JPH06104633A - Anechoic chamber - Google Patents

Abstract

PURPOSE:To obtain the anechoic chamber having excellent anechoic chamber performance in which no disturbance of an electromagnetic field is caused especially even at a high frequency band by connecting a transmission section and a reception section with a taper-shaped waveguide section so as to obtain a structure that a coupling border between the transmission section and the waveguide section is reduced by a radio wave absorbing body. CONSTITUTION:A transmission section 11 and a reception section 12 are connected by a taper-shaped waveguide section 15. Three side faces except the floor of the waveguide section 15, that is, part or all of the left right side wall faces and a ceiling face 15C is made of a flat plate ferrite radio wave absorbing body 16. An earth equivalent floor having a characteristic equivalent to the earth in terms of a radio wave is formed for floor faces 11e, 12e, 15e except a part by combining a ferrite tile and a conductive film. Then the radio wave absorbing body 20 is projected inward at a coupling zone 19 between the transmission section 11 and the radio wave section 15 to reduce the aperture cross section of the transmission section 11. Thus, the propagation of a harmonic component even at high frequencies is suppressed and a radio wave in the single mode is sent to the waveguide section 15 over a wide band.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is for measuring the characteristics of receiving antennas and mobile communication antennas mounted on automobiles, aircrafts, etc., and for evaluating unnecessary radio waves and noises generated from electronic devices and externally. The present invention relates to an anechoic chamber used for measuring EMI and EMS, which tests the influence of radio waves from EMI on electronic devices.

[0002]

2. Description of the Related Art Conventionally, as an environment for measuring the radio wave propagation characteristics of an antenna, measuring the noise generated from an electronic device, and testing the influence of an interference wave from the outside on the electronic device, weather conditions, temperature and humidity conditions have been used. A stable and highly reliable indoor space that can remove the influence of external noise is desired. The anechoic chamber is one in which the wall surface, ceiling, and floor surface are covered with an electromagnetic wave absorber in order to provide such an indoor space, and its superiority is well known and widely applied.

As a characteristic of such an anechoic chamber, it is a major issue to realize a free space in the room free from radio wave obstructions, and it is reflected from the side wall surface, ceiling surface and floor surface of the room. It is desired to reduce unnecessary electromagnetic wave energy and to obtain excellent electric field uniformity in the receiver.

Incidentally, the radio wave propagation characteristic in free space means that when the transmission antenna, which is a radio wave generation source, is modeled as a point wave source, the electric field of the radiated radio wave spreads concentrically and propagates sufficiently. The electric field uniformity is ensured by realizing a so-called plane wave in which the magnitude and phase are aligned in the plane in a limited region at a long distance. However, at a sufficiently long distance, as the propagation distance increases, the electric field strength attenuates in inverse proportion to the distance.

The anechoic chamber has, in addition to a general rectangular parallelepiped shape, a shape in which a wall surface, a ceiling surface, and a floor surface in an intermediate region between the transmitting portion and the receiving portion are widened to reduce reflection from them. Recently, a tapered anechoic chamber has been developed in which a transmitter in a narrow space and a receiver in a wide space are connected by a tapered waveguide.

The taper type anechoic chamber is economical because it can be constructed with a smaller volume when the same transmitting and receiving distance is taken, as compared with a rectangular anechoic chamber. In addition, because of the taper angle of the waveguide portion, there is almost no influence of reflection from the sidewall portion, and the path difference of the sidewall reflected wave can be reduced in the transmission portion, so that the phase difference is extremely small and therefore the electric field uniformity in the reception portion is reduced. Become excellent.

FIG. 8 is a plan view schematically showing the conventional taper type anechoic chamber of this kind, and FIG. 9 is a sectional view taken along the line IX-IX of FIG.

As shown in these figures, the conventional tapered anechoic chamber has a tapered planar shape and a side sectional shape, and all the wall surfaces, that is, the side wall surfaces 80,
The ceiling surface 81 and the floor surface 82 are covered with a pyramid-shaped or wedge-shaped radio wave absorber 83 made of a carbon-containing foam which is a resistance loss material. Narrow space transmitter 8
A horn antenna type transmitting structure 85 having a waveguide is provided at the end of 4. The transmitting section 84 and the receiving section 86 having a wide space are connected by a tapered waveguide section 87. The side wall surface, the ceiling surface, and the floor surface of the waveguide section 87 are tapered so that the cross section area gradually increases from the transmission section 84 toward the reception section 86.

