Near-Field Test Bench for Complete Characterization of Components Radiated
Emissions
D. Baudry, L. Bouchelouk, A. Louis, B. Mazari
IRSEEM, 1 rue du Maréchal Juin BP 14, 76131 Mont Saint Aignan cedex
Abstract - A completely automatically near-field
mapping system has been developed within IRSEEM
(research institute for electronic embedded systems) in
order to determine the electric and magnetic fields
radiated by electronic systems. This paper presents
experimental results realized on a microstrip line and a
quadrature hybrid junction. The different components of
the electric and magnetic fields are measured and
compared to 3D electromagnetic simulations.
1. INTRODUCTION
The electromagnetic near field mapping appears to be
extremely useful in the EMC design of industrial, active
or passive circuits. This kind of measurements allows a
better knowledge of the electromagnetic characteristics of
internal components of devices in comparison with
conventional techniques of circuits analysis which can
only be applied to the ports. Cartography of the
electromagnetic field can be used during the design
process to localize area of high emission levels and to
prevent interference problems due to some components.
Different near field measurement methods exist such as
direct measurement [1], modulated scattering techniques
[2], …
A near-field measurement test bench has been developed
within IRSEEM (research institute for electronic
embedded systems) to collect electromagnetic field close
to systems of any size with a good mechanical accuracy.
All components of the electric and the magnetic field can
be measured with the test bench by using several probes.
In this paper, we present a validation of the bench on two
passive microwave planar circuits : a microstrip line and a
quadrature hybride junction.
2. EXPERIMENTAL SETUP
The system is based on a direct measurement method. The
field sensor is connected to the spectrum analyser and is
mounted on a five axes robot (see Figure 1).
Figure 1: The near field test bench.
The mechanical resolution of the system is 10 µm in the
three directions (x, y, z). For the two rotations, the
accuracy is 0.009°. The scanning volume is 200 cm
(x)*100 cm (y)*60 cm (z). A PC drives the probe
displacement above the device under test (DUT) and
acquires data provided by the spectrum analyzer (see
Figure 2).
PC Spectrum
analyzer
Microwav
e generator
Figure 2: Synoptic of the test bench.
To measure the different components of the electric and
magnetic fields, we use three kinds of probe. Two probes
are used for the electric field and one probe for the
magnetic field.
Probe
z
y
x
DUT
The probe used for measuring the normal component of
the electric field (Ez) consists in a 50Ω open-ended
coaxial cable oriented parallel to this field. This probe
(EPZ1) has an outer diameter of 2.79mm and an inner
conductor diameter of 0.51mm.
To measure the other components of the electric field (Ex
and Ey) we use a balanced wire dipole [3] made with two
adjacent coaxial cables and a hybrid 180° junction to
balance the dipole (Figure 3). Each arm of the dipole has
a length of 5mm and is made with the center conductor of
the coaxial cable. A spectrum analyzer measures the
difference between the two signals of the junction output
ports. By rotating the probe with an angle of 90°, Ex and
Ey components of the electric field are measured.
Figure 3:Electric dipole probe.
The last probe used to measure the magnetic field consists
in a small wire loop [4]. The square loop is made with
center conductor of two adjacent coaxial cables (Figure
4). Each side of the square loop is 3mm long. Coaxial
cables are connected to a hybrid 180° junction and a
spectrum analyzer measures the difference between the
two signals of the junction output ports. The probe
measures the magnetic field perpendicular to the loop.
The three components of the magnetic field are then
obtained by rotating the probe with an angle of 90°
around the three x, y and z directions.
Figure 4:Magnetic loop
3. CHARACTERIZATION OF A 50Ω
MICROSTRIP LINE
In order to validate the test bench, a simple microwave
circuit is measured and experimental results are compared
to simulated ones. Simulations are obtained with a 3D
electromagnetic simulations software : CST Microwave
Studio. The sample circuit tested is a 50Ω microstrip line
in short circuit at a frequency of 1GHz. The line has a
length of λ (wavelength of radiation). Substrate’s height
and relative permittivity are 0.8mm and 4.4 respectively.
All the measurements are realized with a distance between
the probe and the DUT of 1mm and a step of 800µm
between each acquisition points. The microstrip line is
oriented along the x axis and the center of the line is at
y=0mm. hybrid 180°
junction ∆
Waves propagating along the microstrip lines are
characterized by a quasi-TEM mode (Transverse
Electromagnetic Mode). So the nontransverse field
components are small in comparison to the transverse
components. Therefore, we only measure the transverse
components (y and z) of the electric and magnetic field.
