JPH11330847A - Antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable stabilization of a transmission/reception level in spite of a position of an antenna, even when installing an antenna near a dielectric by providing an antenna element on one side of a substrate and providing an antireflection means on one side of the substrate around the antenna element. SOLUTION: On one side of a substrate 3, an antenna element 1 composed of a patch element, for example, is provided via a dielectric plate 2 and on one side of the substrate 3 around that antenna element, a antireflection means made of a radio wave absorber 5 is provided. The antenna element 1 is constituted of the patch element provided with a conductor layer via the dielectric plate 2 onto a ground plate 4, and formed into dimension so as to enable transmission/reception with resonance caused by the signal at the desired frequency. A power feeding line 1a is led via a through-hole 3a provided on the substrate 3 to the rear side of the substrate 3 and connected to a circuit provided on the rear side of the substrate 3. For the radio wave absorber 5, a magnetic material such as ferrite, for example, is used and provided on the ground plate 4 of the substrate 3 with a thickness such that a reflection coefficient becomes '0' with respect to the frequency of a transmission/reception signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to transmission / reception to / from a partner via a dielectric material such as glass, for example, in a case where an antenna is installed in a car to communicate with the outside of the car. The present invention relates to an antenna device. For more information,
The present invention relates to an antenna device having stable performance in which a transmission / reception level does not vary even if a distance from a dielectric such as glass differs depending on an installation location of the antenna device.

[0002]

2. Description of the Related Art In recent years, an automatic toll collection system on a highway has been developed, and a system for communicating with automobiles lined up on the road in a microwave band has been developed. In such a case, the vehicle side installs an antenna device in the vehicle, and the management side installs a transceiver having the antenna device beside the road and performs communication between them.
Therefore, communication between the two is performed via the windshield of the automobile.

An antenna device used in such an automatic toll collection system and installed in an automobile has a ground plate provided on one surface of a dielectric substrate such as a ceramic substrate and a strip line provided on the opposite surface. In addition, a patch antenna device or the like is used in which a circuit is formed by mounting electronic components and a patch antenna element is provided via a dielectric plate on the side on which the above-described ground plate is provided. Then, the power supply section of the antenna element is directly connected to the circuit on the opposite surface. This structure is not limited to the patch antenna, and other antennas such as a curl element and a helical element are provided with an antenna element so as to protrude above the ground plate, and an electronic component is provided on the opposite surface side. ing.

[0004]

The body of an automobile is mostly made of metal. However, if the antenna device only needs to be able to communicate in a specific direction, such as an automatic toll collection system, a windshield is required. Communication can be performed via a dielectric such as glass, and communication can normally be performed without being affected by radio waves. However, when the antenna device is actually installed in the vehicle and communication with the management side outside the vehicle is performed, the transmission / reception level greatly varies depending on the installation location of the antenna device in the vehicle. Therefore, when designing the antenna, it is necessary to provide these fluctuation widths as a margin, and there is a problem that the antenna design is extremely restricted.

The present inventors have conducted intensive studies to solve this problem, and as a result, as shown in FIG. 4, for example, an antenna device provided near a windshield transmits a signal radiated from an antenna element 1. A part of the signal is reflected by the windshield 10 or the like, returns to the antenna device side, is reflected again by the substrate 3 including the ground plane, is radiated from the windshield 10 as a transmission signal T2, and is directly reflected without reflection. Signal T1 radiated through
And propagated as a combined wave signal, and found that the combined wave signal changes depending on the phase of the transmission signal T2 due to reflection. That is, since the phase of the signal once reflected by the glass changes depending on the distance L between the antenna surface and the glass, the level of the transmission signal synthesized by the distance L of the antenna device from the glass is changed. Fluctuates. Conventionally, if the distance between the antenna device and a dielectric such as glass is large or the distance is always constant, fluctuations in transmission and reception levels do not pose a problem, and the effects thereof are not taken into account. However, in the case of a special use, such as when an antenna device is installed in a vehicle of a car toll collection system that communicates over a short distance, the reflection of a dielectric material becomes a problem, and the dielectric material intervenes depending on the installation location. It has been found that when the distance from the dielectric is different, the transmission characteristics are changed.

