Committee:

Dr. Gregory Durgin, ECE, Chair , Advisor

Dr. Andrew Peterson, ECE

Dr. John Barry, ECE

Dr. Paul Steffes, ECE

Dr. Michael Buehrer, Virginia Polytechnic Institute

Abstract:

Passive and semi-passive backscatter communication systems such as radio-frequency identification (RFID) experience several challenges that limit their proliferation especially at microwave and millimeter-wave (mm-wave) frequencies, a consequence from the round-trip and low-powered nature of these systems. These challenges manifest themselves in the forms of backscatter-communication range reduction, deep spatial nulls caused by the rapid change in the received power within a small area, or both. To overcome these challenges, a retrodirective-array-equipped backscatter transponder (an RFID tag) is used to replace the standard single-antenna transponder. The benefits of using retrodirective tags are twofold: First, since retrodirective tags that operate at microwave and mm-wave frequencies have similar propagation properties—in terms of power losses and field-of-view—to the current single-antenna RFID tags, which operate at ultra-high frequency (UHF) band, the higher-frequency retrodirective tags maintain the same coverage distance as the UHF tags and permit faster data rates by leveraging the spectrum availability at microwave and mm-wave regimes. Second, retrodirective tags reduce the randomness of the backscatter RFID channel by changing the small-scale statistical behavior of the channel from  double- to single-fading statistics, much like current one-way wireless channels—an  original contribution of this research.