Removal of measurement artifacts present in high-power RF transistor loadpull test-fixtures

In this paper we investigate the effect of a discontinuity, at the measurement reference plane, on loadpull measurements of high-power RF transistors. The discontinuity is created by transition from the microstrip transformers on the printed-circuit board of the test-fixture to the packaged transistor. Our measurements indicate that the discontinuity does not change the peak performance of a packaged transistor but it can significantly alter the impedances at which this performance occurs. Through a straight-forward electromagnetic simulation we are able to characterize the discontinuity and remove it from measurement.