The developed network analyser with four ports allows very fast measurements of S-parameters in comparison with a conventional network analyser. This is possible because highly linear analogue frequency ramps are used. Thus the settling times of stepped frequency sweeps of conventional analysers are eliminated. The required high linearity and high stability of the frequency ramps is achieved by using fractional divider phase locked loop circuits. For a practical realization it is necessary to

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... cept small nonlinearities for the linear analogue frequency ramps. For this reason investigations were performed to clarify effects of small nonlinearities on the measurement precision. Nonlinearities are willingly implemented by programming the fractional frequency ramps accordingly. The gained expertise allows for a further improvement of measurement accuracy and dynamic range.