A Ka-band RF-MEMS phase shifter approach based on a novel dual-state microstrip line

This paper presents the design and realization of a 3-bit RF-MEMS based phase shifter at 34 GHz using a very-low complexity and highly reliable RF-MEMS technology on silicon. The three bits of the circuit use different techniques to achieve the necessary phase shifts. One new design technique, the dual-state microstrip line, is enabled by the presented RF-MEMS technology and changes the effective epsiv_r of a microstrip transmission line by lifting part of it into the air. This leads to a change in the electrical length of the microstrip transmission line, which in turn results in a phase shift. The related insertion loss of the 45deg bit is less then -0.35 dB and a matching better -19 dB for both switching states. Further on, a loaded-line bit with 45deg of phase shift is realized by switching between a capacitive and an inductive load. The capacitive switching state shows an insertion loss of -0.4 dB and a matching better -13 dB, while the inductive load has an insertion loss of -0.7 dB and a matching of -25 dB. The loaded-line bit combined with the dual-state microstrip line is used for the 90deg-bit. An additional miniaturized switched line phase shifter is implemented for the 180deg state. The three bits were combined and measured in all states. The results of the 3-bit phase shifter are shown with a mean insertion loss of -2.2 dB and a phase derivation of 13.25deg at 34 GHz.