Bruno Audone

The use of MUSIC algorithm to characterize emissive sources

This paper applies the MUSIC algorithm to finite-distance sources without omnidirectional radiation patterns to identify their positions and radiation characteristics. This technique can be used to obtain the image of a radiating source and therefore can be successfully utilized in many disciplines such as EMC, biomagnetic data evaluation, geophysical studies. The canonical cases herein discussed may be generalized to define a methodology to localize and characterize emissive sources in the same manner as the radar imaging technique is used for passive reflecting targets.

A new approach to immunity testing

The need of performing immunity tests with the aim of meeting the functional safety requirements is addressed proposing an approach based upon the statistical data processing of test results, which allows to determine the susceptibility threshold of the device under test (DUT) and its safety margin intended as the distance between the actual DUT performance in the presence of the susceptibility signal and the susceptibility threshold. This represents a clear improvement with respect to the present situation of EMC standards based upon simple qualitative checks, which do not offer any warranty of safety because it is not clear how far the DUT is from its susceptibility threshold: even if the device under test is declared to be immune in normal operative conditions it may happen that a simple environmental effect such as temperature variation has catastrophic consequences.

Uncertainty evaluation of conducted emission measurements by means of conformal mapping

Conformal mapping is used to investigate the uncertainties of conducted emission tests on power supply lines, taking into account the requirements of test components specified by most EMC standards. Unfortunately, there is no clear common approach in the definition of the coupling devices located between the EUT (equipment under test) and the EMI receiver. Therefore, test reproducibility may be affected and an additional contribution may be added to the overall uncertainty of the test.

The use of adaptive filters in the suppression of interference on signal lines

Adaptive active filters can be successfully used to filter out interference on power and signal lines, where passive filters have great limitations especially if interference is at low frequency and is known to drift slowly. Three possible solutions of adaptive filters are examined. Conventional LMS filters generate intermodulation products, which in some cases are not acceptable. The novel solution of training phase LMS (least mean square) filter, which has the best filtering characteristics, is described and simulated.

Interaction between test site and amplifier nonlinearities in susceptibility tests

Susceptibility tests performed with nonlinear power amplifiers may give nonrepeatable test results or even show susceptibility levels at the spurious frequencies which may be wrongly related to the frequency characteristics of the specified emitted signal. The control of the emission system can be performed in three different ways: local-field AGC, net-power AGC, and incident-power AGC. The first two modes may interact with the test site forcing the amplifier to work in saturation and therefore to generate a large amount of spurious signals which do not represent the wanted test signal. The test site interacts with the instrumentation because of reflections from the environment (mainly the ground plane) and-the high values of VSWR of the transmitting antenna. The incident-power AGC which is adopted in most recent EMC specifications may overcome these problems but only if the test site is carefully standardized-at least in the same manner as done for emission tests. >

Radiated Fields in Close Proximity

The problem of harmonic generation in susceptibility testing is discussed; in close proximity testing it may become more critical with respect to the case of conventional radiation immunity tests used in statistical signal processing.

Field uniformity in radiated field immunity tests

The calibration requirements of radiated immunity tests performed in semi-anechoic chambers and fully anechoic rooms are analyzed by means of electromagnetic computational tools to verify the severity of the allowed tolerance requirements of their anechoic environments. Some proposals of alternative figures of merit directly related to the electric field distribution in the test area or volume are illustrated taking into account the need of proposing system metrics capable of rendering radiated immunity tests comparable, reliable and repeatable.

Median filters to suppress interference

Median filters can be successfully used to eliminate impulsive interference and noise on signal lines overcoming the difficulties of linear filters, which are not suitable to address this problem. Median and median type filters have been popular for the last forty years; they found their main applications in image and speech processing. Unfortunately they are rather unknown to the EMC community. The purpose of this paper is to illustrate the practical implementation of median filters in system applications addressed to meet the demanding requirements of EMC problems.

Processing of EMC data with factor analysis

Large amount of data are obtained from simulation or experimental activities. In most cases they are not of easy interpretation; factor analysis provides a tool to highlight those situations of major interest in EMC related to interaction mechanisms between electrical, geometrical and mechanical parameters. The case of field to cable coupling, a typical immunity problem, is presented to illustrate the procedure which can easily be extended to more complex situations including conducted and radiated emission patterns.

The rationale to define when EMC antennas shall be calibrated

The calibration of EMC antenna has always been a frustrating subject for most EMC laboratories for various reasons. On the other hand in many cases EMC antennas are recalibrated when it is not strictly necessary. This paper proposes a procedure to establish when EMI antennas shall be calibrated on the basis of technical considerations without making reference to abstract quality assurance rules.