JPH08102608A - Antenna system - Google Patents

Abstract

PURPOSE: To prevent the generation of a dip in a received electric field due to the interference of a multiple reflection wave generated between a metallic surface on the front of a casing to which an antenna is fixed and window glass or the like existing in the front of the antenna with a direct incident wave transmitted through the window glass or the like. CONSTITUTION: By sticking an electric wave absorber 4 to the metallic face 3 formed on the front of the casing 6 to which the antenna 1 is fixed and causing multiple reflection, multiple reflection to be generated between the casing 6 and a radome or the like is suppressed and interference with a direct incident wave is reduced.

Description

Detailed Description of the Invention

[0001]

[Industrial applications]

2. Description of the Related Art The structure of a conventional antenna device is shown in FIG.

In the figure, reference numeral 1 denotes a small transmitting / receiving antenna, which is directly attached to a metal surface 3 on the front surface of a rectangular parallelepiped casing 6 containing a transmitter / receiver for transmitting and receiving high frequency signals. Since it is a parabolic antenna that transmits and receives U-band (quasi-millimeter wave, millimeter-wave band) signals, the shape of the reflecting mirror is smaller than the size of the housing 6, and the front metal surface 3 (height 107 (mm), width 141 (mm))
The diameter of the reflector is 21 (mm), which is very small with respect to the central part of the.

Further, the casing 6 is entirely housed in a case of a metal conductor, which provides a shielding effect. The distance in front of such an antenna device (10 in this embodiment)
FIG. 12 shows the direction of the received radio wave when the window glass 2 is placed with 0 mm). The window glass 2 has a thickness of 8.3 (mm) and a relative dielectric constant of 7.0.

In this figure, a radio wave 5 arriving at a certain angle
The a transmits through the window glass 2 and directly enters the antenna 1 as a radio wave 5a '. On the other hand, the radio wave 5b is transmitted through the window glass 2 to become a radio wave 5b ', and then the metal surface 3 on the front surface of the housing 3
Is reflected by the window glass 2 to be the radio wave 5C, is reflected by the window glass 2 to be the radio wave 5C, and is further reflected by the window glass 2 to be the radio wave 5C.
d will be input to the antenna 1.

As a result, the radio wave 5a 'and the radio wave 5d are incident on the antenna 1 at the same time, which causes interference due to multiple reflection.

As described above, when an obstacle having a high dielectric constant such as the window glass 2 is present in front of the antenna 1, the antenna is attached to the front metal surface 3 of the housing 6 and the antenna. The multiple reflection wave generated between the window glass and the like existing in front of the window may directly interfere with the incident wave, and depending on the incident angle, the received electric field strength may largely drop.

FIG. 13 shows the window glass 2 based on the above conditions.
It is a figure which shows the difference of a radiation pattern with and without. In the figure, when there is no window glass, the maximum reception electric field is obtained when the azimuth angle is 0 °, and the reception electric field gradually attenuates as the azimuth angle increases.

On the other hand, when the window glass 2 is present, a large dip of the received electric field intensity occurs at a constant period because multiple reflection occurs due to the metal surface 3. Especially, the azimuth angle is 0
In case of °, the maximum dip has occurred.

In this embodiment, the frequency is 50.9 GH.
Although the reflection pattern for z is shown, the same result can be obtained for signals in the U band.

In order to improve the effect of such multiple reflection, various methods have been conventionally used.

For example, when a radome having a high dielectric constant is present on the front surface of the antenna, a method of attaching a radio wave absorber to the radome side is used in order to suppress multiple reflection that occurs between the radome and the housing. It was This method, for example,
It is described in Japanese Utility Model Publication No. 2-60308.

[0012]

In the prior art, a radio wave absorber is attached to a part of the radome in order to prevent multiple reflections, but it is effective when the radio wave is in a certain direction. However, when the communication direction changes, the position of the electromagnetic wave absorber must be changed, and there is a problem that the communication direction is limited without being affected by multiple reflection.

[0013]

SUMMARY OF THE INVENTION An antenna device according to the present invention includes a radio wave absorber attached to a metal surface of a front surface of a housing to which an antenna causing multiple reflection is attached, or one or a plurality of radio wave absorbers. By using a flat or curved surface, the multiple reflections generated between the housing and the window glass are suppressed, and the interference with the direct incident wave is reduced.

[0014]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is an external view showing a first embodiment of an antenna device of the present invention. In this figure,
Both antennas 1 have the same shape as that shown in FIG. Here, what is different from FIG. 11 is that the electromagnetic wave absorber 4 having a thickness of about 10 mm is attached to the metal surface 3 on the front surface of the housing.

FIG. 2 is a diagram showing the directions of received radio waves when the radio wave absorber 4 is attached.

In the figure, the radio wave 5a passes through the window glass 2 and then becomes a radio wave 5a 'and directly enters the antenna 1.

After passing through the window glass 2, the radio wave 5b becomes a radio wave 5b 'and enters the radio wave absorber 4. Radio wave 5
Since b'is absorbed by the radio wave absorber 4, there are no reflected waves 5c, 5d, etc., which have been conventionally generated. As a result, multiple reflection can be completely suppressed.

