Intermodulation Distortion Analysis in Cascaded D-Band GaN Amplifiers

This paper presents a method to measure intermodulation distortion and conventional small-signal network parameters of an amplifier in D-band without reconfiguring the measurement setup. The two-tone signal is generated with a high degree of flexibility through the use of the internal direct digital synthesis source of the network analyzer. State-of-the-art gallium-nitride power amplifier modules are used as a device under test. Conventional small-signal parameters such as the forward transmission of 19 dB were measured, as well as the continuous wave large-signal behavior, which yielded 18 dBm of saturated output power at 135 GHz. The intermodulation distortion measurement indicates a third-order intercept point at 23 dBm with respect to the output of a single module. A cascaded measurement is performed with both power amplifier modules to quantify the influence of each non-linear contribution from each stage, as outlined in the relevant theory.