1. Measuring principle

The measurement chain described below determines the layout of this article: a radio-frequency source must emit an electromagnetic signal that best matches the impulse response of the cooperative target formed by the sensor. An antenna linked to the sensor couples this incident field with the sensor, respecting the impedance matching conditions in a variable environment. The sensor couples certain spectral components of the incident signal into its passband and either back-propagates certain spectral components after storing the energy (resonator), or delays the incident wave (figure 1 ).