| Summary: | 碩士 === 國立臺灣大學 === 電信工程學研究所 === 94 === Compact parallel-coupled bandpass filters with good selectivity and better stopband rejection are proposed in this study. They are designed with quarter-wavelength resonators such that there is no repeated passband at twice the center frequency, and the lengths of coupled-line sections can be reduced by using additional capacitors or inductors. In addition, by introducing the capacitive or inductive cross-coupling effect, transmission zeros can be achieved to improve the selectivity. The open stub which works as a K-inverter can also introduce a transmission zero at high frequency so as to suppress the spurious passband. Suitable equivalent models and design formulas are establish, from which the proposed filter can be design and investigate. Finally, compact 4th and 6th order bandpass filters with better selectivity and wider stopband up to four times the center frequency are accomplished. Comparing to the conventional parallel-coupled bandpass filter, the size reduction is over 60%.
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