Design of Substrate Integrated Waveguide Transversal Filter With High Selectivity

A substrate integrated waveguide (SIW) transversal bandpass filter (BPF) using Modified Doublet (MD) with high selectivity is presented in this letter. The modified doublet contains two resonators that are not coupled to each other. However, the source and the load are directly coupled in order to generate two transmission zeros. By changing the sign of one coupling coefficient and detuning the resonators in the modified doublet, two transmission zeros can be simultaneously placed below or above the passband, or one can be placed below and the other above the passband. In addition, a dedicated input and output SIW are used to suppress the lower mode for maximum selectivity. A second-order 14.87 GHz transversal BPF with 130 MHz bandwidth is designed, fabricated and measured. The measured result confirms the theoretical prediction, and validates the new structure for high-selectivity applications.