Radiated Emissions and Experimental Precautions of Equipment with Cables in GTEM Cells Zaid Muhi-Eldeen Al-Daher #1 , Angela Nothofer #1 , Christos Christopoulos #1 , Steve Greedy #1 #1 George Green Institute for Electromagnetic Research 1 zaid.muhi-al-daher@nottingham.ac.uk Abstract— Any electric or electronic equipment sold within the European Union has to comply with the EC Directive on Electromagnetic Compatibility (EMC). To achieve compliance, the equipment must be tested for radiated/conducted emissions and immunity. A wide range of national and international testing methods and standards are in force such as the IEC 61000-40-20 [1]. However, standards in general lack of describing testing methods for equipment with cables. Since most devices and systems contain leads and cables; the current standards cannot be directly employed. In an effort to approach this crucial matter, we present the outcomes of measurements conducted on an EUT (metal box) with different cable bundle configurations, in conjunction with both, the correlation algorithm given in the standards and the repeatability concerns between different GTEM cells. I. INTRODUCTION There is an apparent lack of standards describing test methods for equipment with cables. The main standards, IEC 61000-4-20 [1] for example, explicitly exclude equipment with external cables. Other standards, like the CISPR 16 and CISPR 22 series [2] [3], include procedures for cable layouts, but these are restricted to specific applications and only valid for a limited frequency range (up to 1 GHz). In the absence of regulations, most of EMC test laboratories would either have their own in-house scenarios or would consider the worst test configuration setup and as a result, repeatability in most cases is unattainable. Therefore, there is a strong demand from industry to improve on repeatability of emission and immunity measurement results by engaging in studies of cable and bundling effects in GTEM cells [1-5].The need to establish more scientifically sound techniques for testing of equipment with cables is not only essential but will also aid in comparing measurement outcomes of different environments to those obtained in GTEM cells. For this purpose, a number of cable bundles have been considered and measured in two different GTEM cells in order to provide an insight into the effects of cable bundles and their repeatability’s in different cells. The latter is another important topic that has rarely been addressed in the literature. Different and even similar size GTEM cells of the same manufacture can perform differently due to their alterable physical construction nature and therefore parts of this paper are devoted to this topic. This paper is organized as follows; section II depicts on important GTEM characterisation methods; section III expounds on cable routing and testing procedures; and section IV presents some measurements precautions and outcomes of experiments conducted in two different GTEM cells which are referred here as to the George Green’s cell (GG) and the National Physics Laboratory cell (NPL). The frequencies investigated range from 30MHz to 2GHz. II. CHARACTERIZATION OF GTEM CELLS As with any RF testing facility, it’s rather important to characterize the GTEM cell prior to any measurements to certify the validity of the recorded data and to ensure reasonable levels of accuracy. There are three important parameters of a GTEM cell operation that ought to be controlled and checked periodically. These are, firstly; the constant characteristic impedance throughout its length which is expected to be 50 +/- 2 . This is usually measured using a Time-Domain-Reflectometry technique which is also used for locating any impedance mismatches across the cell’s length. Secondly, the cells reflections at the input port which are often ignored (also known as the return loss S 11 ), ought to be below -20dB (equivalent to a VSWR value of 1.22) across the frequency range of interest. The GTEM consists of a two termination modes; one is for the surface currents terminated by a 50 resistor network and another is for the RF fields terminated by a wideband pyramidal absorber. Any defects in these termination modes can lead to significant effects on the cell’s response and the measurement system dynamic range. Additionally, any changes in the GTEM geometrical structure (and consequently its characteristic impedance) or the existence of any obstacles within the cell (such as ropes or supporting objects) could easily disturb the propagating fields and the cell’s reflections particularly at high frequencies. Therefore, when using GTEM cells it’s extremely vital to ensure what is measured is purely due to the EUT’s response and not due to a contribution from the cell itself. The obtained S 11 responses of GG and NPL’s GTEM cells are shown in Fig. 1. Strong peaks are observed below 200MHz. These are mainly due to the crossover region from the current to the wave termination whereby at these intermediate frequencies, both terminators are not completely effective [6]. Such frequencies are referred to as the characteristic frequencies of the cell. The difference in their values between the two cells is mainly down to the quality and size of the RF pyramidal absorbers. Further away from the characteristic frequency, S11 peaks tend to occur at 2 λ intervals. Thirdly, the dominance of the primary (vertical) electrical field component and its uniformity within the working volume of the GTEM cell; verification methods and processes can be found in [1]. 978-1-4244-7306-9/10/$26.00 ©2010 IEEE 2010 Loughborough Antennas & Propagation Conference 8-9 November 2010, Loughborough, UK 133   978-1-4244-7307-6/10/$26.00 ©2010 IEEE  brought to you by CORE View metadata, citation and similar papers at core.ac.uk provided by Glamorgan Dspace