Electronically Reconfigurable Doublet in Dual-Mode Coaxial SIW

This paper proposes an electronically reconfigurable C-band doublet topology based on a dual-mode coaxial substrate integrated waveguide (SIW) resonator with source-load coupling. Varactor diodes in a back-to-back configuration have been used to tune the filter response in terms of center frequency, bandwidth (BW) and return loss (RL) level. The proposed approach presents a high design flexibility in a very compact size, allowing us to prove both tunable BW and constant absolute BW over a tuning range of about 15% at C-band. As a validation example, a single dual-mode coaxial SIW resonator with 10 varactor diodes is used to implement a 2-pole tunable bandpass filter (BPF) with two transmission zeros (TZs) that has been designed, fabricated and tested. The filter has a fractional BW (FBW) range and insertion loss (IL) better than 100% and 5 dB, respectively, over the entire tuning range.