Low-loss cascadable MEMS distributed X-band phase shifters

A wideband distributed coplanar-waveguide (CPW) phase shifter has been developed for X-band operation. The design is based on the distributed MEMS transmission line (DMTL) loaded with high capacitance-ratio varactors. The varactors are fabricated using a series combination of MEMS bridges and fixed-value MIM capacitors. A high-capacitance ratio varactor (1.5-2.5) results in a large loading on the CPW line and therefore a large phase shift. A distributed phase shifter was fabricated on a 500 μm quartz substrate, and achieved a true-time delay operation from 1 to 10 GHz with a reflection coefficient less than /spl sim/15 dB, and 1800/dB of insertion loss at 8-10 GHz. It is possible with this design to cascade the DMTL to result in 2- and 3-bit phase shifters with excellent wideband performance at X-band frequencies.