JPH03138999A - Radio wave dark room using reflecting plate - Google Patents

Abstract

PURPOSE:To reduce an entire construction cost by providing a radio wave reflecting plate in which its reflecting surface is obliquely inclined upward and a reflected wave shielding screen having an air gap for passing only a direct wave from an antenna on the entire inner area of its peripheral wall. CONSTITUTION:A radio wave reflecting plate 2 in which its reflecting surface is obliquely directed upward and a reflected wave shielding screen 6 having an air gap 7 for passing only a direct wave from an antenna 3 are provided on the entire inner area of its peripheral wall 1. Part of a radio wave radiated from the antenna 3 directly reaches a device 4 to be tested through the air gap of the screen 6, other part is reflected on the plate 2 provided inside the peripheral wall, absorbed by a radio wave absorber, and a portion of the radio wave, reaching from the antenna 3 to the device 4 becomes only the direct wave. Thus, the cost required to build a radio wave dark room can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to electromagnetic field compatibility (ELECTR) of various electronic devices.
OMAGNETIC COMPATIBILITY), that is, the ability of various electronic devices to operate with well-defined efficiency in an electromagnetic field environment, or measurement of electromagnetic interference (ELECTR) due to electromagnetic noise generated from within various electronic devices.
This relates to a radio anechoic chamber (radio wave non-reflection chamber) used for measuring OMAGNETIC INTERFERENCE+ and obtaining data on electromagnetic environment countermeasures.

2. Description of the Related Art Conventional anechoic chambers have a pyramid or serrated pyramid (deformed pyramid) shape over the entire inner surface of the peripheral wall and the entire ceiling wall. For example, carbon is contained in a sheet of foamed polyethylene. The radio wave absorber is formed by stacking a plurality of sheets with different ratios and is arranged without gaps.

Problems to be Solved by the Invention The current frequencies of radio waves used when measuring electromagnetic field compatibility or electromagnetic interference as described above in an anechoic chamber are approximately 30 MHz to looo MHz (wavelength: approximately 10 MHz). meters to 0.3 meters).

Therefore, the height of the radio wave absorber having the shape of a pyramid or a sawtooth pyramid (deformed pyramid) provided on the entire inner surface of the peripheral wall and the ceiling wall of the anechoic chamber is determined by the height of the maximum wavelength of the radio wave (%). (approximately 5 meters to 2.5 meters), and each radio wave absorber is large, so the volume of the anechoic chamber becomes large and the site area required to construct the anechoic chamber also increases. be.

In addition, it is economically difficult to realize a radio wave absorber that completely absorbs radio waves, and the radio wave absorbers that are normally used reflect a portion of the radio waves and the reflection effect differs depending on the frequency, so it is difficult to realize a radio wave absorber that completely absorbs radio waves. Therefore, it is difficult to obtain good frequency characteristics.

Furthermore, if equipment other than the equipment under test or people are present in the anechoic chamber, the influence of their presence on the measurement results cannot be ignored. It is necessary to provide a separate room from the anechoic chamber, which also has the disadvantage of increasing the site area and increasing the overall construction cost.

Means for Solving the Problems 1 The anechoic chamber of the present invention has a radio wave reflecting plate provided with a reflecting surface facing diagonally upward over the entire inner side of a peripheral wall with an open top, and a mounting table for an antenna and a device under test. and a reflected wave blocking screen having a gap that allows only direct waves from the antenna to pass through.

A part of the radio waves radiated from the working antenna directly reaches the equipment under test through the gap in the screen for blocking reflected waves, and a part is reflected by the radio wave reflector. The reflected waves from the surface are blocked by the reflected wave blocking screen, and some of the reflected waves from the radio wave reflector are directed upward and radiated into the sky from the open upper part of the radio anechoic chamber.

Since the sky is an ideal absorber of radio waves, the upward reflected waves do not return to the anechoic chamber.

The propagating radio wave component that reaches the equipment under test from the antenna is only the direct wave.

Means for Solving the Problems 2 The anechoic chamber of the present invention is provided between a radio wave reflecting plate provided with a reflecting surface facing diagonally upward throughout the inner side of a peripheral wall, and a mounting table for an antenna and a device under test. This device comprises a reflected wave blocking screen having a gap that allows only direct waves from the antenna to pass through, and a radio wave absorber provided on the ceiling wall surface.

A part of the radio waves radiated from the working antenna directly reaches the equipment under test through the gap in the screen for blocking reflected waves, and a part is reflected by the radio wave reflecting plate installed inside the surrounding wall. Some of the reflected waves are blocked by the reflected wave blocking screen, and some of the reflected waves from the radio wave reflector are directed upwards and absorbed by the radio wave absorber installed on the ceiling wall of the anechoic chamber, and are transmitted from the antenna to the sample. The propagating radio wave components that reach the equipment are only direct waves.

