JPH04276700A - Radio wave anechoic chamber - Google Patents

Abstract

PURPOSE:To provide a radio wave anechoic chamber in which a volume and an installation area are relatively small, a composite wave of a direct wave and a reflected wave from a floor can be measured and an accurately measured value can be obtained. CONSTITUTION:A radio wave reflecting plate 2 is provided on a floor, and radio wave reflecting plates 31, 32, 33, 34 in which a lower edge is brought into contact with the reflecting surface of the plate 2 and the surface is formed obliquely upward, are provided on an entire inner side of the inner wall of a peripheral wall electromagnetically opened at its top to constitute a radio wave dark chamber. In the chamber, when a trial unit 5 and an antenna 4 are provided at a suitable interval, part of electromagnetic noise radiated from the unit 4 directly reaches the antenna 4, and the noise directed toward a floor is reflected on the plate 2 so that the part reaches the antenna 4. Part of the noise radiated from the unit 5 and the part of the noise reflected on the plate 2 are reflected toward the top of the chamber via the plates 31, 32, 33, 34, and not returned again to the chamber.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to electromagnetic field compatibility of various electronic devices (ELECTROMAGNETIC COMPA).
TIBILITY), that is, the ability of various electronic devices to operate satisfactorily at a planned efficiency in an electromagnetic field environment (
Measurement of electromagnetic interference (hereinafter referred to as noise tolerance) or electromagnetic interference (ELECT) due to electromagnetic noise generated from inside various electronic devices.
ROMAGNETIC INTERFERENCE)
This relates to a radio anechoic chamber (radio wave non-reflection chamber) that is used to perform measurements such as the above and obtain data on electromagnetic environment countermeasures.

0002

[Prior Art] In order to obtain data on the electromagnetic environment countermeasures,
Conventionally, outdoor measurement sites (open area test sites) based on the recommended standards of the U.S. Federal Communications Commission (FCC) have been used. The indoor measurement field configured, i.e.
An anechoic chamber is used in which a pyramid-shaped radio wave absorber made of, for example, foamed polyethylene containing an appropriate amount of carbon is provided over the entire inner surface of the peripheral wall and the entire ceiling wall surface.

Furthermore, in order to eliminate various defects in the outdoor measurement field and the anechoic chamber, FIG. 17 shows a plan view, FIG. 18 shows a sectional view taken along line A-A in FIG. 17, and FIG. 20 shows a sectional view taken along the line BB in FIG. 21, FIG. 21 shows a sectional view taken along the AA line in FIG. 20, and FIG. A radio anechoic chamber as shown in FIG. 17 to 22, 11 is a peripheral wall, 13 is a radio wave reflecting plate, 14 is an antenna, 15 is a device under test, 16 is a mounting table for the device under test 15, and 1
7 is a reflected wave blocking screen, 18 is a gap, and 19 is a radio wave absorber.

0004

[Problem to be solved by the invention] United States Federal Communications Commission (
F. C. The main points of the outdoor measurement field standards based on recommendation C) are listed below: (1) Distance between transmitting or receiving antenna and equipment under test: 3 m
, 10m or 30m (2) Usage frequency: 30MHz to 1000MHz (
3) Environmental conditions of the transmitting or receiving antenna and the device under test: Within the border of a nearly elliptical shape with the long axis being 2D (D is the distance between the transmitting or receiving antenna and the device under test) and the short axis being approximately 1.732D. The transmitting or receiving antenna and the device under test are arranged on the long axis, and the distance between the transmitting or receiving antenna and the boundary line and the distance between the device under test and the boundary line are respectively D/2, and the distance outside the boundary line is D/2. , Choose a location where there are no radio wave reflectors over as wide a range as possible, and the ground within the boundaries to be sufficiently flat. Therefore, if the distance D between the transmitting or receiving antenna and the equipment under test is 3 m, then the long axis 2 of the almost elliptical boundary line
D is 6 m, and the short axis is approximately 5.2 m.

[0005] Regarding the area outside the boundary line where the absence of radio wave reflectors is required, it is only stated that it is as wide as possible, and no specific numerical value is given. Regarding the outdoor measuring field used in the experiment, in the ``FY1986 Measurement Survey Report'' published by the ``Measurement Survey Report'', there is a statement regarding the outdoor measuring field used for the experiment: ``The outdoor measuring field used for this experiment was located on the ground surface. Width approx. 6
A steel plate is laid over a length of approximately 36 m, and a non-reflective area for radio waves is secured as specified to avoid reflection from surrounding buildings, etc., but the area outside the ellipse, approximately 20 m behind the receiving antenna. There is a triangular receiving tower at the site, and there is some concern that it may cause some reflected interference when measuring vertically polarized waves. ”, and using this as a reference, assume an area where there are no radio wave reflectors within a range of 20 meters outside the ellipse boundary line, and calculate the required area of the outdoor measurement site including this area for convenience of calculation. If we look at the shape of the area as a rectangle, the long side = 6m + 20m x 2 = 46m, the short side = 5.2m + 20m x 2 = 45.2m. Therefore,
The required area is 46m x 45.2m ≒ 2080m2.

