JP2889090B2 - Radio wave absorber evaluation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for evaluating electromagnetic wave reflection characteristics of a radio wave absorber.

[0002]

2. Description of the Related Art Radar frequency waves, broadcast frequency waves, unnecessary electromagnetic radiation, and the like fly through the air, and they are reflected and scattered by structures such as buildings to interfere with each other. Therefore, it may cause noise for devices using digital high frequency signals. A radio wave absorber is used to prevent these. Therefore, it is necessary to evaluate the characteristics of the radio wave absorber.

In a low frequency band of 100 MHz or less, since one wavelength is as long as 3 m or more, it is difficult to evaluate the electromagnetic wave reflection characteristics of the radio wave absorber. One of the conventionally used measuring methods is a free space standing wave measuring method.
Since an absorber to be evaluated that is installed in an area of about wavelength × 2 wavelengths is required, the apparatus becomes large-sized, and is not practical as an evaluation apparatus in a low frequency band.

On the other hand, a large rectangular coaxial tube having a structure in which a standard type radio wave absorber having a square bottom surface can be installed between an inner conductor and an outer conductor by enlarging the size of a coaxial tube used for material evaluation measurement is free. In the lower frequency band than the spatial standing wave measurement method, the measurement can be performed accurately using a small number of samples. However, if the standard type radio wave absorber is installed, the impedance will be 63Ω, and since the measuring system such as the transmitting / receiving equipment and the coaxial cable is 50Ω, impedance mismatch will occur at the terminals and the reflection of the DUT will occur. Since not only waves but also unnecessary reflections are synthesized, measurement becomes impossible. As a method of removing the unnecessary reflected wave, there is a method of applying a gate using a time domain because the positions of the unnecessary reflection and the reflection of the device under test are different. It is necessary to keep a sufficient distance from the installation position, and it is necessary to lengthen the evaluation device.

[0005]

When the internal impedance of a radio wave absorber evaluating device having an inner conductor and an outer conductor is different from the impedance of a measuring system such as a transmitting device, a receiving device, and a coaxial cable, the electromagnetic wave input from the transmitting device is Since an unnecessary reflected wave due to impedance mismatch exists, it is impossible to accurately measure the amount of reflection of the radio wave absorber.
An object of the present invention is to eliminate the unnecessary reflected wave so that the characteristics of the radio wave absorber can be measured accurately and easily.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to an impedance in which a resistance which is a difference between an internal impedance of a radio wave absorber evaluating device and an impedance of a measuring system is connected in series to an inner conductor. Provided is a radio wave absorber evaluation device having a converter at both ends.

[0007]

When the electromagnetic wave emitted from the transmission device is guided to the radio wave absorber evaluation device, a part of the electromagnetic wave is reflected due to impedance mismatch at the terminal portion. The reflected wave or transmitted wave from the terminal can be matched at the terminal by the series resistance connected to the inner conductor, so that unnecessary reflection does not occur. In addition, the reflection described above can be removed using a simple correction method, so that unnecessary reflection does not occur.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A radio wave absorber evaluating apparatus 1 shown in FIG. 1 has an outer conductor 2 having a main body 4 having a square cross section, and an inner conductor 3 having a main body 5 having a square cross section which is separated from the inner side surface of the outer conductor 2. Has. The straight bodies 4 and 5 of the inner and outer conductors 2 and 3 have tapered portions 6, 7, 6 'and 7' at both ends thereof. , 8 '. The tapered portions 7, 7 'at both ends of the inner conductor 3 converge and close, and resistors 9, 9' are connected in series at the convergence point.
The resistors 9, 9 'are arranged in the converters 8, 8'.

A tapered or pyramid-shaped radio wave absorber 10 of an object to be measured is arranged in a space between the main bodies 2 and 3 as shown in FIG. Electromagnetic waves are transmitted to the terminals 11, 1 integrated with the converters 8, 8 '.
1 ′, the electromagnetic wave reflected from the device under test 10 and the electromagnetic wave transmitted through the device under test 22 are measured.

The electromagnetic wave input from the terminal 11 or the terminal 11 'is transmitted in the radio wave absorber evaluating apparatus as follows. (1) When an electromagnetic wave is introduced from the terminal unit 11, (1-1) the conversion unit 8 from the terminal unit 11 (input from the measurement system to the evaluation apparatus) The electromagnetic wave input to the terminal unit 11 from the 50Ω measurement system ,
Since the combined impedance from the terminal portion 11 to the tapered portions 6 and 7 is 76Ω according to the equation (1), impedance mismatch occurs, a part of the electromagnetic wave is reflected, and the remaining electromagnetic waves are reflected by the tapered portions 6 and 7 and the main body 4. , 5. Combined impedance = impedance of series resistor 9+
Impedance of taper portions 6 and 7 = 13Ω + 63Ω = 7
6Ω Expression (1) (1-2) Transformation unit 8 from object to be measured (reflected wave from object to be measured) The electromagnetic wave that reaches object to be measured 10 is partially reflected by object to be measured 10, Via the tapered portion, the terminal portion 11 again
To reach. At this time, the combined impedance of the conversion section 8 from the tapered sections 6 and 7 is 63Ω according to the equation (2), and no unnecessary reflection due to mismatching occurs. Combined impedance = impedance of series resistor 9+
Impedance of terminal part 11 = 13Ω + 50Ω = 63Ω
.. (2) Equation (1-3) From the part to be measured to the converter 8 '(transmitted wave from the object to be measured) On the other hand, the electromagnetic wave transmitted through the object to be measured 10 is a tapered part 6'
After passing through 7 ', it reaches the conversion unit 8'. Taper 6 ',
The combined impedance of the conversion unit 8 'from 7' is
Since the value is 63Ω according to the expression (3), no unnecessary reflection occurs. Combined impedance = impedance of series resistor 9 '+ impedance of terminal 11' = 13Ω + 50Ω = 6
3Ω ... Equation (3)

