JP2648495B2 - Mobile antenna - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile antenna used for a car phone or the like, and more particularly to an improvement in a vertically polarized radiation characteristic thereof.

[Prior Art] Conventionally, in mobile communication such as a car phone,
Vertically polarized radio waves are used. For this reason, various antennas that generate vertically polarized waves, such as a vertical dampole antenna, are used as antennas for automobiles.

Here, an antenna that generates such vertical polarization is
A pole antenna projecting vertically from the vehicle body is suitable. However, the antenna projecting from the vehicle body has a problem that the aesthetic appearance is impaired and the risk of breakage is large. For this reason, it is desired to install the antenna inside the vehicle body. However, the radio wave incident on the inside of the vehicle body is weakened by the influence of the vehicle body. For this reason, if an antenna is installed inside a vehicle body, sufficient reception power cannot be obtained in many cases.
Therefore, in order to improve this, a method of installing a plurality of antennas having directivity such as directivity diversity has been adopted.

On the other hand, it is preferable that the antenna to be installed inside the vehicle body is as small and thin as possible. As such an antenna, there is a microstrip type antenna shown in FIG. 7 and FIG.

In FIG. 7, the radiation conductor plate 10 is arranged parallel to the ground conductor plate 12 at a predetermined interval. The inner conductor 14a of the coaxial feed line 14 is connected to the feed point 15 on the radiation conductor plate 10.
The outer conductor 14b of the coaxial feed line 14 is connected to the ground conductor plate 12. Note that a dielectric substrate 16 is disposed between the radiation conductor plate 10 and the ground conductor plate 12.

The length L ₁ of the radiating conductor plate 10 is approximately the propagation wavelength lambda] g 1/2
Is formed. The inner conductor 14a of the connection location of the coaxial feed line 14, that is, the position of the feeding point 15 is in the position shifted by a distance d ₁ from the center of the radiation conductor plate 10 with respect to the radiation conductor plate 10. It This is for matching the impedance between the coaxial feed line 14 consisting of an inner conductor 14a and the outer conductor 14b, that the length adjustment of the d _1, to adjust the input impedance in the range of 0 to the number of 100Ω Can be.

It should be noted that the dielectric substrate 16 can be used as an air layer without being provided. However, in this case, the dielectric constant is low,
It is necessary to increase the size of the radiation conductor plate 10 as compared with the case where the dielectric substrate 16 is used.

In such a microstrip type antenna, when power is supplied to the radiation conductor plate 10 through the coaxial feed line 14,
A current flows through the radiation conductor plate 10 in the direction indicated by the arrow A.
As a result, a radio wave having a plane of polarization in the same direction as the direction of arrow A is emitted. Therefore, if this antenna is arranged in the vertical direction, vertical polarization can be generated.

FIG. 8 shows a microstrip type antenna called an inverted-F antenna because of its shape. This inverted-F antenna has a structure in which one end of a radiation conductor plate 10 is bent and connected to a ground conductor plate 12.
The length L ₂ of the radiating conductor plate 10, the propagation wavelength λg of about 1 /
It is formed in four lengths. The inner conductor 14a of the coaxial feeder 14 is connected to a location remote from the bent portion 10a of the radiation conductor plate 10 by a distance d _2. Such an inverted-F antenna can also generate vertically polarized waves in the same manner as that shown in FIG.

The above-described micro-trip type antenna is disclosed in, for example, JP-A-60-58704 and JP-A-56-12102.

[Problems to be Solved by the Invention] As described above, when an antenna is installed inside a vehicle body, it is necessary to make the antenna as small as possible. The microstrip type antenna is small and thin, but has sufficient characteristics as an antenna alone. However, when it is mounted inside the body of an automobile, its directivity, input impedance, and the like greatly change, and its characteristics often deteriorate significantly.
That is, when it is mounted near a conductor such as a rearview mirror (room mirror) of an automobile, a fender mirror, a door mirror, or a heat ray of a rear window, radiation characteristics of vertically polarized waves are significantly deteriorated.

