A novel band-stop filter with wide upper pass-band performance is proposed and discussed in this paper. This band-stop filter includes two three-section transmission-line stubs and a parallel coupled-line section. Because three-section transmission-line stubs and coupled-line section are used, this filter not only features good band-stop filtering property, but also has wide upper pass band. In order to verify this new filter circuit structure and its corresponding design theory, three groups of numerical examples are demonstrated. Finally, two practical band-stop filters using common microstrip technology are designed, simulated and measured. The simulated and measured results indicate that both the coupled-line section with weak coupling and two three-section stubs can improve the upper pass-band performance. Furthermore, the measured results of the second fabricated microstrip band-stop filter (Filter B) show that the 20-dB insertion-loss band-stop bandwidth at 0.46 GHz is 90 MHz and the 1.2-dB transmission coefficient upper pass band is from 0.66 GHz to 2.52 GHz. Thus, the highest pass-band frequency is extended to larger than five times of the operating center frequency of stop band.
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