As applications are explored at sub-millimeter-wave frequency bands, basic signal-processing components such as switches are required to assembly such systems as receivers and analyzers. Researchers from the KTH Royal Institute of Technology in Stockholm, Sweden and the Jet Propulsion Laboratory of the California Institute of Technology (Pasadena, Calif.) investigated several design approaches for an RF microelectromechanical systems (MEMS) switch capable of operating from 500 to 750 GHz with low insertion loss in the non-blocking state and high isolation in the blocking state. Suitable for signal routing, signal control, frequency band selection, and beam scanning, the MEMS waveguide switch was fabricated by means of metallized silicon to achieve the fabrication accuracy (15 to 20 μm) for high performance at terahertz frequencies.
Two different single-pole, single-throw (SPST) switch concepts were investigated, relying on ohmic contact or capacitive contact between the contact cantilevers. The switch functions by using a MEMS-reconfigurable surface for blocking and unblocking wave propagation into the waveguide. In the non-blocking state, a sufficient gap between the contact cantilevers allows an electromagnetic (EM) wave to propagate freely through the MEMS-reconfigurable surface. In the blocking state, the movable contact cantilevers come in contact with fixed contact cantilevers to form a series of vertical columns which short circuit the electric field lines of the transverse-electromagnetic TE10 mode, preventing EM wave propagation.
The switches were based on WM-380 (WR-1.5) rectangular waveguide. They were designed and simulated using the CST Microwave Studio commercial simulation software from Computer Simulation Technology. The switches were fabricated by aligning MEMS waveguide switch chips to the waveguide flanges. Following measurements, the ohmic-contact design was found not to work properly in the blocking state, with low isolation (5 dB). The capacitive-contact switch delivered 19 to 24 dB isolation with only 2.5 to 3.0 dB insertion loss, including losses from a micromachined waveguide section. The switch showed high reliability and consistent performance with a +28 V dc actuation voltage even after 100 million switching cycles.
See “A 500-750 GHz RF MEMS Waveguide Switch,” IEEE Transactions on Terahertz Science and Technology, Vol. 7, No. 3, May 2017, p. 326.