Wide-Stopband Bandpass Filters Using Asymmetric Stepped-Impedance Resonators

This letter presents novel bandpass filters (BPFs) with a wide stopband using asymmetric stepped-impedance resonators (SIRs). An uncoupled section located within conventional coupled lines functions as a means of achieving additional transmission zeros between each existing zeros, created by the conventional coupled lines. Designing two types of resonators, which have the same fundamental resonant frequency f₁ with different spurious harmonic resonances, results in extending the stopband bandwidth with the better suppression level. Embedded inserted feeder structure is also designed to create supplementary transmission zeros at about 9.0 and 13.0 GHz. Measured results of the proposed filter show the suppression level of -23.7 dB up to 10.6f₁ with the FBW of 8.9%.