JP2942205B2 - Anechoic box with reduced wall reflection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorbing sheet having a radio wave absorbing characteristic corresponding to a specified frequency band near the operating frequency of a device under test. More specifically, the metal enclosure has an inner space that has a central part that extends outward and narrows both sides, and a radio wave absorbing sheet is attached along the inner surface. The present invention relates to a wall reflection-reduction type anechoic box worn. The anechoic box is useful for simple measurement tests and inspections of small, especially portable various wireless devices.

[0002]

2. Description of the Related Art In recent years, various communication devices utilizing ultra high frequency (UHF) have been put into practical use, and in research and development and manufacture thereof, it is necessary to frequently perform electromagnetic wave performance tests and sensitivity tests. . Traditionally, these tests have been performed in an anechoic chamber. The anechoic chamber has a special structure in which radio wave absorbers are attached to the walls, ceiling, and floor all around the electromagnetically shielded room to block electromagnetic waves entering from the outside and absorb electromagnetic waves generated inside. Room. Even in a simple case, the height and width are all about several meters (for example, 5 m ×
It is a rather large measuring space (8m x 4m), and is a large-sized facility where workers can enter inside. As the electromagnetic wave absorber, for example, a ferrite tile (a flat sintered product of ferrite) or a pyramid-shaped dielectric is used.

As is well known, recently, various small wireless devices have been developed and manufactured. For example, an analog mobile phone in the 800 MHz band, a GPS (Global Positioning System) antenna in the 1.5 GHz band, and a digital mobile phone have been developed. Phone, 1.9G
There are a PHS (simplified mobile phone) in the Hz band, a wireless LAN in the 2.5 GHz band, a VICS (road traffic information communication system), a wireless card, and the like. In the prior art, they are all tested in the same anechoic chamber.

[0004]

The anechoic chamber has the advantage of being able to measure with high accuracy any of the above-mentioned devices under measurement in various frequency bands, regardless of their size, and provides an extremely important measurement space. doing. However, it is necessary to attach thick ferrite tiles or bulky pyramid-shaped radio wave absorbers on the entire inner wall to maintain high measurement accuracy and to support a wide frequency band. There is a drawback that it requires space and requires time and cost in construction. In particular, when the number and types of devices that need to be measured increase, a large number of anechoic chambers must be provided, and the above drawbacks become extremely serious.

However, in actual research and development, improvement of manufacturing technology, product inspection, etc., strict measurement results are not required for mass-produced equipment using a specific frequency band. For the time being, it is often sufficient to perform simple measurement tests and inspections and to know the approximate measurement level or relative values and trends. In such an application, a small and inexpensive measurement space is required instead of a large and expensive measurement space such as an anechoic chamber. However, it is needless to say that not only small size and inexpensive but also excellent performance are required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a device under test using a specific frequency, which corresponds to the designated frequency band, suppresses modes caused by reflection on a wall surface, has excellent radio wave absorption performance, and is simple. It is an object of the present invention to provide a small and inexpensive measurement space in which an anechoic chamber can be used for stable measurement tests and inspections.

[0007]

According to the present invention, there is provided a radio wave absorbing sheet having radio wave absorbing characteristics corresponding to a specified frequency band near the operating frequency of a device under test, over the entire inner surface of a metal casing having good shielding properties. Is a dedicated anechoic box provided with a transmitter and a receiver on both sides in the measurement space. Here, the metal casing has an internal space in which the central portion is outwardly spread and the side portions are narrowed, and a radio wave absorbing sheet is adhered along the inner surface, whereby the wall surface is formed. It constitutes a reflection-reduction type anechoic box. In the present invention, the term anechoic chamber, rather than an anechoic chamber, is used to clarify that it is not a large facility such as a room, but a small device that can be placed on a workbench. It is.

