The read range of passive, backscatter radio frequency (RF) tags is limited by the power delivered to the RF tag’s integrated circuit. This project seeks to increase the power delivered to passive backscatter RF tags using transmit diversity – a method that uses multiple antennas and channel knowledge to deliver power to the tag. By adjusting the phase of the signal transmitted from each reader antenna to cancel the phase delay of the channel, the signals from each antenna add constructively at the RF tag; hence, the power delivered to the RF tag is maximized. This technology can improve the read range and reliability for radio frequency RF tags in applications with time-varying channels — e.g., backscatter sensors operating near moving people or where radio frequency identification (RFID) tags cannot be confined to a portal.
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