This paper describes a novel wireless passive sensors interrogation technique based on a three-dimensional analysis. Variable impedances acting as passive sensors are remotely read by a 24 GHz bistatic FMCW radar at distances of 2.0 meters and 5.5 meters. The radar performs a mechanical beam scanning to receive the electromagnetic echo level response in a volume. Several estimators are compared to calibrate and quantify the passive sensor input impedance. From this impedance the physical quantity of interest (temperature, pressure, strain …) can be derived.