[0006] Even when the setting is considered to be relatively narrow, in view of the drawbacks of outdoor measurement sites that require a large area as described above, an indoor measurement site has been proposed and put into practical use, that is, a pyramid-shaped radio wave absorber. Even in an anechoic chamber that is provided over the entire inner surface of the peripheral wall and the entire ceiling wall surface, there are the following problems. When measuring the noise resistance of various electronic devices or electromagnetic interference due to electromagnetic noise emitted from inside various electronic devices in an anechoic chamber based on the recommendations of the U.S. Federal Communications Commission (FCC). The frequency of radio waves currently in use ranges from approximately 30MHz to approximately 1000MHz.
z (in terms of wavelength, from approximately 10 meters to approximately 0.3 meters), the height of the pyramid-shaped radio wave absorber provided on the entire inner surface of the peripheral wall and the entire ceiling wall of the anechoic chamber is the maximum of the radio wave. The height is 1/2 to 1/4 of the wavelength (approximately 5 m)
Since each radio wave absorber is large in size, the volume of the anechoic chamber is also large, and the site area required to construct the anechoic chamber is also relatively large. .

The anechoic chambers shown in FIGS. 17 to 22, which have been proposed for the purpose of further reducing the required area compared to the outdoor measurement field and the anechoic chamber described above, will also be described below. There is a problem like this. Figure 1
Regarding the radio wave anechoic chambers shown in FIGS. 7 to 22, for example, among the radio waves generated and radiated by the device under test 15, radio waves other than those that directly reach the antenna 14 are reflected by the reflected wave blocking screen 17 and the radio wave reflecting plate 13. The device under test 15 will not travel upwards through the ceiling-mounted atrium for radio waves toward the sky, or will be absorbed by the radio-wave absorber 19 mounted on the ceiling and return to the anechoic chamber.
It is explained that the radio waves that reach the antenna 14 are only direct waves.

FIG. 23 is a curve showing an example of actually measured values of the transmission attenuation characteristics of the anechoic chamber (the anechoic chambers shown in FIGS. 17 to 19) in the UHF band in comparison with the free space theoretical value of direct waves. It is a diagram.

This figure shows the antenna 1 in the anechoic chamber.
4 is formed by a broadband antenna, and a broadband antenna is temporarily installed in place of the equipment under test 15, the distance between both antennas is kept at 3 m, and one of the antennas is used as a transmitting antenna and the other antenna as a receiving antenna. The height of the side antenna is fixed at 1 m, and the height of the receiving side antenna is fixed at 1.5 m. The short side of the rectangular floor surrounded by the lower edge of the radio wave reflector 13 is set at 2.5 m and the long side at 7 m. The angle of inclination (hereinafter simply referred to as the inclination angle) of the two radio wave reflectors with respect to the floor surface whose lower edges touch the short sides of the floor surface is 45.
°, the angle of inclination of each of the two radio wave reflectors whose lower edges touch the long sides of the floor is 60°, and the frequency from the transmitting side is 300MHz to 1
000MHz radio waves (horizontal polarization) are emitted at a constant output,
It was obtained by plotting the received electric field strength for each frequency separated by an appropriate frequency interval. The solid line is a curve diagram showing the characteristics in the anechoic chamber, the dashed-dotted line is the theoretical free space value of the direct wave, and the horizontal axis is the curve diagram. sets the frequency f to 300MHz or 1
It is expressed on a scale with equal intervals over 000 MHz, and the vertical axis is the attenuation amount ATT (dB).

As is clear from FIG. 23, in the UHF band, the characteristics of the anechoic chamber exhibit a tendency similar to the free space theoretical value of direct waves. This is because the dimensions of the radio wave reflecting plate 13 and the reflected wave blocking screen 17 provided in the anechoic chamber are sufficiently large for the wavelength of the radio waves used, and as a result, the reflected waves are blocked in almost the same way as light beams. The screen 17 effectively reflects and blocks reflected waves from the floor, and
This seems to be because the unnecessary reflected waves are reflected by the radio wave reflected waves 13 and are radiated toward the sky from the atrium of the ceiling and do not return again, so that no standing waves are created. However, the attenuation of the transmission attenuation characteristic in the anechoic chamber is large compared to the free space theoretical value of the direct wave, and although the details of this reason are not clear, it is as a result that a part of the direct wave is blocked by the reflected wave blocking screen 17. I think so.

If this estimation is correct, it is possible to improve the attenuation characteristics by appropriately adjusting the shape and dimensions of the opening of the reflected wave blocking screen 17 and the installation location of the reflected wave blocking screen 17 to find optimal conditions. It seems that there is something sexual.

[0012] Improving the attenuation characteristics by finding the optimum conditions such as the shape and dimensions of the opening of the reflected wave blocking screen 17 and the installation location of the reflected wave blocking screen 17 is possible if the radio wave reflecting source is a point radiation source such as an antenna. Although this is possible in some cases, it is practically impossible when measuring electromagnetic interference due to electromagnetic noise generated and radiated by the equipment under test 15.

