A compact ferroelectric phase shifter using lumped-element quarter-wave-length transmission lines

This paper presents the design and implementation of an all-pass network phase shifter based on a BaSrTiO₃ coated Al₂O₃ substrate for an 802.11b WLAN application. Two different variable resonant circuits are connected between two identical quarter-wave-length transmission lines, resulting in an all-pass network. The size of the phase shifter is reduced by employing Π-section lumped-element networks, and thus the total size is only 2.4 mm x 2.6 mm. The optimum values of the inductor and the maximum phase shift are discussed with respect to the different capacitance and tunability (C_max/C_min) of the capacitor at the series resonant circuits. The measured performance of the phase shifter shows a phase shift of more than 147° is achieved with an average insertion of 3.2 dB from 2.4 GHz to 2.5 GHz. The return loss of the phase shifter in the same frequency range is better than 10 dB for all bias states.