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 reflectometry (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° and 600° phaseshift was demonstrated at 30GHz and 50 GHz, respectively with a figure of merit better than 60°/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.