Compact ultra-wideband bandpass filter using stub-loaded resonator

A compact filter for ultra-wideband (UWB) applications is proposed and developed through quasi-equal allocation of the first three resonant frequencies of a stub-loaded resonator together with strong input/output excitation. Measured results show low insertion loss and flat group delay in the entire passband as well as a wide stopband. The size for this single-layer UWB filter without feeding lines is only 9.5times5 mm (0.53 lambda_gtimes0.28 lambda_g in which lambda_g is the guided wavelength of 50 microstrip at the centre frequency).