[0006] This phenomenon is not limited to the transmission signal, and even in the case of the reception signal, the signal directly incident on the antenna element via the windshield and the entire antenna surface including the ground plane reflects the glass and is again reflected by the glass. The reflected wave enters the antenna element as a composite wave, and the phase of the signal reflected by the antenna surface and the glass changes depending on the position of the antenna device, and the level of the received signal of the composite wave fluctuates. .

[0007] The present invention has been made based on such knowledge, and it is an object of the present invention to provide an antenna device having a stable transmission / reception level regardless of its position even when an antenna is installed near a dielectric. Aim.

[0008]

SUMMARY OF THE INVENTION An antenna device according to the present invention is an antenna device which is disposed near a dielectric and transmits and / or receives signals to / from a partner through the dielectric. An antenna element is provided, and antireflection means is provided on one surface side of the substrate around the antenna element.

With this configuration, a constant transmission / reception level can be always obtained regardless of the distance from the dielectric to the installation place of the antenna, and even if the type of the dielectric changes, the design of the antenna can be improved. , It is not necessary to take a large margin.

As the anti-reflection means, a radio wave absorbing material is used, or a dummy antenna formed so as to operate at the same frequency as the antenna element and connected to a matching load is used.

[0011]

Next, an antenna device according to the present invention will be described with reference to the drawings.

As described above, the antenna device of the present invention
For example, when installing an antenna device near the windshield of a car for an automatic toll collection system on a highway, and transmitting and receiving relatively near the outside of the car,
This is based on the finding that the transmission / reception signal level fluctuates depending on the distance from the windshield of the antenna device. As shown in a plan view and a cross-sectional view of one embodiment in FIG. An antenna element 1 composed of, for example, a patch element is provided via a dielectric plate 2, and an antireflection means composed of a radio wave absorber 5 is provided on one surface side of the substrate 3 around the antenna element 1.

In the example shown in FIG. 1, the antenna element 1 is constituted by a patch element having a conductor layer provided on a ground plate 4 via a dielectric plate 2, and resonates with a signal of a desired frequency. It is formed in dimensions so that it can transmit and receive. Then, the feeder line 1a is led out to the back surface side of the substrate 3 through the through hole 3a provided in the substrate 3, and is connected to a circuit formed by circuit elements (not shown) provided on the back surface side of the substrate 3. Has become. However, the antenna element 1 is not limited to the patch element, and is the same in an antenna device in which another antenna element such as another helical element or curl element is provided on the ground plane.

The substrate 3 is made of, for example, a ceramic substrate, on one side of which a copper film or the like is provided to form a ground plate 4, and on the back surface, although not shown, a wiring pattern is similarly formed by the copper film or the like. In addition, a transmission / reception circuit for processing signals is formed by connecting strip lines and circuit elements. The substrate 3 does not need to be a ceramic substrate, and is the same even when a normal printed board or the like is used.

The electromagnetic wave absorber 5 is made of a magnetic material such as ferrite, and is provided on the ground plate 4 of the substrate 3 so that its thickness has a reflection coefficient of 0 with respect to the frequency of a transmission / reception signal. Have been. The radio wave absorber 5 may be formed of a dielectric material such as rubber, in addition to the radio wave absorber of such a magnetic material.
A material that causes dielectric loss such as graphite powder may be mixed or applied. The radio wave absorber 5 may be provided by applying a plate-shaped member on the ground plate 4 around the antenna element 1 or by directly applying the ground absorber 4 on the ground plate 4.

