An active tagging system using circular-polarization modulation

An active read/write microwave tagging system using circular-polarization m odulation as a novel modulation scheme for radio-frequency identification s ystems is presented. The proposed modulation scheme reduces demodulation co mplexity and power consumption on the battery-powered tag, Additional codin g of the circular-polarization modulated data reduces transmission errors d ue to polarization inversion at multipath propagation, In multiple-reader e nvironments, the main jamming threat occurs from power carriers of differen t interrogators, A combination of circular-polarization modulation and freq uency hopping is presented that shows an increased immunity against multipa th phenomena for multiple-tag and multiple-reader environments.