Jérôme Sol

Various estimations of composite Q-factor with antennas in a reverberation chamber

This paper deals with the estimation of the composite Q-factor in a reverberation chamber using one or two antennas (possibly a set of them). Most of Q-factor estimations provided in literature are based on the estimation of the ensemble average of the electric power captured at the terminal of a receiving antenna, the EM field being produced with another one. We first highlight that using two antennas and a vector network analyzer, three different estimations are possible and they are found experimentally to be almost equivalent. Second, removing one antenna the Q-factor may change mainly in the frequency range for which the Q-coefficient of an antenna is no more negligible. Furthermore a post-processing of these two types of measurements allows to extract an estimation of this Q-coefficient alone. This estimation is quite favorably compared to its theoretical estimation based on ideal random field hypothesis.

Measurement Method for Evaluating the Probability Distribution of the Quality Factor of Mode-Stirred Reverberation Chambers

An efficient experimental technique is presented for determining the empirical probability distribution of the quality factor ( Q) of a mode-stirred reverberation chamber. The method is based on triplets of S-parameters that are measured at three locations of the receiver and spectrally averaged across a narrow frequency interval. It avoids the need for detailed spatial mechanical scanning of a field sensor. Statistics of the fluctuations of the stored and dissipated energy can be deduced individually. The effective number of excited cavity modes per stir state M at a selected frequency serves as a degrees-of-freedom parameter of the distribution. The value of M is estimated with the method, by fitting the empirical distribution of Q to a Fisher-Snedecor theoretical distribution using nonlinear minimization. Measurement results across 0.1-6.1 GHz support the validity of the theoretical distribution and the experimental technique, indicating that spectral averaging over a band as narrow a few MHz is sufficient within this frequency range to obtain good agreement. For a chosen averaging bandwidth, M is found to increase rapidly with frequency below approximately 1 GHz in our chamber, followed by a slow decrease at higher frequencies. This frequency dependence is interpreted physically.

Experimental evaluation method for the probability distribution of the quality factor of mode-stirred reverberation chambers

An efficient experimental technique is presented for determining the empirical probability distribution of the quality factor ( Q) of a mode-stirred reverberation chamber. The method is based on triplets of S-parameters that are measured at three locations of the receiver and spectrally averaged across a narrow frequency interval. It avoids the need for detailed spatial mechanical scanning of a field sensor. Statistics of the fluctuations of the stored and dissipated energy can be deduced individually. The effective number of excited cavity modes per stir state M at a selected frequency serves as a degrees-of-freedom parameter of the distribution. The value of M is estimated with the method, by fitting the empirical distribution of Q to a Fisher-Snedecor theoretical distribution using nonlinear minimization. Measurement results across 0.1-6.1 GHz support the validity of the theoretical distribution and the experimental technique, indicating that spectral averaging over a band as narrow a few MHz is sufficient within this frequency range to obtain good agreement. For a chosen averaging bandwidth, M is found to increase rapidly with frequency below approximately 1 GHz in our chamber, followed by a slow decrease at higher frequencies. This frequency dependence is interpreted physically.

Experimental validation of the Statistical Energy Analysis for coupled reverberant rooms

The Statistical Energy Analysis (SEA) is a statistical approach employed to solve high frequency problems of electromagnetically coupled reverberant cavities at a reduced computational cost. The key aspect of this approach is to avoid solving Maxwells equations inside the cavity, using the power balance principle, which leads directly to the ensemble mean response of the system. In addition, the SEA gives an estimate of the standard deviation of the cavitys energy. Moreover, the diffuse field reciprocity formula is used to calculate the coupling coefficient induced by an aperture, which is neither electrically small nor large. The numerical results obtained for two rooms coupled through a circular aperture are compared with experimental data obtained in the reverberation chamber at IETR. After a brief introduction of the motivation for such a method, the SEA equations are presented, and then the experimental setup is described in section III. Finally, the good agreement between simulation and experiment is presented in section IV.

Radiation pattern measurements in reverberation chamber based on estimation of coherent and diffuse electromagnetic fields

In a recent publication, authors showed that measurements of the maximum directivity of antennas were achievable in a reverberation chamber through extraction of the coherent part of the field. In this communication, we extend the method to the measurement of the radiation pattern within the main lobe of radiation. One is thus able to estimate the 3dB aperture of the antenna without need of an anechoic chamber. Some preliminary results are reported and possible improvements are discussed.

Statistical estimation of antenna gain from measurements carried out in a mode-stirred reverberation chamber

This paper proposes for the first time a method for estimating the gain of an antenna in a mode-stirred reverberation chamber. The method is based on the estimation of the Ricean K-factor which provides the relative transmitting power level of the line-of-sight path. Experimental results are compared with anechoic chamber measurements using a set of different antennas.