A Sparse Retrodirective Transponder Array With a Time Shared Phase-Conjugator

With the recent emergence of various radio frequency identification (RFID) applications, the desire for simpler, more efficient, and lower cost passive transponders has increased. Retrodirective arrays have been demonstrated as a good candidate for such systems due to their unique function of high-speed, automatic source tracking. A four-element, high-performance retrodirective transponder array is presented in this paper. The architecture uses a sparse array design to reduce the amount of radiating elements. A time sharing switching feature is used in conjunction with this architecture to further reduce RF hardware requirements and cost of the system. The switching network can also serve as a built-in modulator for simple data transfer tasks.