Dual-Band Balanced to Unbalanced Multilayer Filtering Magic-T Based on SIW Cavity

A new dual-band balanced to unbalanced (BTU) multilayer filtering magic-T (FMT) based on square substrate integrated waveguide (SIW) cavity is proposed in this letter. Degenerate TE
₂₀₁
and TE
₂₀₃
modes are exploited to realize the requested dual-band filtering responses and in-/out-of-phase characteristic. The requested differential-mode (DM) transmission, common-mode (CM) suppression, and port-to-port isolation can be obtained by appropriately placing the input–output ports and coupling slots. Multiple transmission zeros (TZs) are introduced to improve frequency selectivity, and the center frequencies (CFs) can be flexibly controlled to some extent. For validation, a prototype dual-band BTU FMT operating at 11.6 and 19.1 GHz is fabricated and measured. It can be obtained that the simulated results are in good agreement with the measured ones.