David Wisell

Licentiate Thesis, Signals and Systems, Uppsala University, Dec. 2004.

Abstract:

In this thesis, a time domain measurement system for RF signals is discussed. The need for such a system is established. Impairments due to non-ideal measurement instruments in the system are discussed as well as methods to compensate for them.

An alternative method for two-tone sweep measurements, including measuring the phase of intermodulation products in addition to the amplitude, is presented. The proposed method is substantially faster, several orders of magnitude, than currently used methods, while having about equal accuracy.

The system is used for input-output measurements of two power amplifiers and the obtained data are fitted to different amplified models including memory. A memoryless model, a Wiener model, a Hammerstein model and an extended Hammerstein model are compared with respect to the total model error and Adjacent Channel Power Ratio (ACPR). It is found that the Extended Hammerstein model, as expected, clearly outperforms the others. It is also found that if the ACPR is of main interest, a higher model order should be used than if the total model error is the property of main interest.

A method to simultaneously find the phase and amplitude ripple of a signal generator and a signal analyser is also presented. The method is verified with measurements.