Microstrip band-pass filters with wide stopband and sharper cutoff response

In this paper, a microstrip band-pass filter (BPF) with the sharper cutoff rate and suppression of the 2^nd, 3^rd, and 4^th harmonics is developed. The half-wavelength transmission resonator with a pair of tap-connected open-ended stubs is adopted for constructing filter with band-edge attenuation poles. Using resistive attenuator and adequate coupling structures can suppress the unwanted harmonics. The resonance characteristic of resonator with embedded attenuator is analyzed with the aid of unloaded quality factor. By means of controlling the coupling structures, the embedded resistive attenuator, and the resonator with tap-connected stubs, the proposed band-pass filters can easily achieve a wide stopband and a sharp skirt property. Band-pass filter of center frequency at 1.96GHz was implemented to confirm our ideas.