for in-vehicle use.
That is, when the storage box is compact, the space for arranging the coaxial cable for feeding in the box is limited, so that it is necessary to bend with a small bending radius particularly in the vicinity of the antenna. There is.

  In the conventional fixing method of the circuit board and the coaxial cable, there is a certain degree of freedom in the direction parallel to the plane of the circuit board 110, but in the perpendicular direction, the outer conductor 122 of the coaxial cable 120 is in close contact with the ground conductor. And fixed, so there is no freedom. Therefore, when the coaxial cable is bent in a direction including a component perpendicular to the plane of the circuit board 110 due to the presence of the inner wall 130 of the storage box in the vicinity of the antenna, the bending angle becomes large, and as a result, it becomes extremely small. A bending radius may occur. However, if the coaxial cable is bent with a bending radius of a certain degree or less, the uniformity as a distributed constant line may be disturbed and the S / N ratio may be deteriorated.

Also, in connection processing between the microstrip line and the center conductor of the coaxial cable, if the connection state of the center conductor is inappropriate or the amount of solder used for soldering is insufficient, the high-frequency characteristics of the small antenna May adversely affect

As described above, since the connection processing conditions such as the state of the connection portion between the microstrip line and the coaxial cable and the amount of solder used for soldering are not clearly defined, the high frequency characteristics of the small antenna fluctuate depending on the connection processing conditions. There is a problem such as.

The present invention has been made in view of the above-described conventional problems, and particularly when the coaxial cable is bent in the direction perpendicular to the circuit board in the vicinity of the coaxial cable fixing portion of the small antenna. An object of the present invention is to provide a small antenna capable of securing a bending radius of a certain degree or more.
It is another object of the present invention to provide connection processing conditions that do not adversely affect the high-frequency characteristics of a small antenna with respect to connection processing between a microstrip line and a cable.

  In order to solve the above-described problems, a first aspect of the small antenna according to the present invention includes a circuit board provided with a power feeding circuit, and a power supplied through the power feeding circuit fixed on the circuit board. In an antenna including an antenna element, a feeding coaxial cable connected to the feeding electrode is parallel to the feeding electrode via a pedestal electrically connected to a ground conductor on the circuit board. It is a small antenna characterized by being fixed on the circuit board at a predetermined angle.

  With this configuration, since the coaxial cable is fixed in advance at a certain angle in a desired bending direction, even when the coaxial cable is bent near the antenna, a certain bending radius is ensured. be able to.

  According to a second aspect of the small antenna of the present invention, the power feeding electrode is provided on a surface of the circuit board opposite to the surface facing the antenna element.

  With this configuration, the coaxial cable can be prevented from affecting the radiation characteristics of the antenna.

  According to a third aspect of the small antenna of the present invention, the outer conductor of the feeding coaxial cable and the ground conductor on the circuit board are electrically connected via the pedestal. It is.

  With this configuration, the coaxial cable can be fixed at a predetermined angle with respect to the circuit board plane, and the outer conductor of the coaxial cable and the ground conductor of the circuit board are electrically connected via the pedestal. There is no need to provide a separate connection means.

  According to a fourth aspect of the small antenna of the present invention, the feeding coaxial cable is located between the central axis of the feeding coaxial cable fixed to the pedestal and between the pedestal and the feeding electrode. The small antenna is characterized in that the central axes of the central conductors of the bull are substantially the same.

  By configuring in this way, there is no possibility that the central conductor of the coaxial cable is connected to the power supply electrode in a state where bending stress remains, so that the reliability of the connection portion is improved.

  A fifth aspect of the small antenna according to the present invention is a small antenna characterized in that the feeding electrode includes a concave portion whose surface is metallized, and a tip portion of the central conductor is inserted into the concave portion.

  With this configuration, even when the central conductor of the coaxial cable has an angle with respect to the feeding electrode, a sufficient contact area can be ensured between the central conductor and the solder. The reliability of the connection portion between the conductor and the feeding electrode can be improved.

  A sixth aspect of the small antenna according to the present invention is a small antenna characterized in that the concave portion is a through hole penetrating the circuit board.

  By comprising in this way, a recessed part can be formed easily.

