Low-dispersion 180° phase shifter using two synchronized MEMS switches

Previously, the design of our novel low-dispersion phase-shifter unit cell with two asynchronous MEMS switches was limited to 90°, so that four unit cells (90°, 90°, 90° and 45°) with a total of eight MEMS switches were required for a 3-bit phase shifter. This not only increased the size and loss of the phase shifter, but also decreased its yield and reliability. Recently, we hypothesized that by using two synchronized MEMS switches, the phase shift of a unit cell could be extended to 180° so that only three unit cells (180°, 90° and 45°) with a total of six MEMS switches would be required for a 3-bit phase shifter. This paper confirms the hypothesis with measured characteristics of a fabricated 180° phase-shifter unit cell. The measured characteristics compare well with both equivalent-circuit model prediction and three-dimensional finite-element electromagnetic simulation, provided the worse-than-expected loss from individual MEMS switches is taken into account. The results provide the proof of the design principle, so that with improved MEMS fabrication process such as thicker metallization, the switch loss can be reduced and low-dispersion phase shifters can be realized with compact size, low loss, low cost, and high reliability.