Wideband MEMS switched delay lines with high phase linearity

This paper presents a study on different microwave structures used to integrate MEMS devices in printed circuit boards, and their effect on the linear phase response for switched delay lines applications. Three different prototypes were designed to realize the RF tracks required to integrate 0.5 mm pitch MEMS devices together with the meander delay lines. The structures includes: microstrip lines, conventional coplanar waveguides (CPW) and finite grounded coplanar waveguides (FGCPW). The three prototypes were designed to deliver a group delay of 600 ps. Simulations were carried out using CST Microwave Studio. The FGCPW proved to have the highest phase linearity with only ± 4 ps (±0.67%) delay deviations up to 2.7 GHz. The paper also presents the design of two wideband MEMS switched time delay line circuits; one used to provide a fine tuning for the group delay with a step of only 10 ps and another for coarse tuning with 50 ps delay step. Finite grounded coplanar waveguides were selected to obtain a high linearity of phase response. The simulation of the two circuits resulted in a constant delay with relatively small deviations, as well as low insertion and return losses of 0.75 dB and 20 dB, respectively for frequencies up to 5 GHz.