JP2000138493A - Radio wave darkroom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve characteristics of an already-existing radio wave darkroom at a low cost and with reliability without changing its construction. SOLUTION: A floor 1 of a radio wave darkroom comprises a metal plate 10. Its ceiling and side walls 3 are comprised of metal plates 11 as reflector, ferrite arranged inside of the reflectors and radio wave absorbers 13 arranged inside of the ferrite 12. In this case, the radio wave absorbers 13 are arranged on the side walls 3 which are parallel or approximately parallel to the measuring axis of the radio wave. Conductive material 20 is placed between adjacent radio wave absorbers 13. The site attenuation characteristics can be improved by the placement of the conductive material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a site attenuation characteristic indicating the goodness of an anechoic chamber, and more particularly to an anechoic chamber having good site attenuation characteristics.

[0002]

2. Description of the Related Art An anechoic chamber is used as a facility for accurately measuring electromagnetic noise generated from electronic equipment products. The anechoic chamber has recently been the mainstream structure in which ferrite and wedge-shaped or pyramid-shaped radio wave absorbers are stuck on the four sides of the wall, the interior side of the ceiling to prevent reflection from the walls shielded by electromagnetic waves with metal plates, Measures electromagnetic noise generated from electronic equipment installed on a turntable in an anechoic chamber. Regulations on the noise of electronic device products that emit electromagnetic waves strongly require that “no strong electromagnetic waves be emitted” (suppression of electromagnetic wave emissions).

Therefore, in order to measure the emission of electromagnetic waves with high reliability and efficiency, a measurement site having excellent measurement accuracy, stability and reproducibility is required.

[0004] Here, a high-performance anechoic chamber is required in order to efficiently and stably measure the emission.
In order to provide a high-performance anechoic chamber, a method of improving the radio wave absorption rate of the radio wave absorber constituting each wall (other than the floor), or a method of providing a baffle or the like on a side wall of the anechoic chamber and forming a special shape, Further, there is a method in which the measurement axis is not parallel to the wall surface but has an angle.

In Japanese Patent Laid-Open Publication No. Hei 4-3499, the floor surface has an angle of ± 45 degrees.
An anechoic chamber in which a conductive material inclined at 10 degrees is laid is disclosed, and a configuration provided with a baffle is also shown.

[0006]

By the way, in the above-mentioned method for improving the radio wave absorption of the radio wave absorber, a method of increasing the length of the radio wave absorber is adopted. However, there is a limit to the improvement of the noise, and the effective space of the anechoic chamber becomes small.

There is also a problem that the effective space is reduced even in a specially shaped anechoic chamber equipped with a baffle or the like, and there is a frequency at which the performance cannot be improved depending on the size of the baffle.

Further, in the method in which the measurement axis is not arranged parallel to the wall surface but has an angle, there is a problem that the layout of a place where a turntable or the like is installed is restricted.

Japanese Patent Application Laid-Open No. 4-3499 discloses that the floor surface is 45 ° ± 1.
It is a method of laying a conductive material inclined at 0 degrees,
It has been proposed that the effective space is reduced due to the laying of conductive material, and a method of burying the conductive material in the radio wave absorber has been proposed. There is.

On the other hand, even when the above method is employed to improve the performance of the existing anechoic chamber, the replacement of the radio wave absorber, the installation of a new baffle, the layout change of a turntable, etc. (floor construction), and Problems such as reduction of the effective space for installation of the floor conductive material occur.

An object of the present invention is to solve such a conventional problem and to provide an anechoic chamber which is inexpensive and whose characteristics can be surely improved without changing the existing structure.

Other objects and novel features of the present invention will be clarified in embodiments described later.

[0013]

In order to achieve the above-mentioned object, the first invention of the present application comprises a metal plate as a floor surface, and a ceiling and side walls laid on a reflector and a room inside the reflector. In an anechoic chamber composed of a ferrite and a radio wave absorber arranged on the indoor side of the ferrite, between adjacent radio wave absorbers disposed on the side wall surface parallel to or substantially parallel to a radio wave measurement axis. In addition, a conductive material is disposed perpendicular to the side wall surface and the floor surface.