The metal casing is preferably made of a conductive and magnetic material such as an iron plate or a stainless steel plate. By having magnetism, the function of a magnetic shield can be fulfilled. The radio wave absorption sheet is a thin sheet formed by kneading a ferrite powder and an EPDM (ethylene / propylene diene monomer) rubber at a predetermined ratio corresponding to the specified frequency band and molding the mixture to a predetermined thickness. A transmitter and a receiver are provided on both sides in the measurement space so as to face each other. In an actual test, one of the transmitter and the receiver is the device to be measured. The metal housing is provided with an opening / closing door portion for taking in / out the device to be measured. In addition, it is preferable that a part of the wall surface has a removable structure. By removing a part of the wall surface, it is possible to easily adjust the attachment / detachment and position / direction of the internal transmission unit or reception unit. In those cases, it is necessary to prevent electromagnetic wave leakage.

Electromagnetic waves are more likely to be absorbed as they are incident on the surface of the radio wave absorbing sheet in a direction nearly perpendicular to the surface. Therefore, when the metal casing shape as in the present invention is used, the electromagnetic wave absorption performance on the wall surface of the electromagnetic wave from the transmission unit to the reception unit is enhanced, and the mode caused by the reflection on the wall surface is suppressed. Only the direct wave is directed to the section, and more stable measurement is possible.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An anechoic box according to the present invention is used to test, for example, an 800 MHz anechoic box, a GSP antenna, or a 1.5 GHz band digital portable telephone for testing an 800 MHz analog portable telephone. 1.5GHz band anechoic box for PHS test
There are a 9 GHz band anechoic box, a 2.5 GHz band anechoic box for testing wireless LAN, VICS, and wireless cards. The designated frequency band of each anechoic box is as follows. Anechoic box for 800 MHz band: 700 MHz to 900 MHz Anechoic box for 1.5 GHz band: 1.4 GHz to 1.65 GHz Anechoic box for 1.9 GHz band: 1.75 GHz to 2.0 GHz Anechoic box for 2.5 GHz band: 2.35 GHz Each of the anechoic boxes of up to 2.65 GHz is constituted by an inner wall surface having characteristics capable of sufficiently absorbing electromagnetic waves in the designated frequency band.

Accordingly, each of the anechoic boxes has the following internal dimensions in the following range corresponding to the designated frequency band (wavelength). Each numerical value represents the minimum and maximum of the housing length. Anechoic box for 800 MHz band: Min. 75 cm to max. 225 cm 1.5 Anechoic box for 1.5 GHz band: Min. 40 cm to max. 120 cm 1.9 GHz band anechoic box: Min. 32 cm to Max. 95 cm Anechoic box for 2.5 GHz band: Min. 24 cm to Max. Therefore, a housing having a different internal size may be manufactured for each of the designated frequency bands, but it is also possible to use a common case in which several types of designated frequency bands use the same inner size of the housing.

The radio wave absorbing sheet used in each anechoic box is as follows. 800 MHz band anechoic box: 1200 g ± 10 g of Mn-Zn ferrite powder per 100 g of EPDM rubber
What was mixed and formed into a sheet having a thickness of 6.7 mm ± 0.1 mm. 1.5 GHz band anechoic box: A 6.3 mm ± 0.1 mm thick sheet formed by mixing 650 g ± 10 g of Mn—Zn ferrite powder with 100 g of EPDM rubber. 1.9 GHz band anechoic box: A 6.3 mm ± 0.1 mm thick sheet formed by mixing 500 g ± 10 g of Mn—Zn ferrite powder with 100 g of EPDM rubber. 2.5 GHz band anechoic box: A 6.3 mm ± 0.1 mm thick sheet formed by mixing 360 g ± 10 g of Mn—Zn ferrite powder with 100 g of EPDM rubber.

FIG. 1 is a perspective view of an example of an anechoic box according to the present invention, and FIG. 2 is a cross-sectional view thereof. The anechoic box is made of a metal casing 10 having an inner dimension corresponding to a designated frequency band and having good shielding properties. The metal housing 10 has a hexagonal cross section, a central portion extending outward,
Both ends are narrowed. Further, an opening / closing door portion 12 for taking in / out the device under test and a connection portion (connector) 14 for exchanging data with the device under test are provided. A radio wave absorption sheet 16 having radio wave absorption characteristics corresponding to the specified frequency band is attached to the entire inner surface of the metal casing 10 (including the inner surface of the door unit 12). The transmission unit 20 and / or the reception unit 22 are installed in the internal measurement space. One of the transmitting unit 20 and the receiving unit 22 is a device under test,
Perform various tests and inspections.

