A bandpass filter with high selectivity and a wide stopband

A filter with high selectivity and a wide stop band is presented in this paper. The filter is fundamentally consisted of two half-wavelength microstrip resonators. The zero-feed structure and loaded open microstrip stub are combined with the open parallel coupling microstrip line to achieve high selectivity and a wide stop band. The operational principle is described and the design steps are concluded. A prototype filter is simulated and fabricated. The measured results show that the presented filter has a wide stop band of 7f0, where f0 is the centre frequency of the passband. Moreover, the observed two transmission zeros outside the passband offer the high frequency selectivity.