L-kequirements for compliance with worldwide requirements. (e.g., European ... Directive [2] or the FCC rules and regulations to keep this field below a certain ...
TesingOusele Levent Sevgi Do~u* University Electronics and Communication Eng. Dept. Zeamet Sokak, No 21, Acibadem - KadikOy Istanbul, Turkey Email: lsevgi~dogus.edu.tr, levent.sevgi~ieee.org hftp://www3.dogus.edu.trllsevgi
AL-kequirements 11systems contain printed for compliance
circuit boards, upon which requirements with worldwide (e.g., European and Asia-Pacific standards, FCC [1], etc.) are imposed. These must be followed to ensure that radiated emissions from a system are below a specified limit. Certification must be performed at an open-field test site (OFIS), or inside an anechoic chamber. When performing compliance testing, the measurement uncertainty of the instrumentation and antennas must be known. Antennas have calibration factors that vary throughout their frequency range of operation.
Mark Montrose Antennas measure electromagnetic fields developed by electrical circuits. Depending on the design of the system, a radiated field may be too small to be considered a threat to the system itself or to the operating environment; it is the intent of the EMC Directive [2] or the FCC rules and regulations to keep this field below a certain value. If a propagated field is measured by an antenna, accurate values are mandatory for compliance purposes. Those who are not an EMC engineer should pretend to be one for the purpose of this quiz. The answer to the following question is elegant and super easy to compute. The quiz for this issue comes from Mark Montrose. Mark is the principal consultant of Montrose Compliance Services, Inc. His expertise includes design, testing, and certification of information technology (IT) hardware and industrial, scientific, and medical equipment (ISM). He specializes in the international arena for the European EMC Directive. Mark graduated from California Polytechnic State University, San Luis Obispo, California, with BSc degrees in both Electrical Engineering and Computer Science in 1979. He completed his MSc Degree in Engineering Management from the University of Santa Clara, Santa Clara, California in 1983. He is very active within the IEEE, having served on many boards, including the IEEE Press Board and the Technical Activities Board. He also served as a Distinguished Lecturer for the IEEE EMC Society. His citations from EMC-S include three of the four highest honors possible. Technical Achievement for contributions to EMC education internationally; the prestigious Laurence G. Cummings award for years of outstanding contributions to the administration of the Society; and he received Honorary Life Membership in the TEEE EMC Society for creative services in enhancing the field of EMC internationally in 2007. Mark has authored best-selling reference and textbooks, published by Wiley/IEEE Press, all sponsored by the IEEE EMC Society.
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The Quiz for this Issue Determine the magnitude of a propagated field measured by an antenna. Determine if the RF field developed by the printed circuit board inside an enclosure complies with FCC or CE (Conformity Europe [2]) Class B regulatory requirements, and at what frequencies one would observe the signal (Note that Class A and B devices are those that are marketed for use in commercial/industrial/business and home environments, respectively; Class B limits are more stringent than Class A limits). Also, determine the probable source location inside the printed circuit board where the radiated field is being generated. 1
The antenna is located at a distance of I mn from the test system.
2.
There is a 125 MHz crystal and two oscillators, of 25 MHz and 400 MHz each.
3.
The processor has a 1:4 PLL using the 400 MHz oscillator signal as input.
4.
The processor has a data-book value of 5A/800 ps for dI/dt for the core circuitry.
5.
There are multiple clock outputs from the processor, all at various harmonics of the three input frequencies.
6.
The routed transmission-line length of all clock traces is 4.5 in (11.43 cm).
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Vol. 50, No. 3, June 2008
7.
The values of decoupling capacitors sprinkled throughout the design are 100 nF, 10 nF, and I nE (hint: calculate the anti-resonant frequencies developed to see if a harmonic of any clock source exists at these frequencies).
8.
There is an open-frame 500 W switching power supply operating at 200 kHz without a secondary line filter and three-wire power cord that includes ground.
Good luck, and welcome to the world of electromagnetic compatibility, as seen through the eyes of an EMC engineer.
References 1. The Federal (http://www.fcc.gov).
Repeat the above calculations for 3 m and 10 m, to determine if the signals measured follow typical extrapolation factors, taking into consideration the measurement uncertainty value of the antenna.
Communications
Commission
(FCC)
2. Directive 2004/1 08/EC of the European Parliament and of the Council, of 15 December 2004, on the approximation of the Laws of Member States relating to EM Compatibility (http://ec.europa.eu/enterprise/electr~equipment/emc).
Antenna Calibration for EMC Tests and Measurements Levent Sevgi1 , Soydan CQakir2, and Gonca gakir3 1Doou§
University, Electronics and Communications Engineering Department Zeamet Sokak 21, Acibadem, Kadik~y, Istanbul, Turkey
2TUBITAK-UME, 3Kocaeli
National Metrology Institute, Gebze, Kocaeli, Turkey
University, Electronics and Communication Eng. Dep., Kocaeli, Turkey
Abstract An antenna is calibrated in an open-field test site (QETS) and/or an anechoic chamber, which facilities themselves need calibration. The procedures for calibrated test sites (CALTS) are given in the CISPR and ANSI/EEE standards. The characteristic parameter for calibr-ated test-sites is the normalized site attenuation (NSA). Theoretical calculations and practical measurements of normalized site attenuation are first presented. Antenna-factor (AF) and/or absolute-gain measurement methods are then reviewed. Finally, an alternative antenna calibration approach is given in this tutorial. Keywords: Antennas; accreditation; calibration; traceability; open-field test site; anechoic chambers (electromagnetic); normalized site attenuation; standard site method; reference antenna method; equivalent capacitance substitution method; antenna factor; three antenna calibration method; antenna radiation patterns; electromagnetic compatibility
1. Introduction David has just received his university diploma, and started to work with the National Metrology Institute as a new antenna engineer. The director of his department told him that there have been a few EMC antennas left in the depot for a long time. His first task will be to make them ready for EMC measurements. It was only last year he took the "Antennas and Propagation" lecture. He remembered that he enjoyed it a lot, while exercising useful virtual tools and antenna software. However, antenna calibration and IEEE Antennas and Propagation Magazine, Vol. 50, No. 3, June 2008
antenna factor (AF) measurements are new to him. These concepts were rarely discussed in that lecture. Where does David need to start? What steps should he follow? What kind of procedures should he apply? On what site and with what instruments should he perform the measurements? As a fresh, ambitious engineer, of course, David never thought to ask for help from his colleagues. He had just read the two tutorials published in the "Testing Ourselves Column" [1, 2], and had become familiar with some antenna and basic measure215
