辐射问题研究

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