Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
2001-06-27
2003-04-01
Nghiem, Michael (Department: 2863)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
Reexamination Certificate
active
06541984
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system and a method for measuring electromagnetic waves, and a recording medium in which electromagnetic wave measurement control program is recorded. More particularly, the invention relates to measurement of electromagnetic waves emitted from an electronic device, which uses at least one electronic circuit, as electromagnetic interference.
2. Description of the Related Art
An apparatus or device including at least one electronic circuit (hereinafter called the electronic device) leaks electromagnetic waves out of the electronic device. The leaked electromagnetic waves would be electromagnetic interference causing malfunction and trouble in its peripheral devices. Consequently, electronic devices now put on the market are bound to suffice a gauge with respect to EMI (electromagnetic interference), which gauge is regulated by the Voluntary Control Council for Information Technology Equipment (VCCI).
For this purpose, electronic device manufacturers generally measure EMI of a model of the object electronic device at first, and then improve the electronic device in design based on the result of the EMI measurement on the model. The term “model” of the electronic device means an aggregation of models of one or more electronic circuits and a cabinet; the electronic circuits unitedly serve to perform operations of the electronic device and emit electromagnetic waves; while the cabinet accommodates and protects the electronic circuits and prohibits the leak of electromagnetic waves out of the electronic device.
Generally, the EMI measurement is performed using an EMI measurement system
100
shown in FIG.
8
. In practice, a model (a measurement object) of an electronic device is disposed on a turntable
111
, which angularly moves or rotates through 360 degrees about a vertical axis, in an anechoic chamber
101
. A measuring antenna
112
measures (receives) electromagnetic waves emitted by (leaked from) the measurement object
113
. And a spectrum analyzer
123
in a measurement room
102
analyzes electric field intensities, which correspond to respective frequencies, of the electromagnetic waves received by the measuring antenna
112
.
The distance between the measurement object
113
and the measuring antenna
112
is approximately 3 meters or 10 meters as regulated in accordance with the gauge. The spectrum analyzer
123
is connected to a control personal computer (hereinafter also called the control PC)
124
by a general purpose interface bus (GPIB). The result of analysis by the spectrum analyzer
123
is sent to the control PC
124
as EMI measurement result data, and the control PC
124
stores the result in a storage unit
125
, such as a hard disk.
The measurement object
113
emits electromagnetic waves in all directions. It is enough that the highest electric field intensity of the electromagnetic waves emitted from the measurement object
113
is lower than an intensity regulated by VCCI as an EMI gauge (hereinafter called the VCCI gauge). For this purpose, it is necessary to identify a point where the electromagnetic wave corresponding to the highest intensity is received. To identify the point, the electric field intensity of the received electromagnetic wave is measured under a measurement condition, which is changed by angularly moving or rotating the turntable
111
to change the orientation or posture of the measurement object
113
within the horizontal plane and also to change the height of the measuring antenna
112
within the range from 1 meter to 4 meters.
Although the measurement condition changing in, e.g., the angle of rotation of the turntable
111
or the height of the measurement antenna
112
, may be manually performed, the control PC
124
disposed in the measurement room
102
automatically controls a turntable rotation motor
111
a
and an antenna height control motor
112
a
using a turntable controller
121
and an antenna height controller
122
, which are connected to the control PC
124
by GPIB or the like.
In the conventional EMI measurement, the measuring antenna
112
receives electromagnetic waves under the various measurement conditions in which the angle of rotation of the turntable
111
and the height of the measuring antenna
112
are changed, thereby measuring the electromagnetic waves (emitted from the measurement object
113
) with respect to all directions. Finally, it is discriminated whether or not the highest electric field intensity meets the VCCI gauge.
The intensity of the electromagnetic waves emitted from the measurement object
113
highly depends on not only the electromagnetic waves emitted from individual electronic circuits but also the electromagnetic shield characteristic of the cabinet accommodating the electronic circuits. When the cabinet has a superior electromagnetic shield characteristic, it is possible for the measurement object
113
to meet the VCCI gauge despite of a relatively high electric field intensity of the electromagnetic waves emitted by the electronic circuits. Therefore, if it is impossible for the electronic circuits to reduce generation of the electromagnetic wave any more, the electromagnetic shield of the cabinet is reinforced so that the electromagnetic waves emitted from the measurement object
113
would meet the VCCI gauge as a whole.
As mentioned above, since the electromagnetic shield characteristic of the cabinet is highly regarded satisfaction with the VCCI gauge, there have been proposed systems for measuring (evaluating) the cabinet module in terms of the electromagnetic shield characteristic. Such measurement system is exemplified by Japanese Patent Laid-Open Publication No. HEI 6-43197 (see a measurement system
200
as shown in
FIG. 9
of the accompanying drawings).
The measurement system
200
of
FIG. 9
performs EMI measurement as follows:
First of all, a transmitting antenna (spheric dipole antenna)
214
, which is supposed to be an electronic circuit that emits electromagnetic waves, is accommodated in the cabinet
213
in an experimental site
201
, such as an anechoic chamber. An oscillator (signal generator)
221
in a measurement room
202
is driven so as to produce an electric signal causing the transmitting antenna
214
to emit electromagnetic waves. Then, the electric signal is converted into an optical signal by an electric/optical (E/O) converter
222
, whereupon the optical signal is introduced to the transmitting antenna
214
via a sending optical fiber cable
203
.
The transmitting antenna
214
is in the form of a spheric conductor having such a size as to be accommodated in the cabinet
213
(e.g., 15 cm in diameter). A non-illustrated optical/electric (O/E) converter and a battery or the like are incorporated in the transmitting antenna
214
. The O/E converter in the transmitting antenna
214
converts an optical signal, which has been received through the optical fiber cable
203
, into an electric signal in the form of electromagnetic waves, which are emitted uniformly in all directions over the experimental site
201
.
Electromagnetic waves leaked from the cabinet
213
are received by a measuring antenna (receiver spheric dipole antenna)
212
, and are converted into an optical signal by a non-illustrated E/O converter incorporated in the measuring antenna
212
. The optical signal is input to an O/E converter
223
in the measurement room
202
via a receiving optical fiber cable
204
. The O/E converter
223
then converts back to an electric signal. Finally, the electric signal is received by the receiver
224
, such as a spectrum analyzer.
Since the electromagnetic wave leaked from the cabinet
213
is measured by the above-mentioned manner, it is possible to examine and evaluate the electromagnetic shield characteristic of the cabinet
213
.
The optical fiber cables
203
,
204
serve to connect the oscillator
221
and transmitting antenna
214
, the measuring antenna
212
and the receiver
224
so as to eliminate possible influence on the result of
Hirose Toru
Kobuchi Kenji
Matsukuma Yutaka
Takano Ryouji
Katten Muchin Zavis & Rosenman
Nghiem Michael
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