Fully tunable filter design using tunable transformers and multiple mode resonators

A fully tunable bandpass filter using tunable transformers and multiple mode resonators (MMRs) is proposed. The proposed tunable MMR makes it possible to realize wide-band tunable filters. Thus the tuning ranges of the center frequency and bandwidth are wide. The novel tunable transformer may help to get the desired external quality factor (Q_e) while the center frequency or bandwidth is tuned. Thus a good passband performance may be got.