[0009]

When an antenna mounted on a ground moving body such as an automobile receives a radio wave in a mounted state, it must receive a radio wave that is a combination of a reflected wave from the ground and a direct wave from a transmission source. Becomes However, in the conventional taper type anechoic chamber as described above, since the floor surface is also constituted by the electromagnetic wave absorber, there is no reflected wave from the ground and only the direct wave is received. Therefore, the radio wave characteristic received in the anechoic chamber and the radio wave characteristic in the practical state are different from each other.

Further, in the conventional taper type anechoic chamber, since the electromagnetic wave absorber made of the resistance loss material is used, in order to obtain excellent electromagnetic wave absorption characteristics, the length of the electromagnetic wave absorber is set to the wavelength of the frequency to be absorbed. It should be at least 1/2 or more. This is because, if the frequency to be absorbed is 100 MHz, for example, the length of the absorber will be 1.5 m or more, the size of the building that constitutes the anechoic chamber will be significantly large, and it will be economically disadvantageous and from each wall surface. The volume of the effective space sandwiched between the tips of the radio wave absorbers becomes extremely small.

Further, in the conventional taper type anechoic chamber, the transmission frequency range of the transmitting section is limited to the frequency range of the waveguide. For this reason, when performing wideband measurements with the recent expansion of radio wave usage and widening of available frequencies, it is necessary to prepare a plurality of transmitters having different frequency bands and exchange them. Causes an inconvenience that not only increases the financial burden but also requires a great deal of labor for replacement.

A problem particularly in the conventional taper type anechoic chamber is that when measuring a wide band, harmonics are generated in the high frequency band and the electromagnetic field is disturbed. This state is clearly shown in the frequency-electric field fluctuation value characteristic of FIG. 5 described later.

Therefore, the present invention solves the above-mentioned problems of the prior art, and particularly provides an anechoic chamber having excellent anechoic chamber performance in which disturbance of the electromagnetic field does not occur even in a high frequency band.

[0014]

According to the present invention, the wall surface of the transmitter and the receiver is covered with a radio wave absorber, and the transmitter and the receiver are connected by a tapered wave guide. Thus, an anechoic chamber having a structure in which the coupling area between the transmitter and the waveguide is narrowed down by the electromagnetic wave absorber is provided.

A floor equivalent to a ground equivalent floor in which the floor surfaces of the transmitter, the waveguide, and the receiver are flat with respect to the ground, and the floor of the receiver and the waveguide are combined with a ferrite tile and a conductive film. It is preferable that

It is also preferable that at least a part of the ceiling surface and the side wall surface of the waveguide is made of a ferrite electromagnetic wave absorber.

Further, it is also preferable that the radio wave absorbers arranged on the wall surfaces of the transmitter and the receiver are composed of a composite type radio wave absorber made of a combination of a ferrite tile and a resistance loss material.

It is also an embodiment of the present invention to dispose an independent transmitting broadband antenna in the transmitting section.

[0019]

With the structure in which the transmitting section and the receiving section are connected by the tapered waveguide section and the coupling boundary portion between the transmitting section and the waveguide section is narrowed by the electromagnetic wave absorber, the opening cross-sectional area of the transmitting section is reduced. Becomes smaller. As a result, propagation of harmonic components is suppressed even in a high frequency having a short wavelength, and a single-mode radio wave is transmitted to the waveguide section, so that a radio wave having a more uniform electric field can be obtained at the receiving section. Furthermore, in order to form the same environment as a practical radio environment in the field, the floor surface of the waveguide is constructed with a ground equivalent floor that has radio characteristics equivalent to the ground. Further, a ferrite wave absorber is arranged on part or all of the ceiling surface and the side wall surface of the waveguide section instead of the wave absorber made of a resistance loss material having a length of ½ or more of the wavelength. The ferrite electromagnetic wave absorber has a large magnetic loss and excellent electromagnetic wave absorbing performance at a thickness of 1/50 to 1/200 of the wavelength, so that a wider effective space can be secured and the electromagnetic wave anechoic chamber can be secured. Can be formed at low cost.