[0013] In other words, not only do the shapes and dimensions of electronic equipment differ depending on the type of electronic equipment, but even in the case of electronic equipment of the same type, the leakage radiation source of electromagnetic noise is not limited to a fixed location; is generally a surface radiation source rather than a point radiation source, so the reflected wave blocking screen 17
It is almost impossible to determine the optimal conditions such as the shape and dimensions of the opening and the installation location of the reflected wave blocking screen 17. Even if it were possible to determine the optimal conditions for each device under test, the reflection It is practically impossible to replace the wave blocking screen 17, and measurement errors due to the partial blocking of direct waves by the reflected wave blocking screen 17 cannot be eliminated.

[0014] By the way, the regulatory limit values for leakage and radiation electromagnetic noise from various electronic devices are indicated by measured values at outdoor measurement sites, that is, composite waves of direct waves and reflected waves from the floor surface. Therefore, when measuring leakage radiated electromagnetic noise from the equipment under test using the anechoic chamber equipped with a screen for blocking reflected waves from the floor surface,
Since the measured value is a measured value of only direct waves, it is necessary to perform correction by adding a value corresponding to the reflected wave component from the floor surface to this measured value.

However, when the radiation source is a point radiation source such as an antenna, and the position of the radiation source is also specified, the actual measurement value when the radiation source is a point radiation source or the point radiation source is Correction is possible by adding a theoretical value determined as a source, but as in the case of measuring leakage radiated electromagnetic noise from various electronic devices, the shape and dimensions of the electronic device and the position of the radiation source are not constant. In addition, if the radiation source is not a point radiation source but a surface radiation source, the actual measured value of the radiation wave from the point radiation source or the theoretically calculated value obtained from the radiation source as a point radiation source should be used as the correction value. In response to this, the International Special Committee on Radio Interference (IEC), a subordinate organization of the International Electrotechnical Commission (IEC),
International standard Pub. 16, ``The difference between the measured value and the theoretical value of the site attenuation characteristics should be used only for the suitability of the site, and should not be used as a correction value for the actually measured radiation value of the equipment under test.'' It is clearly stated.

[0016] Therefore, when measuring electromagnetic noise emitted from various electronic devices, it is mandatory to measure it in a measurement field where there is reflection from the floor, and it is necessary to install a reflected wave blocking screen to block the reflected waves from the floor. The anechoic chambers shown in FIGS. 17 to 22 configured to do this are unsuitable for measuring electromagnetic noise emitted from various electronic devices.

FIG. 24 is a curve diagram based on actual measurements showing an example of the transmission attenuation characteristics in the VHF band of the anechoic chamber shown in FIGS. 17 to 19, where the frequency of the radio waves used is 30 MHz.
to 300 MHz (10 m to 1 m in wavelength), measurements were made under the same conditions as when measuring the transmission attenuation characteristics shown in Fig. 23. The horizontal axis is the frequency f (MHz), and the vertical axis is the attenuation amount ATT ( dB).

FIG. 25 is a curve diagram based on actual measurements showing an example of the transmission characteristics in the VHF band of the anechoic chamber shown in FIGS. 17 to 19, in which the short side of the floor surface is 2 m and the long side is 7 m. The other results are the results measured under the same conditions as when measuring the transmission attenuation characteristics shown in Figure 24, where the horizontal axis is the frequency f (MHz),
The vertical axis is relative gain G (dB).

FIG. 26 is also a curve diagram based on actual measurements showing an example of the transmission characteristics in the VHF band of the anechoic chamber shown in FIGS. Other than that, the results were measured under the same conditions as when measuring the transmission characteristics shown in FIG. 25, and the horizontal and vertical axes are the same as in FIG. 25.

As is clear from FIGS. 24 to 26,
In all cases where measurements were taken with different antenna heights and floor dimensions, large attenuation undulations and sharp attenuation peaks at a number of specific frequencies were observed in the characteristic curves.

This is because the dimensions of the radio wave reflecting plate 13 and the reflected wave blocking screen 17 are very close to or smaller than the wavelength of the radio waves being used, so that the radio wave reflection on the radio wave reflecting plate 13 and the reflected wave blocking screen 17 is extremely small. However, the reflection is not the same as that of a light ray, and as a result, all of the unnecessary reflected waves are not radiated to the sky from the ceiling atrium, and all of the unnecessary reflected waves are not radiated to the sky from the ceiling atrium. This is thought to be due to the interference of unnecessary diffuse reflection components remaining in the anechoic chamber without being absorbed.With such transmission attenuation characteristics, it is difficult to use them for measuring and evaluating electromagnetic noise leaked and radiated from various electronic devices. Can not.

The conventional anechoic chamber is also unsuitable for measuring the noise resistance of various electronic devices. In other words, the International Electrotechnical Commission (IEC) recommends that when measuring the noise resistance of various electronic devices, a completely anechoic chamber should be used;
Alternatively, when using a semi-anechoic chamber with radio wave absorbers on the surrounding walls and ceiling and a radio wave reflector on the floor, arrange the radio wave absorbers on the radio wave reflector on the floor. We recommend that you take measurements.

