High-Q RF-mems tunable resonators and filters for reconfigurable radio frequency front-ends

Recent development in wireless communication has resulted in ever more complex systems for multi-frequency multi-standard operations. Reconfigurable RF/microwave components have the potential to significantly reduce the system complexity. In particular, tunable filters are important components in the RF/microwave front-ends for band/channel selection and image rejection. The objective of this dissertation is to develop the technologies and design concepts for highly tunable low loss front-end filters for the next generation reconfigurable wireless communication systems. The first part of the dissertation focuses on the design of novel electrostatic MEMS tunable evanescent-mode cavity resonators. These high-Q widely tunable resonators form the basis for creating more complex tunable filters. The electrostatic MEMS tuners enable highly stable actuation with near zero hysteresis while preservating high unloaded quality factor Qu of the evanescent-mode cavity resonators. A detailed discussion on the various design parameters reveals the inter-dependence between quality factor, actuation voltage, tuning range, and tuning speed. State-of-the-art performances (tuning range of 1.9–5.1 GHz and Qu of 300–650) have been demonstrated with such tunable resonators. In the second half of the dissertation, the technologies developed above are used to make novel tunable bandpass filters. A two-pole filter with 0.7% constant frac- tional bandwidth has been demonstrated state-of-the-art performances (tuning range of 3.0–4.7 GHz and insertion loss of 3.55–2.38 dB). The power handling capabilities of MEMS enavenescent-mode tunable resonators and filters are also investigated by theoretical analysis, circuit modeling and experimental validation. A closed-form for- mula is derived for the prediction of the power handling capabilities of such resonators and filters. The power handling capability is found to be dependent on a few factors, including stiffness of the MEMS tuner, overall quality factor and initial capacitive gap. In the last part of the dissertation, a novel dual-band filter design based on dual-capacitively-loaded cavity resonators has been proposed. The design concept is very flexible and allows arbitrary placement of the two passband frequencies. It has also been demonstrated that the bandwidth of the two passbands can be adjusted individually. This design concept can be further applied to make tunable multi-band filters for multi-band concurrent communication systems