Bandstop Filter Design Using Two-Section Structure and Z-domain Method

Three planar structures including embedded line, spur-line and conventional microstrip are employed to implement bandstop filters and their performances of bandwidth, center frequency and higher-order stopbands are studied in the discrete-time domain. A two-section, equal-length stub is presented to improve the ratio of the next higher-order harmonic frequency to the fundamental frequency. It is found that filters having upper passband widths of up to nine times the fundamental stopband central frequency can be obtained by using conventional microstrip.