Designing power amplifiers for spectral compliance using spectral mask load-pull measurements

This paper demonstrates power amplifier design using load-pull measurements to determine spectral mask compliance as a function of load impedance. In most cases demonstrated in the open literature, the spectral spreading of the device is indirectly assessed by a metric such as the adjacent-channel power ratio or third-order intermodulation product. In the present paper, a spectral mask compliance metric is introduced that is less than or equal to zero for compliant spectra and positive for noncompliant spectra. The paper first examines the load-pull measurement for the spectral mask compliance metric, including the use of averaging to smooth the contours. Direct, dual-objective design of power amplifiers for spectral mask compliance and efficiency is then demonstrated by choosing the load impedance that provides the highest measured power-added efficiency while maintaining spectral compliance. With the device terminated in the chosen optimum impedance, measurement of the output spectrum and comparison with a spectral mask are performed to demonstrate spectral compliance at the selected design impedance.