Fully Reconfigurable Dual-Mode Bandpass Filter

This paper presents a fully reconfigurable dual-mode bandpass filter based on substrate integrated circular cavity technique (SICC). Dual-modes are excited orthogonally for miniaturization, which can be mutually coupled by the use of a cavity perturbation technique. Varactor diodes are used to tune cavity resonant frequencies independently since the arranged tuning units are only set for affecting one of the related modes. Combining controlled external coupling, all parametric tunings are achieved such as center frequency, bandwidth, transmission zero and other reconfigurable filtering characteristics. On the basis of tunable resonant frequencies, quasi-elliptical, linear phase and intrinsic-switching capability are obtained. For an experimental validation of the proposed structure, a dual-mode bandpass filter was fabricated and measured. As one example of the quasi-elliptical response, a constant absolute bandwidth of 200 MHz in the tuning range 2.83–3.55 GHz with insertion loss of 1.76–5.08 dB is observed in our experiments.