  According to a seventh aspect of the small antenna of the present invention, the small antenna is characterized in that the feeding electrode is constituted by a microstrip line.

  By configuring in this way, the connecting portion between the central conductor of the coaxial cable and the feeding electrode can be arranged at a position away from the feeding pin, so that the degree of freedom in design can be increased.

In a first aspect of the method for connecting a microstrip line and a cable according to the present invention, the tip portion of the center conductor is inserted into the through hole provided in the microstrip line, and the hole on the surface of the previous through hole is blocked. The method of connecting the microstrip line and the cable is characterized in that soldering is performed.

By such a method, the center conductor can be reliably connected to the microstrip line.

According to a second aspect of the method for connecting a microstrip line and a cable according to the present invention, the amount of solder used for the soldering is 150 vol% or more with respect to the volume of the cavity of the through hole. This is a method of connecting a microstrip line and a cable.

By such a method, not only stable soldering can be performed, but also the excess and deficiency of the amount of solder used for soldering can be eliminated.

A third aspect of the method for connecting a microstrip line and a cable according to the present invention is a method for connecting a microstrip line and a cable, wherein a cross-sectional shape of the through hole is a circle or an ellipse.

By such a method, the dispersion | variation in the connection process of the said microstrip line and the said center conductor can be reduced.

According to a fourth aspect of the method for connecting the microstrip line and the cable of the present invention, the long axis of the cross-section of the through hole is substantially in the same direction as the central axis of the central conductor. It is a connection method with a cable.

By such a method, the length in which the central conductor is inserted into the through hole can be increased, and the high frequency characteristics of the small antenna can be prevented from being adversely affected.

According to a fifth aspect of the method for connecting a microstrip line and a cable according to the present invention, the cross-sectional shape of the through hole is an ellipse having a ratio of a minor axis to a major axis of approximately 1: 3. This is a method of connecting a stripline and a cable.

By such a method, the dispersion | variation in the connection process of the said microstrip line and the said center conductor can further be reduced.

According to a sixth aspect of the method of connecting the microstrip line and the cable according to the present invention, the diameter of the cross-section of the through hole is larger than the diameter of the central conductor. It is.

By such a method, it becomes possible to easily connect the microstrip line and the central conductor.

According to a seventh aspect of the method of connecting the microstrip line and the cable according to the present invention, the center conductor is inserted and soldered to the wall surface of the through hole. Is the method.

By such a method, the dispersion | variation in the connection state of the said microstrip line and the said center conductor can be reduced.

An eighth aspect of the method for connecting a microstrip line and a cable according to the present invention is applied to a method for connecting a microstrip line through which a high-frequency signal is conducted and a coaxial cable. This is the connection method.

By such a method, not only a small antenna but also a connection process between a microstrip line of a circuit device that conducts a high-frequency signal and a coaxial cable can be performed without adversely affecting the high-frequency characteristics.

  As described above, according to the small antenna of the present invention, when the antenna is placed in a particularly compact antenna storage box and the coaxial cable is bent in a direction having a component perpendicular to the circuit board in the vicinity of the antenna. On the other hand, a bending radius of a certain degree or more can be secured, and as a result, deterioration of the S / N ratio at the bent portion of the coaxial cable can be suppressed.

Further, according to the method for connecting the microstrip line and the cable of the present invention, it is possible to perform reliable connection processing with little variation in the connection state without adversely affecting the high frequency characteristics of the small antenna.

Hereinafter, the best mode for carrying out the small antenna of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view showing a structure of a planar antenna, which is a small antenna according to an embodiment of the present invention, as viewed from the side.

  As shown in FIG. 1, the small antenna (planar antenna) according to this embodiment includes a circuit board 10, a ground conductor 11 formed as a thin film on the surface of the circuit board 10, and a laminate on the surface of the ground conductor 11. The dielectric 12, the radiating element 13 formed on the surface of the dielectric 12, the through hole 14 penetrating the dielectric 12 vertically, and a part of the circuit board 10 immediately below the through hole 14 are formed. The microstrip line 15, the through hole 16 penetrating a part of the microstrip line 15, the feed pin 17 that electrically connects the radiating element 13 and the microstrip line 15, and the ground conductor 18 of the circuit board 10. A pedestal for attaching an outer conductor 22 of the coaxial cable 20 to be described later, that is, a mounting bracket 31 is provided. The ground conductor 18 is electrically connected to the ground conductor 11. The tip of the central conductor 21 of the coaxial cable 20 is inserted into a through hole provided on the circuit board 10 and connected to the microstrip line 15 by a solder portion 19.