According to a second invention of the present application, the floor is made of a metal plate, and the ceiling and the side wall are made of a reflector, a ferrite laid on the indoor side of the reflector, and a radio wave arranged on the indoor side of the ferrite. In an anechoic chamber configured with an absorber, between adjacent radio wave absorbers arranged on the ceiling parallel to or substantially parallel to a measurement axis of radio waves, between the radio wave measurement axis and the ceiling, and perpendicular to the ceiling and substantially parallel to the measurement axis. It is characterized in that a conductive material is disposed perpendicularly to the side wall surface.

The conductive material may be arranged at a plurality of positions on the side wall surface or the ceiling.

The conductive material may be in the form of a sheet or a film, and may have a sheet resistance of 100 to 600Ω.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an anechoic chamber according to the present invention will be described below with reference to the drawings.

FIG. 1 is a plan sectional view of an anechoic chamber showing a first embodiment of the present invention, and FIG. 2 is a front sectional view of the same. FIG. 3 is a detailed sectional view showing a state where a conductive material is installed. In these figures, a floor surface 1 of an anechoic chamber is formed of a metal plate 10, and a ceiling 2 and a side wall surface 3 are formed of a metal plate 11 as a reflector (electromagnetic wave shield) and a shield surface 11 a formed by the metal plate 11. It comprises a ferrite tile 12 laid on the indoor side and a radio wave absorber 13 arranged on the indoor side of the ferrite tile 12.

The metal plate 11 is joined to the metal plate 10 on the floor surface to form a continuous electromagnetic wave shielding surface. A ferrite tile 12 is spread over the shielding surface 11a of the metal plate 11, and The radio wave absorber 13 is spread. In the present embodiment, the radio wave absorber 13 is formed of a wedge-shaped (wedge-shaped) foam containing graphite as an ohmic loss body, and a triangular shape is formed inside the radio wave absorption plate 13a combined in an inverted V shape. It has a structure in which a columnar internal radio wave absorber 13b is arranged. The distal end of the radio wave absorber 13 has a low-permittivity foam 1 having radio wave permeability.
4 is fixed, and its indoor side surface 14a is a white flat surface to perform an indirect lighting function, and is a part unrelated to the characteristics of the anechoic chamber. This radio wave absorber 1
Reference numeral 3 has a bottom area of, for example, 60 cm × 60 cm.

Then, between adjacent radio wave absorbers 13 arranged on a wall surface of the side wall surface 3 parallel (or substantially parallel) to the radio wave measurement axis, the wall surface is perpendicular to the wall surface and vertical (perpendicular to the floor surface). ), A conductive material 20 having a predetermined length is arranged.
The conductive material 20 is in the form of a sheet (including a cloth, a net, a thin plate, a film, etc.) or a film, and has a sheet resistance of 100 to 100.
600Ω □. In the example of FIG. 3, the width is about 90 cm and is continuous in the vertical direction, and the length in the vertical direction is slightly shorter than the height of the side wall surface. The conductive material 2
No. 0 can be configured by applying a conductive paint to a plastic film, depositing a metal oxide or the like on a plastic film, or weaving conductive fibers into a non-conductive cloth. When the sheet resistance is less than 100Ω □, the resistance loss of the conductive material 20 is small, and the effect as a radio wave reflector is rather increased, which is not preferable. Also,
If the sheet resistance exceeds 600Ω □, the properties of the insulator approach, and the effect of improving the characteristics is lost.

Reference numerals 30 and 31 denote doors for entering and exiting the anechoic chamber. Reference numeral 32 denotes a turntable on which a measurement target (device under test: EUT) is placed in the case of normal electromagnetic noise measurement, 33 denotes a reception antenna, and 34 denotes a transmission antenna. In the evaluation of dark room performance, the transmission antenna 34 is regarded as a measurement target. It is placed on a turntable 32 for evaluation.

