In this paper, a balanced ultra-wideband (UWB) band-pass filter (BPF) with compact size and simple structure is proposed. The proposed filter is fed by microstrip-slotline transition structures. A UWB differential-mode (DM) passband is achieved by employing H-type sandwich slotline structure. The fractional bandwidth of proposed balanced BPF could reach as much as 132%. In order to improve the selectivity, a source-load coupling is introduced. Meanwhile, one more layer of substrate is employed to reduce the DM passband insert loss. In addition, due to the symmetrical structure, a high UWB commonmode suppression without influencing the DM passband is realized. Therefore, the filter design method can be simplified significantly. In order to validate the effectiveness of the design method, a balanced UWB BPF is fabricated and the simulated results agree well with the measured ones.
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