Continuously Tunable Phase Shifter Based on Defected Ground Structures

A continuously tunable phase shifter with low loss characteristic is present in this paper. This phase shifter is based on a 4th order lowpass filter constructed by a 50 Ω microstrip line and defected ground structures (DGSs). High-Q varactors are loaded on the etched DGSs on the ground to adjust cut-off frequency of the employed lowpass filter. Therefore, phase shift can be continuously tuned while cut-off frequency is changed. Equivalent circuit of a unit cell has been given to illustrate the mechanism of phase variation. The proposed phase shifter has been designed at L band and simulated using full-wave EM solver Ansys HFSS. Simulated results demonstrate a tunable phase shift of 98° at the operation frequency of 2 GHz when the bias voltage varies from 1 V to 10 V. This phase shifter shows a maximum insertion loss of 0.5 dB and return losses at both ports are more than 10 dB during the entire tuning process, which indicates good impedance matching.