Backscatter enhanced retrodirective systems

The aim of this work is to provide novel solutions for robust radio communication for longer range microwave RFID (Radio Frequency Identification), systems through the use of retrodirective arrays (RDA). The retrodirective Array is a self-steering antenna array which automatically transmits a radio signal back in the direction of signal arrival without the requirement of complex signal processing. Analogue implementation of retrodirective arrays allows real time, multi functional and signal tracking operations at low physical complexity and power consumption. To date the majority of the research undertaken on retrodirective array technology, focuses heavily on passive implementation such as transponder and retroreflector for radar application. The work presented in this thesis places largely emphasis on the integration of active retrodirective array as a basestation technology in RFID situations, where high quality performance and multifunctional operations are required. The systems presented in this thesis exploit various features of retrodirective array such as automatic beam forming, multipath signal recombination and multiple beams forming. Theoretical analysis of retrodirective arrays and implementation techniques for various applications are discussed. By deploying different retrodirective array architecture such as Van Atta and phase conjugating at the RFID interrogator and transponder, the self-steering action of retrodirective anays is shown to relax antenna alignment requirements and lead through to range extension for RFID systems. The retrodirective signal recombination/focusing effect in multipath rich environments improves signal strength at the target position. Therefore, instead of transmitting a high EIRP line-of-sight signal to the interrogator, the same power density can occur by utilizing the presence of multipath.EThOS - Electronic Theses Online ServiceGBUnited Kingdo