This is to make the electric field strength in the vertical plane including the surface of the equipment under test facing the radiation antenna uniform within the specified value ±3 dB. Even if a radio wave absorber is installed on the floor of the anechoic chamber shown in Figure 22, the frequency of the radio waves used is 3.
In the case of 00 MHz or less, for the above-mentioned reason, all unnecessary radio waves are not absorbed by the radio wave absorber 19 installed on the ceiling, and the uniformity of the electric field is maintained by the interference of unnecessary diffuse reflection components remaining in the anechoic chamber. Therefore, it is not suitable for measuring the noise immunity of various electronic devices.

The present invention has been made to solve these problems, and has a relatively small volume and site area, can measure a composite wave of direct waves and reflected waves from the floor surface, and can provide accurate measurement values. The purpose of this is to provide an anechoic chamber in which the following can be obtained.

[0025]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a relatively large-sized anechoic chamber without providing a reflected wave blocking screen as in the conventional anechoic chambers shown in FIGS. 17 to 22. In addition to installing a radio wave reflecting plate on the floor, a radio wave reflecting plate with the reflecting surface facing diagonally upward is provided all over the inside of the surrounding wall, and in detail, the anechoic chamber is configured as shown in (1) to (8) below. It is.

(1) A radio wave reflecting plate provided on the floor surface and a reflective surface are formed on the entire inner side of the peripheral wall whose upper part is electromagnetically open, by making the lower edge contact the reflecting surface of the radio wave reflecting plate provided on the floor surface. A radio anechoic chamber equipped with a radio wave reflector that is oriented diagonally upward.

(2) The radio anechoic chamber according to (1) above, wherein the reflecting surface of the radio wave reflecting plate provided on the floor is formed into a rectangle with a short side of about 3.375 m or more and a long side of about 8 m or more.

(3) The radio anechoic chamber according to (1) above, wherein the angle of inclination of the radio wave reflecting plate with respect to the floor surface, which is provided with the reflective surface facing diagonally upward, is set between approximately 25° and approximately 70°.

(4) The radio wave reflector provided on the floor has a rectangular reflecting surface with a short side of about 3.375 m and a long side of about 8 m, with the reflecting surface facing diagonally upward. Among them, the radio wave reflecting plate whose lower edge is in contact with the short side of the reflecting surface of the radio wave reflecting plate provided on the floor surface has an inclination angle of approximately 45° with respect to the floor surface, and the lower edge is provided on the floor surface. The radio wave anechoic chamber according to (1) above, wherein the radio wave reflecting plates that contact the long sides of the reflecting surfaces of the plates are formed with an inclination angle of approximately 60° with respect to the floor surface.

(5) A radio wave reflector provided on the floor and a radio wave provided throughout the inner side of the peripheral wall with the lower edge in contact with the reflective surface of the radio wave reflector provided on the floor with the reflective surface facing diagonally upward. An anechoic chamber equipped with a reflector and a radio wave absorber installed on the entire ceiling and wall surface.

(6) The radio wave anechoic chamber according to (5) above, wherein the reflecting surface of the radio wave reflecting plate provided on the floor is formed into a rectangle with a short side of about 3.375 m or more and a long side of about 8 m or more.

(7) The radio anechoic chamber according to (5) above, wherein the angle of inclination of the radio wave reflecting plate with respect to the floor surface, which is provided with the reflective surface facing diagonally upward, is set between approximately 25° and approximately 70°.

(8) The radio wave reflector provided on the floor has a rectangular reflecting surface with a short side of about 3,375 m and a long side of about 8 m, with the reflecting surface facing diagonally upward. Among them, the radio wave reflecting plate whose lower edge is in contact with the short side of the reflecting surface of the radio wave reflecting plate provided on the floor surface has an inclination angle of approximately 45° with respect to the floor surface, and the lower edge is provided on the floor surface. The radio wave anechoic chamber according to (5) above, wherein the radio wave reflecting plates in contact with the long sides of the reflecting surfaces of the plates are formed at an angle of inclination of approximately 60° with respect to the floor surface.

[0034]

[Operation] According to the configurations (1) to (8) above, when the equipment under test and the antenna are installed at appropriate intervals in the anechoic chamber, electromagnetic noise (radio wave ) reaches the antenna directly, and electromagnetic noise directed toward the floor is reflected by a radio wave reflector installed on the floor, and a portion of it reaches the antenna. In addition, part of the electromagnetic noise emitted from the equipment under test and part of the electromagnetic noise reflected by the radio wave reflection plate installed on the floor surface can be absorbed by a radio wave reflection plate installed inside the surrounding wall with the reflective surface facing diagonally upward. The light is reflected by the plate toward the top of the anechoic chamber.

In cases (1) to (4), the reflected waves toward the top of the anechoic chamber are radiated to the sky from the open top, but since the sky is an ideal absorber of radio waves, the waves are radiated upward. The reflected waves heading toward the anechoic chamber will never return to the anechoic chamber. Furthermore, in cases (5) to (8), the reflected waves directed toward the top of the anechoic chamber will be absorbed by the radio wave absorber.

