Wide Stopband Parallel-Coupled Stacked SIRs Bandpass Filters With Open-Stub Lines

In this letter, spurious passband suppression in parallel-coupled stacked stepped-impedance-resonators (SIRs) bandpass filters (BPFs) by means of open-stub lines is proposed and implemented. These filters are composed of parallel-coupled stacked SIRs and open stubs. Moreover, the structure with tapped feeding is employed to create transmission zeros near both sides of the passband skirt. The proposed structure can improve the harmonic suppression so that a wide upper stopband with a satisfactory attenuation level would appear in this BPF. Measured results of the fabricated circuits show that the idea works very well