JP2003075490A - Test site for measuring electric wave having multiple fence and standard design method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the application of a reflection wave prevention fence due to the tendency for high performance of the free space such as an EMC site has many advantages as compared with an old method using an electric wave absorber but is not complete, the influence of the irregular reflection of an exposed reflection surface and the diffraction wave in a multi path may not be avoided depending on measurement conditions in the tendency for free space by a single fence, mutual reflection countermeasures are required in a multiple metal fence, and hence a simplified standard design method in a multiple fence system is desired. SOLUTION: A main fence for covering the entire reflection surface is provided in the middle of transmission/reception points, and a sub fence is placed at an optimum position in a shielded region to attain a complete free space. The mutual reflection interference in the metal fence is prevented by the inclination of opposing surfaces. A graphical solution in the standard design method that becomes a criterion of an economical design for VHF-microwaves is created.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly belongs to the technical field relating to a test facility for measuring electric field strength of VHF and microwave radio waves.

[0002]

2. Description of the Related Art Conventional VHF / microwave band measurement test sites include an open site installed outdoors and an anechoic chamber installed indoors. This is classified into a metal floor reflection type and a free space type in terms of radio wave propagation format. In order to realize a free space site, it is necessary to suppress the influence of reflected waves on the floor (ground) surface and the surroundings (walls, ceiling, nearby objects) to an allowable value.
There are two methods of suppression, the classical method using a wave absorber and the new method using a reflected wave prevention fence. According to international recommendations (CISPR, CENELEC), measuring distance 3
The allowable limit of the influence of the reflected wave on the free space type test site of m to 10 m is defined as "free space deviation of site attenuation 4 dB.
It is defined as "below", and this is recognized as a "free space site" for practical use. The standard design method of the present invention aims to achieve this internationally recommended standard.

A method for realizing a free space condition using a reflected wave prevention fence is disclosed in, for example, Japanese Patent No. 20144463.
No. "Anechoic chamber with reflector" and JP-A-7-558.
There are 63 "Fully reflective and non-reflective EMC test sites". Patent No. 20144463 "Anechoic chamber with a reflector" is a type in which a single reflected wave prevention fence is installed. Japanese Unexamined Patent Publication No. 7-55863, "EMC test site for both full reflection type and non-reflection type", is a multi-fence type in which a plurality of reflected wave prevention fences each having a front side made of a metal plate and a back side made of a radio wave absorption plate are arranged in parallel.

Although they have many advantages as compared with the reflected wave prevention method which depends on the electromagnetic wave absorber, there are cases where the required performance cannot be achieved depending on the application conditions. The present invention is an improved system that complements those deficiencies, and presents an economical standard design method of structural dimensions, which is premised on the international recommendation standard together with the embodiment.

[0005]

As shown in FIG. 5 (a), the object in the area (9) where radio waves are blocked by the reflected wave prevention fence is not affected, but if there is an exposed surface, Irregular reflections (residual reflections) can interfere with the direct wave (3).

In the case of a single reflected wave prevention fence, as shown in FIG. 5B, when the height of the direct wave path (3) is low and the distance is large, the reflected wave prevention fence (top F) is used. In some cases, multipath diffracted waves due to reflections at points P and Q between the transmission point (1) and the reception point (2) are combined, and their influence cannot be ignored. The paths of the diffracted waves that interfere with the direct wave (3) are (1-P-F-2) and (1-F-Q-
2) and (1-P-F-Q-2).

Whether the installation surface of the reflected wave prevention fence is single or multiple, and the installation surface of the fence is made of a material such as wood or plastic that transmits radio waves, and there is a reflection surface (4) such as a metal surface on the outside,
As shown in FIG. 5C, the reflected wave may pass through the bottom of the fence, impairing the shielding effect.

When the reflection wave preventing fences made of metal plates are arranged side by side on both the front and back sides, as shown in FIG. 5D, mutual reflection between the fences and the floor surface impairs the reflection wave preventing effect of the fences. There is.

Conventionally, a standard design method for the structural dimensions of a test site for measuring electromagnetic waves having multiple fences has not been known.

[0010]

By installing one or more reflected wave prevention fences so that the entire reflecting surface (4) between the transmitting point (1) and the receiving point (2) can be shielded, Prevents the occurrence of residual reflection due to the exposed reflective surface.

A fence for shielding the entire reflecting surface is used as a main fence (5), and one or more sub-fences (6) are provided in the shielding area. This can prevent the generation of multipath diffracted waves. Since it is within the shielding area, the influence of interference due to mutual reflection between fences does not appear.

By attaching a shield bottom plate (metal plate or the like) that does not transmit radio waves to the installation bottom surface of the multiple fence, detour reflection of the bottom surface can be prevented.