  The small antenna (planar antenna) may be the aforementioned ETC antenna, GPS antenna, or VICS antenna. Further, it may be an ETC antenna, a GPS antenna, or a VICS antenna provided in a compact antenna housing box.

  As the dielectric 12, a dielectric substrate made of ceramics or the like can be used. In general, the higher the dielectric constant of the dielectric body 12, the smaller the antenna can be made.

  In the state shown in FIG. 1 where the surface of the radiating element 13 is leveled, the mounting bracket 31 holds the outer conductor 22 of the coaxial cable 20 so that the extending direction of the coaxial cable 20 is obliquely downward.

  The portion of the mounting bracket 31 that holds the outer conductor 22 of the coaxial cable 20 may be a hanger structure that hangs down the outer conductor 22 or a ring structure that can be caulked after passing through the outer conductor 22. It may be. Further, it may be a simple flat plate that can be soldered to the outer conductor 22.

  Since the mounting bracket 31 has such a configuration, it is bent when the coaxial cable 20 is bent in the direction perpendicular to the circuit board in the vicinity of the inner wall or the like of the storage box or the direction including the perpendicular direction as a component. The angle can be reduced, and as a result, the bending radius applied to the coaxial cable 20 can be increased as compared with the case of FIG. Thereby, it can suppress that the arrangement | positioning result of the coaxial cable 20 in an antenna storage box influences an antenna characteristic.

  The central conductor 21 inserted into the through hole 16 of the microstrip line 15 can be soldered to the microstrip line 15 after insertion.

  FIG. 2 is an explanatory view showing the cross-sectional shape of the through hole of the microstrip. The through hole is generally a circular through hole, but is not necessarily limited thereto.

In the method of bending the center conductor 121 and contacting the microstrip line 115 as shown in FIG. 3 and soldering the contact portion, not only the operation of giving a bend is required, but also the center when the bend is inappropriate. In some cases, stress remains in the connection portion between the conductor 121 and the microstrip line 115.
On the other hand, in the present invention, by connecting the microstrip line 15 while keeping the central conductor 21 in a straight state, the stress from the central conductor 21 is not applied to the connection portion, and the contact area with the solder is sufficient. Can be secured.

If the outer conductor 22 of the coaxial cable and the ground conductor 18 of the circuit board are electrically connected using the mounting bracket 31 or the like, a slight impedance is generated between them. Therefore, if the characteristic impedance of the microstrip line 15 is set equal to the characteristic impedance of the coaxial cable, a slight impedance mismatch occurs.
Therefore, it is desirable to design the microstrip line 15 in consideration of the impedance between the outer conductor 22 and the ground conductor 18.

Next, a method for connecting a microstrip line and a cable according to the present invention will be described in detail with reference to the drawings.
The method for connecting a microstrip line and a cable according to the present invention provides a suitable connection method that defines connection processing conditions that do not adversely affect the high-frequency characteristics of a small antenna.

FIG. 4 is a diagram for explaining a method of inserting the central conductor 21 of the coaxial cable 20 into the through hole 16 formed on the microstrip line 15 and soldering the central conductor 21. The front end portion of the center conductor 21 housed in the through hole 16 is firmly soldered to the inside of the through hole 16 by the solder portion 19. For the soldering, a sufficient amount of solder is used so as to reliably close the hole on the surface of the through hole 16.

Thus, the microstrip line 15 and the center conductor 21 are securely connected by inserting the tip of the center conductor 21 into the through hole 16 and soldering with a sufficient amount of the solder portion 19. Can do.

In the method of connecting a microstrip line and a cable according to the present invention, in order to more reliably connect the microstrip line 15 and the central conductor 21, as shown in FIG. The diameter of the conductor 21 is larger than that of the conductor 21 so that the tip of the center conductor 21 can be easily inserted into the through hole 16. This improves the soldering workability.

