Low-loss analog and digital reflection-type MEMS phase shifters with 1:3 bandwidth

Broad-band analog and digital reflection-type phase shifters (RTPSs), showing constant phase shift over 1:3 bandwidth, have been developed using microelectromechanical systems (MEMS) technology. Two-unit RTPSs centered at two different frequencies have been cascaded to achieve flat phase responses over a wide frequency band. Each phase shifter uses airgap overlay coplanar-waveguide couplers for low-loss 3-dB coupling and bridge-type MEMS capacitors for reflective terminations. The fabricated analog phase shifter shows the average insertion loss of 3.5 dB, and maximum phase error of +4.9(degree) from 15 to 45 GHz. The 2-bit digital RTPS shows reduced maximum phase error of +-2.8(degree) together with a comparable insertion loss of 3.1 dB from 5 to 15 GHz. The details of the circuit design, analysis, and fabrication procedures are presented together with the measurement results. Compared with the similar constant phase shifters using semiconductor diodes and transistors, the micromachined RTPS of this study shows superior performance in terms of phase errors, insertion losses, and bandwidth.