Patterns of the electric field on the microstrip line is given
on Figure 5.
dipole
coaxial cable
Ez Ey
z
y
x
Figure 5: Patterns of the electric field on the microstrip
line.
The amplitude of the measured signal detected by the
EPZ1 probe is shown in left picture on Figure 6 (For all
the following mapping figures, the left picture represents
the measurement and the right one the simulation). We
can see that fields maximum is located on the center of the
line as expected by the theory. Measurements show also
the standing wave patterns due to the short circuit. The
standing wave patterns has a period of λ/2 with the
maximum of field at λ/4 and 3λ/4. We can note a good
agreement between measurement and simulation.
hybrid 180°
junction ∆
coaxial cable
loop
Figure 6: Mapping of the normal (Ez) component of the
electric field.
For the transversal (Ey) component of the electric field
(see Figure 7), maximums are located on the edges of the
line.
Figure 7: Mapping of the Ey component of the electric
field.
Patterns of the magnetic field on the microstrip line is
given on Figure 8.
Figure 8: Patterns of the magnetic field on the microstrip
line.
The Hy component of the magnetic field (see Figure 9)
presents the same profil that the Ez component of the
electric field with a shift of λ/4.We can do the same
comparison between the Hz component of the magnetic
field (see Figure 10) and the Ey component of the electric
field.
Figure 9: Mapping of the Hy component of the magnetic
field.
Figure 10: Mapping of the normal (Hz) component of the
easurements on the microstrip line show the ability of
4. MEASUREMENT OF A QUADRATURE
he following circuit is a quadrature hybrid junction (see
Figure 11: Device topology.
For the normal component of the electric field (see Figure
magnetic field.
M
the test bench to deliver maps of the different components
of electric and magnetic fields. Next step will be to
calibrate the different probes to make absolute
measurements of the electromagnetic field.
HYBRID JUNCTION
T
Figure 11). The coupler is realized with microstrip line on
FR4 substrate (εr=4.4 and h=0.8mm) material. The device
is tested at 1GHz. Port 1 is connected to the generator.
y
z
x
1
2
3
4
12 and Figure 13), we can see that the field is maximum
over the microstrip line between port 1 and port 3 and
between port 1 and port 4, while the field is less important
on port 2. As expected by theory, transmission is
maximum between port 1 and ports 3 and 4 and port 2 is
isolated. We can also note a good agreement between
simulations and measurements.
y
z
Hy
Hz
x
Figure 12: Measurement of the normal (Ez) component of
the electric field.
Figure 13: Simulation of the normal (Ez) component of
the electric field.
The other components of electric and magnetic field are
presented on Figure 14 to Figure 18. Measurements made
with the near field test bench are coherent with
simulations.
Figure 14: Mapping of the Ex component of the electric
field.
Figure 15: Mapping of the Ey component of the electric
field.
Figure 16: Mapping of the Hx component of the magnetic
field.
Figure 17: Mapping of the Hy component of the magnetic
field.
Figure 18: Mapping of the Hz component of the magnetic
field
5. CONCLUSION
In this paper, we have presented a near-field test bench
used to characterize electromagnetic interference
problems. The bench is able to collect all components of
the electric as well as the magnetic field. The data
provided by the near-field test bench can be used to
localize high or low field areas. Measurements are in
progress on active devices.
6. REFERENCES
[1] Y. Gao and I. Wolff, “A simple electric near-field
probe for microwave circuit diagnostics”, in IEEE MTT-
S ..Int. Microwave Symp. Digest., Vol. 3, San Fransisco,
CA, pp. 1537-1540, 18-20 June, 1996.
[2] T. P. Budka, S. D. Waclawik, M. Rebeiz, “A Coaxial
0.5-18 GHz Near Electric Field Measurement system for
Planar Microwave Circuits Using Integrated Probes”,
IEEE MTT, vol. 44, no. 12, December 1996.
[3] J.J. Laurin, Z. Ouardhiri, J. Colinas, “Near-field
Imaging of Radiated Emission Sources on Printed-Circuit
Boards”, IEEE International Symposium on
Electromagnetic Compatibility, pp. 368-373, 2001.
[4] S. Kazama, K. I. Arai, “Adjacent Electric Field and
Magnetic Field Distribution”, IEEE International
Symposium on Electromagnetic Compatibility,
,Minneapolis, pp. 395-400, 2002.
INTRODUCTION
EXPERIMENTAL SETUP
CHARACTERIZATION OF A 50( MICROSTRIP LINE
MEASUREMENT OF A QUADRATURE HYBRID JUNCTION
CONCLUSION
REFERENCES