Further, it is preferable to solder the center conductor 21 in a state where the tip end portion is inserted up to the wall surface of the through hole 16. Thereby, not only the contact area between the microstrip line 15 and the central conductor 21 can be increased, but also the variation in the connection state between the microstrip line 15 and the central conductor 21 can be reduced.

FIG. 5 shows how the influence on the antenna characteristics is different between the case where soldering is performed so as to block the hole on the surface of the through hole 16 and the case where soldering is performed without blocking the hole. It explains using.

FIG. 5 compares the antenna reflection coefficients when the hole on the surface of the through hole 16 is blocked by soldering and when the hole is not blocked. In the figure, the reflection coefficient on the vertical axis is indicated by the amount of change from the value of the reflection coefficient when the hole is blocked.

As shown in FIG. 5, the reflection coefficient is increased when the hole is not blocked as compared with the case where the hole on the surface of the through hole 16 is blocked by the soldering. That is, when the hole is not blocked by soldering, the reflection loss increases and the antenna gain decreases. In order to solve such a problem, in the method for connecting a microstrip line and a cable according to the present invention, soldering is performed so as to close the hole on the surface of the through hole 16.

Next, the relationship between the amount of solder used for soldering and the reflection coefficient will be described with reference to FIG. In the figure, the horizontal axis represents the amount of solder as a ratio (percent) to the volume of the cavity of the through hole 16, and the vertical axis represents the antenna reflection coefficient.

From FIG. 6, it can be confirmed that when the amount of solder used for soldering is smaller than the volume of the hollow portion of the through hole 16, the reflection coefficient increases. Further, the reflection coefficient decreases as the amount of solder increases, but the reflection coefficient hardly changes at 150 vol% or more.

Based on the relationship between the amount of solder and the reflection coefficient as shown in FIG. 6, in the method for connecting the microstrip line and the cable of the present invention, the amount of solder is 150 vol% or more with respect to the volume of the cavity of the through hole 16. It is supposed to be. By defining the solder amount of the solder portion 31 in this way, not only can stable soldering be performed, but also the excess and deficiency of the solder amount used for soldering can be eliminated.

Next, a preferable shape of the cross-section of the through hole 16 formed on the microstrip line 15 will be described below with reference to the drawings.

In order to reduce variations in connection processing with the central conductor 21 of the coaxial cable 20 as much as possible, the cross-sectional shape of the through hole 16 is preferably circular or elliptical, and more preferably elliptical rather than circular. . By making the cross-section of the through hole 16 elliptical, a favorable effect can be given to the high frequency characteristics. As an example, when applied to antenna connection, the effect of widening the bandwidth of the antenna can be obtained.

The effect of the cross-sectional shape of the through hole 16 on the VSWR characteristics of the antenna will be described with reference to FIG. The figure shows the relationship between the cross-sectional shape of the through-hole 16 and the bandwidth of the VSWR, and the vertical axis shows the bandwidth at which the VSWR is 2 or less in the relative bandwidth (%).

From FIG. 7, the cross section is circular (the case of “round hole” in the figure) or elliptical (the “long hole” in the figure), compared with the case where the through hole 16 is not provided (the case of “no hole” in the figure). The specific bandwidth is larger when the through hole 16 is provided. Therefore, by forming the through-hole 16 having a circular or elliptical cross section on the microstrip line 15 and soldering the central conductor 21 of the coaxial cable 20 to the through-hole, an excellent effect that the antenna characteristic can be widened can be obtained. Is obtained.

In the case where the cross-sectional shape of the through hole is an ellipse, the major axis of the ellipse is preferably in the same direction as the central axis of the central conductor 21. Thereby, the length in which the center conductor 21 is inserted into the through hole 16 can be increased, and the high frequency characteristics of the antenna can be prevented from being adversely affected.

From FIG. 7, it is preferable that the cross-sectional shape of the through hole 16 is an ellipse having a ratio of the minor axis to the major axis of approximately 1: 3. By making the cross-sectional shape of the through hole 16 such an ellipse, the variation in the connection processing between the microstrip line 15 and the central conductor 21 of the coaxial cable 20 can be further reduced.

