Half frequency instability on a 1W bipolar part

Half frequency instability is investigated on a 1W bipolar part. The small signal scattering parameters are measured at 500 MHz while the bipolar part is operating at 1 GHz. The measurement is done over various drive levels ranging from linear to saturation regions of operation. An algorithm is used to calculate the small signal S-parameters at 500 MHz without having to present 50-ohm termination to the device but instead the optimum load at 1 GHz. This is significant because the microwave power transistor needs a suitable load termination (not a 50-ohm termination) in order to operate at that large signal level.