Here, both end surfaces of the metal casing 10 (one of which is provided with the opening / closing door portion 12) are parallel to each other, and the outer surface excluding them is composed of four surfaces bent at the center. Have been. It is preferable that one of the surfaces (for example, the upper panel 10a) is configured to be removable. For example, it can be attached to and detached from the main body of the metal housing by mounting screws. Then, there is an advantage that the attachment of the radio wave absorbing sheet 16, the attachment and detachment of the transmission unit 20 and the reception unit 22, the adjustment of the installation position and the direction, and the like can be easily performed. In order to prevent leakage of electromagnetic waves, a conductive elastic contact member such as a shield finger is attached to a joint between the opening / closing door portion 12 or the upper panel 10a and the main body of the metal housing to improve shielding performance. Plan. Also, the connection part 14 for data transmission / reception with the device under test uses a shielded wire or a shielded connector to prevent radio wave leakage. Note that a structure in which the connector is directly drawn out with a shielded wire without using a connector may be employed.

Since such an anechoic box is small (for example, the maximum size for the 800 MHz band is 225 cm), it can be mounted on the work table 24. To move freely and perform necessary measurements.

FIG. 3 shows another example of the anechoic box. Here, the metal casing 30 has a rhombic shape, and the radio wave absorbing sheet 36 is attached to the entire inner surface thereof. Although illustration is omitted, an opening / closing door unit for taking in / out the device to be measured and a data transfer unit with the device to be measured are provided. Further, it is preferable that one surface of the metal housing is configured to be removable. FIG.
3, the hexagonal shape or the rhombic shape of the metal housing has an advantage that it can be easily assembled only by cutting and welding a flat metal plate (for example, an iron plate). It is also convenient for attaching a radio wave absorbing sheet.

The metal housing may have any shape as long as its central portion is widened outward and its both sides are narrowed. The metal housing may have a flat surface as in the above embodiment, or may have a curved surface.
Examples are shown in FIGS. FIG. 4 shows a case 40 made of metal.
The two end faces are planes parallel to each other, but the other parts are curved surfaces. Therefore, the central portion is in a state of bulging outward in a curved shape. A radio wave absorbing sheet 46 is attached to the entire inner surface. FIG. 5 shows a case 50 made of metal having an elliptical surface, and a radio wave absorbing sheet 56 attached to the entire inner surface. Although not shown in these examples,
It is preferable to provide an opening / closing door for taking in and out the device to be measured, a data transfer unit with the device to be measured, and a structure in which a part of the metal housing can be removed. It should be noted that the present invention is not limited to only these shapes, but in a flat surface or a curved surface,
Alternatively, the central portion may be configured to spread outward by a surface obtained by combining them.

[0018]

EXAMPLE An electric wave absorbing sheet for 800 MHz band was attached to the entire inner surface of a housing by welding an iron plate, and FIG.
An anechoic box for 800 MHz band having the structure shown in FIG. Shield fingers were attached to the door and the part of the panel that contacted the housing body. The 800-MHz band electromagnetic wave absorption sheet is a sheet obtained by kneading Mn-Zn-based ferrite powder at a rate of 1200 g ± 10 g with EPDM-based rubber 100 g and forming a sheet having a thickness of 6.7 mm ± 0.1 mm. is there. Using this anechoic box, various tests such as a performance test and an operation check of an 800 MHz-band analog mobile phone were performed. As a result, stable measurements were obtained with little wall reflection, and good measurement data was obtained.