When the reflective surface is shielded by a plurality of fences,
The shielding effect may be impaired due to mutual reflection between adjacent fences. In order to prevent this, FIG. 6 (a), (b)
As shown in, the relative angle of the opposing surface of the fence is 20 degrees to 60 degrees.
Just do it once.

The material of the fence for preventing reflected waves used in the present invention has a transmittance of radio waves of frequencies above the VHF band of 10% (-20 dB) or less, in other words, a shielding ratio of 20.
The material type and surface shape do not matter as long as they are at least dB. For example, the cheapest material that can be easily manufactured is a thin metal plate or thin film of aluminum, copper, or iron, which may be attached to or vapor-deposited on a wooden board, a plastic board, a cloth, or the like.

Next, a method of economic design aiming at the international recommended standard will be shown with reference to FIGS. How to install the main fence; The most reasonable position of the main fence is the regular reflection point when there is no fence. Therefore, the intersection (F) of the diagonal lines (8a) and (8b) of the quadrangle connecting the transmitting point (1) and the receiving point (2) and the legs (A) and (B) of the perpendicular line drawn down to the installation surface is set as the apex. Provide a main fence (5). In this case, the height of the main fence and the clearance between the main fence and the direct wave path (3)
Are equal.

A method for determining the height of the transmitting point and the height of the receiving point; the measuring distance (AB) is defined in advance, and the height of the transmitting point, the height of the receiving point and the height of the main fence (equal to the clearance) are mutually restricted. I have a relationship. In order to avoid diffraction loss for direct waves, it is desirable to have a large clearance with the main fence, but this is not economical because the height of the transmitting and receiving points becomes high. Therefore, the diffraction loss is allowed up to 2 dB, and the clearance (main fence height) is applied. 1/3 of the radius of the first Fresnel zone at the fence position of the lowest frequency.
Set to. The calculation for this is complicated and time-consuming,
It is relatively easy to obtain graphically as follows.

In FIG. 3, lengths (A-F-B) and (A
The locus (point on the ellipse with A and B as the focal point) of the first Fresnel zone in which the difference of −B) becomes ½ of the wavelength of the applicable lowest frequency is obtained, and F of 1/3 of the height is obtained. Plot the points. For each point of F, the positions of the transmission point (1) on the extension of (BF) and the position of the reception point (2) on the extension of (AF) are provisionally obtained. From among them, an appropriate combination of (F) (1) (2) is adopted. For this work, drawing with a thread is convenient. For example, (A−B) = 3 m, frequency 50 MH
If z (wavelength 6 m), (A−F−B) = 6 m, so if both ends of the thread corresponding to 6 m are fixed at points A and B and an ellipse is drawn upward, the trajectory of the first Fresnel zone will be can get.

Sub-fence installation method: In order to suppress the generation of diffracted waves in multiple paths, a sub-fence may be placed at the reflection point between the main fence and the transmission / reception point. Therefore, a straight line connecting the foot of the main fence with the transmitting point and the receiving point and a diagonal line (8a)
The sub-fence (6a) and the sub-fence (6b) are provided with the intersections of (1) and (8b) as vertices. Since there is a vertex on the diagonal of the upper limit of the shielding area, mutual reflection between adjacent fences does not occur. Normally, the above three fences can satisfy the international recommendation standard, but in special cases such as when the height of the direct wave path is low and the measurement distance is large, it is necessary to add an additional fence. That is, the straight line connecting the foot of (6a) and the transmission point and the diagonal line (8a) and the straight line connecting the foot of the sub-fence (6b) and the receiving point and the diagonal line (8b).
The sub-fences (6c), (6
d) is provided.

Clearance between the direct wave path and the main fence;
The direct wave diffraction loss is determined by the clearance between the main fence and the direct wave path and the radius of the first Fresnel zone at that location. For a fence that is long laterally, if the clearance is 1/2 or more of the radius of the first Fresnel zone, the diffraction loss is negligible, and if it is 1/3 or more, the diffraction loss is 2 dB or less. Clearance is 0, that is,
If the top edge of the fence directly contacts the wave path, the diffraction loss will be about 6 dB. From these points, the standard design value of economical clearance is set to 1/3 of the radius of the first Fresnel zone of the lowest frequency to be applied.

When the measurement distance is 3 m and the main fence is in the center, the first Fresnel zone radius is 3.
1.7m at 7m and 100MHz, 0.5 at 1GHz
m. The 1/3 clearance is about 1.2 each
m, 0.6 m and 0.17 m are design values that are practically easy to handle.

Lengths of the main and sub-fences; as shown in the plan view of FIG. 4, the radiation points of radio waves from the EUT are (1
a) to (1b), if the triangles connecting (1a) and (1b) to the receiving point (2) have right and left lengths outside the fence that are equal to or greater than the height of the fence, respectively. That is, practically enough.

