Image parameters design of MEMS phase shifters with switched inductors and capacitors

This paper presents a new design technique based on the image parameters (IP) method for loaded-lines MEMS phase shifters consisting of transmission lines periodically loaded with switched inductors and capacitors. The use of both inductors and capacitors allows large phase shifts with low return loss to be achieved, thus leading to very compact devices. The presented design procedure allows an effective control of both the total phase shift and the return loss of the phase shifter as well as its frequency band of operation. Simulated results of a 4-bit MEMS phase shifter are introduced, the prototype being presently fabricated on high resistivity silicon substrate at ITC-irst Trento. As a proof of concept experimental test circuits have been fabricated and measured exhibiting a 105°/0.25 dB phase shift at 4.5 GHz with return loss of 20 dB over a two-octave frequency band.