JPS5810902A - Electromagnetic wave absorbing body - Google Patents

Abstract

PURPOSE:To obtain a large attenuation of reflection over a wide frequency, by providing the 1st layer of a low impedance active like an absorber and the 2nd layer operating as a tranaformer on a conductor plate. CONSTITUTION:The 1st layer 1 having a low input impedance viewed from other side when one side is short-circuited is provided on a conductor plate A. A layer 2 acting like an impedance transforming action is provided on the layer 1. The layer 1 is constituted with an electromagnetic wave absorber, but it can not be a good electromagnetic wave absorber only with a single layer because of the surface reflection. The layer 2 becomes an impedance transformer between air and the layer 1. Thus, the layer can be a dielectric substance without loss. An excellent electromagnetic wave absorbing body is obtained through the mutual action of the two layers.

Description

[Detailed description of the invention] The present invention relates to a radio wave absorber.

Radio waves 1 aimed at suppressing unnecessary dispersion of electromagnetic waves IL#IL
In the 111L body, the one with the simplest structure is the first one.
As shown in the figure, an electromagnetic wave collection layer 1 is provided on a conductive plate, which is called a nine-match electrolyte absorber.

The matched electromagnetic absorber has a complex dielectric constant (:
), complex magnetic permeability (b) and thickness) are adjusted to obtain the normalized input impedance tlK as seen from the surface of the electromagnetic wave absorbing layer 10.
By doing so, a large return loss can be obtained. However, =
1 holds true only under critical conditions, so the frequency width at which a large return loss can be obtained is very narrow, and the drawback is that there is little tolerance for changes in the optical thickness d.

The object of the present invention is to provide a layer 1 on a conductor plate which has a low input impedance characteristic when viewed from the other side when one side of the tube is short-circuited, and a layer 2 having an impedance modification effect on the layer 1. It is an object of the present invention to provide a radio wave absorber that overcomes the above-mentioned drawbacks by using a laminated radio wave collector.

The present invention will be explained in detail below.

Layer 1 provided by the present invention has a low input impedance characteristic when viewed from the other side when one side is short-circuited, so layer 1 is placed alone on a conductive plate as shown in Figure 1. If only provided, the electromagnetic waves would be reflected on the surface of the layer 1, so it would not be a good radio wave absorber. The layer 2, which also has an impedance modification effect, can be made of a lossless material, so the layer 2 alone cannot serve as a radio wave absorber. As shown in Fig. 2, if materials with two types of characteristics that cannot be used alone as a good radio wave absorber are stacked together as shown in Fig. 2, a radio wave absorber with true tkI# properties can be obtained. can form a body.

In the configuration shown in Figure 2, the normalized input impedance when there is no layer 2 and only layer 1 is present, and the normalized input impedance when layer 2 is present are expressed by the broken lines on the Smith diagram in Figure 3, respectively.
Indicated by solid line. However, the complex permittivity of layer 1 g=4Q−j1
5. Complex permeability;=0.88-jo, 3. Thickness is 1.4
complex permittivity of layer 2:=3. to-jo, complex permeability tμ=1-jO.

The thickness is 41- and was calculated at frequencies from 5caz to 15GHz. In the case of layer 1 alone, the normalized input impedance deviates greatly from the center of the Smith diagram (Z=X), as shown by the broken line in Figure 113, so it can be seen that it is not a good radio wave absorber. However, when the layer 2t is provided on the layer 1, the normalized input impedance passes through the center of the Smith diagram as shown by the solid line in FIG. 3, so it becomes a good radio wave absorber. The solid line in FIG. 4 shows the characteristic shown by the solid line in FIG. 113 in terms of the relationship between return loss and frequency. The broken line in FIG. 4 indicates the complex dielectric constant a'=+12-jO, 55, complex permeability μ=1-jo, 4. Although the calculations were made with the thicknesses t-2 and 4 cm, the frequency width where the return loss increases is narrower than the characteristic shown by the solid line.

For example, in Fig. 4, the frequency width that results in a return loss of 20 dl1 or more is at most soo in the conventional matched absorber.
MHz is 8 degrees, but in the radio wave absorber having the configuration shown in Fig. 2 according to the present invention, it is approximately 3500 MHz', which is significantly lower.

Honestly! In the configuration shown in Figure 2 by IK, layer 2 is air and layer 1
It is thought that it works as an impedance transformer. Therefore, if we understand this from the concept of the 1/4 wavelength impedance conversion method in microwave engineering technology, if the frequency t f Oe where the imaginary part becomes 0 in the normalized input impedance of layer 1 alone is the real part tR, then Layer 2 wave impedance, +Cjw (My = q) t Zv
= 1 m, the thickness is 1/4 of the wavelength corresponding to foK at 1 s in layer 2, and the impedance transformation effect can be completely expressed.

For simplicity, if layer 2 is a lossless dielectric, then 113
According to the broken line in the figure, Rz = 0.27, f o = 9
500MHz and the dielectric constant ξ of 7 layers 2 is g=i=3.7
0. Its thickness is 4.10- and 1-), which is the same as the value used in the calculations described above.

The above is a relationship that generally holds true no matter what value the normalized input impedance of the 1m-layer body shown as broken @7t'' in Fig. 3, but as a result of numerical experiments, 20
R
Good to property is obtained when is 0.5 or less. Therefore, in the structure O electrolyte absorber according to the invention shown in FIG.
By reducing the normalized input impedance of the m body, RtO,
It is important that the value be 5 or less.

This has the advantage that the thickness of the layer 2, which is made into a quarter wavelength, becomes thinner.

Also, setting Rt to 0.5 or less has the advantage of making it easier to select the material for layer 2, since the dielectric constant ε of layer 2 (the dielectric constant of dielectrics is often 2 or more in this frequency range) .

In the above calculation example, layer 2 is a lossless dielectric material and its thickness is assumed to be 174 wavelengths (a simple case); however, it is possible to include some electrical and magnetic loss in layer 2. It is also possible to change the characteristics of return loss by changing the thickness from 1/4 wavelength, etc., but basically there is nothing wrong with giving layer 2 an impedance transformation effect. .

Figure 6 shows the layer 1 using a material in which mold metal and ferrite are mixed with the paint material to increase the electrical loss and magnetic loss, and the above-mentioned R is set to a value of 0.3 at about 11 GHzK. A dielectric material with a dielectric constant C close to 1.3 was used as layer 2, and this was placed in front of the coaxial short-circuit end, and its return loss was measured.

The frequency at which the return loss is 20d1 or more is approximately 8700M
HS to 11,000MHzK, which is a much wider frequency width than conventional matched radio wave collectors1.
*Experimental K1m1! did.

As described above, according to the present invention, it is possible to realize a radio wave absorber that obtains a large return loss over a significantly wider frequency range than conventional matched radio wave absorbers.

[Brief explanation of drawings]

Figure 1 is a diagram showing the structure of a conventional matching type radio wave absorber, IE
Figure 2 shows the structure of the radio wave absorber according to the present invention; The aS diagram is a diagram showing the relationship between R and the frequency width that results in a return loss of 20d1 or more, and Figure 6 is a diagram showing the experimental results of the radio wave absorber according to the present invention. . Dormitory 17 Ant 2 @ Diagram Φ J (Mm)

Claims (1)

[Claims] Set up a K111O layer on the conductor board, and add 2 layers on layer 0 of Hina 1.
In a radio wave absorber constructed by laminating layers of
When one of the 0-layer sides is short-circuited, it has low input impedance when viewed from the L side, and 11
The 120th layer is a radio wave absorber made of K and T41 mold to have an impedance transformation effect.