[0036]

[Examples] The present invention will be explained in detail below using examples. 1 is a plan view of an "anechoic chamber" which is a first embodiment of the present invention, FIG. 2 is a sectional view taken along line AA in FIG. 1, and FIG. 3 is a sectional view taken along line B--
In each figure, 1 is the peripheral wall of the anechoic chamber, 2 is the radio wave reflecting plate provided on the floor, and 31 to 34 are the peripheral walls 1.
4 is a height-adjustable antenna, such as a biconical antenna or a log periodic antenna, although a rod-shaped antenna is shown as an example in the figure. Any wideband antenna can be used. 5 is the device under test, 6 is the device under test 5
The mounting table is made of, for example, a turntable made of an insulator.

The smaller the angle of inclination of the radio wave reflecting plates 31 to 34 is, and the higher the height of the upper edge of the reflecting surface, the greater the electromagnetic effect. However, considering economic efficiency, the radio wave reflector 31 or 3
It is desirable that the inclination angle of antenna 4 is selected between approximately 25° and approximately 70°, and the height of the upper edge of the reflecting surface is appropriately higher than the upper edge of antenna 4. Radio wave reflector 31
The material of 34 to 34 may be any material as long as it does not transmit radio waves and can form a smooth reflective surface, but for example, metal plates such as aluminum plates, iron plates, copper plates, or plate-like wire mesh may be used. Alternatively, it may be formed by attaching a conductive sheet to the surface of a commercially available construction board material or the like. The radio wave reflecting plate 2 provided on the floor is made of the same material as the diagonal radio wave reflecting plates 31 to 34.

Although the figure shows an example in which the upper part of the peripheral wall 1 is kept open electromagnetically and mechanically, it is desirable to provide a roof made of a material that can prevent rain and snow without interfering with the transmission of radio waves. .

Next, the operation of the anechoic chamber of this embodiment will be explained. Of the electromagnetic noise generated and radiated within the equipment under test 5, a direct wave directed toward the antenna 4 and a reflected wave reflected by the radio wave reflector 2 provided on the floor and directed toward the antenna 4 are combined and received by the antenna 4. , electromagnetic noise emitted from the device under test 5 and directed to the sides and rear of the device under test 5 is reflected by the diagonal radio wave reflectors 31 to 34 and directed upward, and is emitted into the sky through the open upper part of the anechoic chamber. However, since the sky is an ideal absorber of radio waves, the radio waves that travel upward will never return to the anechoic chamber.

Therefore, since the propagating radio wave components from the equipment under test 5 toward the antenna 4 are only direct waves and reflected waves reflected by the radio wave reflector 2 provided on the floor, the height of the antenna 4 is adjusted. By adjusting the difference in the propagation path lengths of both waves appropriately, both waves are received in the same phase, and the received electric field strength can be kept at the maximum and the received electric field strength can be measured accurately.

Since the propagation of radio waves is reversible, the propagating radio waves radiated from the antenna 4 and reaching the equipment under test 5 are both direct waves and reflected waves reflected by the radio wave reflecting plate 2 provided on the floor. Therefore, for example, the noise resistance of the device under test 5 can be properly tested.

FIG. 4 is a curve diagram based on actual measurements showing an example of the transmission attenuation characteristics in the anechoic chamber of the present invention shown in FIGS. 1 to 3.
It is formed of a rectangular metal plate with a short side of 2.5 m, and each of the diagonal radio wave reflecting plates 31 to 34 is formed of a wire mesh, and the lower edge touches the short side of the radio wave reflecting plate 2, and the long side of the radio wave reflecting plate 2 The oblique radio wave reflectors 31 and 32 facing each other have an inclination angle of 45°, and the radio wave reflectors 33 and 34 have lower edges touching the long sides of the radio wave reflector 2 and face the short sides of the radio wave reflector 2.
The inclination angle of each is 60°, the height of each upper edge of the radio wave reflecting plates 31 to 34 is 4 m, and a broadband antenna (log periodic antenna) is used instead of the device under test 5.
Assuming that the distance between the wideband antenna (log periodic antenna) 4 and the hypothesized wideband antenna is 3 m, one of the wideband antennas will be used as the transmitting antenna and the other wideband antenna will be used as the receiving antenna. The antenna height on the receiving side is fixed at 1m, and the antenna height on the receiving side is made variable in the range of 1m to 4m, and 300MH from the transmitting side.
z to 1000MHz radio waves (horizontally polarized waves) are radiated at a constant output, and the antenna height on the receiving side is adjusted appropriately to maximize the received electric field strength for each frequency separated by an appropriate frequency interval. What was obtained by plotting,
The horizontal axis represents the frequency f from 300MHz to 1000MHz on a scale with equal intervals, and the vertical axis represents the attenuation amount ATT (dB).
So, one scale is 10 dB.

