JPH07193388A - Micro wave and millimeter wave absorber - Google Patents

Abstract

PURPOSE:To improve wave absorption property by forming a wave dark room of an aggregate of a specified unit absorber having a cone-like part. CONSTITUTION:Complex dielectric constant at a frequency 3GHz is expressed by a formula I. An absolute value thereof can be expressed by a formula II. The title absorber is constituted of a dielectric loss material of the absolute value of 2 or more and 9 or less and dielectric dissipation factor tan6 is 0.6 or more. A total length H of a unit absorber is 150mm or more and a length L of a cone part is 100mm or more. The length L of the cone-like part is at least three times as long as a length W of one unit of a bottom part of the unit absorber and the length W of one unit is 100mm or less. When wave absorption characteristic is measured by the above constitution, wave absorption characteristic at 3GHz is 40db or more and wave absorption characteristic can be improved. A wave dark room inside is formed of an aggregate of wedge- like, square cone-like or a circular cone-like unit absorber comprised of a stand part D and a cone-like part E.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorber, and more particularly to a radio wave absorber for an anechoic chamber.

[0002]

2. Description of the Related Art An anechoic chamber is used for evaluation of electronic devices and various antennas. However, as an electromagnetic wave absorber for an anechoic chamber, it is generally used in order to achieve a wide band of corresponding frequencies and high electromagnetic wave absorption performance. Widely used are wedge-shaped ones or quadrangular pyramid-shaped ones.

These anechoic chambers and wave absorbers are mainly used in the frequency band below the SHF band where radio waves are generally used.

[0004]

By the way, in recent years, the frequencies used in radar and communication equipment are shifting to the EHF band.
Along with that, SHF, which has been used for radio wave absorbers
In addition to the frequency range below the band, high electromagnetic wave absorption performance is also required in the EHF band.

On the other hand, current radio wave absorbers are generally designed for frequencies below the SHF band, and how to shorten the length of the radio wave absorber from the low frequency to improve the performance, Broadband design including absorption performance at high frequencies above the EHF band has not been performed. Therefore, when the electromagnetic wave absorber used in the current SHF band or lower is used as it is, the absorption performance is deteriorated in the EHF band.
It has been reported that a radio wave absorber having a radio wave absorption characteristic of about 50 dB in the HF band has a radio wave absorption characteristic reduced to about 26 to 43 dB in the EHF band. (Physics (B-II), J72-
B-II, 9, pp.494-498 and Theological Theory (B-II), J73-B-II, 2, p
p.124-126) On the other hand, electromagnetic wave absorbers designed for the EHF band show good absorption characteristics in the EHF band, but such electromagnetic wave absorbers have high performance in the SHF band and below. 10 to 2 at a frequency of 3 GHz
The electromagnetic wave absorption characteristic is about 0 dB.

An object of the present invention is to provide a radio wave absorber having high radio wave absorption characteristics in a wide frequency range from the SHF band to the EHF band.

[0007]

In order to achieve the above object, the radio wave absorber of the present invention comprises an aggregate of unit absorbers having a conical portion, and has a complex relative dielectric constant at a frequency of 3 GHz.

[0008]

[Equation 3]

Magnitude of absolute value of

[0010]

[Equation 4]

Is 2 or more and 9 or less, the dielectric loss tangent tan δ (=
ε _"r / ε _'r) is composed of 0.6 or more dielectric loss material,
The total length (H) of the unit absorber is 150 mm or more,
The length (L) of the conical portion is 100 mm or more, and the length (L) of the conical portion is one unit length (W) of the bottom of the unit absorbent body.
3 times or more, and the length (W) of the one unit is 100
mm or less.

The base material of the radio wave absorber according to the present invention is
An organic resin foam material such as expanded polyethylene, expanded polyurethane, expanded polystyrene or the like is used, but it is preferable to use expanded polyethylene as a base material in terms of durability and processability.

[0013]

[Function] For the wavelength λ of the lower limit frequency of the target electromagnetic wave, the length of the electromagnetic wave absorber is 1.5λ or more in order to sufficiently attenuate the energy of the electromagnetic wave, and the wedge shape or the pyramid shape where the electromagnetic wave is introduced. By setting the length of the conical shape to be λ or more, the change of the input impedance becomes smooth, the radio waves are efficiently absorbed, and the absorption performance can be secured in the low frequency region.

