An Analog RF MEMS Slotline True-Time-Delay Phase Shifter

An analog RF microelectromechanical systems (MEMS) slotline true-time-delay (TTD) phase shifter is presented for use in conjunction with tapered slot antennas, such as the Vivaldi aerial and the double exponentially tapered slot antenna. The design is a scalable distributed loaded-line cascade of 62 novel differential slow-wave unit cells. Each differential slow-wave unit cell comprises an electrically short slotline section, which is loaded with a shunt impedance consisting of two center-pulled contactless fixed-fixed beam RF MEMS varactors in series, sharing a common electrode. The analog RF MEMS slotline TTD phase shifter is demonstrated on a borosilicate glass wafer using a microfabrication process requiring six masks. It is designed for transistor-transistor logic bias voltage levels and exhibits a measured phase shift of 28.2deg/dB (7.8 ps/dB) and 59.2deg/cm at 10 GHz, maintaining a 75-Omega differential impedance match (S_11dd < -15.8 dB). The input third-order intercept point is 5 dBm at 10 GHz for a Deltaf of 50 kHz, measured in a 100-Omega differential transmission line system. Design and fabrication opportunities, concerning distortion and loss reduction, as well as packaging, are highlighted.