Broadband Passive Circulator with 30 dB Isolation For RF Reflectometry Applications

A broadband passive circulator is designed to provide high isolation better than 30 dB over 1.5 GHz. The broadband phase inversion response is achieved by using the Schiffman phase shifters. As compared to the approach of using directional couplers, the bandwidth can be enlarged by 60% to provide leakage cancellation better than 30 dB. The method is verified by a printed board circuit. The measured result has maximum isolation of 50 dB, and more than 30 dB over the frequency range from 1.8 to 3.3 GHz. The insertion loss is limited within the range of 6-10 dB. The design is applicable to rf reflectometry applications.