According to the antenna device of the present invention, even if there is a ground plane around the antenna element 1, anti-reflection means including the radio wave absorber 5 is provided on the surface side. for that reason,
For example, this antenna device is installed inside a car,
As shown in FIG. 2, even when there is an electromagnetic wave R reflected and returned by the windshield 10, the electromagnetic wave R is absorbed by the radio wave absorber 5 and provided again in front of the windshield 10. There is no reflection on the glass 10 side. Therefore, as for the signal radio wave radiated from the antenna element 1, only the transmitted electromagnetic wave T that passes through without being reflected by the windshield 10 becomes a transmission signal, and does not depend at all on the distance between the antenna element 1 and a dielectric such as the windshield 10. Do not send at a stable output level.

As for the reception signal, the reception signal incident on the antenna device is received by the antenna element 1 as it is and resonated by the antenna element. Absorbed by body 5. Therefore, no signal is reflected on the entire antenna surface of the antenna device, and no signal is reflected on the antenna surface, reflected on the windshield 10 again, and incident on the antenna element 1. Therefore, there is no change in signal level due to synthesis with signals having different phases.

As a result, both the transmission and reception signal levels are very stable, and the trouble of designing in consideration of the margin that the antenna characteristics fluctuate depending on the installation location of the antenna is eliminated. Further, since the reflection by the dielectric such as the windshield becomes irrelevant, even when the antenna device is arranged near a dielectric made of a different material such as a different vehicle type, the transmission / reception level hardly fluctuates.

FIG. 3 is an explanatory diagram of another embodiment of the antenna device of the present invention. In this example, a dummy antenna element 6 is provided instead of a radio wave absorber, and the dummy antenna element 6 is connected to a matching load 7 to form an anti-reflection means. Is prevented from being reflected again on the antenna surface.

Although shown in a simplified manner in FIG. 3, the antenna element 1 is provided on a ground plate (not shown) of the substrate 3 via a dielectric plate (not shown), as in the example shown in FIG. ing. Then, a feeding line (not shown) is connected to the antenna element 1 and connected to a circuit formed on the back surface of the substrate 3. In this example, a dummy antenna element 6 formed so as to resonate with a signal of the same frequency as the antenna element 1 is provided around the antenna element 1 via a dielectric plate (not shown) similarly to the antenna element 1, not shown. It is provided on a ground plate. The dummy antenna element 6 is connected to the feed line 6 in the same manner as the antenna element 1.
a is connected, and the feed line 6a is connected to a matching load 7 of 50Ω.
Grounded. That is, the electromagnetic wave incident on the dummy antenna element 6 resonates at the dummy antenna element 6 and is absorbed by the load 7. As a result, as in the case where the radio wave absorber is provided, the electromagnetic wave incident around the antenna element 1 is absorbed by the matching load 7 and is not reflected on the front side thereof.

[0021]

According to the present invention, as in the case of transmitting / receiving a signal to / from a transmitter / receiver installed on the shoulder of a road via a windshield or the like, the dielectric member is disposed in the interior of a car. In this case, even when communication is performed via the dielectric, a transmission / reception signal of a stable transmission / reception level can be obtained without being affected by the dielectric. as a result,
An antenna device to be installed in a vehicle such as an automatic toll collection system on a highway can be manufactured with a certain performance, and mass production is possible and costs can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of an antenna device of the present invention.

FIG. 2 is a diagram illustrating levels of transmission and reception signals when the antenna device of FIG. 1 is installed near a dielectric.

FIG. 3 is an explanatory diagram of another embodiment of the antenna device of the present invention.

FIG. 4 is a diagram illustrating a change in signal level of a conventional antenna device installed near a dielectric.

[Explanation of symbols]

 Reference Signs List 1 antenna element 3 substrate 4 ground plate 5 radio wave absorber 6 dummy antenna element

Claims (3)

[Claims] 1. An antenna device disposed near a dielectric and transmitting and / or receiving with a counterpart through the dielectric, wherein an antenna element is provided on one surface side of a substrate, and the periphery of the antenna element is provided. An antenna device comprising an antireflection means provided on one surface side of the substrate. 2. The antenna device according to claim 1, wherein said reflection preventing means is made of a radio wave absorbing material. 3. The antenna apparatus according to claim 1, wherein said antireflection means is a dummy antenna formed to operate at the same frequency as said antenna element and connected to a matching load.