Compact wideband differential bandpass filter based on the double-sided parallel-strip line and transversal signal-interaction concepts

Two compact wideband differential bandpass filters based on the double-sided parallel-strip line (DSPSL) and transversal signal-interaction concepts are proposed in this study. Two transmission zeros and good harmonic suppression can be achieved for the first wideband differential DSPSL filter, because of the two transmission paths with different lengths for input/output ports. In addition, another improved common suppression wideband differential DSPSL filter with two 180/ phase inverters is introduced. Four λ/4 shorted lines are added to improve the passband transmission characteristic for the two differential DSPSL filters. Two prototypes with 3/dB fractional bandwidth of 94 and 117.6/, and return loss greater than 15/dB for differential mode are designed and fabricated. The measured results show good agreement with the theoretical expectations.