Reconfigurable 1.5-2.5-GHz phase shifter with 360^o relative phase-shift range and reduced insertion-loss variation

This paper proposes a varactor-based reflection-type phase shifter that allows for 360^o relative phase-shift range and reduced insertion-loss variation over the entire frequency tuning range. In particular, a novel and compact reconfigurable 90^o coupler is devised and it is, theoretically, able to achieve perfect return loss and isolation at each tuning state. Thus, when this 3-dB coupler is terminated with two reflective loads, the phase shifter can operate at a wide range of center frequencies. Moreover, a tunable transformation network is proposed to optimally reduce the insertion-loss variation within the 360^o continuous phase-shift range for any operational frequency. Experimental results show that the fabricated phase shifter, in a frequency range of 1.5-2.5 GHz, can realize 360^o relative phase-shift range with greater than 16.5 dB in return loss and less than 3.8 dB in insertion-loss variation.