Nonlinear device characterization using harmonic load pull measurement

There has been a large amount of work and effort in the area of high and medium power MMICs recently. Today nonlinear microwave active devices such as power amplifiers can still benefit from better performance (such as power output and efficiency) by having suitable terminations at various harmonic frequencies. On the other hand, sub-harmonic terminations can affect the stability of the device. The main reason lies in the nonlinear behavior of the device that causes the device to generate various harmonic frequencies apart from the fundamental frequency.; Harmonic Balance (HB) has been a widely used and by far the most popular method to solve for a steady state solution of a nonlinear microwave circuit. It is done by splitting the nonlinear circuit into two parts: a linear part consisting of all the linear circuit elements and a nonlinear part consisting of all the nonlinear parts. Voltages and currents at a number of ports at the interface between the linear and nonlinear part are then computed and matched together using Kirschoff s voltage and current law. The result is a solution for the voltages and currents and their harmonics at all the ports. In order to use the harmonic balance method, we need some characterization or model of both the linear and nonlinear part. We already have a very good characterization in form of governing equations for the linear part (such as transmission lines, linear resisters, capacitors and inductors). That is not true for the nonlinear active device operating at a large signal level. We still lack a good and sound characterization method for the nonlinear device. This is what we are set to do in this paper. We use a large signal harmonic source/load pull system to present a variety of terminations to the nonlinear device. Measurements of some parameters (such as current, voltage or power variables) of the nonlinear device are performed. We make use of the measured data to come up with a large signal characterization of the nonlinear device that gives the relationship between signals at various frequencies (harmonics) in addition to the frequency of interest.