This book offers state of the art information about a novel range of applications for electromagnetic reverberation chambers. It is written by international experts in electromagnetic theory, electromagnetic compatibility (EMC), and antenna design and measurement. For each application area a renowned researcher introduces the general concepts and then describes the recent advances in that field. The following topics are thus addressed in the context of reverberation chambers in the 9 chapters of the book: Calibration of reverberation chambers with the "well stirred condition" method; Performance assessment of the most popular stirring techniques for broadband tests; Probabilistic model in the context of radiated susceptibility tests; Over-the-air testing of wireless devices; Material absorption and dosimetry for animal exposure; Characterization of antenna efficiency and radiation pattern; Radar cross section estimation. Finally, a concluding chapter identifies and explores some of the exciting developments and open issues that represent emerging trends in reverberation chamber research. The book is aimed at advanced students and researchers in signal processing, antenna design or EMC who need to know about new applications of reverberation chambers.
Other keywords: vibrating intrinsic reverberation chambers; innovative applications; frequency performance assessment; time-domain performance assessment; well-stirred condition method; electromagnetic reverberation chambers; radiated susceptibility test; probabilistic model; material absorption; stirring techniques; over-the-air testing; heavily loaded reverberation chambers; dosimetry; wireless devices; animals exposure; antenna radiation pattern; reverberating enclosures; antenna efficiency; radar cross-section estimation; stirring conditions
Pioneer works about electromagnetic reverberation chambers (RC) have been made at the university of Naples in the 1970s under the direction of Paolo Corona and in parallel in the United States at the National Bureau of Standard (which is right now the National Institute of Standards and Technology (NIST)). At the origin, the main purpose was to perform electromagnetic compatibility (EMC) measurements, in particular shielding effectiveness of cables and connectors, radiated susceptibility tests and total radiated power of systems or subsystems (a brief history of the work made during the first 20 years (roughly) after the appearance of RCs can be found in). The last 20 years have shown a spectacular diversification of the RC applications in parallel with a spectacular growth of the number of RCs installed all around the world and of people working with this facility.
In this chapter, the well-stirred condition method is presented in the case of a mechanically stirred reverberation chamber. This method is able to determine the frequency fwscwhere the well-stirred condition of an reverberation chamber is achieved. The method focusing on the ability of the reverberation chamber to produce stirred contributions compatible with the well-stirred condition presents the advantage to be independent of the type, location and orientation of the emitting antenna if the antenna is sufficiently matched over the whole bandwidth. The method based on S11 measurements of an antenna is simple to set up (only a VNA is required) and fast (a few minutes). The method relies on a clear definition of the well-stirred condition and uses threshold values related to theory. Finally, the method is usable in the presence of an EUT (even a heavily lossy one) provided that the antenna is located sufficiently far from it. This has the double advantage to give an overview of the reverberation chamber performance in the exact conditions of the subsequent test and also allows the field strength generated in the reverberation chamber for a given injected power to be predicted. The inherent uncertainty of the method outputs combining the overall uncertainty of the reverberation chamber itself and of the PCF process is estimated to be lower than 10%.
This chapter presents a "critical" review of the stirring techniques based on some fundamental criteria; among them are the complexity of the required setup, the available space within the reverberation chambers and the ease to assess the efficiency of the technique. In addition, performance of the most common techniques are assessed by taking advantage of the "well-stirred condition method" presented in details in the first chapter of this book. In reality, the method is extended in this chapter to all the techniques able to be implemented quite easily in the RC of the XLIM Laboratory. The results presented in the first chapter with the RC mechanically stirred, which is traditionally the most used stirring technique, are considered as the reference results and allow the performance of all the tested stirring techniques to be compared.
In this chapter, a complete framework able to characterize the performance of a vibrating intrinsic reverberation chamber and of its associated stirring process in both frequency and time-domains has been presented. In the frequency-domain, the "well-stirred" condition method is extended to the case of VIRCs, using N successive vector network analyzer sweeps. The method highlights the fact that VIRC performance in the frequency-domain are similar to the ones obtained in a mechanically stirred RC of similar volume. In the time-domain, the approach aims first at determining the decorrelation time td. In reason of the continuous movement of the metallized tent, it is shown that the decorrelation time td(defined as the minimum time interval to respect in order to collect two independent samples at the same location) can be lower than 1 second using the straightforward proposed stirring process. Second, no periodical repetition of the stirring process as a function of time has been observed. This fundamental result implying a proportionality between the number of collectable independent samples and the acquisition time could contribute to decrease the uncertainty budget of RC measurements (for instance antenna efficiency or over-the-air testing of wireless devices) with respect to measurements performed in classical parallelepipedic RCs. Moreover, there is probably, at a given frequency, an upper limit potentially linked to the modal density at this frequency.
