US 3631492 A
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United States Patent 11 3,631,492
 inventors Kunihiro Suetake 56 References Cit d 10-11, Minami 3-chome, Meguro-ku, UNITED STATES PATENTS Tokyo; Yasutaka Shimizu 2969 om yams, 2,875,435 2/1959 McM llan 343/18 A 3,234,549 2/1966 McMillan. 343/18 A nyma'shimdlapm 3 315 259 4/1967 Wesch 343/18 A  Appl No 863,447  Filed Oct. 3, 1969 Primary Examiner-T. H. Tubbesing  Patented Dec. 28, 1971 l Attorney-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.  Priority Oct. 9, 1968  Japan  43/73677 ABSTRACT: A superwide band wave absorbing wall of a thin multilayer type, which comprising a plate-shaped dielectric  g g gggfggiggg f WALL layer, a plate-shaped magnetic material lossy material, and a metal plate backing said magnetic material lossy material  U.S. Cl. 343/ 18 A plate. The plate-shaped dielectric layer may be made in a plu-  Int. Cl H01q 17/00 rality of the same layer and also may be provided at front sur-  Field of Search 343/18 A face a tapered part made of a dielectric lossy material.
Patented Dec. 28, 1971 Z Sheets-Sheet 1 0 mm s o M m T E l. N mUH R 4m N T 3? A wV W5 A KY DISTANCE Patented Dec. 28, 1971 3 531 492 2 Sheets-Sheet 2 NEYS 1 MU L'Il-LAYER WAVE ABSORBING WALL x This invention relates to superwide band wave absorbing walls.
There are recently required wave-absorbing walls for frequencies above about 100 MHz. for the researches of antennae for space communications and colored televisions. However, a wave-absorbing wall in which a conventional dielectric material has been used has had such defects that, as its wall thickness has been about 1.5 m., its cost has been high and the effective space of the anechoic chamber has been made small. Further, a wave-absorbing wall in which only a conventional magnetic material is used has a defect that its characteristics at frequencies higher than 1,000 MI-Iz. are low. Also a wave-absorbing wall in which a ferrite and zigzag type dielectric absorbing plate are combined has a defect that as it is of a zigzag structure, it is diflicult to manufacture.
The present invention is to provide a multilayer type waveabsorbing wall which is thin in total thickness and is yet high in the frequency characteristics, by eliminating the above-mentioned defects and combining dielectric layers and magnetic material layers.
Other objects and advantages will become apparent as the following description proceeds, taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a perspective view showing an embodiment of the present invention.
FIG. 2 is a graph showing a profile of the distribution of attenuation constants in the dielectric layer part in the present invention.
FIG. 3 is an impedance chart for explaining the frequency characteristics of the reflection coefficient of the present invention.
FIG. 4 is a graph showing the frequency characteristics of the embodiment of the present invention.
Now, the present invention shall be explained with reference to an embodiment for I MI'Iz. In FIG. 1, l is a tapered part of a dielectric lossy material and 2, 3, 4, and 5 are a plurality of plate-shaped dielectrics, which are piled respectively in the form of a sandwich on the base part of the dielectric lossy material of the above-mentioned tapered part 1. 6 is plate-shaped magnetic material lossy material laminated on the plate-shaped dielectric 5. 7 is a metal plate backing the above-mentioned plate-shaped magnetic material 6. The total thickness of the absorbing wall of this embodiment is 53 cm. corresponding to about 1/6 the minimum used wave length (of 300 cm.) and is the smallest of the thicknesses of absorbing walls of this kind now available.
An exemplary method of constructing the wave-absorbing wall of the present invention shall now be shown explained with reference to the embodiment, and subsequently it shall be explained how the wave absorbing wall according to the present invention is excellent over the conventional walls.
First of all, the distribution of attenuation constants of the materials of the dielectric layer parts 1 to 5 is shown in FIG. 2. In FIG. 2, the abscissa represents the distance measured from the front surface of the absorbing wall, and the ordinate represents the attenuation constants of these materials. It is already known that, in such step-shaped curve distribution, the
frequency characteristics of the high frequency band part of the absorbing wall are improved (See "A new method of designing thin multilayer matching loads for microwaves" by Shimizu and Suetake, .Iour. Inst. Elect. Comm. Engrs, Japan, Mar, 1968).
In order that the voltage standing wave ratio on the front surface of the absorbing wall will be less than l.2 for each frequency f in the lower frequency band, the load impedance Z of the above-mentioned dielectric layer part must not be allowed by be of any value but must have a value in a certain range. Now, if such ranges are calculated, they will be represented by such circles and their interiors as are shown in FIG. 3 for respective frequencies. (In this case, the numerals attached to the circles represent respective frequencies). That is, the way of reviewing this chart is as follows. IN the chart for example, the circle off 200 MHz. shows that, if a Ioa having such impedance as is within this circle is arranged on the back surface of the above-mentioned dielectric layer parts 1 to 5, the standing wave ratio of the absorbing wall will be less than 1.2 at a frequency of 200 MHz. Therefore, in order to realize such impedance load, a magnetic material 6 with the metal plate 7 attached to the back surface is prepared and the frequency characteristics of its impedance are so selected as to be those marked with small circles (o) in FIG. 3. If it is combined with the above-mentioned dielectric layer part, an absorbing wall of a standing wave ratio of less than 1.2 at a frequency above I00 MHz. will be easily obtained. The frequency characteristics of the embodiment obtained as described above are shown in FIG. 4, in which frequencies are taken on the abscissa and standing wave ratios are taken on the ordinate. As evident from this graph, the absorbing wall according to the present invention is of a thickness of 53 cm. and has characteristics of a standing wave ratio of less than 1.2 at a frequency above I00 MHz.
It should be appreciated, while an embodiment of the absorbing wall for a frequency band above MHz. has been here explained, the present invention is not to be limited to such a particular one, and that various absorbing walls for any desired frequency bands can be also obtained by properly selecting the materials of the dielectric layer and magnetic material layer.
As described above, the present invention has effects that the entire structure is of a thin layer and simple, that a superwide band absorbing wall can be easily obtained, and further that, in case it is used for an anechoic chamber, the effective space of the chamber will become large.
What is claimed is:
l. A multilayer-type wave-absorbing wall comprising a plate-shaped dielectric layer disposed at the side upon which the incidence of waves occurs, a magnetic lossy material layer disposed rearwardly of said dielectric layer, and a metal plate disposed rearwardly of said magnetic lossy material layer.
2. A multilayer-type wave-absorbing wall according to claim 1 wherein aid plate-shaped dielectric layer being provided at its front surface with a tapered part of the dielectric lossy material.
3. A multilayer-type wave-absorbing wall according to claim 1 wherein said plate-shaped dielectric layer being formed of a plurality of component plate-shaped dielectric layers as piled on each other.
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