The present inventors have conducted detailed experiments on this cause. And when the microstrip antenna alone is mounted near the rearview mirror, the vertical polarization radiation is very weak, and on the other hand, the horizontal polarization radiation that was not generated by the antenna alone becomes strong. . Then, as shown in FIG. 9, the dielectric current B flows through, for example, a conductive film coated on the mirror due to the current A flowing through the antenna.
Caused strong horizontal polarization components.

That is, a conductor provided in a vehicle such as a rearview mirror has a larger electrical length in the horizontal direction than the radiating conductor plate 10, and most of the power supplied due to the asymmetry in the structure of the antenna system causes the induced current B to flow. It is used for. For this reason, the radiation of the vertically polarized wave becomes very weak, and a large horizontally polarized wave component is generated. Therefore, the power that contributes to the flow of the current A is much smaller than when the antenna is used alone, and as a whole, the antenna operates like a horizontal polarization generating antenna. by this,
As a result, sufficient gain could not be obtained for vertically polarized waves.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has been made for a mobile object having a sufficient vertical polarization radiation characteristic despite being attached near a conductor of the mobile object such as an automatic operator. It is intended to provide an antenna.

[Means for Solving the Problems] A moving body antenna according to the present invention is a moving body antenna mounted near a conductor of an automobile, and is provided with a ground conductor plate and a predetermined distance from the ground conductor plate. A pair of antenna bodies each composed of a radiation conductor plate disposed so as to face each other, a coaxial feed line composed of an outer conductor connected to the ground conductor plate and an inner conductor connected to the radiation conductor plate, Power supply means for supplying power to the antenna body so as to generate vertical polarization in the antenna body via a coaxial feed line; anda pair of antenna bodies are separated from each other at a predetermined interval in substantially the same vertical plane. By arranging the pair of antennas in parallel with each other at the symmetric position and feeding the pair of antennas with the same phase and the same amplitude by the feeder, the current flowing through the pair of antennas increases. Preventing each other canceling generation of horizontally polarized wave induced current generated in the conductor portion of the motor vehicle, characterized in that to prevent a reduction in the vertical polarization component.

That is, the mobile object antenna according to the present invention is mounted near the conductor of the automobile. A pair of antennas that generate vertically polarized waves are arranged in parallel at symmetrical positions at predetermined intervals in substantially the same vertical plane. Then, power is supplied to the pair of antennas with the same phase and the same amplitude by the feeding means. With this configuration, the current in the horizontal direction induced in the conductor by the power supply to each of the antennas is exactly 180 degrees out of phase. For this reason, these induced currents can cancel each other and prevent the occurrence of horizontal polarization. Thereby, the gain of the vertical polarization generation can be sufficiently increased.

As a conductor for an automobile or the like, a rearview mirror (room mirror), a fender mirror, a door mirror, and a rear window heat ray are conceivable, and it is particularly preferable to attach an antenna to the back of the mirror. An inverted F antenna as shown in FIG. 8 is suitable for the antenna body composed of the ground conductor plate and the radiation conductor plate. Further, if the configuration is such that an additional conductor plate is added as shown in FIG. 5, an effect that the resonance frequency band of the antenna can be widened can be obtained.

In addition, the antenna of the present invention is not limited to automobiles,
It can also be applied to work vehicles in factories.

[Operation] Since the mobile object antenna according to the present invention has the above-described configuration, when a predetermined current is supplied to the radiating conductor plate by the coaxial feeder, the vertical polarization caused by the current is reduced. Generated. Here, the pair of antennas are arranged in parallel in the same vertical plane. For this reason, induced currents induced in the conductors of the vehicle by the currents of the radiation conductor plates of both antennas cancel each other out. That is, since the currents supplied to both antennas have the same phase and the same amplitude, the induced currents flowing through the conductors of the vehicle are different by exactly 180 degrees. Thus, the induced current induced by both antennas is canceled.

