Large-Signal Characterization of pHEMT Under Different Load Conditions by Using X-Parameters

In this letter, output power of pseudomorphic high electron mobility transistors (pHEMTs) under different load conditions and output impedance under large-signal drive are investigated by using novel X-parameters. By further considering the
$X^{T}$
terms of X-parameters, characterization of fundamental output power at different load can be more accurate when compared with the results by using conventional hot-S-parameters without
$X^{T}$
terms. Good agreement between measured fundamental output power of pHEMTs obtained from load-pull measurements and calculated results from the X-parameters under different load conditions is achieved. Besides, output impedance
$X_{2121}^{Z}$
under large signal drive incorporating with the
$X^{S}$
and
$X^{T}$
terms can be more accurate for output impedance characterization than the conventional hot-
$Z_{2121}$
without the
$X^{T}$
coefficients considered. This analysis of large-signal characterization can be beneficial to power amplifier designs.