A Coupled-Line Band-Stop Filter with Three-Section Transmission-Line Stubs and Wide Upper Pass-Band Performance

A novel band-stop fllter with wide upper pass-band performance is proposed and discussed in this paper. This band- stop fllter 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 fllter not only features good band-stop flltering property, but also has wide upper pass band. In order to verify this new fllter circuit structure and its corresponding design theory, three groups of numerical examples are demonstrated. Finally, two practical band-stop fllters 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 fllter (Filter B) show that the 20-dB insertion-loss band-stop bandwidth at 0.46GHz is 90MHz and the 1.2-dB transmission coe-cient upper pass band is from 0.66GHz to 2.52GHz. Thus, the highest pass-band frequency is extended to larger than flve times of the operating center frequency of stop band.

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