Staggered pattern energy harvesting and retro-directive backscatter communications for passive RFID tags and sensors

Abstract

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.