FIG. 5 shows the transmission attenuation characteristics of the anechoic chamber of this embodiment using the outdoor measurement field with the area dimensions explained in paragraphs 0002 and 0004, and the distance between antennas, antenna height, and frequency used. 4 is a curve diagram showing an example of the transmission attenuation characteristic in an outdoor measurement field measured under the same conditions as when measuring . The horizontal axis and the vertical axis are the same as in FIG. 4.

Comparing the transmission attenuation characteristic curves in FIGS. 4 and 5, the two curves match extremely well, and when the frequency of the radio waves used is higher than 300 MHz, the anechoic chamber of this embodiment is compatible with the outdoor measurement field. It is clear that they have equivalent performance.

[0045] However, the frequency used is 300MHz.
In the following cases, the dimensions of the radio wave reflecting plates 31 to 34 are very close to the wavelength or are small, so the same reflection as the light beam does not occur, and in the case of the dimensions of each part explained in relation to FIG. It is estimated that this is because the residual reflected waves repeat diffuse reflection without all of the board being radiated to the sky, and as shown in Figures 6 to 10, small ripples are superimposed on the transmission attenuation characteristic curve, and the frequency of approximately 50MHz This resulted in attenuation peaks below.

FIG. 6 shows that the operating frequency is between 30 MHz and 30 MHz.
00MHz, the antenna is a biconical antenna, but the curve diagram shows the results measured under the same conditions as when measuring the transmission attenuation characteristics shown in Figure 4. Figure 7 is a curve diagram showing the results measured under the same conditions as when measuring the transmission attenuation characteristics shown in Figure 4. is a curve diagram showing the results measured under the same conditions as when measuring the transmission attenuation characteristics shown in Figure 6, and Figure 8 is a curve diagram showing the results measured under the same conditions as when measuring the transmission attenuation characteristics shown in Figure 6.
The transmission shown in Figure 6 was the same except that the center position between the transmitting and receiving antennas was moved 1m in the direction of the transmitting antenna while keeping the distance between the transmitting and receiving antennas at 3m. A curve diagram showing the results measured under the same conditions as when measuring the attenuation characteristics. Figure 9 is a curve diagram showing the results measured under the same conditions as when measuring the transmission attenuation characteristics shown in Figure 8, except that the antenna height on the transmitting side was fixed at 2 m. Figure 10 is a curve diagram showing the results obtained under the same conditions as when measuring the transmission attenuation characteristics shown in Figure 6, except that the long side of the radio wave reflecting plate 2 provided on the floor was 7 m long and the short side was 2 m long. It is a curve diagram showing the results measured by.

As is clear from FIGS. 6 to 10, in all of the transmission attenuation characteristic curves measured by changing some of the measurement conditions, fine ripples and approximately 50MHz
It was not possible to eliminate the attenuation peak below z. In particular, the transmission attenuation characteristic curve shown in FIG. 10 has more significant curve distortion than other transmission attenuation characteristic curves, but among the measurement conditions for the transmission attenuation characteristic shown in FIG. 10, the conditions that are significantly different from the others are: The length of the short side of the radio wave reflecting plate 2 provided on the floor was shortened from 2.5 m in other measurements to 2 m. As a result of reducing the length of the short side of the radio wave reflector 2 installed on the floor,
The distance between the diagonal radio wave reflectors 33 and 34 narrows, and since the dimensions of the radio wave reflectors 31 to 34 are very close to the wavelength or are small, the same reflection as a light beam does not occur, and all unnecessary reflected waves are is not radiated to the sky, and the energy of the standing waves generated by repeated diffuse reflections of the residual reflected waves is transmitted to the diagonal radio wave reflectors 33 and 34.
This is thought to be due to an increase in the distance between the opposing faces.

Therefore, on the contrary, the radio wave reflecting plate 2 provided on the floor
The measurement results are shown in FIGS. 11 and 12 after enlarging the dimensions so that the long side is 8 m and the short side is 3.375 m.

In FIG. 11, measurements were taken under the same conditions as when measuring the transmission attenuation characteristics shown in FIG. 6, except that the dimensions of the radio wave reflecting plate 2 provided on the floor were enlarged as described above. can be,
Figure 12 shows the same measurement conditions as the transmission attenuation characteristics shown in Figure 6, except that the antenna height on the transmitting side was fixed at 2 m and the dimensions of the radio wave reflector 2 provided on the floor were expanded as described above. The horizontal and vertical axes in both figures are the same as in FIG. 6.

FIG. 13 shows paragraph number 000 with the distance between the transmitting side and receiving side antennas, the height of each antenna, and the frequency used being the same as when measuring the transmission attenuation characteristics shown in FIG.
6 is a curve diagram showing the results of measurement at the outdoor measuring field of the dimensions and areas described in Section 4,0005, and the horizontal and vertical axes are the same as in FIG. 6.