Embodiment FIG. 1 is a plan view showing an embodiment of the present invention, and FIG. 2 is a plan view showing an embodiment of the present invention.
FIG. 1 is a cross-sectional view taken along line AA in FIG. 1, and FIG. 3 is a cross-sectional view taken along line B-B in FIG.

Although a rod-shaped body is shown in the figure, any antenna such as a biconical antenna or a parabolic antenna can be used. Reference numeral 4 denotes a device under test; 5, a mounting table for the device under test 4; and 1, for example, a turntable made of an insulator. Reference numeral 6 denotes a screen for blocking reflected waves, and as shown in FIG. 3, a substantially U-shaped gap 7 is provided in the center.

The radio wave reflecting plate 2 is installed over the entire inner side of the peripheral wall l with the reflecting surface facing diagonally upward, but the smaller the angle of the reflecting surface with respect to the floor surface, and the higher the height of the upper edge of the reflecting surface, the more electrical the It can increase the effect.

However, considering economic efficiency, it is desirable to select the angle of the first reflecting surface to the floor between approximately 70° and 25°, and the height of the upper edge of the first reflecting surface to be appropriately higher than the upper end of the antenna 3. to form.

The material for radio wave reflection 2 may be any material as long as it does not transmit radio waves and can form a smooth reflective surface, such as a metal plate such as an aluminum plate, iron plate, or copper plate, or a plate-shaped wire mesh. The conductive sheet may be formed by attaching a conductive sheet to the surface of a commercially available construction board or the like.

The reflected wave blocking screen 6 is used to protect the antenna 3 and the equipment under test 4.
The device under test 4 (or the antenna 3) can be seen through the antenna 3 (or the device under test 4) through the air gap 7.

The reflected wave blocking screen 6 may be made of any material as long as it does not allow radio waves to pass through it, and similarly to the radio wave reflecting plate 2, it may be formed using, for example, a metal plate such as an aluminum plate, iron plate, or copper plate, or a plate-shaped wire mesh. Alternatively, a conductive sheet may be attached to the surface of a commercially available construction board or the like.

To explain the installation relationship between the radio wave reflector 2 and the reflected wave blocking screen 6, the path difference between the direct wave and the reflected wave reaching the device under test 4 from the antenna 3 (the difference between the path of the direct wave and the path of the reflected wave) ) is less than % of the wavelength, there is no problem in omitting the reflected wave blocking screen 6, but the path difference between the direct wave and the reflected wave is longer than the half wavelength. If the reflection coefficient of the radio wave reflecting plate 2 is large, it is necessary to provide a screen 6 for blocking reflected waves.
When looking at the device under test 4 from the antenna 3, or when looking at the antenna 3 from the device under test 4, all the radio wave reflectors 2
The size of the gap 7 is selected so that the image of the other party cannot be clearly recognized.

Although the figure shows an example in which the upper part of the peripheral wall l is kept open, it is desirable to provide a roof made of a material that does not impede transmission of radio waves (and can prevent rain and snow).

Next, the operation of the anechoic chamber of the present invention will be explained.

When the screen 6 for blocking reflected waves is omitted, the propagating radio wave component radiated from the antenna 3 and reaching the device under test 4 is a direct wave, a reflected wave from the floor surface, and a reflected wave from the radio wave reflecting plate 2. However, in the anechoic chamber of the present invention, a reflected wave blocking screen 6 having a gap 7 that allows only direct waves from the antenna 3 to pass is provided between the antenna 3 and the device under test 4, so that a radio wave reflecting plate is used. A part of the reflected wave from the radio wave reflecting plate 2 and a reflected wave from the floor surface are blocked by the reflected wave blocking screen 6, and a part of the reflected wave from the radio wave reflecting plate 2 is directed upward and is transmitted from the upper open part of the anechoic chamber. radiated into the sky.

Since the sky is an ideal absorber of radio waves, radio waves traveling upward will never return to the anechoic chamber.

Therefore, the propagating radio wave component that reaches the device under test 4 from the antenna 3 is only a direct wave.

Since the propagation of radio waves is reversible, even when the noise radio waves generated in the device under test 4 are received by the antenna 3, only direct waves are received in exactly the same way.

4 is a sectional view (BB sectional view in FIG. 5) showing another embodiment of the present invention, FIG. 5 is a sectional view taken along AA in FIG. 4, and FIG. In each figure, l is the peripheral wall, 2 is the radio wave reflector, 3 is the antenna, 4 is the equipment under test,
Reference numeral 5 denotes a mounting table for the equipment under test 4, which has the same configuration as that shown in FIGS. 1 to 3.

6 is a screen for blocking reflected waves; 5 In this embodiment,
The difference from the reflected wave blocking screen in the previous embodiment is that a substantially circular gap 8 is provided instead of the substantially U-shaped gap 7 as in the previous embodiment, and the material of the reflected wave blocking screen 6 and the radio wave The installation relationship with the reflecting plate 2, etc. are completely the same as in the previous embodiment.

