Experimental demonstration of directive pulsed wavefront generation in reverberation chambers

Abstract

The first experimental demonstration of coherent directive and polarised wave-front generation within a reverberation chamber is presented. This feature is possible with the use of a time reversal electromagnetic chamber, a concept previously introduced by the present authors which mainly relies on the use of time-reversal techniques in a highly reverberating medium. The rationale for developing such a system is to provide the control of a field distribution in time and space without any mechanical movement of either sources or an equipment under test while preserving the high-intensity field levels achieved with reverberation chambers. Introduction:We have recently shown [1, 2] that the use of time reversal techniques, as applied in highly reverberating mediums, allows control of the spatial distribution and polarisation of pulsed wavefronts as long as the system developed is reciprocal and time invariant. The interest of the system proposed, called a time reversal electromagnetic chamber (TREC), resides in the ability to control the wavefront propagation direction, polarisation and time dependence in real time. This is achieved by modifying the excitation signal applied to a set of antennas, placed within the facility. These antennas are referred to as the time reversal mirror (TRM) in the literature [3]. The advantage here is that there is no need of any mechanical movements of the antennas or the equipment under test (EUT) thanks to the multiple reflections on the cavity walls. The procedure for obtaining these signals will be described in the following Section.In this Letter, we prove that the TREC can be implemented in a reallife scenario thanks to an experimental validation of the system.

Multiple-Source Time-Reversal Transmissions in Random Media

“…While increasing B T leads to a clear improvement in the peak contrast, as already well documented in the available literature about TRT, a further important information is that the resulting fields are practically independent of the number of sources involved. This observation confirms the results obtained in (25), stating that the peak-value of the coherent part is proportional to N A , i.e., the individual contributions are practically identical. Still, Fig.…”

“…In the ideal case ofμ r = 0, we expect D(N A ,μ r ) = N A , resulting in a potentially dramatic improvement of the energy contrast. Since (25) proves that the coherent parts of each individual contribution are hardly distinguishable, the improvement of the energy contrast should not be interpreted as solely due to an increase in the overall coherent transmission. The reasons for the improvement in the overall energy contrast is rather to be found in the perfect decorrelation between the residual fluctuations contributed by each source.…”

Emulating an Anechoic Environment in a Wave-Diffusive Medium Through an Extended Time-Reversal Approach

“…This reflection has motivated our proposing an alternative approach based on the use of synthetic sources (Section IV), leading to a new paradigm for TR that is not only suitable for EMC purposes but also brings in new advantages for any test based on submitting an EUT to impinging wavefronts. This approach, that we have named the time-reversal electromagnetic chamber (TREC) was originally introduced in [10] while the first experimental validation was proposed in [8].…”

“…A more powerful technique disposing of these limitations was introduced in [10] and experimentally validated in [8]. It is based on the use of synthetic sources, leading to a generalized technique for the generation of time-reversed wavefronts whose features can be controlled in a very simple manner.…”

“…The dyadic operator describing how a target wavefront will be modified on average by the proposed technique is derived, and numerical examples are provided to illustrate our results. No experimental result is provided, since they are already available in the literature [8], [11].…”