FIG. 3 is a diagram showing radiation patterns in the configuration shown in FIG. 2 in the case where the electromagnetic wave absorber 4 is attached to the metal surface 3 on the front surface of the housing and in the case where it is not attached.

According to this figure, when the window glass 2 is present,
By attaching the electromagnetic wave absorber to the front surface 3 of the housing,
It has been shown that the level change with incident angle is significantly reduced.

FIG. 4 is a diagram showing a second embodiment of the present invention. In this figure, the shape of the front part of the casing 7 is such that the central part is inclined and projected at an appropriate angle α. . The antenna 1 is attached to the front center portion of this bent portion. FIG. 5 shows a case where the window glass 2 is present in front of the antenna device having this structure and the incident wave is incident at an angle θ.

Here, if the above-mentioned inclination angle α is more than θ / 2 in relation to the incident angle θ, multiple reflection does not occur between the metal surface 3 on the front surface of the casing 7 and the window glass 2.

FIG. 6 shows a radiation pattern when the specially shaped casing shown in FIG. 5 is used, the front surface shown in FIG. 3 is a flat metal plate, and an electromagnetic wave absorber is attached. It is a figure showing the radiation pattern of.

In this figure, there is almost no difference in the received electric field between the former and the latter, and it is shown that multiple reflection can be prevented by providing an inclination. In this embodiment, the front metal surface is bent in two from the center, but it is also possible to make a plurality of bends and branch the incident wave by a plurality of surfaces to prevent multiple reflection.

7 and 8 are diagrams showing a third embodiment of the present invention.

With respect to the front surface of the housing 8, the front metal surface 3 is formed into a curved surface to prevent multiple reflection.

That is, as shown in FIG. 8, the incident wave incident at a certain angle is reflected by the curved metal surface 3 on the front surface, and thereby an effect equivalent to that of the structure shown in FIG. 4 is brought about. You can

Further, FIGS. 9 and 10 are views showing a fourth embodiment of the present invention, which is different from the structure shown in FIG.
By mounting the radio wave absorber 4 on the metal surface 3, it is possible to reduce multiple reflections to an almost negligible level.

[0029]

As described above, the antenna device according to the present invention suppresses the multiple reflection occurring between the housing and the window glass by attaching the electromagnetic wave absorber to the front surface of the housing to which the antenna is attached. However, it is possible not to interfere with the radio waves that directly enter the antenna. It is also possible to suppress multiple reflections that occur between the housing and the window glass by using a metal surface on the front surface of the housing that is a curved surface or a curved surface from the center so that it does not interfere with the radio waves that directly enter the antenna. it can. As a result, regardless of the distance between the window glass and the antenna, a large drop in the received electric field due to the angle of incidence of the radio waves can be prevented, and the attenuation due to the window glass is eliminated compared to the radiation pattern without the window glass. Therefore, it has an effect that almost the same radiation pattern can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of an antenna device of the present invention.

FIG. 2 is a diagram showing an incident state of the radio wave of FIG.

FIG. 3 is a diagram showing a radiation pattern when a window glass is provided on the front surface of the antenna device of FIG.

FIG. 4 is a diagram showing a second embodiment of the antenna device of the present invention.

5 is a diagram showing an incident state of the radio wave of FIG.

6 is a diagram showing a radiation pattern when a window glass is provided on the front surface of the antenna device of FIG.

FIG. 7 is a diagram showing a third embodiment of the antenna device of the present invention.

FIG. 8 is a diagram showing an incident state of the radio wave of FIG. 7.

FIG. 9 is a diagram showing a fourth embodiment of the antenna device of the present invention.

FIG. 10 is a diagram showing an incident state of the radio wave of FIG. 9.

FIG. 11 is a diagram showing a structure of a conventional antenna device.

FIG. 12 is a diagram showing an incident state of the radio wave of FIG. 11.

13 is a diagram showing a radiation pattern when a window glass is provided on the front surface of the antenna device of FIG.

[Explanation of symbols]

 1 antenna 2 window glass 3 metal surface in front of housing 4 radio wave absorber 5 incident wave 6 housing 7 housing 8 housing

Claims (6)

[Claims] 1. An antenna device comprising a metallic casing containing a transmitting / receiving device for transmitting and receiving a high frequency signal, and a small antenna mounted on the front face of the casing, wherein the antenna is provided on the front face of the casing. An antenna device characterized in that a radio wave absorber is attached except. 2. An antenna device comprising a metallic housing containing a transmitting / receiving device for transmitting and receiving high frequency signals, and a small antenna attached to the front surface of the housing, wherein the metal surface on the front surface of the housing is An antenna device, wherein the antenna device is inclined from the center by a predetermined angle with respect to a horizontal plane and protrudes. 3. An antenna device comprising a metallic casing containing a transmitting / receiving device for transmitting and receiving high-frequency signals, and a small antenna mounted on the front face of the casing, wherein the metal surface on the front face of the casing is An antenna device having a curved shape. 4. The antenna is a U-band band signal transmitting / receiving antenna, and the diameter of the reflecting mirror is sufficiently smaller than the metal surface of the front surface of the housing. The antenna device described. 5. The antenna device according to claim 2, wherein the predetermined angle is equal to or more than ½ of an angle of incidence on the antenna. 6. The antenna device according to claim 2, wherein a radio wave absorber is attached to a metal surface of the front surface of the housing.