Millimeter-Wave Filtering Power Divider With Sharp Roll-Off Skirt Using Rectangular Waveguide-Spoof Surface Plasmon Polariton Structure

A full-metal millimeter-wave (mmWave) filtering power divider (FPD) featuring sharp roll-off skirt which employs rectangular waveguide (RW)–spoof surface plasmon polariton (SSPP) structure is proposed in this paper. Both upper and lower cut-off frequencies depend on the dimensions of RW-SSPP unit cells, realizing excellent filtering characteristic. The TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode electromagnetic (EM) wave input in the RW is first converted to SSPP<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> mode by loading double-sided RW-SSPP structure, which is finally transformed to two SSPP<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> modes through single-sided RW-SSPP structure. To validate the proposed concept, a prototype is fabricated and measured. The proposed FPD achieves a wide 3-dB bandwidth from 22.1 GHz to 27.5 GHz with a 30-dB shape factor (SF) of about 1.15, implying a sharp roll-off skirt. The measured return loss and insertion loss are less than 10 dB and 1 dB within the operation bandwidth, respectively. The measured phase and magnitude imbalances between the two output ports maintains below 11° and 0.68 dB, respectively.