Continuously Tunable True-Time-Delay Phase Shifter Based on Transmission Lines With Simultaneously Reconfigurable Impedance and Phase Constant

This article reports on the design of continuously tunable true-time-delay (TTD) phase shifter using transmission lines with simultaneously reconfigurable impedance and phase constant. The reconfigurable transmission lines are designed with an independent control of equivalent series inductance and capacitance, which thus can achieve tunable phase constant (i.e., phase shift) while maintaining constant characteristic impedance. With the perfect matching property for all tuning states of phase constant, the proposed reconfigurable transmission-line units are cascaded to construct a tunable TTD phase shifter. For the proof-of-concept demonstration, three TTD phase shifters based on the proposed reconfigurable transmission lines with phase shifts of 45°, 90°, and 180° at center frequency of 1 GHz (f
₀
) are designed and fabricated. The measured 2-unit phase shifter is tuned from -128° to -175° at f
₀
while the insertion loss is better than 0.8 dB. The return loss is better than 15 dB from dc to 1.28 f
₀
. For the 4-unit phase shifter, the phase shift tuning range is 93° at f
₀
with insertion loss better than 1.4 dB. The return loss is better than 15 dB from dc to 1.03 f
₀
for all states. The 8-unit phase shifter shows a measured tuning range of 183° at f
₀
with insertion loss better than 2.0 dB. The return loss is better than 15 dB from dc to 1.03 f
₀
for all states. The measured continuously tunable delay time is 507 ps. The measured 1-dB compression point is better than 12 dBm at f
₀
for all states. As compared with the state-of-the-arts, the main merits of the proposed phase shifter are large phase shift/unit and wide matching bandwidth.