This work introduces an optimal backscatter and energy harvesting solution for radio frequency identification (RFID) by using N antennas with N ports called a staggered patterned and retro-directive (SPAR) tag. By using multiple ports and a unitary scattering matrix on the SPAR tag, the structure is able to create multiple orthogonal radiation patterns to improve range of passive RFID tags. This is demonstrated on a 5.8 GHz RFID tag using a two-element patch antenna array fed by a 90˚ hybrid. In addition to canonical designs, new SPAR structures are hypothesized with optimized size, bandwidth, etc. A co-simulator is developed capable of searching a vast space of possible feed networks with N-by-N ports that meet the requirements of a unitary scattering matrix. A new structure that meets the 2-by-2 SPAR scattering matrix requirements is presented to demonstrate the capabilities of the software. The software can also be generalized to discover new physical structures of larger N−by−N SPAR tags or other microwave devices.
Michael Varner’s publication at IEEE SPAWC 2018 is now available for download in IEEExplore. Entitled “Reflection of Modulated Radio (ReMoRa): Link Analysis of Ambient Scatter Radio Using Perfect Pulses“, the work explores the spectral properties for perfect pulse modulation of ambient backscatter. The impact on this modulation scheme and the link budget is explored. The ideas in this paper will allow long-range communications by embedding information on existing RF sources and reflecting them to collection nodes. There are numerous applications in machine-to-machine, internet-of-things, and sensor networks.
At the recent IEEE Antennas and Propagation Symposium (APS), Mike Varner presented work by Alhassoun, Varner, and Durgin on the use of perfect pulses to suppress specular reflections on a highly reflective surface. A classic use of this problem is the reduction of radar signatures of aircraft hangers and other buildings near runways. The flat faces of these structures can often produce large radar returns/multipath that distort ranging by either the air traffic control tower or a descending plane. This presentation provides a unique use of the perfect pulse theory invented here at Georgia Tech to build a solution.
In this work, the author discusses the unique challenges and opportunities of implementing a frequency-hopping scheme for backscatter communications. The author even designs and implements a frequency-hopping algorithm on the GTPG’s custom frequency hopping board, consisting of a programmable microcontrollers and voltage-controlled oscillator + phase locked loop chips.