[Effects] As described above, according to the mobile object antenna of the present invention, the power supplied to the antenna body is efficiently used for generation of vertical polarization. Therefore, a small and thin antenna attached near a conductor of an automobile or the like can obtain a sufficient gain with respect to vertical polarization.

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

First Embodiment FIG. 1 is a configuration diagram of a moving object antenna according to an embodiment of the present invention, and FIG. 2 is a perspective view showing an appearance thereof. In this example, an inverted-F antenna is incorporated in a rearview mirror for the purpose of receiving or transmitting vertically polarized radio waves. That is, the rearview mirror 20 includes a mirror body 22 made of a metal deposition film and glass, a cover 24 for mounting and fixing the mirror body 22, and a mounting bracket 26 for mounting the cover to the vehicle body. An antenna is arranged in a space behind the mirror body 22.

That is, the pair of antenna bodies 100 are arranged on both sides of the rear surface of the mirror body 22. Since the mirror body 22 is planar, the pair of antenna bodies 100 are arranged on the same plane. Also, the radiation conductor plate 1 of the antenna body 100
The directions of 0 are also set to be parallel to each other.

Since the rearview mirror 20 is arranged such that the longitudinal direction of the mirror body 22 is substantially horizontal, the open ends of the radiating conductor plate 10 of the pair of antenna bodies 100 face downward.

The coaxial feed line 14 is for connecting the transceiver (feed device) and the pair of antenna bodies 100, and has an impedance set to about 50Ω. The inner conductor of the coaxial feed line 14 is connected to the pair of radiating conductor plates 10 via the pair of connecting feed lines 30, 30. The outer conductor of the coaxial feeder is connected to the ground conductor plate 12. Here, the impedances of the connection feeder lines 30 and 30 are respectively coaxial feeder lines.
It is set to about 100Ω which is twice as large as 14
The lengths are the same so that the currents supplied to 00 have the same phase. In addition, the inner conductor of
30a is connected to a predetermined position of the radiation conductor plate 10 via a feed point 15, and this position is an antenna body composed of an inverted F antenna.
It is determined that the impedance of 100 is about 100Ω. The length of the radiation conductor plate 10 is set to a length that resonates at the transmission / reception frequency. By setting in this manner, the antenna body 100 in which the frequency band for transmission and reception is set to the predetermined resonance matching band can be formed.

In this example, the ground conductor plate 12 is large enough to cover most of the back surface of the mirror body 22, and a pair of antenna bodies 100
Share one ground conductor plate 12.

In such a mobile antenna, if a current having the same phase and the same amplitude is supplied from a power supply device (not shown) to the pair of antennas 100, the same vertically polarized radio wave is generated from the pair of antennas 100. Will be radiated. That is, the current flowing through the pair of radiation conductor plates 10 is
In this case, the conductor flows in a substantially vertical direction flowing between the connection side of the inner conductor 30a and the open end side, and accordingly vertical polarization occurs.

On the other hand, this current flowing through the pair of antenna bodies 100 generates an induced current on the metal deposition surface of the mirror body 22 and the like.
This induced current flows in a direction perpendicular to the current flowing through the radiation conductor plate 10, that is, in the horizontal direction.

However, in the mobile object antenna according to the present invention, the pair of antennas 100 are provided at symmetrical positions in the same plane, and currents having the same phase and the same amplitude are supplied to the pair of antennas 100. For this reason, the induced current generated on the metal deposition surface of the mirror body 22 by the two currents is exactly 180 degrees different as shown in FIG. 1 (A). Since the amplitudes are the same, the magnitudes of the two are equal, and the two cancel each other out. Therefore, generation of horizontally polarized radio waves due to the induced current is prevented, and the supplied current is effectively used for generation of vertically polarized waves. Therefore, despite the configuration of being mounted on the conductor of the automobile, which is the rearview mirror 20, a sufficient gain for vertical polarization can be obtained without disturbing the characteristics due to the occurrence of horizontal polarization. In addition, since a small and thin antenna body according to the combination of the radiating conductor plate 10 and the grounding conductor plate 12 is used, it can be housed inside the cover body 24 of the rearview mirror 20, thereby deteriorating the aesthetic appearance of the vehicle interior. Nor.

