Balanced UWB BPF with wideband common‐mode suppression

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ABSTRACTIn this letter, a new balanced ultrawideband (UWB) bandpass filter (BPF) is proposed and designed using a slotline resonator (SLR) with radial end‐sections for better wideband response. The SLR is fed by microstrip lines, and the whole BPF circuit is deployed symmetrically across the plane of symmetry to provide balanced operation. When the BPF is excited differentially, the SLR half circuit behaves as a similar resonator of half width, and by locating its first three resonant modes in the passband, the desired UWB response can be achieved. Conversely, while the BPF is in common‐mode (CM) operation, the symmetry plane is virtually open‐circuited, and the SLR is incomplete in structure, rendering CM signal suppression very effective. In this design, bandstop filters are embedded in the feeding lines to increase the upper stopband bandwidth. The achieved performances for this proposed balanced UWB BPF are a 3‐dB fractional bandwidth of 114% and a minimum measured (simulated) in‐band insertion loss of 1.17 (0.92) dB for differential‐mode operation and very good CM rejection with an insertion loss of larger than 25 dB over 1–20 GHz frequency range. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2461–2464, 2015