A stepped-impedance bandstop filter with extended upper passbands and improved pass-band reflections

A high-performance planar bandstop filter with extended upper passbands and improved pass-band return loss is proposed in this article. In this proposed bandstop filter, a novel three-section stepped-impedance structure is suggested to improve the pass-band reflections without affecting the desired band-stop and extended upper passband performances. The analysis and design considerations of this filter are provided while the proposed design approach is verified by full-wave simulation, microstrip implementation and accurate measurement of a typical fabricated filter operating at 1 GHz(fo). Compared to the conventional one, the proposed bandstop filter has main and obvious advantages of simple single-layer structure, perfect band-stop filtering performance (Suppression of better than 20 dB), excellent low/high pass-band return loss (Reflection of lower than -17 dB) in the extended upper passbands(Larger than 5.96 fo), and flat group-delay transmission (Variations of smaller than 0.22 ns).