[0020]

EXAMPLES Examples of the present invention will be described in detail below.

FIG. 1 is a plan view schematically showing the construction of an embodiment of the anechoic chamber of the present invention, and FIG. 2 is a sectional view taken along the line II--II of FIG.

As shown in these figures, the tapered anechoic chamber 10 has one end as a transmitting portion 11 having a narrow space and the other end having a receiving portion 12 having a wide space. The transmitter 11 is designed to transmit a single-mode radio wave as much as possible by suppressing unnecessary reflected waves from its wall surface. The four wall surfaces other than the floor surface of the transmitter 11, that is, the left and right side wall surfaces 11a and 11b, the ceiling surface 11c, and the inner wall surface 11d are the composite electromagnetic wave absorber 1 formed by combining a ferrite electromagnetic wave absorber and a resistance loss material.
Covered with 3. In addition, the receiving unit 12 is designed so that unnecessary reflected waves from the wall surface are suppressed as much as possible in order to reproduce the situation in which an infinite space continues for the transmitted electric wave, and only the traveling wave component is obtained in the receiving area. Has been done. Four wall surfaces other than the floor surface of the receiver 12, that is, the left and right side wall surfaces 1
2a and 12b, the ceiling surface 12c, and the back wall surface 12d are also covered with the composite type electromagnetic wave absorber 14 made of a combination of a ferrite electromagnetic wave absorber and a resistance loss material. The radio wave absorbers 13 and 14 are formed in a pyramid shape, a wedge shape, or a plate shape having different material constants in the thickness direction.

As described above, since the composite type electromagnetic wave absorber in which the ferrite electromagnetic wave absorber and the resistance loss material are combined is used as the electromagnetic wave absorbers 13 and 14, excellent electromagnetic wave absorption characteristics can be obtained from low frequencies and the resistance can be improved. It is possible to obtain equal or more absorption characteristics with a length of ½ or less as compared with the case where only the lossy material is used. As a result, not only the effective space in the anechoic chamber can be expanded, but also the building itself can be made small and the cost can be largely reduced as a whole.

The transmission section 11 and the reception section 12 are connected by a tapered waveguide section 15. The waveguide unit 15 minimizes the reflection of the single mode radio wave transmitted from the transmission unit 11 due to the local non-uniformity of the wall surface, and is close to the radio wave propagation characteristics of the far region in the free space with a short transmission distance. Is designed to obtain the highest possible radio wave attenuation effect. Three wall surfaces of the waveguide portion 15 excluding the floor surface, that is, the left and right side wall surfaces 15a and 15b, and the ceiling surface 1
All or a part of 5c is formed of a flat ferrite wave absorber 16. This ferrite wave absorber 16
Has a large magnetic loss, has a large radio wave attenuation effect in a wide band, and has a wavelength of 1/50 to 1/20.
Even if the thickness is 0, it has excellent electromagnetic wave absorption performance, so that it can be made extremely thin. As a result, a uniform electric field can be obtained with a shorter propagation distance, a large effective space can be secured, and an effective anechoic chamber can be realized in an economical small building.

The transmitter 11, the receiver 12, and the waveguide 15
The floor surfaces 11e, 12e, and 15e have a flat structure parallel to the ground. This is because the ground is generally flat. Furthermore, these floor surfaces 11e, 12e, and 15e are ground equivalent floors having a characteristic equivalent to the ground in terms of radio waves by combining a ferrite tile and a conductive film, except for a part.

An independent array type antenna 17 having a wide band characteristic is installed at the center of the transmitter 11.
The entire transmitter 11 is configured as a broadband transmitter.
Therefore, it is not necessary to prepare a plurality of transmission units for each frequency band, and the labor for exchanging them can be saved.

At the center of the receiver 12, there is provided a turntable 18 on which an object to be measured, for example, a car W is placed.

A coupling region 19 between the transmitting section 11 and the waveguide section 15
In the above, the radio wave absorber 20 is provided so as to project inward, and has a structure in which the opening cross section of the transmitting unit 11 is narrowed.

