Miniaturized hybrid ring bandpass filter with a notched band and an improved upper stopband using double-sided parallel-strip lines

A wideband stepped-impedance hybrid bandpass filter with a notched band and an improved upper stopband is proposed. The double-sided parallel-strip line (DSPSL) is employed to implement the proposed filter. The stepped-impedance structure improves the upper stopband performance and reduces the size. Besides, the open-circuited stub embedded in the stepped-impedance line of the hybrid ring is used to create a notched band. The low impedance portion of the stepped-impedance line is formed by the DSPSL while the high impedance portion of that is constructed by the offset double-sided parallel-strip line (ODSPSL). The design example is fabricated on a 20 mil RO4003 substrate. The measurement results show excellent agreements with the electromagnetic simulation.