Résumé
Since years, we have developed many near-field experiments using CW millimetre wave sources in the 60-100 GHz band with aim of a high-resolution imagery [1,2,4], a material characterization [3,5], or the evaluation of electronic circuit immunity [6]. Image formation and resolution intimately depends on the probe to sample interaction, which is dictated by the probe type via its predominant electric field component, and also on the signal acquisition technique, which separate near-field and far-field contributions. As such VNA are hugely affected by far-field components that are only removed using a vibrating probe and a lock-in detection, thus requiring home-made mm-wave systems. Nevertheless, measurement results still mix either topological, material dependent and polarization effects that must be elucidated for correct interpretation and optimization. A record resolution of 2 µm @60 GHz was thus obtained with pyramidal antennas (Fig. 1 left) [4]. Work in progress is currently to integrate these performances with a vector detection for more accurate material discrimination. When high spatial resolution is not needed, very simple microwave systems with open waveguides are very efficient and low cost. We built such systems for material characterization with chirped sources [5] to characterize material dispersion, and for a totally different purpose of direct IC perturbation via electromagnetic injection (Fig. 1 right) [6]. This last experiment is novel and reveals possible new threats toward security and cryptography of numeric ICs. Fig.1. Left: 60 GHz high-resolution image of a metallic bow-tie antenna, resolution is l/2500. Right: Perturbation of the response of a RF front-end with a near-field signal @60 GHz as chopped by the yellow square modulation (mm-wave applied on the low level).