FIGS. 3 and 4 are for explaining this narrowing structure, and are a plan view and a sectional view showing in detail only the coupling region 19 portion of FIGS. 1 and 2, respectively.

The side wall surfaces 19a and 19b, the ceiling surface 19c, and the floor surface 19e in the coupling region 19 are covered with the composite type electromagnetic wave absorber 13 described above. Then, the combined region 19
Further, an electromagnetic wave absorber 20 preferably made of a similar composite electromagnetic wave absorber is provided on the composite electromagnetic wave absorber 13 so as to project therefrom.
0 has a structure in which the opening surface of the transmission unit 11 is narrowed down.

Since the transmitting unit 11 as a whole is a broadband transmitting device due to the antenna 17, if the opening area of the transmitting unit 11 is large, multiple waves or multiple waves in the horizontal and vertical directions occur in the high frequency band. Harmonics will propagate,
It is possible to suppress the generation of harmonics by adopting a narrowing structure that does not impair the propagation of low frequencies by the radio wave absorber 20.

FIG. 5 and FIG. 6 respectively show the variation value characteristics of the electric field with respect to the frequency of the vertically polarized wave in the conventional tapered anechoic chamber without a diaphragm structure and the tapered anechoic chamber 10 of the above-mentioned embodiment provided with a diaphragm structure. It represents. This characteristic shows the electric field distribution in a circle with a height of 1.3 m and a diameter of 6 m.

As shown in FIG. 5, in the conventional anechoic chamber,
The maximum-minimum electric field fluctuation value may be 7 dB or more in the high frequency band, but in the taper type anechoic chamber of the present embodiment, as shown in FIG. 6, not only in the low frequency band but also in the high frequency band- The minimum electric field fluctuation value is 4 dB or less, which is very stable.

Further, according to the present embodiment, in order to make the conditions same as the outdoor radio wave propagation environment, a ground equivalent floor which is radio equivalent to the ground is provided in the waveguide section 15, so that the transmitting section 11
The direct wave from and the reflected wave from the floor surface 15e of the waveguide section 15 are combined in the same manner as in the practical state, enter the receiving section 12, and a reception state close to radio wave propagation in the field is realized.

When the floor is a ground equivalent floor that is radio equivalent to the ground, the direct wave from the transmitter 11 and the reflected wave from the ground equivalent floor interfere with each other and have ripples having large maximum and minimum values. This may cause a phenomenon, and it is necessary to prevent electric field nonuniformity due to mutual interference. For that purpose, it is necessary to select the distance between transmission and reception such that the difference between the phase of the reflected wave and the phase of the direct wave is at least ½ wavelength or more.

As shown in FIG. 7, the height of the transmitting antenna 70 is h ₁ , the height of the receiving antenna 71 is h ₂ , the linear distance between the transmitting and receiving antennas is l ₀ , the reflecting distance between the transmitting and receiving antennas is ₁ and If l ₂ and the wavelength are λ, this satisfies the relation of l ₁ + l ₂ −l ₀ = √ {l ₀ ² + (h ₁ + h ₂ ) ² } −l ₀ ≧ λ / 2. For example, the transmitting antenna 70
Of the height h ₁ of the receiving antenna 71 and the height h ₂ of the receiving antenna 71 is h ₁
When + h ₂ = 3 m, the linear distance l ₀ between the transmitting and receiving antennas
Is l ₀ ≧ 2.25 m when the frequency is 100 MHz, and l ₀ ≧ 8.75 m when the frequency is 300 MHz
Therefore, if the frequency is 600 MHz, then l ₀ ≧ 17.9
m. When h ₁ + h ₂ = 4 m, the frequency is set to 1
At 00 MHz, l ₀ ≧ 4.58 m, at frequency 300 MHz, l ₀ ≧ 15.75 m, and at frequency 600 MHz, l ₀ ≧ 32 m. Setting to satisfy such a condition realizes a radio wave propagation environment in which the reception antenna receives a radio wave from a transmission point which is practically distant.