As is clear from FIGS. 11 to 13,
When the long and short sides of the radio wave reflecting plate 2 provided on the floor were made longer, results comparable to those obtained at the outdoor measurement site could be obtained. This is because as a result of lengthening the long and short sides of the radio wave reflector 2 provided on the floor, the opposing distance between the diagonal radio wave reflectors 31 and 32 and the opposing distance between 33 and 34 are both enlarged. This seems to be because the energy of the standing wave caused by the reflected wave is attenuated. Note that among the transmission attenuation characteristics measurement conditions shown in FIGS. 11 and 12, the transmission attenuation characteristics when the operating frequency was changed to a range of 300 MHz to 1000 MHz were also almost the same as those at the outdoor measurement site.

FIG. 14 is a sectional view (BB sectional view in FIG. 15) showing a second embodiment of the present invention, and FIG. 15 is a sectional view taken along A--
A sectional view and FIG. 16 are CC sectional views of FIG.
34 to 34 are radio wave reflecting plates provided with reflective surfaces diagonally upward, 4 is an antenna, 5 is the equipment under test, and 6 is the equipment under test 5
These mounting tables have the same structure as the first embodiment shown in FIGS. 1 to 3. Reference numeral 7 denotes a radio wave absorber, which is composed of an absorber having the same structure as the conventional one, and is provided over the entire ceiling wall surface.

This embodiment differs from the first embodiment in that the upward radio waves are absorbed by the radio wave absorber 7, but the other radio wave propagation conditions are the same as in the first embodiment, and the antenna 4 ( Alternatively, only the direct wave from the device under test 5 (or the antenna 4) and the reflected wave from the radio wave reflecting plate 3 provided on the floor surface reach the device under test 5).

Although not shown in the drawings, it is desirable to provide a roof above the ceiling wall if necessary in this embodiment as well.

In the embodiments shown in FIGS. 14 to 16, by arranging appropriate radio wave absorbers on the radio wave reflecting plate 2 provided on the floor, the above-mentioned International Electrotechnical Commission (IEC) It can satisfy the recommended measurement conditions for noise resistance of various electronic devices.

[0056]

[Effects of the Invention] As explained above, according to the present invention,
The reflected waves other than the direct waves between the equipment under test and the antenna and the radio waves reflected by the radio wave reflecting plate provided on the floor and directed toward the antenna (or the equipment under test) are directed upward, according to claims (1) to (4). In the invention of claim (5), the reflected wave directed upward is radiated into the sky and does not return to the anechoic chamber again.
In the inventions (8) to (8) above, the reflected waves directed upward are absorbed by the radio wave absorber 7, so in any of the inventions, the antenna (or the equipment under test) receives both the direct waves and the radio wave reflection provided on the floor. Only the radio waves that are reflected by the plate and directed toward the antenna (or the equipment under test) will reach the antenna, making it possible to obtain transmission attenuation characteristics that are almost the same as those at conventional outdoor measurement sites used for electromagnetic interference measurements. can.

[0057] Furthermore, when the required area of the anechoic chamber of the present invention is compared with the required area of 2080 m2 of the outdoor measurement field explained in paragraphs 0004 and 0005, it is found that The long side is 8 as mentioned above.
m, the short side is rounded up to 4 m, diagonal radio wave reflector 2
Since the height of the upper edge is 4 m and the angle of inclination is 60° and 45°,
The long side of the rectangle formed by the upper edge of the diagonal radio wave reflector is 16 m, and the short side is 8.6 m. If we take a 4 m width margin around the outer periphery of this rectangle as an area where no radio wave reflector exists, this area The long side of the rectangle formed by the outer circumference of is 24 m.
, the short side is 16.6m, so the required area is approximately 39m.
8.4m2, and the required area of the outdoor measurement site is 208m2.
It is approximately 1/5.2 of 0 m2, making it extremely compact from a three-dimensional perspective.

Furthermore, in the conventional anechoic chambers shown in FIGS. 17 to 22, reflected waves from the floor are blocked by a reflected wave blocking screen, and only direct waves are transmitted between the antennas or between the antenna and the equipment under test. Since the basic idea is to allow transmission, in order to make the reflected wave blocking screen effective at blocking the reflected wave, the shape and dimensions of the reflected wave blocking screen are made appropriate, and the floor area is narrowed to reduce the amount of reflected waves from the floor surface. As a result of configuring it to suppress
Although the anechoic chamber of the present invention is unsuitable for measuring and evaluating electromagnetic noise leaked and radiated from various electronic devices over a range of 1000 MHz to 1000 MHz, and measuring the noise resistance of various electronic devices, the anechoic chamber of the present invention has a Although the size is somewhat large, it is suitable for measuring and evaluating electromagnetic noise leaked and radiated from various electronic devices, and measuring the noise resistance of various electronic devices, etc., according to the recommended standards of the Federal Communications Commission (FCC) of the United States. This can be done in accordance with the law, and the consequences would be enormous.