That is, when the lower limit frequency of the target electromagnetic wave is 3 GHz, which is the lower limit frequency of the SHF band, the wavelength is 100 mm, so the length of the electromagnetic wave absorber is 150 mm or more, and the length of the wedge shape, the pyramid shape, or the conical shape. By setting the thickness to 100 mm or more, high absorption performance can be obtained at the lower limit frequency of the SHF band. Also, frequency 3
When the radio wave absorber is made of an absorbing material having a complex relative permittivity at GHz of less than 2 and a dielectric loss tangent of 0.6 or less, sufficient radio wave attenuation cannot be obtained.
The magnitude of complex relative permittivity at z is 2 or more, and the dielectric loss tangent is 0.
By constructing a radio wave absorber with six or more absorbing materials, good radio wave absorption characteristics can be obtained.

On the other hand, as the frequency of the radio wave becomes higher, the wavelength becomes shorter, so that the straightness of the radio wave is improved and the radio wave is directly incident on the wedge-shaped portion or the gap between the pyramid and the cone-shaped portion. By setting the ratio of the length of the pyramid shape, the cone shape to the wedge shape, or the width of one unit of the pyramid shape and the cone shape to 3 or more, the radio waves are multiplexed in the wedge shape portion, the pyramid shape portion, and the cone shape portion. Since reflection increases and radio waves are efficiently attenuated, good radio wave absorption characteristics can be obtained even in a high frequency region. However, if the gap between the wedge-shaped, pyramidal-shaped, and conical-shaped portions becomes too large with respect to the wavelength, radio waves easily enter the gap and scattered waves increase, so the width of the gap is preferably 100 mm or less. Further, by suppressing the reflection of radio waves on the surface of the radio wave absorber by configuring the radio wave absorber with an absorbing material having a complex relative permittivity of 9 or less at a frequency of 3 GHz,
It is possible to prevent the deterioration of the radio wave absorption characteristics due to the increase of the reflection of radio waves on the surface of the radio wave absorber. As a result, good radio wave absorption characteristics can be obtained in a wide frequency range.

As the wavelength is further shortened, the ratio of the area of the tip of the wedge shape, the pyramid shape, or the conical shape to the wavelength is increased, and the reflection of the radio wave from the tip causes the deterioration of the absorption characteristic. Good absorption characteristics can be obtained by suppressing the area of the tip of the pyramid-shaped or conical-shaped portion to 1/100 or less of the area of the bottom.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the wall, ceiling, or floor of an anechoic chamber is covered with an aggregate of unit absorbers made of a cone-shaped or wedge-shaped dielectric material.

The unit absorber has a pedestal portion D and a conical portion E, and its structural example is shown in FIG. (A) is a pyramid shape, the length of one side of the base is W, the total length of the radio wave absorber is H, and the length of the pyramidal part is L. (B) has a wedge shape, and the base has a rectangular parallelepiped having a long side length of LW, a short side length of W, a total length H, and a conical portion length L. (C) has a conical shape, and the base has a cylinder with a diameter W, the total length H, and the length of the conical portion L. Here, as one unit length (W) of the bottom of the unit absorber, the length of the shorter one of the sides of the base D in the case of a pyramid and a wedge, and the diameter of the base D in the case of a cone. take.

Although it is theoretically preferable that the tip of the pyramid is sharp, it actually has a certain area. In the present invention, as shown in FIG. 10D, the area S of the bottom of the unit absorber is
The ₀ and tip ratio S ₀ / S ₁ of the area S ₁ of defining the structure of the tip.

The unit absorber used in the present invention is a dielectric,
The absolute value of complex relative permittivity at a frequency of 3 GHz is 2 or more and 9
The value of the dielectric loss tangent tan δ, which is the ratio of the complex relative permittivity to the real part of the imaginary part, is 0.6 or more.

FIG. 11 shows the relationship between the absolute value (horizontal axis) of the complex relative permittivity measured at 3 GHz and the return loss (vertical axis). When the absolute value is approximately 2 or more, the return loss is 30 d.
It turns out that it becomes B or more. In FIG. 11, tan δ =
It is 0.6.

The upper limit of the absolute value of the complex relative dielectric constant is specified by the manufacturing conditions of the unit absorber. An organic resin such as expanded polyethylene is used as the absorber, and carbon is mixed to adjust the dielectric constant. If the mixing ratio of carbon is increased to increase the dielectric constant, molding becomes difficult. Therefore, practically, use 9 or less.

FIG. 12 shows the measurement results of the dielectric loss tangent tan δ and the return loss, and it can be seen that the return loss becomes 30 dB or more when the value of tan δ is about 0.6 or more.

Next, the dimensional relationship of the unit absorber will be described.

