Modeling and Synthesis of UWB Bandpass Filters Using a Single Parallel-Coupled SIR and Short-/Open-Circuited Stubs

This paper presents a systematic design methodology for a class of ultra-wideband (UWB) bandpass filters composed of multi-section parallel-coupled stepped-impedance resonators (SIRs) and short-circuited stubs (SCSs). After analyzing the relationship between the filter order and the number and loading positions of the SCSs connected at the SIR junctions, a corresponding synthesis theory is established. A Chebyshev-type filtering function is introduced, and the corresponding synthesis equations are derived. To demonstrate the versatility of the proposed approach, seven fifth-order filter configurations are designed for the FCC UWB band. Their performance is verified using circuit/EM simulation tools, and key practical considerations for microstrip implementation are discussed. Furthermore, simulation-based analyses are carried out to investigate the effect of replacing SCSs with open-circuited stubs (OCSs) for enhanced roll-off characteristics. The conclusions provide practical design guidelines for this class of UWB bandpass filters.