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 <inline-formula> <tex-math notation="LaTeX">$f_{0}$ </tex-math></inline-formula> of employed resonators. The phase slope K at f0 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 <inline-formula> <tex-math notation="LaTeX">$\text{C}_{\mathrm{ max}}/\text{C}_{\mathrm{ min}}$ </tex-math></inline-formula> 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° to 370° with a maximum phase error of only ±17°. 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.