The connection method between the microstrip line and the cable of the present invention described above is not limited to a small antenna, but can be applied to a connection method between a microstrip line through which a high-frequency signal is conducted and a coaxial cable.

It is sectional drawing which shows the structure which looked at the planar antenna which is a small antenna which concerns on embodiment of this invention from the side surface. It is explanatory drawing which shows the cross-sectional shape of the through hole of a microstrip. It is sectional drawing which shows the structure which looked at the planar antenna which is the conventional small antenna from the side surface. FIG. 4 is a diagram for explaining a method of soldering the central conductor 21 of the coaxial cable 20 to the through hole 16 formed on the microstrip line 15. FIG. 5 is a comparison diagram of the antenna reflection coefficients when the hole on the surface of the through hole 16 is blocked by soldering and when the hole is not blocked. FIG. 6 is a diagram for explaining the relationship between the amount of solder and the reflection coefficient. FIG. 7 is a diagram illustrating the relationship between the cross-sectional shape of the through hole 16 and the bandwidth of the VSWR.

Explanation of symbols

10, 110 Circuit board 11, 111 Ground conductor 12, 112 Dielectric 13, 113 Radiating element 14, 114 Through hole (dielectric side)
15, 115 Microstrip line 16 Through hole (circuit board side)
17, 117 Feed pin 18, 118 Ground conductor 19, 119 Solder part 20, 120 Coaxial cable 21, 121 Central conductor 22, 122 Outer conductor 23, 123 Cover 30, 130 Inner wall of storage box 31 Mounting bracket 129 Solder part

Claims (15)

An antenna including a circuit board provided with a power feeding circuit, and an antenna element fixed on the circuit board and fed through the power feeding circuit;
A power supply coaxial cable connected to the power supply electrode is mounted on the circuit board at a predetermined angle not parallel to the power supply electrode via a pedestal electrically connected to a ground conductor on the circuit board. Fixed to the
A small antenna characterized by that. The power supply electrode is provided on a surface opposite to a surface facing the radiation element of the circuit board.
The small antenna according to claim 1. An outer conductor of the power feeding coaxial cable and a ground conductor on the circuit board are electrically connected via the pedestal;
The small antenna according to claim 1, wherein the antenna is a small antenna. The central axis of the portion of the feeding coaxial cable fixed to the pedestal and the central axis of the central conductor of the feeding coaxial cable located between the pedestal and the feeding electrode are substantially the same. ,
The small antenna according to any one of claims 1 to 3, wherein the small antenna is provided. The power supply electrode has a recess whose surface is metallized,
The tip portion of the central conductor is inserted into the recess,
The small antenna according to any one of claims 1 to 4, wherein the antenna is a small antenna. The recess is a through hole penetrating the circuit board;
The small antenna according to claim 5. The feeding electrode is constituted by a microstrip line;
The small antenna according to claim 1, wherein the antenna is a small antenna. The tip portion of the center conductor is inserted into the through hole provided in the microstrip line,
A method of connecting a microstrip line and a cable, wherein soldering is performed so that the hole on the surface of the previous through hole is blocked. The method for connecting a microstrip line and a cable according to claim 8, wherein the amount of solder used for the soldering is 150 vol% or more with respect to the volume of the cavity of the through hole. The method for connecting a microstrip line and a cable according to claim 8 or 9, wherein a cross-sectional shape of the through hole is a circle or an ellipse. The method of connecting a microstrip line and a cable according to claim 10, wherein a major axis of a cross section of the through hole is substantially in the same direction as a central axis of the central conductor. The method for connecting a microstrip line and a cable according to claim 10, wherein a cross-sectional shape of the through hole is an ellipse having a ratio of a minor axis to a major axis of approximately 1: 3. The method of connecting a microstrip line and a cable according to any one of claims 8 to 12, wherein a diameter of a cross section of the through hole is larger than a diameter of the central conductor. The method of connecting a microstrip line and a cable according to any one of claims 8 to 13, wherein the central conductor is inserted and soldered to a wall surface of the through hole. The method for connecting a microstrip line and a cable according to any one of claims 8 to 14, wherein the method is applied to a method for connecting a microstrip line through which a high-frequency signal is conducted and a coaxial cable.

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