Band-Reconfigurable Tunable Bandpass Filters Based on Mode-Switching Concept

This article presents an approach to the development of band-reconfigurable tunable bandpass filters (BPFs) using a mode-switching concept. The key to realize this feature is that the first higher-order mode TE201 can be switched to the diagonal modes TE201 and TE102 using tuning elements in a square waveguide cavity. A pair of tuning elements are deployed along the diagonal line of a cavity while the other pair are arranged at its anti-diagonal line. If the two pairs of tuning elements have the same depths in the cavity, the first higher-order mode TE201 can be formed, and its resonant frequency can be tuned effectively. If the tuning elements have different depths, the TE201 mode can be switched to the diagonal modes TE201 and TE102, whose resonant frequencies can be tuned individually. Accordingly, the corresponding tunable BPF can be reconfigured between single- and dual-band states. Moreover, a flexible number of transmission poles can also be implemented in the dual-band state. For experimental verifications, two band-reconfigurable tunable BPFs are designed, fabricated, and measured in Ku-band. The first design has 2 and 2+2 poles in the single- and dual-band states, respectively, whereas the second design introduces one transmission zero (TZ), which has 3 and 3+2 poles in the single- and dual-band states, respectively. Regardless of single- and dual-band responses, each band can be frequency-tuned.