Compact Wideband Parallel-Coupled Microstrip Line Bandpass Filter with In-Line Structure

摘要

A compact wideband microstrip bandpass filter constructed by a parallel-coupled microstrip line and a parallel-connected half-wavelength (lambda(g)/2) microstrip line is proposed in this letter. The proposed bandpass filter showcases wideband bandpass response with four transmission zeros within the operating bandwidth from DC to 2f(0) (f(0) center frequency). The transmission zeros located at DC and 2f(0) are inherently generated by the parallel-coupled microstrip line while the other two are realized by the parallel-connected lambda(g)/2 microstrip line. For validation, a wideband bandpass filter centered at 4.15 GHz with bandwidth of 3 GHz is designed, fabricated and measured. The size of the in-line bandpass filter is 0.27 lambda(g)x0.045 lambda(g), which features very compact size and can be integrated conveniently with other microwave components.