This paper deals with the ability to perform radar cross-section (RCS) pattern measurements within reverberation chambers (RCs). The characterization principle is based on the estimation of the back-scattered field from the target at a farfield distance and takes advantage of the diffuse field within the RC. A frequency sweep of scattering parameters is achieved in presence and absence of the target installed on a rotating mast and the pattern is retrieved from these measurements. This paper explains the underlying theory and discusses the impact of several parameters on the performances. This includes the effect of the stirrer rotation which enables to enhance the dynamic range of the measurements. Experiments in two different RCs show the relevance of the proposed approach for RCS extraction and confirm the theoretical analysis.

This paper presents the antenna gain pattern estimation from backscattering coefficient measurement performed within a reverberation chamber (RC). The antenna backscattering coefficient is measured for two load conditions, namely an open circuit and a 50 Ω load, enabling to distinguish the radiation and structural modes from the total backscattered field. This approach is applied to the measurement of the gain pattern of a Vivaldi antenna at 6.5 GHz and compared to a conventional transmission-type measurement within an anechoic chamber. The main lobe of the radiation pattern is in good agreement between both measurements. The difference between maximal gains, retrieved after a reference measurement using a metallic plate, is equal to 0.04 dB. A second validation is performed using a log-periodic antenna at 3.5 GHz, showing less than 0.76 dB difference over the measured angular range. To the author's knowledge, this is the first time that a contactless gain pattern measurement is performed and validated within an RC.

This paper presents the evaluation of the Radar Cross Section (RCS) pattern of a rectangular metallic plate from Reverberation Chamber measurement. It is seen that the measured RCS strongly depends on the environment and especially on the stirrer position. An approach based on averaging the measurement over a stirrer rotation is presented and allows increasing the measurement accuracy when compared to simulated data.

Abstract. Nuclear magnetic resonance (NMR) experiments are usually carried out at very high and homogenous magnetic fields. However, portable systems have emerged in recent years at low fields, offering many advantages like easier maintenance and open design that permit us to imagine a variety of coil configurations in order to maximize the homogeneity of the static field B0 and the radio-frequency field B1. The wire winding distribution based on space harmonics suppression (SHS) of the cosine current density distribution offers new possibilities of producing homogenous static fields B0. In this work, an extension of the SHS method, allowing homogeneity enhancement and flexibility of the coil design, is presented. The efficiency of the method is demonstrated through the construction of homogenous magnetic field coils dedicated to a very low magnetic field (8 mT) 1H NMR spectrometer. The performance of these coils in terms of magnetic field intensity and homogeneity as well as self-heating behavior is compliant with in planta experiments for agronomic studies.

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