FIGS. 4A and 4B show the positional relationship between the receiving antenna 33 and the transmitting antenna 34 for evaluating the performance of the anechoic chamber. FIG. 4A is a plan view and FIG. 4B is a perspective view. The plane distance between the transmitting antenna 34 and the receiving antenna 33 is kept constant. When the transmitting antenna 34 is at the position, the receiving antenna 33 is at the position, when the transmitting antenna 34 is at, the receiving antenna 33 is at the position. When the position is 34, the receiving antenna 33 is set to the position, when the transmitting antenna 34 is set to the receiving antenna 33, and when the transmitting antenna 34 is set, the receiving antenna 33 is set to the position. The receiving antenna 33 can scan at a height of 1 to 4 m at each position.

In the case of the first embodiment, the site attenuation characteristics of the conventional anechoic chamber without the conductive material 20 were measured using vertically polarized radio waves, and compared with the theoretical values of the site attenuation characteristics. However, it has been found that the first embodiment in which the conductive material 20 is provided is closer to the theoretical value and has excellent site attenuation characteristics. Specific measurement conditions and measurement results will be described in Examples 1, 2, and 3 and Tables 1, 2, and 3 described below.

FIG. 5 is a bottom sectional view (viewing the ceiling from the floor) of an anechoic chamber showing a second embodiment of the present invention, and FIG. 6 is a front sectional view of the same. In this case, the conductive material 20 is perpendicular to the ceiling and parallel (or substantially parallel to the measurement axis) between adjacent radio wave absorbers 13 arranged on the ceiling 2 parallel (or substantially parallel) to the measurement axis of the radio wave. A conductive material 20 having a predetermined length is horizontally arranged vertically on a (parallel) side wall surface. The conductive material 20 has a width of about 90 cm and is continuous in the horizontal direction, and the length in the horizontal direction is somewhat shorter than the width dimension of the ceiling surface (the length dimension orthogonal to the radio wave measurement axis). About half to about half. The other configuration is the same as that of the first embodiment.

In the case of the second embodiment, the site attenuation characteristics of the conventional anechoic chamber without the conductive material 20 were measured using horizontally polarized radio waves and compared with the theoretical values of the site attenuation characteristics. However, it has been found that the second embodiment in which the conductive material 20 is provided is closer to the theoretical value and has better site attenuation characteristics. Specific measurement conditions and measurement results will be described in Example 4 and Table 4 described later.

[0026]

The present invention will be further described in the following examples.

Example 1 As a conductive material 20, a cloth (sheet resistance: 400Ω □) in which a yarn impregnated with copper sulfide was knitted in polyester was used, and a plan sectional view of FIG. 7 and a front sectional view of FIG. Position A,
Change from B, C, D to 6.6 from 0.6m above the floor
1 is provided on each of both side wall surfaces 3 parallel to the measurement axis of the radio wave up to m (the same parts as those in the first embodiment are denoted by the same reference numerals in the figure). A half-wave dipole antenna is used as the receiving antenna 33 and the transmitting antenna 34. As shown in FIG. 4, the transmitting antenna 34 is located at the center of the turntable 32 and three positions before and after the range where the device under test is installed. The distance between the antennas is 10
m, transmitting antenna height 2.75 m, receiving antenna height 2.
The site attenuation characteristic was measured at a frequency of 30 MHz and vertical polarization while changing the distance from 75 to 4 m. The measurement results are shown in Table 1 below in comparison with a state where no conductive material is provided.

