The phase difference method for transmit diversity in monostatic RFID systems

For passive backscatter radio frequency identification (RFID) systems, the power incident on the radio frequency (RF) tag can be improved by applying transmit diversity. In this paper, we have demonstrated a new scheme, the phase difference method, in which the phase of the forward links of a multi-antenna monostatic backscatter system are aligned at the RF tag by compensating for the phase difference between different channels. It is shown that dynamic application of transmit diversity can increase the power delivered to the RF tag at multiple points, sequentially.