Dual-band Class III loaded-line phase shifters

A design method for dual-band Class III loaded-line phase shifters is presented. The center line and the loads of the phase shifter are designed to meet dual-band requirements. Two single-pole-double-throw switches are used to switch between two reactive loads in the two phase states. Four possible reactive loads are considered and closed-form formulas are provided to achieve dual-band operation. For practical design purposes, the switches are modeled as short transmission lines, which can transform the impedance of the loads. The closed-form formulas are modified to incorporate these effects. To verify the design method, a 45° dual-band phase shifter operating at 900 MHz and 1800 MHz is designed and measured. The measured phase shift is 46.1°±2° from 841 MHz to 930 MHz and 44.9°±2° from 1743 MHz to 1924 MHz. The measured return loss is larger than 14.5 dB and 15 dB and the amplitude imbalances are smaller than 0.33 dB and 0.4 dB within the respective bandwidths.