Small-signal distributed model for GaAs HBT's and S-parameter prediction at millimeter-wave frequencies

The development of a new Heterojunction Bipolar Transistor (HBT) distributed electrical model suitable for millimeter-wave applications is reported. Each section of the distributed model is composed of an active slice, modeled as an intrinsic HBT, and connected to other slices through a passive connecting network. It is shown that, for large size and high power HBT's, a distributed model is more accurate than a lumped-element one. This is confirmed by comparing the S-parameters calculated using both models to the measured data over a wide frequency band. It is also shown that the distributed model allows accurate prediction of S-parameter behavior at higher frequencies where the lumped model may not have accurate prediction.