Tunable Phase Shifter With Small Phase Error and Insertion Loss Fluctuation Using a Resonator-Based Structure

A novel resonator-based approach for the design of a tunable phase shifter is proposed in this brief. In this approach, the phase shift is realized by tuning the resonant frequency f(0) of employed resonators. The phase slope K at f(0) is calculated and analyzed by studying a half-wavelength resonator loaded by varactors, so as to achieve small phase errors. It is also found that, the required varactor capacitance ratio Cmax/Cmin is relatively small in this approach and therefore, the series resistance of utilized varactors is almost irrelevant to shifted phases and able to remain stable, resulting in a small in-band insertion loss fluctuation. To validate this approach, a full-circle prototype with a 10% relative operating bandwidth centered at 6.5 GHz is designed and fabricated. Measured results indicate that, this proof-of-concept phase shifter provides a continuous phase shift from 0 degrees to 370 degrees with a maximum phase error of only +/- 17 degrees. The fluctuation of insertion loss is within +/- 0.35 dB. To the best knowledge of the authors, the proposed design is the first tunable phase shifter based on resonators and shows great potential in reducing the phase error and improving the flatness of insertion loss.

Automated summary

A novel resonator-based approach for designing a tunable phase shifter is proposed. The phase shift is achieved by tuning the resonant frequency of the employed resonators. By analyzing a resonator loaded with varactors, the phase slope and required varactor capacitance ratio are calculated to ensure small phase errors and stable insertion loss fluctuation. A prototype is designed and fabricated to validate the approach, showing continuous phase shift with a small phase error and insertion loss fluctuation. The proposed design is the first of its kind and has potential for reducing phase errors and improving insertion loss flatness.