[Brief explanation of the drawing]

[Figure 1] Plan view of the first embodiment

[Figure 2] Cross-sectional view of the first embodiment

[Figure 3] Cross-sectional view of the first embodiment

[Figure 4] Curve diagram showing an example of transmission attenuation characteristics in the first embodiment

[Figure 5] Curve diagram showing an example of transmission attenuation characteristics in a conventional outdoor measurement field

[Figure 6] Curve diagram showing an example of transmission attenuation characteristics in the first embodiment

[Figure 7] Curve diagram showing an example of transmission attenuation characteristics in the first embodiment

[Figure 8] Curve diagram showing an example of transmission attenuation characteristics in the first embodiment

[Figure 9] Curve diagram showing an example of transmission attenuation characteristics in the first embodiment

[Figure 10] Curve diagram showing an example of transmission attenuation characteristics in the first embodiment

[Figure 11] Curve diagram showing an example of transmission attenuation characteristics in the first embodiment

[Figure 12] Curve diagram showing an example of transmission attenuation characteristics in the first embodiment

[Figure 13] Curve diagram showing an example of transmission attenuation characteristics in a conventional outdoor measurement field

[Figure 14] Cross-sectional view of the second embodiment

[Figure 15] Cross-sectional view of the second embodiment

[Figure 16] Cross-sectional view of the second embodiment

[Figure 17] Plan view showing an example of a conventional anechoic chamber

[Figure 18] Cross-sectional view showing an example of a conventional anechoic chamber

[Figure 19
] Cross-sectional diagram showing an example of a conventional anechoic chamber

[Figure 20]
A cross-sectional diagram showing an example of a conventional anechoic chamber

[Figure 21] Cross-sectional view showing an example of a conventional anechoic chamber

[Figure 22] Cross-sectional view showing an example of a conventional anechoic chamber

[Figure 23] Curve diagram showing an example of transmission attenuation characteristics in a conventional anechoic chamber

[Figure 24] Curve diagram showing an example of transmission attenuation characteristics in a conventional anechoic chamber

[Figure 25] Curve diagram showing an example of transmission characteristics in a conventional anechoic chamber

[Figure 26] Curve diagram showing an example of transmission characteristics in a conventional anechoic chamber

[Explanation of symbols]

1. Surrounding wall 2 Radio wave reflector 31 Radio wave reflector 32 Radio wave reflector 33 Radio wave reflector 34 Radio wave reflector 7 Radio wave absorber

Claims (8)

[Claims] Claim 1: A radio wave reflecting plate provided on the floor surface and a peripheral wall whose upper part is electromagnetically open, the lower edge of which is brought into contact with the reflecting surface of the radio wave reflecting plate provided on the floor surface, and the reflecting surface is tilted. A radio anechoic chamber characterized by comprising a radio wave reflecting plate facing upward. [Claim 2] The reflective surface of the radio wave reflector provided on the floor is
The anechoic chamber according to claim 1, characterized in that it is formed into a rectangle with a short side of about 3.375 m or more and a long side of about 8 m or more. 3. The radio anechoic chamber according to claim 1, wherein the angle of inclination of the radio wave reflecting plate with respect to the floor surface, which is provided with the reflecting surface facing diagonally upward, is set between approximately 25° and approximately 70°. [Claim 4] The reflective surface of the radio wave reflector provided on the floor is
Among the radio wave reflectors formed in a rectangular shape with a short side of approximately 3.375 m and a long side of approximately 8 m, with the reflective surface facing diagonally upward, the lower edge of the reflective surface of the radio wave reflector provided on the floor surface is The inclination angle with respect to the floor surface of the radio wave reflector whose short side is in contact with the floor surface is approximately 45 degrees, and the inclination angle with respect to the floor surface of the radio wave reflector whose lower edge is in contact with the long side of the reflective surface of the radio wave reflector provided on the floor surface. 2. The anechoic chamber according to claim 1, wherein the anechoic chamber is formed at an angle of approximately 60°. 5. A radio wave reflecting plate provided on the floor surface, and a radio wave reflecting device provided on the entire inner side of the peripheral wall, with the lower edge in contact with the reflective surface of the radio wave reflecting plate provided on the floor surface, with the reflective surface facing diagonally upward. A radio anechoic chamber characterized by comprising a board and a radio wave absorber provided over the entire ceiling and wall surface. [Claim 6] The reflective surface of the radio wave reflector provided on the floor is
The anechoic chamber according to claim 5, characterized in that it is formed into a rectangle with a short side of approximately 3.375 m or more and a long side of approximately 8 m or more. 7. The radio anechoic chamber according to claim 5, wherein the angle of inclination of the radio wave reflecting plate with respect to the floor surface, which is provided with its reflective surface facing diagonally upward, is set between approximately 25° and approximately 70°. [Claim 8] The reflective surface of the radio wave reflector provided on the floor is
Among the radio wave reflectors formed in a rectangular shape with a short side of approximately 3,375 m and a long side of approximately 8 m, with the reflective surface facing diagonally upward, the lower edge of the reflective surface of the radio wave reflector provided on the floor surface is The inclination angle with respect to the floor surface of the radio wave reflector whose short side is in contact with the floor surface is approximately 45 degrees, and the inclination angle with respect to the floor surface of the radio wave reflector whose lower edge is in contact with the long side of the reflective surface of the radio wave reflector provided on the floor surface. 6. The anechoic chamber according to claim 5, wherein the anechoic chamber is formed at an angle of approximately 60°.