9 is a radio wave absorber, which consists of an absorber with the same structure as the conventional one,
It is installed over the entire ceiling and wall surface.

This embodiment differs from the previous embodiment in that the upward radio waves are absorbed by the radio wave absorber 9, but the other radio wave propagation conditions are the same as in the previous embodiment, and the device under test 4 has an antenna 3. Only direct waves from the

Although not shown in the figure, a roof may be provided above the ceiling wall if necessary.

Effects of the Invention In the anechoic chamber of the present invention, reflected waves other than direct waves between the antenna 3 and the device under test 4 mainly direct upward, and in the embodiments shown in FIGS. 1 to 3, they direct upward. The reflected waves are radiated into the sky and do not return to the anechoic chamber again.
In the embodiments shown in FIGS. 4 to 6, the reflected waves 5 directed upward are absorbed by the radio wave absorber 9, so that only direct waves reach the device under test 4 in any of the embodiments. Therefore, the propagation stability of radio waves is good, standing waves due to repeated reflections are difficult to stand up, and the impedance of the antenna 3 is not adversely affected, so there is little possibility of measurement errors occurring.

Conventional radio wave absorbers vary in size, shape, absorption rate, etc. depending on the wavelength of radio waves, but the radio wave reflector used in the present invention has good broadband properties.

In addition, the structure is simple, and there is almost no possibility that the quality of processing will affect the electrical characteristics.

Since the space between the peripheral wall l and the radio wave reflecting plate 2 provided inside the anechoic chamber of the present invention is electrically isolated, it can be used as a storage area for test equipment, an installation location for air conditioning equipment, a test preparation room, etc. Since it can be used effectively, there is no need to set up a separate room like in the past.

The anechoic chamber of the present invention has a simple structure, a small volume, inexpensive constituent materials, and a small site area, making it possible to significantly reduce construction costs and construction period.

Since the embodiments shown in FIGS. 4 to 6 are electrically completely sealed, they can be installed on the middle floor of a building in a large city, for example, where there are many external noise radio waves.

FIGS. 7 and 8 are curve diagrams for explaining the suppressing effect of unnecessary reflected waves in the anechoic chamber of the present invention. In both figures, the horizontal axis represents the transmission frequency f (30 MHz in single part in MHz,
The vertical axis is the transmission loss L (dB) with a -scale of 1 OdB, the solid line is the measured value of horizontal polarization, the broken line is the measured value of vertical polarization, and the dotted line in Figure 8 is the calculated value equivalent to free space. Two reflectors, each 5 meters wide and 2.5 meters high, were installed vertically at an interval of 10 meters in an open space between buildings, and a transmitting biconical antenna and a receiving biconical antenna were installed between them. The figure shows actual measurements of transmission characteristics in the frequency range from 30MHz to 330MHz with antennas placed 5 meters apart.As is clear from the figure, there are standing waves and irregular waves with amplitudes exceeding 20dB. Figure 8 shows a reflector with a height of 1.77 meters on the upper edge of the biconical antenna installed at the same location as in Figure 7 and under the same conditions as above, with the upper edge of the reflector plate 1.77 meters above the ground. angle 4
This is an example of an actual measured value of transmission loss in the same frequency band as above, arranged and surrounded by 5 degrees.

As is clear from the figure, large standing waves are almost suppressed, and the transmission loss is several dB lower than the free space value due to direct waves only.
It has been shown that the difference is close.

[Brief explanation of the drawing]

1 to 3 are cross-sectional views showing one embodiment of the present invention,
4 to 6 are cross-sectional views showing other embodiments, and FIGS. 7 and 8 are curve diagrams for explaining the electrical effects of the present invention. Wave reflector, 3: antenna, 4: equipment under test, 5: mounting table,
6: Screen for blocking reflected waves, 7 and 8 voids, 9: Radio wave absorber.

Claims (2)

[Claims] 1. Between the radio wave reflecting plate (2), which is installed with the reflective surface facing diagonally upward, over the entire inner side of the peripheral wall (1) with its top open, and the mounting table (5) for the antenna (3) and the equipment under test (4). 1. A radio anechoic chamber comprising: a reflected wave blocking screen (6) having a gap (7) that allows only direct waves from the antenna (3) to pass through. 2. A radio wave reflecting plate (2) is provided throughout the inner side of the peripheral wall (1) with the reflecting surface facing diagonally upward, and a radio wave reflecting plate (2) is provided between the antenna (3) and the mounting table (5) for the equipment under test (4), It is characterized by comprising a reflected wave blocking screen (6) having a gap (8) that allows only direct waves from the antenna (3) to pass through, and a radio wave absorber (9) provided on the ceiling wall surface. Anechoic chamber.