| Summary: | 博士 === 國立臺灣大學 === 電信工程學研究所 === 106 === This dissertation focuses on the research of reconfigurable filters using microstrip resonators and acoustic wave resonators. The first part is the constant fractional bandwidth (CFBW) reconfigurable filter with frequency invariant passband characteristics using tunable external quality factors. A grounded-stub loaded net-type dual-mode resonator and two sets of varactors for tuning both the center frequency and the return loss level are used to design the reconfigurable filter. The design is featured with the net-type dual-mode filter of a short grounded-stub so that the CFBW property can be assured. In addition to conventional design, a pair of varactors is added at the ends of feeding transmission lines to keep the external quality factors constant while tuning. From the design concept, the return losses of reconfigurable CFBW filter with tunable external quality factor maintain at 20dB and the insertion losses are below 2.9dB over the entire frequency tuning range. The design can improve the return loss and insertion loss of reconfigurable filters when the center frequency decreases.
The second part is the reconfigurable filters using film bulk acoustic resonators (FBARs), including high electromechanical coupling coefficient (kt2) FBARs and tunable FBARs. The FBAR resonator and a series inductor are first represented by a simplified parallel RLC circuit model. The reconfigurable FBAR filters are then designed by applying the general coupled resonator filter theory, with tunable capacitors to adjust center frequencies, coupling coefficients and external quality factors. To increase the tuning ranges of reconfigurable filters, high kt2 FBARs and variable capacitors with high quality factor are used. In the presented reconfigurable filters using high kt2 FBARs, the tuning range is about 8.2% with < 4dB insertion loss by using high-Q digital capacitors of Q = 150. For deceasing the losses of extra tunable capacitors for tuning the center frequency, tunable FBARs are used to design the reconfigurable filters. By the mechanism of tunable FBARs, the center frequency of reconfigurable filters is tuning by TFBARs, not extra tunable capacitors. The tuning range of reconfigurable filters is determined by tunable FBARs. In same specification, the tuning range of reconfigurable filters using tunable FBARs is about 10% and the insertion loss is below 2.24dB.
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