Active load characterization of a microwave transistor for oscillator design

This paper describes the use of a six-port active load measurement system to determine the optimal large-signal loading of transistors for the design of microwave oscillators providing maximum output power. Our system has been used to measure the optimal large-signal terminating impedance for a potentially unstable microwave transistor and to apply the device line characterization technique. This technique, which is used to characterize a negative resistance monoport and predict the level of oscillator output power, is implemented for the first time using active loading. An oscillator designed using our measurements generated an output power of 11.3 dBm at a frequency of 3.5 GHz. This result is in good agreement with the value predicted from the device line technique and our measurement system.