On the Load-Pull Effect in MMIC Oscillator Measurements

Low phase-noise MMIC oscillators are key components for microwave and mm-wave systems. As a consequence, phase-noise measurements of these circuits have become a subject of growing interest and importance. This paper demonstrates that MMIC oscillator circuits with their relatively low Q factors are prone to specific measurement errors. Caused by a load-pull effect, the measurement system can become part of the oscillator, which yields phase-noise data significantly below reality. Special care has to be taken in order to avoid such phenomena.

I. Introduction

Since low phase-noise MMIC oscillators in the frequency range beyond 10 GHz are of interest for various applications, the number of publications reporting on better and better phase noise values is continuously growing. In many cases, only phase noise values at a single offset frequency or spectrum analyzer plots are presented. Mostly, details on the phase-noise measurement setup are missing. As shown in this paper, however, such measurements are not at all trivial and the setup may induce hidden effects, which lead to phase-noise values significantly better than the correct data.