A Novel Ultra-Wideband Differential Filter Based on Microstrip Line Structures

A novel differential filter with ultra-wideband (UWB) response is proposed in this letter based on microstrip line structures. 180 UWB phase shifters and 360 degrees transmission lines are employed in the design to get the 180 degrees phase shift over broad bandwidth. In this way, the broadband conversion between in- and out-of-phase signals can be realized. Utilizing this characteristic, the undesired common-mode noises will be cancelled out at the center of the filter, while the input differential-mode signals can still propagate well. The proposed new differential filter was calculated by transmission line model, simulated by full-wave electromagnetic simulator, and validated by the measurement. The simulation and measurement results verify its good performance. It is validated that, in the proposed filter, the differential-mode signals can propagate well with UWB frequency response, while the common-mode noises are well suppressed with more than 10 dB suppression in the concerned frequency band.