(2) When an electromagnetic wave is introduced from the terminal section 11 '(2-1) From the terminal section 11' to the conversion section 8 '(input from the measurement system to the evaluation device) From the 50Ω measurement system to the terminal section 11' Since the combined impedance of the electromagnetic wave input to the terminal portion 11 'and the tapered portions 6' and 7 'from the terminal portion 11' is 76Ω according to the equation (4), impedance mismatch occurs at the terminal portion 11 ', and a part of the electromagnetic wave is The reflected electromagnetic waves are guided to the tapered portions 6 ′ and 7 ′ and the main bodies 4 and 5. Combined impedance = impedance of series resistor 9 ′ + impedance of tapered portions 6 ′ and 7 ′ = 13Ω + 63
Ω = 76Ω (4) Equation (2-2) Conversion part 8 ′ from object to be measured (reflected wave from object to be measured) Part of the electromagnetic wave reaching object to be measured 10 by object to be measured 10 The light is reflected and returns to the terminal portion 11 ′ via the tapered portion.
To reach. At this time, the converter 1
From equation (5), the combined impedance at 1 'is 63Ω, and no unnecessary reflection due to mismatching occurs. Combined impedance = impedance of series resistor 9 '+ impedance of terminal 11' = 13Ω + 50Ω = 6
3Ω Equation (5) (2-3) Conversion part 8 ′ from object to be measured (transmitted wave from object to be measured) On the other hand, the electromagnetic wave transmitted through the object to be measured passes through taper parts 6 and 7 and is converted. It reaches the part 8. Since the combined impedance of the conversion section 8 from the tapered sections 6 and 7 is 63Ω according to the equation (6), unnecessary reflection does not occur. Combined impedance = impedance of series resistor 9+
Impedance of terminal part 11 = 13Ω + 50Ω = 63Ω
・ ・ ・ ・ ・ ・ (6) terminal part 11 or terminal part 11 'of this wave absorber evaluation device
When an electromagnetic wave is input to the terminal, reflection occurs at the input terminal portion, but other unnecessary reflected waves are completely removed by the above principle. The reflection at the terminal can be removed by the following calibration method.

(Measurement Method) An object to be measured is placed in the radio wave absorber evaluation apparatus, and the amplitude component and the phase component of the reflected wave and the transmitted wave are measured, respectively. The measured values at this time are shown in FIG.
When the reflected wave S ₁₁ sample, S ₂₂ sample, and transmitted wave S ₂₁ sample are used, the calibration value from which the reflection at the terminal is removed is (7),
The reflected waves S ₁₁ cor and S ₂₂ cor and the transmitted wave S ₂₁ cor are obtained by equations (8) and (9).

[0013]

(Equation 1)

[0014] _S 11air, S 22air, S 21air is reflected wave S ₁₁ including an amplitude component and the phase component when not installed object to be measured wave absorber evaluating apparatus, S _22, the transmitted wave S ₂₁
Is the measured value.

Here, RPR _S11 , RPR in equation (1)
_S22 and RPR _S21 are represented as in Equation 2.

[0016]

(Equation 2)

[0017]

As described above, according to the present invention, in an electromagnetic wave transmission device having an inner conductor and an outer conductor such as a coaxial tube, it is possible to provide a converter in which a series resistor is connected to the inner conductor and to provide a simple structure. Unnecessary reflection in the absorber evaluation apparatus can be completely removed by the calibration method, so that the reflected wave and the transmitted wave of the measured object can be accurately measured.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an evaluation device according to an example of the present invention.

FIG. 2 is a front sectional view of an example of the present invention.

FIG. 3 is an S parameter circuit diagram.

[Explanation of symbols]

 2 outer conductor 3 inner conductor 4,5 body 6,7,6 ', 7' taper section 8,8 'conversion section 9,9' resistance 10 DUT 11,11 'terminal section

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-105853 (JP, U) Patent 2514862 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 22/00 -22/04 H05K 9/00

Claims (3)

(57) [Claims] 1. A radio wave absorber evaluation apparatus having a radio wave absorber to be evaluated installed in a space between a metal inner conductor and an outer conductor, and an impedance converter having series resistors inserted at both ends of the inner conductor. . 2. The radio wave absorber evaluation apparatus according to claim 1, wherein the series resistance corresponds to a difference between the internal impedance and the impedance of the measurement system. 3. The radio wave absorber evaluation device according to claim 2, wherein the radio wave absorber is tapered.