Constant intermodulation loci measure for power devices using HP 8510 network analyzer

The distortion level of a FET output signal is deeply affected by the radio-frequency (RF) load. A method of characterizing the intermodulation distortion (IMD) behaviour due to loading for power FET amplifier is described. An HP 8510 network analyzer in combination with commonly available measuring equipment is used to determine load reflection coefficient for various load conditions, and relating the value to constant power gain circles drawn on a Smith chart. The locus of points generated allows the selection of the appropriate load for the FET that maximizes the device linearity. An example illustrating the method is discussed.<
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