Field sampling of incoherent sources

Abstract

The problem of characterizing random sources from near-field measurements performed on a domain DI and of devising the random field sampling procedure is tackled by a stochastic approach. The presented technique is an extension of that introduced in [A. Capozzoli, et al., Field sampling and field reconstruction: a new perspective, Radio Sci., vol. 45, 2010] and successfully adopted to experimentally characterize deterministic (CW) radiators and fields. Under the assumption that the source is wide sense stationary, quasi-monochromatic and incoherent, its intensity is reconstructed by time-domain field measurements aimed at extracting information from the mutual coherence of the field on DI. The linear relation between the field coherence on DI and the source intensity is inverted by using the Singular Value Decomposition (SVD) approach, properly representing the source intensity distribution by exploiting the a priori information (e.g., its size and shape) on the radiator. The sampling of the radiated random field is devised by a singular value optimization procedure of the relevant linear operator. Numerical results sketch the performance of the approach

Experimental Field Reconstruction of Incoherent Sources

“…We underline that emission measurements for the EMC check of device must be carried out, according to the standards [49], in the frequency domain by sweeping in frequency and measuring the emissions at each frequency. The signals recorded for each sampling point have been then transformed in the time domain so to work out an estimate of the coherence matrix under the hypothesis of ergodicity [30,32].…”

“…where · denotes an average over the ensemble of source realizations, which can be computed as a time average under the hypothesis of ergodicity [30,32]. Accordingly, the field is wide sense stationary and its mutual coherence function Γ e (x 1 , x 2 , τ ) can be expressed as…”

“…The presented technique is an extension of that introduced in [21,22] and successfully adopted to experimentally characterize deterministic (CW-multifrequency) radiators and fields [19]. Under the assumption that the source is wide sense stationary [28] and quasimonochromatic [29], its second order statistics can be reconstructed by time-domain NF field measurements aimed at forming the mutual coherence of the measured field itself [30]. The linear relation between the coherence of the NF and the second order statistics of the source can be inverted by using the SVD [31] approach, properly representing the source statistics by exploiting the a priori information (e.g., its size and shape) available on the radiator.…”

“…For such a problem, preliminary results have been presented in [30]. Here, we illustrate experimental results aimed at showing how the approach is capable to correctly reconstruct the intensity distribution of random radiators with a number of measurements which is significantly smaller than those required by more "standard" techniques, as it has been already proven in the CW, multi-frequency or narrow-band cases [21,22,30]. In this paper, random incoherent sources have been produced by properly slotting one of the walls of a reverberation chamber with one or more narrow apertures.…”