Realization and measurements of a novel Dual Frequency Circulator for POW-RFID

In this paper we present the first results for multi-carrier RFID systems incorporating a Dual Frequency Circulator (DFC). Besides simulations of the RF front-end itself to verify the theoretical working principle, we also present the realized DFC. The main advantage of a system with a DFC is the increased efficiency of the transponder rectifier due to the use of a Power Optimized Waveform without causing intermodulation problems. The use of two single carriers without increasing the average power compared to a traditional single carrier RFID system, leads to higher efficiencies. The DFC further includes leakage cancellation circuits without the need of an actual ferrite circulator to increase the reader sensitivity. Measured leakage cancellation in the test setup of up to 71 dB and 61 dB were reached for the path from Tx1 to Rx1 and Tx2 to Rx2, respectively. The crosstalk from Tx1 to Rx2 and Tx2 to Rx1 can be suppressed by up to 66 dB and 60 dB, respectively. Additionally, the DFC was used in a system as it is generally used for passive RFID systems. We conducted first measurements including the DFC in a system and compared it to a state of the art RFID system, with much focus on the communication link. The signal to noise ratio at the Rx ports of the DFC were approximately increased by at least 4 dB. The latest results show that the system including the DFC is useable in passive RFID systems to increase the rectifier efficiency in the transponder as well as the receiver sensitivity which is important for the operational communication link from transponder to reader.