MEMS-based 180° phase switch for differential radiometers

In this paper, a new uniplanar 180° phase switch suitable for space differential radiometers is proposed. It is based on two dc-contact- microelectromechanical system (MEMS) single-pole-double-throw switches that switch between two different back-to-back coplanar-to-slotline transitions. Since these transitions are multimodal structures, rigorous multimodal models are developed to analyze them and to assess the effects of the unwanted coplanar odd mode. These models are capable of predicting under what conditions the transitions produce a good wideband, 180° -phase-shift and/or matching behavior; they are applied to the design of the 180° phase switch. A compact implementation of the phase switch in the frequency range 14-20 GHz is fabricated using the FBK-irst eight-mask surface micromachining process, featuring a 180° phase-shift bandwidth of 35% for a maximum phase error of 5° and insertion loss better than 2 dB. Experimental results show a very good agreement with the multimodal model predictions. The designed dc-contact MEMS switches fulfill the typical requirements of differential radiometers, featuring measured mechanical switching and release times of 100 and 15 μs, respectively.