An iron plate was welded to assemble the casing, and a 1.5-GHz band electromagnetic wave absorbing sheet was adhered to the entire inner surface of the casing to produce a 1.5-GHz band anechoic box having a structure as shown in FIG. Shield fingers were attached to the opening / closing door and the panel in contact with the housing body. The 1.5 GHz band radio wave absorption sheet is made of Mn-Z with respect to 100 g of EPDM rubber.
n-type ferrite powder is kneaded at a rate of 650 g ± 10 g,
It is formed into a sheet having a thickness of 6.3 mm ± 0.1 mm. Using this anechoic box, a GPS antenna and 1.5
Various tests such as a performance test and operation check of a digital mobile phone in the GHz band were performed. As a result, stable measurements were obtained with little wall reflection, and good measurement data was obtained.

An iron plate was welded to assemble the housing, and a 1.9 GHz band electromagnetic wave absorbing sheet was adhered to the entire inner surface of the housing to produce a 1.9 GHz band anechoic box having a structure as shown in FIG. Shield fingers were attached to the opening / closing door and the panel in contact with the housing body. The radio wave absorbing sheet for 1.9 GHz band is made of Mn-Z with respect to 100 g of EPDM rubber.
knead the n-based ferrite powder at a rate of 500g ± 10g,
It is formed into a sheet having a thickness of 6.3 mm ± 0.1 mm. Using the anechoic chamber, various tests such as PHS performance tests and product inspections were performed. As a result, stable measurements were obtained with little wall reflection, and good measurement data was obtained.

An iron plate was welded to assemble the casing, and a 2.5-GHz-band electromagnetic wave absorbing sheet was attached to the entire inner surface of the casing to produce a 2.5-GHz-band anechoic box having a structure as shown in FIG. Shield fingers were attached to the opening / closing door and the panel in contact with the housing body. The radio wave absorbing sheet for 2.5 GHz band is made of Mn-Z with respect to 100 g of EPDM rubber.
n-type ferrite powder is kneaded at a rate of 360 g ± 10 g,
It is formed into a sheet having a thickness of 6.3 mm ± 0.1 mm. Using this anechoic box, we performed various tests such as next-generation wireless cards (highway, commuter pass, entrance certificate, etc.) and wireless LAN performance tests and operation checks. Good measurement data was obtained.

[0022]

According to the present invention, the central portion extends outward,
Using a metal case with a narrow shape on both sides, attach a thin radio wave absorption sheet corresponding to the specified frequency band to the UUT that uses a specific frequency to form a special anechoic box With this configuration, it is possible to reduce the size of the housing while securing an effective space for internal measurement, to further improve the radio wave absorption on the inner wall surface, and to suppress a mode caused by wall surface reflection. Therefore, a simple measurement test or inspection can be easily and accurately performed. Further, even when a large number of measurement spaces are required, there is an effect that the installation space can be reduced and the equipment can be installed at low cost.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of an anechoic box according to the present invention.

FIG. 2 is a cross-sectional view thereof.

FIG. 3 is a cross-sectional view showing another example of the anechoic box according to the present invention.

FIG. 4 is a cross-sectional view showing still another example of the anechoic box according to the present invention.

FIG. 5 is a cross-sectional view showing another example of the anechoic box according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Metal housing 12 Opening / closing door part 14 Connecting part 16 Radio wave absorption sheet 20 Transmitting part 22 Receiving part

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-122880 (JP, A) Japanese Utility Model Showa 62-5700 (JP, U) Japanese Utility Model Showa 63-193899 (JP, U) (58) Field (Int.Cl. ⁶ , DB name) H05K 9/00

Claims (3)

(57) [Claims] 1. A radio wave absorbing sheet having a radio wave absorbing characteristic corresponding to a specified frequency band near the operating frequency of a device under test is attached to the entire inner surface of a metal casing having a good shielding property. A dedicated anechoic box provided with a transmitting unit and a receiving unit on both sides, wherein the metal casing has an inner space in which a central part is spread outward and both sides are narrowed, and along an inner surface thereof. A radio wave anechoic box of a reduced wall reflection type to which the radio wave absorbing sheet is attached. 2. The anechoic box of reduced wall-reflection type according to claim 1, wherein the cross-sectional shape of the measurement space is hexagonal or rhombic. 3. The anechoic box according to claim 1, wherein the inner surface of the measurement space is a curved surface.