(Example 1) Complex relative permittivity at a frequency of 3 GHz

[0026]

[Equation 5]

[0027]

[0028]

[Equation 6]

Using the electromagnetic wave absorbing material (1), an electromagnetic wave absorber having a length of 150 mm, a quadrangular pyramid-shaped portion having a length of 100 mm, and a quadrangular pyramid having a width of 30 mm is manufactured.
The electromagnetic wave absorption characteristics were measured at 10 GHz. The measurement result of the radio wave absorption characteristics is shown in FIG. The electromagnetic wave absorption characteristic at 3 GHz is 4
It is 0 dB or more, and good absorption characteristics are obtained.

(Example 2) Complex relative permittivity at a frequency of 3 GHz

[0031]

[Equation 7]

[0032]

[0033]

[Equation 8]

Using the electromagnetic wave absorbing material (1), an electromagnetic wave absorber having a length of 150 mm, a quadrangular pyramid shaped portion of 100 mm, and a unit width of quadrangular pyramid of 30 mm, 50 mm, and 100 mm is manufactured, and the frequency is 100 GHz. Radio wave absorption characteristics were measured. FIG. 2 shows the relationship between the width of one unit of the quadrangular pyramid and the electromagnetic wave absorption characteristics. The ratio of the width of one unit of the pyramid to the length of the pyramid is 3
When the width of the quadrangular pyramid is 30 mm as described above, the radio wave absorption characteristic is 50 dB or more, which shows a good absorption characteristic.

(Example 3) Complex relative permittivity at a frequency of 3 GHz

[0036]

[Equation 9]

[0037]

[0038]

[Equation 10]

Using the electromagnetic wave absorbing material (1), an electromagnetic wave absorber having a length of 150 mm, a wedge-shaped portion of 100 mm, a wedge unit width of 30 mm, 50 mm, and 100 mm is manufactured, and the electromagnetic wave is absorbed at a frequency of 100 GHz. The properties were measured. The relationship between the width of one unit of the wedge and the electromagnetic wave absorption characteristics is shown in FIG. The ratio of the width of one unit of wedge to the length of wedge is 3
When the width of the wedge is 30 mm as described above, the radio wave absorption characteristic is 50 dB or more, which shows a good absorption characteristic.

(Example 4) Complex relative permittivity at a frequency of 3 GHz

[0041]

[Equation 11]

Is

[0043]

[Equation 12]

Using the radio wave absorbing material of, the length of the radio wave absorber is 500 mm, the length of the quadrangular pyramid portion is 450 mm, the width of one unit of the quadrangular pyramid is 100 mm, 150 mm, 200 mm, 3
A radio wave absorber was manufactured with a length of 00 mm, and the radio wave absorption characteristics were measured at a frequency of 100 GHz. FIG. 4 shows the relationship between the width of one unit of the quadrangular pyramid and the electromagnetic wave absorption characteristics. The width of one unit of square pyramid is 10
When it is 0 mm, the electromagnetic wave absorption characteristic is 50 dB or more, indicating a good absorption characteristic.

(Embodiment 5) Complex relative permittivity at a frequency of 3 GHz

[0046]

[Equation 13]

Is

[0048]

[Equation 14]

Using the electromagnetic wave absorbing material of, the length of the electromagnetic wave absorber is 300 mm, the length of the quadrangular pyramid is 250 mm, the width of one unit of the bottom of the quadrangular pyramid is 100 mm, and the width of one unit of the tip of the quadrangular pyramid is 1 mm, Radio wave absorbers were manufactured with 5 mm, 10 mm, and 20 mm, and the radio wave absorption characteristics were measured at a frequency of 100 GHz. FIG. 9 shows the relationship between the area ratio between the tip and the bottom of the quadrangular pyramid and the electromagnetic wave absorption characteristics. When the area ratio of the tip part to the bottom part of the quadrangular pyramid is 0.01, the radio wave absorption characteristic is 50 dB or more, which shows a good absorption characteristic.

(Comparative Example 1) Complex relative permittivity at a frequency of 3 GHz

[0051]

[Equation 15]

Is

[0053]

[Equation 16]

Using the electromagnetic wave absorbing material of, the electromagnetic wave absorber having a length of 100 mm, a quadrangular pyramid shaped portion of 100 mm in length, and a width of 30 mm of one unit of the quadrangular pyramid is manufactured, and a frequency of 2
The electromagnetic wave absorption characteristics were measured at 10 GHz. The measurement result of the radio wave absorption characteristics is shown in FIG. Electromagnetic wave absorption characteristic at 3 GHz is 1
It is about 0 dB, and the radio wave absorption characteristics are greatly reduced as compared with the first embodiment.

