Broadband bandpass filters using slotted stepped impedance resonators for improving upper stopband performances

This paper proposes new broadband microstrip bandpass filters based on slotted stepped impedance resonator (SSIR) for improved stopband performances. A comprehensive treatment of slotted resonators and both ends of the resonator with interdigital coupled lines is described. The design concept is demonstrated with a slotted stepped impedance resonator. These filters have wider upper stopband resulting from resonator bandstop characteristics. The simulated and experimental results of stopband performances are better than 15 dB for a frequency range up to 25 GHz.