Multi-path design for stepped-impedance low-pass filter to create transmission zeros and wide rejection band

Based on multi-path design, a new method is proposed for design of stepped-impedance low-pass filters (LPFs) with improved attenuation levels and rejection bandwidth by creating transmission zeros. In a third-order circuit, an extra short microstrip section is introduced to shunt with the low-Z section and provides a second signal path. Two-port network analysis is formulated to predict the zeros. Design parameters include the electric length and characteristic impedance of the shunt section. Measured results show good agreement with simulation.