(Comparative Example 2) Complex relative permittivity at a frequency of 3 GHz

[0056]

[Equation 17]

Is

[0058]

[Equation 18]

Using the electromagnetic wave absorbing material of, the electromagnetic wave absorber is manufactured with a length of the electromagnetic wave absorber of 150 mm, a length of the quadrangular pyramid portion of 50 mm, and a width of 30 mm of one unit of the quadrangular pyramid.
The electromagnetic wave absorption characteristics were measured at 10 GHz. The measurement result of the radio wave absorption characteristics is shown in FIG. The electromagnetic wave absorption characteristic at 3 GHz is 30
It is about dB, and the radio wave absorption characteristic is lower than that of the first embodiment.

(Comparative Example 3) Complex relative permittivity at a frequency of 3 GHz

[0061]

[Formula 19]

Is

[0063]

[Equation 20]

Using the electromagnetic wave absorbing material (1), an electromagnetic wave absorber having a length of 150 mm, a quadrangular pyramid-shaped portion having a length of 100 mm, and a quadrangular pyramid having a width of 30 mm was manufactured.
The electromagnetic wave absorption characteristics were measured at 10 GHz. The measurement result of the radio wave absorption characteristics is shown in FIG. The electromagnetic wave absorption characteristic at 3 GHz is 2
It is about 0 dB, and the electromagnetic wave absorption characteristic is lower than that of the first embodiment.

(Comparative Example 4) Complex relative permittivity at a frequency of 3 GHz

[0066]

[Equation 21]

Is

[0068]

[Equation 22]

Using the electromagnetic wave absorbing material of, the electromagnetic wave absorber was manufactured with a length of the electromagnetic wave absorber of 150 mm, a length of the quadrangular pyramid portion of 100 mm, and a width of one unit of the quadrangular pyramid of 30 mm, 50 mm, and 100 mm, and a frequency of 100 GHz. Radio wave absorption characteristics were measured. FIG. 8 shows the relationship between the width of one unit of the quadrangular pyramid and the radio wave absorption characteristics. The ratio of the width of one unit of the pyramid to the length of the pyramid is 3
When the width of the quadrangular pyramid is 30 mm, the radio wave absorption characteristic is 50 dB or less, which is lower than that of the second embodiment.

[0070]

As described above, the electromagnetic wave absorber of the present invention is SH
Since a good electromagnetic wave absorption characteristic can be obtained from the F band to the EHF band, by using the electromagnetic wave absorber of the present invention in the anechoic chamber, it is possible to cope with the SHF band to the EHF band in one anechoic chamber.

[Brief description of drawings]

FIG. 1 is a diagram showing a radio wave absorption characteristic at 2 to 10 GHz according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a radio wave absorption characteristic at 100 GHz according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a radio wave absorption characteristic at 100 GHz according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a radio wave absorption characteristic at 100 GHz according to a fourth embodiment of the present invention.

FIG. 5 is a diagram showing radio wave absorption characteristics at 2 to 10 GHz of Comparative Example 1 of the present invention.

FIG. 6 is a diagram showing radio wave absorption characteristics at 2 to 10 GHz of Comparative Example 2 of the present invention.

FIG. 7 is a diagram showing radio wave absorption characteristics at 2 to 10 GHz of Comparative Example 3 of the present invention.

FIG. 8 is a diagram showing radio wave absorption characteristics at 100 GHz of Comparative Example 4 of the present invention.

FIG. 9 is a diagram showing a radio wave absorption characteristic at 100 GHz according to a fifth embodiment of the present invention.

FIG. 10 shows a structural example of a unit absorber.

FIG. 11 shows the relationship between the absolute value of the complex relative permittivity and the return loss.

FIG. 12 shows the relationship between dielectric loss tangent and return loss.

[Explanation of symbols]

 D stand E cone

Claims (2)

[Claims] 1. A complex relative dielectric constant at a frequency of 3 GHz, which is composed of an aggregate of unit absorbers having a conical portion. The magnitude of the absolute value of But 2 or more, 9 or less with a dielectric loss tangent _{tanδ (= ε "r / ε} 'r)
Is made of a dielectric loss material of 0.6 or more, and the total length (H) of the unit absorber is 150 mm or more,
The length (L) of the conical portion is 100 mm or more, and the length (L) of the conical portion is one unit length (W) of the bottom of the unit absorbent body.
3 times or more, and the length (W) of the one unit is 100
A radio wave absorber characterized by being less than or equal to mm. 2. The pyramidal portion is one selected from a wedge shape, a pyramid shape, and a conical shape, and an area of a tip portion thereof is 100 with respect to an area of a wedge shape, a pyramid shape, or a conical bottom surface portion. The electromagnetic wave absorber according to claim 1, wherein the electromagnetic wave absorber is one-third or less.