Sensitivity analysis for wireless dielectric reflectometry with modulated scatterers

Load-modulated scattering antenna technology has been very efficiently developed these last decades. Low-cost RFID tags for identification and low-invasive Modulated Scattered Technique (MST) probes for EM field measurements constitute two relevant examples. More recently, remote sensing applications of modulated scatterers have been considered. In such applications, the general objective is to remotely retrieve some local property of a material or environment under test via its impact on a modulated scattering probe. This paper is more particularly focused on the case where the sensing mechanism is expected to result from the change of the probe impedance, due to variations of the refractive index in its close vicinity. This problem is usually addressed under empirical and global viewpoints, by combining numerical modeling and optimization. Often, such a blind approach may result in some disappointment. This paper aims to develop a more comprehensive analytical-based approach, thanks to a general reciprocity-based formulation. Inspired from standard reflectometer techniques, the ternary load modulation scheme is shown to remove specific difficulties inherent to wireless reflectometry such as propagation effects or misalignment between the probe and the reader antennas. The test case of center-loaded dipoles is considered for the sake of illustration.