Note that the dielectric substrate 16 is provided to shorten the propagation wavelength λg and downsize the radiation conductor plate 10. And as this dielectric, various things can be adopted,
For example, fluororesins such as polytetrafluoroethylene having a relative dielectric constant of about 2.6 are particularly suitable because of their excellent high-frequency characteristics.

A feed line 30 for connection to the feed point 15 of the antenna body 100 is provided.
The connection is made by passing the connection power supply line 30 through the radiation conductor plate 10. With this configuration, as compared with the configuration in which power is supplied from the back side of the ground conductor plate 12 as shown in FIGS. 7 and 8, an effect that the whole can be made compact can be obtained.
Further, the inside of the mounting bracket 26 is hollow, and the coaxial feeder 14
Is passed through this, the coaxial feeder 14 is not exposed, and the appearance can be further improved.

FIG. 3 shows a power gain directivity pattern in a horizontal plane using the mobile antenna of the first embodiment manufactured for the 800 MHz band. As is clear from this figure,
It is understood that the antenna of this embodiment has sufficient directivity in a direction perpendicular to the mirror surface of the rearview mirror 20, that is, in both the front and rear directions of the vehicle.

In this embodiment, an inverted-F antenna is used as the antenna body 100. However, the present invention is not limited to this, and a microstrip-type antenna body 100 as shown in FIG. 7 can also be used. Further, in the antenna body 100 in the embodiment, the open end side of the radiation conductor plate 10 is directed downward, but there is no problem even if the open end is directed upward as is clear from the above-described operation principle.

Second Embodiment FIG. 4 shows the configuration of a second embodiment of the present invention. Also in this embodiment, the antenna body is similar to the first embodiment.
An inverted F antenna is used as 100.

What is characteristic in this embodiment is that a dielectric substrate 30 coated with copper on both sides is used as a material of the ground conductor plate 12. Then, the mirror body of the dielectric substrate 30 which is copper-clad on both sides
A strip line 32 for supplying power to the radiation conductor plate 10 is formed on the surface on the 22 side, and a ground conductor plate is formed on the opposite surface.
12 are arranged. The ground conductor plate 12 serves as a ground conductor for the radiation conductor plate 10 and also serves as a ground conductor for the strip line 32.

The strip line 32 extends to the back surface of the pair of radiating conductor plates 10 and is connected to predetermined respective electric points of the radiating conductor plate 12 by the feed conductor 34. The portion of the ground conductor plate through which the power supply conductor 34 passes is not covered with copper. Further, the outer conductor 14b of the coaxial feed line 14 is connected to the connection installation conductor surface 36 connected to the ground conductor plate 12, and the inner conductor 14a of the coaxial feed line 14 is connected to the central portion 32a of the strip line 32. .

Here, the impedance of the strip line 32 can be changed by adjusting its width. Therefore, there is no need to use a 100Ω coaxial feed line as used in the first embodiment, the antenna can be made thinner, and the impedance can be adjusted over a wider range. In this example, the width W of the strip line 32 is 50
The impedance is set to 100Ω in order to match with the connection point 32a of the Ω coaxial feeder 14 with the inner conductor 14a.

Further, the connection point 32a is located at the center of the strip line 32 in order to achieve power supply with the same phase and the same amplitude. Also, the feed point 15 of the feed conductor 34 with respect to the radiation conductor plate 10
Are located such that the impedance of the radiation conductor plate 10 becomes 100Ω. The connection between the ground conductor plate 12 and the connection ground conductor surface 36 may be made by a through hole or the like. According to the mobile object antenna of this embodiment, since the dielectric substrate 30 with copper clad on both sides is used, the whole antenna can be made thin.
In addition, an antenna suitable for mass production can be obtained with a small variation in impedance due to etching or the like.

