A Q-Band Rf-Mems Tapered True Time Delay Line For Fusion Plasma Diagnostics Systems

In this work, we present the design and demonstration of a novel MEMS-based true-time delay (TTD) unit for microwave imaging refiectometry (MIR) diagnostics of thermonuclear fusion plasmas. The TTD unit is designed using a coplanar waveguide loaded with extended tuning range cantilever-type varactors. The capacitance value of the varactors are tapered at the input and output ports, allowing for better impedance matching in the highly loaded case. More than 360 degrees and 600 degrees phaseshift was demonstrated at 30 GHz and 50 GHz, respectively with a figure of merit better than 60 degrees/dB over the entire frequency range. As a TTD unit, the device can provide near constant delay of 0-33 ps adjustable in an analog fashion. To the authors' knowledge, this is the best TTD unit demonstrated to date in terms of maximum adjustable delay range and FoM in Q-band.