RF-MEMS Uniplanar 180 Phase Switch Based on a Multimodal Air-Bridged CPW Cross

In this paper, a new compact broadband uniplanar 180 phase switch, based on an air-bridged coplanar-waveguide (CPW) cross loaded with two capacitive-contact microelectromechancial systems (MEMS) switches in opposed (ON/OFF) states, is presented. The two phase-switch states ��0 180 are defined by actuating the MEMS switches from ON/OFF to OFF/ON. The asymmetry in the states of the MEMS switches results in a complex multimodal interaction between the two fundamental even and odd CPW modes at the air-bridged cross. Using the multimodal theory, the phase switch is analyzed, its frequency-independent 180 -phase-shift properties are proven, and a set of design equations for perfect port matching are derived. A multimodal circuit model for the phase switch is then presented, and design equations and conditions for compact phase switches are derived. Finally, a very compact phase switch is designed and fabricated using an eight-mask surface micromachining process, featuring a measured phase shift of 180 1.8 in a very wide frequency range (1–30 GHz) and an insertion loss better than 2.1 dB in the design band (10–20 GHz). Experimental results are in very good agreement with electromagnetic and multimodal circuit simulations, thus validating the proposed approach and design procedure.