Compact SIW Diplexer With Flexibly Allocated Bandwidths Using Common Dual-Mode Cavities

A realization method for compact diplexers using mixed dual-mode and single-mode resonators is presented based on an advanced coupling scheme. An example with one common dual-mode (TE
₁₀₁
and TE
₂₀₁
) cavity and each channel of two single-mode (TE
₁₀₁
) cavities is demonstrated using substrate-integrated waveguide technology. The footprint of the diplexer is reduced compared to the traditional ones since the dual-mode cavity acts as a T-junction between the input port and the two channels and provides one pole for each channel filter. In addition, the fractional bandwidths (FBWs) of the two channel filters can be allocated flexibly based on the FBW design graph. A prototype centered at 12 and 14 GHz with respective FBWs of 3.25% and 3.75% is designed for demonstration.