Synthesis of Transmission Line Dual-mode Resonator and Filter with Increased Stopband and Reduced Dimensions

The problem of increased stopband and reduced dimensions of dual-mode T-shaped resonator is solved. Stepped-impedance transmission line segments (SILS) with the required arrangement of resonant frequencies are synthesized for this. Two ends of the SILS are open-circuited. To the middle of the synthesized SILS an open-circuited stub is connected. The method of parametric synthesis of SILS was used, which provides the required arrangement of resonant frequencies at the minimum value of the parameter $\boldsymbol{m}=\boldsymbol{Z}_{\boldsymbol{0\max}}/\boldsymbol{Z}_{\boldsymbol{0\min}}$. As result, the new dual-mode T-shaped filter with increased stopband and reduced dimensions is obtained. A new effect is observed in the synthesized filter. It contains both dual-mode and simple oscillations, which alternate with each other. The measurement data and EM simulation of an experimental microstrip filter are presented.