[0037]

As described above in detail, according to the present invention, the transmitting section and the receiving section are connected by the tapered waveguide section, and the coupling boundary portion between the transmitting section and the waveguide section is the electromagnetic wave absorber. The cross section of the aperture of the transmitter is made smaller as the structure is narrowed down. As a result, propagation of harmonic components is suppressed even in a high frequency having a short wavelength, and a single-mode radio wave is transmitted to the waveguide section over a wide band, so that a radio wave having a more uniform electric field can be obtained at the receiving section.

Furthermore, by making at least the floor surface of the waveguide part the ground equivalent floor, it is possible to obtain characteristics almost similar to the radio wave propagation in the actual field. Moreover, by constructing at least a part of the ceiling surface and side wall surface of the waveguide part with a ferrite electromagnetic wave absorber, effective electromagnetic wave attenuation can be obtained and excellent electric field uniformity can be obtained in a shorter distance. It is possible to provide an economical anechoic chamber that is not only excellent but can be configured with an extremely short electromagnetic wave absorber so that a wide space can be secured and which is economically inexpensive. Also,
By arranging a wideband antenna in the transmitter, it is not necessary to prepare a plurality of transmitters for each frequency band, which is economically low cost and the labor of replacing the transmitters can be saved. be able to.

[Brief description of drawings]

FIG. 1 is a plan view schematically showing the configuration of an embodiment of an anechoic chamber of the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a plan view showing in detail a coupling region portion of FIG.

4 is a cross-sectional view showing in detail a coupling region portion of FIG.

FIG. 5 is a characteristic diagram showing an electric field fluctuation value in a conventional technique.

FIG. 6 is a characteristic diagram showing electric field fluctuation values in the examples of FIGS. 1 and 2.

FIG. 7 is a model diagram of radio wave propagation showing a relationship between a direct wave and a reflected wave of a radio wave.

FIG. 8 is a plan view schematically showing a conventional tapered anechoic chamber.

9 is a sectional view taken along line IX-IX in FIG.

[Explanation of symbols]

10 Tapered anechoic chamber 11 Transmitter 11a, 11b, 12a, 12b, 15a, 15b Side wall surfaces 11c, 12c, 15c Ceiling surface 11d, 12d Inner wall surface 11e, 12e, 15e Floor surface 12 Receiver section 13, 14 Combined electromagnetic wave absorption Body 15 Waveguide 16 Ferrite electromagnetic wave absorber 17 Array type antenna 18 Turntable 19 Coupling region 20 Radio wave absorber

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiaki Kobayashi 1-13-1, Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Shingo Seki 3-5-11, Doshomachi, Chuo-ku, Osaka-shi, Osaka No. Nippon Sheet Glass Co., Ltd. (72) Inventor Kazuhiko Ogawa 3-5-11 Doshumachi, Chuo-ku, Osaka City, Osaka Prefecture Japan Plate Glass Co., Ltd. (72) Inventor Harunori Murakami 3-5, Doshomachi, Chuo-ku, Osaka Prefecture, Osaka No. 11 within Nippon Sheet Glass Co., Ltd. (72) Inventor Keisuke Tanaka 3-5-11 Doshomachi, Chuo-ku, Osaka City, Osaka Prefecture Within Nippon Sheet Glass Co., Ltd.

Claims (5)

[Claims] 1. A tapered anechoic chamber in which the wall surfaces of the transmission unit and the reception unit are covered with a radio wave absorber, and the transmission unit and the reception unit are connected by a tapered waveguide unit. An anechoic chamber characterized in that the coupling area with the wave portion is narrowed down by an electromagnetic wave absorber. 2. The floor surfaces of the transmitter, the waveguide, and the receiver have a flat structure with respect to the ground, and the floor of the receiver and the waveguide are combined with a ferrite tile and a conductive film. The anechoic chamber according to claim 1, wherein the anechoic chamber comprises a ground equivalent floor. 3. The anechoic chamber according to claim 1 or 2, wherein at least a part of a ceiling surface and a side wall surface of the waveguide is formed of a ferrite electromagnetic wave absorber. 4. The electromagnetic wave absorber disposed on the wall surfaces of the transmitting unit and the receiving unit is composed of a composite type electromagnetic wave absorber made of a combination of a ferrite tile and a resistance loss material. The anechoic chamber according to any one of items. 5. The anechoic chamber according to claim 1, wherein an independent wideband antenna for transmission is arranged in the transmitting unit.