A microwave sensor system based on reverse modelling of the array factor

The paper describes a possible circuit implementation of a low-cost, non-invasive sensor system for wireless structural monitoring. It consists of a two-tags array and one reader: the former is the sensor placed on the structure to be monitored, the latter is placed in a predetermined position with respect to the array phase center. Particular attention is devoted to the antenna design, in order to manage cross-polarized signals in the system activity. The simple operating principle of the system exploits the far-field array-factor definition, in particular the positions, on the reader side, of the nulls of the received radiation surface. A proof of concept of the sensor is experimental demonstrated for two operating frequencies, 2.45 and 5.8 GHz.