May 2008 Issue: Technical Feature

Harmonic Load Pull with High Gamma Tuners

Automated load pull has become a standard tool for characterizing microwave power devices. Power devices operate in a nonlinear mode in order to achieve reasonable efficiency, so testing must be done with actual drive power and impedance matching. This includes the harmonic impedances, which can have a significant effect on both efficiency and linearity performance. This article reviews the common types of tuners used for load pull, and methods that have been used for harmonic tuning. Finally, it will show how the High Gamma Tuner, used with the Cascaded Tuner method of harmonic tuning, can produce exceptionally high gamma at both the fundamental and harmonic frequencies. This provides an excellent measurement solution for low impedance power devices when both efficiency and linearity are important parameters.

From: Vol. 51 | No. 5 | May 2008 | Page 232

by Gary Simpson, Maury Microwave Corp.

Microwave power devices, widely used in modern wireless and communications systems, must operate in a nonlinear mode in order to operate efficiently. Nonlinear operation means that the only valid way to test them is under actual operating conditions of DC bias, RF power and impedance. Small-signal S-parameters are not sufficient.

Because of the need to control impedances seen by power devices, load pull has become a primary method for characterizing active RF and microwave devices. Load pull systems generally include tuners for impedance control, in addition to whatever equipment is needed for the stimulus and measurement of the Device Under Test (DUT). Typically, whatever can be measured in a matched environment, such as 50 Ω, can then be measured as a function of impedance.

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