Analysis and Exploitation of Multiple Antennas Interaction in the Near-Field

This thesis is structured in two parts. The former, and main one, introduces a novel solution for portable devices to exploit their existing communication antennas for bi-directional near-field wireless re-charging, without compromising their far-field properties. To demonstrate the concept, the GSM 900/1800MHz and the 433MHz, bands are adopted for the far-field communication and for the near-field wireless recharging, respectively. Starting with a full-wave analysis of two identical printed dipoles faced at several distances, then each antenna is fed by a frequency-selective three-port network in order to simultaneously ensure data communication at the higher frequency bands and wireless re-charging at the lower frequency band. As a proof-of-concept a system prototype is built. Port insulation, RF-to-RF and RF-to-DC power efficiency measurements demonstrates that a wireless charging and communication it is possible with the proposed link arrangement and it can thus be used to exploit the charged state of an available device to recharge another one, without limiting the respective communication capabilities. The latter part focuses on a fast design method for an RFID antenna, used as a transducer, to realize an RFID bent sensor tag. The method exploits a space mapping technique, using a coarse circuit model (CM) and a fine electromagnetic model (EM). The CM represents, in a CPU-time efficient way, the antenna transducer states to fast evaluate the sensor tag efficiency. The EM model is then used to verify the sensing states and to rapidly prototype the antenna. To demonstrate the procedure, the corresponding EM-based and CM input impedances of a T-matched dipole are compared for several sensing states over a frequency band of 840-890MHz. An innovative Figure of Merit has been. Finally the sensor tag efficiency is computed to compare the CM results with respect to the EM ones and in order to validate the entire space mapping technique.