High Selectivity Bandpass Filter Using Three Pairs of Coupled Lines Loaded with Shorted Stubs
Keywords:
Bandpass filter, parallel-coupled lines, roll-off rates, shorted-circuit stubs, transmission poles, transmission zerosAbstract
A high selectivity bandpass filter with multiple transmission poles (TPs) and transmission zeros (TZs) has been presented. By employing three pairs of parallel-coupled lines and two shorted stubs, sharp rolloff skirts and high stopband rejections can be achieved with five TPs and ten TZs. Theoretical analysis is explained and simulated results are illustrated on this high-performance filter. Finally, a bandpass filter example with center frequency of 2.15 GHz and 3-dB fractional bandwidth of 19% is designed, fabricated, and measured. It is shown that the measured transition band roll-off rates are better than 425 dB/GHz. Good agreement between the simulations and measurements validates the design method.
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