A microstrip ultra-wideband differential filter with shorted parallel coupled-line

In this paper, a novel microstrip differential filter with shorted parallel coupled-line is proposed. Based on the transversal signal-interference concept, a passband can be achieved when the differential mode signal is excited, while a stopband can be obtained when the common mode signal is excited. The proposed differential filter was analyzed and simulated. A prototype is fabricated for demonstration of the design strategies. The measured results show that the differential mode signals have ultra-wideband response with 10 dB fractional bandwidth of 110%, while the common mode signals are suppressed in the whole frequency band. Good agreement can be observed between the simulation and measurement.