Effect of Current Crowding on Frequency Response of a Stepped Planar RF Transmission-Line Lowpass Filter for Power Electronics

This paper relates to prototype design studies of a stepped-tapered (in width) planar Cu-Al₂O₃-Ni-BaTiO₃-Ni-Al₂O ₃-Cu radio frequency (RF) lowpass filter for an integrated power electronics module. An empirical cascaded one-dimensional (1-D) current-crowding model, using ABCD matrices, is employed to explain the anomalous, and degraded, high-frequency roll-off slope of the Ni-BaTiO ₃-Ni attenuator segment in the desired (wide-to-narrow) forward connection. Good agreement between theory and experiment is obtained with the empirical current-crowding model, which incorporates changes in the resistance and self-inductance of the Ni conductor as functions of current crowding and skin depth. Additional support for postulated current crowding was inferred from two-dimensional (2-D) finite-element analysis (FEA) modeling of the electromagnetic field distributions in the individual attenuator segments. Such studies could serve as an aid to the design of other planar structures of improved tapered or exponential shape for enhancing the high-frequency roll-off response and slope