Third Embodiment FIG. 5 shows still another embodiment of the antenna of the present invention. In this example, an attempt is made to widen the resonance frequency band of the antenna body 100.

That is, the L-shaped additional conductor plate 40 is arranged opposite to the open end of the radiation conductor plate 10 formed by the inverted L antenna. That is, the additional conductor plate 40 having the same shape as the radiation conductor plate 10 is arranged so that its open end faces the open end of the radiation conductor plate 10 at a predetermined interval.

Therefore, the induced current induced in the additional conductor plate 40 causes
Utilizing the fact that the impedance of the radiation conductor plate 10 changes, the real part of the antenna impedance in a resonance state (when the imaginary part of the impedance is zero) changes the impedance of the coaxial feed line 14 with respect to the frequency change (the above-described example). In
50Ω) or a frequency band that can be maintained at a value very close to this value.

Further, in this example, a certain gap is provided between the lower end of the radiation conductor plate 10 connected to the coaxial feeder and the flat surface of the ground conductor plate 12, and the capacitance caused by this gap is smaller than that of the antenna body 100. This is to cancel the reactance component corresponding to the imaginary part of the impedance component. By adjusting this gap, the imaginary part of the impedance can be maintained in a state of substantially zero or close to it in a wide frequency band, that is, in resonance.

In this example, the length from the bent portion to the free end of the radiation conductor plate 10 is slightly longer than 1/4 of the wavelength λg of the radio wave to be used, and the length of the additional conductor plate is slightly shorter than λg / 4. It has been set.

When the antenna body 100 of this embodiment is used, the resonance frequency band of the antenna can be extremely widened, and the antenna can be more suitably used as an antenna for an automobile telephone or the like.

Fourth Embodiment A fourth embodiment is shown in FIG. In this embodiment, the antenna is incorporated in the fender mirror 40.
As described above, even in the case of being incorporated in the fender mirror 40, the radiation acquisition efficiency of vertical polarization can be obtained similarly to the above-described embodiment.

The conductor on which the antenna is mounted is not limited to the above-described conductor, and various conductors such as a door mirror can be used.

[Brief description of the drawings]

1 is a schematic configuration diagram of a first embodiment of a mobile object antenna according to the present invention, FIG. 2 is an external perspective view of the embodiment, FIG. 3 is a power gain directivity pattern diagram of the embodiment, FIG. FIG. 4 is a schematic configuration diagram showing the configuration of the second embodiment, FIG. 5 is a schematic configuration diagram showing the configuration of the third embodiment, FIG. 6 is a schematic configuration diagram showing the configuration of the fourth embodiment, FIG. FIG. 8 is an explanatory diagram showing the configuration of a conventional example, and FIG. 9 is an explanatory diagram showing the state of current in the conventional example. 10 Radiating conductor plate 12 Ground conductor plate 14 Coaxial feed line 100 Antenna

Claims (1)

(57) [Claims] An antenna for a mobile unit mounted near a conductor of an automobile, comprising a grounding conductor plate and a radiation conductor plate opposed to the grounding conductor plate at a predetermined interval. A pair of antennas, a coaxial feed line composed of an outer conductor connected to the ground conductor plate and an inner conductor connected to the radiation conductor plate, and a vertical polarization in the antenna body through the coaxial feed line. Power supply means for supplying power to the antenna body so as to generate the antenna element, and the pair of antenna bodies are arranged in parallel at symmetrical positions at predetermined intervals in substantially the same vertical plane, and By feeding power to the pair of antennas with the same phase and the same amplitude, the induced currents generated in the conductors of the vehicle due to the current flowing through the pair of antennas cancel each other out. Mobile antenna that prevents the occurrence of the wave, characterized in that to prevent a reduction in the vertical polarization component.