The above is a guideline for economic design and is not a constraint. It is a feature of the present invention that the design values can be changed relatively freely according to the installation environment of the site and the requirements of technical performance.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the invention will be described with reference to the drawings. 1 and 2 are examples of three fences. The position of the main fence is near the position of the standard design, but the height is larger than the standard value, so the shielding against the installation plane is sufficient. Sub-fence (6a),
Since (6b) is within the shielding region (9), there is no concern about mutual reflection, and it is useful for preventing diffraction of multiple paths. In this format, if the distance (A-B) is 3m, the transmitting point height is 2.5m, the receiving point height is 2m, the main fence height is 1.2m.
m, clearance for direct wave path is about 1m
Becomes This corresponds to 1/3 of the radius of the first Fresnel zone of about 3 m at 40 MHz, so it is 40 MH in economic design.
It can be applied as a free space type test site for VHF of z or higher and microwave band. FIG. 6 shows an example of preventing reflected waves by two fences, in which (a) is inclined in a vertical plane to avoid mutual reflection. In (b), both are formed in a receding shape in a horizontal plane.

[0024]

EXAMPLES FIGS. 1 and 2 show a three-fence type embodiment.
3 and 4 show the standard design method for the embodiment. Figure 6
An example of the fence mutual reflection prevention type is shown in FIG.

[0025]

Since the main fence or a plurality of fences shields the entire reflecting surface below the direct wave, there is no risk of interference due to irregular reflection of the exposed reflecting surface.

The sub-fence installed in the shielding area of the main fence prevents the generation of multipath diffracted waves, thus enhancing the effect of preventing reflected waves.

By attaching a shielding bottom plate to the bottom surface of the multiple fence, it is possible to prevent detour reflection by an external reflection surface or the like.

When the reflecting surface is shielded by a plurality of fences, mutual reflection interference can be prevented by setting the relative angle of the adjacent opposing surfaces to 20 to 60 degrees.

Since the fence used in the present invention can use a low-priced metal thin plate such as an aluminum plate, it has a great advantage that the entire system can be economically constructed.

Since the shielding loss of a fence having a finite size increases as the frequency increases (the wavelength decreases), the present invention is particularly effective for making the microwave band free space.

[Brief description of drawings]

FIG. 1 is a side view for explaining an embodiment.

FIG. 2 is a plan view for explaining the embodiment.

FIG. 3 is a side view for explaining the standard design method.

FIG. 4 is a plan view for explaining a standard design method.

FIG. 5 is an explanatory diagram of a problem that needs to be solved. (A) Irregular reflection of exposed surface (b) Multi-path diffraction (c) Bottom detour reflection (d) Fence mutual reflection

FIG. 6 is an embodiment of a fence mutual reflection prevention type, in which (a) an inclined fence type and (b) a retracted fence type

[Explanation of symbols]

1 transmission point 2 reception points 3 direct wave path 4 Reflective surface 5 main fences, 6 Deputy fence, 7 Shield bottom plate 8a, 8b Diagonal line for standard design 9 Shielding area A Feet of a perpendicular line dropped from the transmitting point to the installation plane B A foot perpendicular to the installation plane from the receiving point 1a Left end of EUT 1b Right edge of EUT

Claims (4)

[Claims] 1. A radio wave measurement with a multi-fence in which a main fence (5) for preventing reflected waves is placed in the middle of a radio wave passage, and one or more sub-fences (6) are provided in an area (9) shielded by the main fence. For test site 2. The test site for measuring radio waves with multiple fences according to claim 1, wherein shield bottom plates (7) are attached to the bottom surfaces of the main fence (5) and the sub fence (6). 3. A transmission point (1) and a reception point (2), and when the intersection of diagonals of a quadrangle connecting the legs (A) and (B) of the respective perpendiculars drawn to the installation surface is (F), The height of the transmitting point and the height of the receiving point are determined so that the height of (F) on the installation surface becomes 1/3 or more of the radius of the first Fresnel zone at the (F) position of the lowest frequency to be applied. Therefore,
The main fence (5) is set with (F) as the apex. Next, with the intersection of the straight line connecting the foot of the main fence and the transmitting point and the receiving point and the diagonal lines (8a) and (8b) as the apex,
A sub fence (6a) and a sub fence (6b) are provided respectively. Next, if necessary, the secondary fence (6a)
Of the sub-fence (6a) and the diagonal of the sub-fence (8a) and the sub-fence (6b) of the sub-fence (6b).
c) and (6d) are provided. In this way, the transmission point height,
A standard design method for a test site for radio wave measurement with multiple fences characterized by determining the height of the receiving point, the position of the main fence, and the height of the secondary fence. 4. The relative angle between opposing surfaces of adjacent fences is 2
Test site for radio wave measurement with multiple fences whose opposing surfaces are non-parallel at 0 to 60 degrees