Table 1 Installation of one conductive material Side wall surface Vertical polarization (30 MHz) No antenna installed Conductive material installation position NSA (dB) Theoretical value position NSA (dB) ABCD NSA (dB) Before 22.4 21.9 21.8 21.6 21.4 Center 19.8 19.3 19.5 19.6 19.7 18.8 After 22.8 21.7 21.8 21.7 21.9 (in Table 1) , NSA: normalized site attenuation) From Table 1, a deviation of -4 dB from the theoretical value (target ideal value) of the site attenuation in the state where the conductive material is not installed (from the measured value in the table) (Difference from theoretical value), within the deviation of -3.1 dB in the state where the conductive material 20 was installed, it was confirmed that the site attenuation characteristic when the conductive material was installed exhibited better. Table 1 shows that the installation position of the conductive material was 1 distance between the transmitting and receiving antennas when compared with the theoretical value of site attenuation.
It is preferable that the transmission electromagnetic waves be installed at a distance of 0 m, and locations B and C where the transmission electromagnetic waves hit in a ray trace (near the locations where the transmission electromagnetic waves are reflected toward the receiving antenna) are particularly preferable.

Example 2 The measurement conditions were the same as in Example 1, and the position C 'of the pair of conductive materials 20-1 on both side walls was set as a fixed position, and the fixed conductive material 20-1 (sheet resistance: 400Ω) was used. □), a conductive material 20-2 (sheet resistance: 400Ω □) is applied to both side walls 3 as shown in the plan sectional view of FIG. 9 and the front sectional view of FIG.
D, E, F about the case of changing the position and installing,
The site attenuation characteristics were measured at a frequency of 30 MHz and vertical polarization. The measurement results are shown in Table 2 below.
9 and 10, the same parts as those in the first embodiment are denoted by the same reference numerals. Although the conductive material 20-2 is indicated by a dotted line, it is continuous like the conductive material 20 in FIG.

Table 2 Installation of two conductive materials Side wall surface Vertical polarization (30 MHz) Antenna not installed Conductive material installation position NSA (dB) Theoretical value position NSA (dB) ABCDEF NSA (dB) Before 22.4 21.6 21.5 21.5 21.4 21.4 21.3 Center 19.8--19.5 19.5 19.3 19.4 18.8 After 22.8 21.4 21.3 21.4 21.3 21.3 21.4 From Table 2, when compared with the theoretical value of site attenuation, the deviation of -4 dB (difference between the measured value and the theoretical value in the table) in the state where the conductive material is not installed, and two places of the conductive material respectively The deviation was within -2.8 dB in the installed state, and it was confirmed that the deviation was further reduced by setting the installation location from one location to two locations, and excellent site attenuation characteristics were exhibited.

Example 3 The measurement conditions were the same as in Example 1, and the plan sectional view of FIG.
As shown in the front sectional view of FIG. 12, conductive materials 20-1 and 20-2 are respectively installed at two places C 'and E on both side walls, and the surface resistance of the conductive material 20-1 is made constant at 400Ω □. Table 3 below shows the results of measuring the site attenuation characteristics at a frequency of 30 MHz and vertical polarization when the sheet resistance of the material 20-2 was changed from 400Ω □ to 200Ω □.

Table 3 Conductive material sheet resistance change Side wall surface Vertical polarization (30 MHz) Antenna not installed Conductive material installation position E NSA (dB) Theoretical value position NSA (dB) 400Ω □ 200Ω □ Before NSA (dB) 22.4 21.4 21.1 Center 19.8 19.3 19.2 After 18.8 22.8 21.3 20.9 From Table 3, theoretical value of site attenuation -2.6d when the conductive material 20-2 is 400Ω □
B, the deviation of -2.3 dB when the conductive material 20-2 is 200Ω □ is within the range of the conductive materials 200 to 4.
It was confirmed that excellent site attenuation characteristics were exhibited in the range of 00Ω □. Note that the range of the sheet resistance of the conductive material is preferably 100 to 600Ω □,
0 to 400Ω □ is particularly preferred.

Example 4 The measurement conditions were the same as in Example 1, and the conductive material 20 was placed on the ceiling as shown in the bottom sectional view of FIG. 5 (view of the ceiling from the floor) and the front sectional view of FIG. In this case, the distance between the antennas was changed to 10 m, the height of the transmitting antenna was changed to 2 m, and the height of the receiving antenna was changed to 1 to 4 m, and the site attenuation characteristics were measured at a frequency of 30 MHz and horizontal polarization. The measurement results are shown in Table 4 below.

