Waveguide-Integrated MEMS Concepts for Tunable Millimeter-Wave Systems

This thesis presents two families of novel waveguide-integrated components based on millimeter-wave microelectromechanical systems (MEMS) for reconfigurable systems. The first group comprises V-band (50–75 GHz) and W-band (75–110 GHz) waveguide switches and switchable irises, and their application as switchable cavity resonators, and tunable bandpass filters implemented by integration of novel MEMS-reconfigurable surfaces into a rectangular waveguide. The second category comprises MEMS-based reconfigurable finlines integrated as phase shifters into a rectangular waveguide array to demonstrate beams steering with a phased array antenna. The first group of the presented reconfigurable waveguide components is based on a novel MEMS-reconfigurable surface structured in the device layer of a silicon-on-insulator (SOI) wafer using metallized mono-crystalline silicon as structural and functional material. The chip containing the reconfigurable surface is integrated in the cross-section of a WR-12 rectangular waveguide perpendicular to the wave propagation. The reconfigurable surface is modified for different states by on-chip push-pull electrostatic comb-drive MEMS actuators. The switch is ON when the reconfigurable surface is in its transmissive state and OFF when the reconfigurable surface is in its blocking state for the propagating wave. This millimeter-wave waveguide switch shows an insertion loss and isolation very similar to high-performance but bulky mechanical rotary waveguide switches, despite being extremely compact (30 μm thick), and thus combines the high electrical performance of mechanical switches with the size of (high power consuming and inferior performance) PIN-diode waveguide switches. This thesis also investigates the optimization to decrease the number of contact points for the OFF state and presents a device yield analysis. The same concept is developed further to MEMS-switchable inductive and capacitive irises, with the performance similar to ideal irises. With such MEMS-reconfigurable irises a switchable cavity resonator was implemented and the potential of tunable bandpass filters are demonstrated. Since these devices feature all-metal design as no dielectric layers are utilized, no dielectric charging effect is observed. Furthermore, this thesis investigates the low-loss integration of millimeter-wave MEMS-reconfigurable devices into rectangular waveguide with conductive polymer interposers. The second group of components comprises finlines which are fabricated out of two bonded silicon wafers with bilateral gold structures integrated into a WR-12 rectangular waveguide. A 2-bit waveguide phase shifter is designed for 77-GHz automotive radar. Such phase shifters are used as individual building blocks of a two-dimensional antenna array for beam steering frontends. Zargham Baghchehsaraei, zargham@ kth. se Department of Micro and Nanosystems, School of Electrical Engineering KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden