Reflection/transmission tuner analysis and applications

The authors present analysis and applications of a versatile coupled-line-based impedance tuner suitable for use in reflection or transmission mode. The impedance tuner can be used to implement complex backscatter modulation schemes for RFID applications while simultaneously tuning the tag antenna in the presence of external loading. A high isolation band-tunable quasi-circulator is developed, which employs the impedance tuner to provide mismatch and leakage cancellation. The quasi-circulator features a peak isolation of over 60 and 30 dB isolation bandwidth of over 5%. The isolation can be tuned across a bandwidth of over 40%.