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

摘要

This paper presents the design and realization of a 3-bit RF-MEMS based phase shifter at 34GHz 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 εr 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 45° bit is less then −0.35dB and a matching better −19dB for both switching states. Further on, a loaded-line bit with 45° of phase shift is realized by switching between a capacitive and an inductive load. The capacitive switching state shows an insertion loss of −0.4dB and a matching better −13dB, while the inductive load has an insertion loss of −0.7dB and a matching of −25dB. The loaded-line bit combined with the dual-state microstrip line is used for the 90°- bit. An additional miniaturized switched line phase shifter is implemented for the 180° 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 −2.2dB and a phase derivation of 13.25° at 34GHz.