Distributed MEMS transmission lines

Microelectromechanical systems (MEMS) for microwave and millimeter wave systems are currently being developed as low-loss control circuits. This thesis presents an application of MEMS technology to millimeter wave circuits in the form of the distributed MEMS transmission line (DMTL). The design consists of a high impedance CPW line capacitively loaded by the periodic placement of MEMS bridges over the center conductor. The impedance and phase velocity of the resulting slow-wave transmission line are determined by the size and periodic spacing of the MEMS bridges.; DMTL phase shifters are designed and optimized at 60 GHz and 100 GHz. The DMTL phase shifters are fabricated at the University of Michigan using standard optical lithography techniques with a quartz substrate and electroplated gold for the MEMS bridges. The measured results demonstrate 90°/dB, or 4 dB loss for 360° phase shift, at 60 GHz and 70°/dB, or 5.1 dB loss for 360° phase shift, at 100 GHz. To our knowledge, this represents the best phase shifter performance at 60 GHz and above.; The DMTLs are also applied as broadband high-isolation switches and BPSK phase modulators. The measured switches have better than 40 dB isolation with bandwidths of 20–40 GHz and 40–60 GHz. Switching times are measured to be 3–12 μs for bridge heights of 0.9—1.2 μm, depending on the applied voltage. Also, a BPSK modulator is demonstrated with a 2 kbps modulation rate and a drive power of less than 2 μW. It has been shown that this design can be extended to 50–100 kbps with appropriate MEMS bridge designs.