Table 4 Installation of One Conductive Material Ceiling Surface Horizontal Polarization (30 MHz) Antenna not installed Conductive material installed Theoretical value position NSA (dB) NSA (dB) NSA (dB) Before 28.8 26.1 Center 28.1 26.2 After 24.1 28.9 25.6 From Table 4, a conductive material was installed for the theoretical value of site attenuation. -4.8 dB deviation without
The deviation was within -2.1 dB in the state where the conductive material was provided, and it was confirmed that the site attenuation characteristics in the case where the conductive material was provided were superior.

Although the embodiments and examples of the present invention have been described above, it is to be understood by those skilled in the art that various modifications and changes can be made within the scope of the claims without limiting the present invention. Would be self-evident. For example, the installation position of the conductive material and the height, length, and width dimensions can be arbitrarily changed to optimize darkroom performance. Although an example in which one conductive material is provided on the ceiling has been described, two or more conductive materials may be provided.

[0036]

As described above, according to the anechoic chamber of the present invention, the space between the adjacent radio wave absorbers disposed on the side wall or the ceiling parallel to or substantially parallel to the measurement axis of the radio wave.
By arranging the conductive material perpendicularly to the side wall surface and the floor surface or perpendicular to the ceiling and parallel to or substantially parallel to the measurement axis, the dark room performance (site attenuation characteristics) is surely improved. Can be In addition, since it is an additional installation of only conductive materials for the existing anechoic chamber,
Since there is no need to change the layout of the anechoic chamber, change the radio wave absorber, etc., there is a great advantage in terms of cost.

[Brief description of the drawings]

FIG. 1 is a plan sectional view showing a first embodiment of an anechoic chamber according to the present invention.

FIG. 2 is a front sectional view of the same.

FIG. 3 is an enlarged longitudinal sectional view of a main component of the first embodiment.

FIG. 4 is an explanatory diagram of antenna conditions for site attenuation measurement.

FIG. 5 is a bottom sectional view showing a second embodiment of the present invention.

FIG. 6 is a front sectional view of the same.

FIG. 7 is a plan sectional view showing the arrangement of conductive materials in the case of Example 1.

FIG. 8 is a front sectional view of the same.

FIG. 9 is a plan sectional view showing a conductive material arrangement in the case of Example 2.

FIG. 10 is a front sectional view of the same.

FIG. 11 is a plan sectional view showing a conductive material arrangement in the case of Example 3;

FIG. 12 is a front sectional view of the same.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Floor surface 2 Ceiling 3 Side wall surface 10,11 Metal plate 11a Shield surface 12 Ferrite tile 13 Radio wave absorber 14 Low dielectric constant foam 20,20-1,20-2 Conductive material 30,31 Door 32 Turntable 33 Reception Antenna 34 Transmitting antenna

Claims (4)

[Claims] 1. A floor comprising a metal plate, and a ceiling and side walls formed by a reflector, a ferrite laid on the indoor side of the reflector, and a radio wave absorber disposed on the indoor side of the ferrite. In the configured anechoic chamber, a conductive material is disposed perpendicularly to the side wall surface and the floor surface between adjacent radio wave absorbers disposed on the side wall surface parallel to or substantially parallel to the radio wave measurement axis. An anechoic chamber characterized by the following: 2. A floor comprising a metal plate, and a ceiling and side walls formed by a reflector, a ferrite laid on the indoor side of the reflector and a radio wave absorber arranged on the indoor side of the ferrite. In the configured anechoic chamber, between adjacent radio wave absorbers disposed on the ceiling parallel or substantially parallel to the measurement axis of the radio wave, on a side wall surface perpendicular to the ceiling and parallel to or substantially parallel to the measurement axis. An anechoic chamber characterized by vertically disposing a conductive material. 3. The anechoic chamber according to claim 1, wherein a plurality of the conductive materials are arranged on the side wall surface or the ceiling. 4. The anechoic chamber according to claim 1, wherein the conductive material is in the form of a sheet or a film, and has a sheet resistance of 100 to 600Ω □.