This chapter details a probabilistic model recently published quantifying the risk r to observe no susceptibility of a faulty EUT during an RS test as a function of n. The method is general as the risk r can be computed for any (fictitious) EUT susceptibility level by quantifying the probability of the maximum stress imposed onto the EUT to be greater. This approach presenting the great advantage to be independent of the EUT size and directivity is, therefore, applicable on any EUT. The model presented is applicable in the case of an RS test done in constant wave mode when the EUT susceptibility is verified after the application of each stirring configuration, or in other terms when all the successive configurations are not analyzed together.
This chapter covers some of the key issues related to the use of heavily loaded reverberation chambers for OTA testing of wireless-device performance. It specifically adresses the cases where the communication signal is spread over a wide modulation bandwidth and must be demodulated and cases in which a particular PDP is to be replicated. Metrics used to characterize the chamber configuration, such as the reference power transfer function, spatial uniformity, isotropy, and chamber decay time, are not significantly different from those used in prior work of the EMC/EMI community. However, their application to the case where significant correlation exists between frequencies and spatial samples requires additional consideration.
This chapter discusses the role of energy absorption in a reverberation chamber and some related applications. The composite Q-factor is the key indicator of the total amount of losses in a reverberation chamber since it quantifies the energy stored (per unit of time) per unit of transmitted/dissipated power. In a first part of this chapter, we settled the definition of this composite quality factor and described a method to estimate it in different ways with a set of two antennas. The scattering parameters at antenna ports enable to estimate the composite Q-factor in three different ways and enables to check for the enhanced backscattered coefficient. Obviously, an accurate enough estimation requires a high number of RC states. We suggest that averaging over small frequency bands is a solution to minimize intrinsic statistical variation of Q-factors estimated from a limited set of stirrer positions. The first application consists of evaluating the average absorption cross section of any piece of material within the RC. This absorption coefficient is retrieved from the contrast of quality factors measurement before and after putting the material in the chamber. For simple geometries of the inserted absorber, it is possible to estimate its efficiency. Moreover, from the knowledge of the intrinsic EM properties of homogeneous and thick (with regard to the skin depth) materials, we showed that the measured AACS computed from the modification of the Q-factor is consistent with the theoretical one. This last fact was at the origin of a specific calibration procedure for mm-wave RC dedicated to animal exposure. This is the second application of this chapter. In order to calibrate the EM dose during exposure, the power density in the RC must be controlled and proved to be consistent with the expected temperature rise. Using a rectangular homogeneous phantom, mimicking the properties of animal's skin, we show that the temperature rise at its surface and measured with an infrared camera was indeed predictable. On a theoretical point of view, the measurement of the Q-factor, the knowledge of intrinsic parameters of the phantom and the properties of the diffuse field in the RC fully determine the heat deposition on the phantom surface. Solving the heat-equation gives then the correct temperature rise prediction with a reasonable accuracy.
In this chapter, five typical methods to measure the antenna radiation efficiency in an RC have been discussed. The standard reference antenna method is general and performs well, but a reference antenna is needed. Three non-reference antenna methods overcome the problem to use a reference antenna of known efficiency. However, they require additional prerequisites or antennas. The time-domain methods are time efficient, especially for UWB antennas. All these methods have different advantages and disadvantages, thus there is not a "best" method. A suitable method can be chosen depending on the measurement conditions, requirements, and type of antennas under test. Statistical analyses of the measured antenna efficiency are also given in this chapter. In particular, the presented method offering an accurate theoretical analysis on the measurement uncertainty has been illustrated on the standard reference method.
An increasing interest appears recently in order to characterize in an oversized (with respect to the wavelength) metallic enclosure (i.e., a reverberation chamber (RC) if a mode stirring process is necessary or a reverberating enclosure (RE) if not) the radiation pattern of antennas, a measurement traditionally done in an anechoic cham-ber. This measurement that may appear counter-intuitive to perform in such a highly multipath environment (see also the case of radar cross-section measurement in such enclosures discussed in Chapter 9) presents some non-negligible advantages. Indeed, such metallic enclosures are not disturbed by the external electromagnetic environ-ment while being substantially less expensive than an anechoic chamber, especially in reason of the absence of absorbers within the facility. Moreover, the efficiency of absorbers used in anechoic chambers is not constant with the frequency and may be insufficient in the lowest frequency range (i.e., below a few hundred of MHz, a value depending on the absorber dimensions).
This chapter is dedicated to recent advances in a rather unexplored range of applications. It deals with the ability of performing radar cross-section (RCS) measurements, using a reverberation chamber (RC). If feasible, it would allow broadband measurements in a simple Faraday cage at a much lower cost, absorbers being no longer required. However, using a RC for RCS measurement seems inadequate at a first glance. Adding an object under test in the chamber consists in introducing another scatterer, indistinguishable in a rich multipath environment offered by the RC.
As a conclusion for this book, we have tried to identify some important open issues the community of RC users will have to face in the future. The following topics are dealt with: OTA test for new protocols; Anechoic measurements; Chaotic cavities; VIRCs; and Future EMC strategy in the transportation industries.
Supplementary File for Electromagnetic Reverberation Chambers: Recent advances and innovative applications
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