Spatiotemporal modulated multi-functional Non-reciprocal filtering phase shifter with continuously tunable frequency and isolator functionalities

This paper presents RF co-design approach for a multi-function filtering phase shifter that integrate functionalities of a tunable bandpass filter, continuously tunable phase shifter, and isolator into a single circuit. To support detailed design, the analytical spectral S-parameters of the proposed multi-function non-reciprocal filtering phase shifter have been derived. The isolator functionality (i.e. |S₂₁| ≠ |S₁₂|) can be achieved using time-varying capacitors modulated by progressive phase shift sinusoidal signal. The frequency and transmission phase can be simultaneously tuned by varying resonant frequency of resonators. For experimental validation, a microstrip line multi-function non-reciprocal filtering phase shifter is designed, fabricated and measured. The measurement demonstrates a phase shift range of 200^o with forward insertion loss less than 4.9 dB and reverse isolation higher than 30 dB across all phase shift and frequency tuning states. The passband frequency is tuned from 1.42 GHz to 1.75 GHz, providing frequency tunability range of 330 MHz (i.e. tuning ratio: 1:1.2324), while maintaining phase shift range of 200^o at each frequency tuning state. Furthermore, the measured input and output return losses are higher than 12 dB for each phase shift and passband frequency tuning states.