Novel microstrip bandpass filter with multiple transmission zeros using open/shorted stubs

A novel microstrip bandpass filter with multiple transmission zeros using open/shorted stubs is presented in this paper. By utilizing shorted coupled lines and the open/shorted stubs, eight out-of-band transmission zeros can be realized for the bandpass filter from 0 to 2f₀ (f₀ is the center frequency of the passband). The eight transmission zeros can be adjusted freely by only changing the electrical length of the open/shorted stubs. A planar bandpass filter (3-dB fractional bandwidth 7.5%, 3.85-4.15 GHz) is designed and fabricated. The theoretical and measured results all show good in-band filtering performances and high selectivity.