Near Field Communication (NFC) as demanded modern technology is subject to a continuous development. New applications like the integration of NFC reader devices into mobile phones bring new challenges and require improvements concerning special boundary conditions. Power consumption and respectively contactless power transmission, which above others determines the communication range of a coupling system, are key issues for this technology. In this thesis the effect of impedance mismatch (de-tuning) is investigated on an NFC reader network, caused by the variation of the coupling factor in normal operation of the NFC device. As an option for improvement, de-tuning compensation is evaluated, which can be provided by a flexible impedance adjustment network. On the one hand fix- and auto-tuning measurements are performed, on the other hand an equation system is formulated to explain the results with theoretical considerations. To proof valid the equation system, simulations are provided, reproducing the measurements. On the basis of these simulations an analysis of the influence of different network parameters (for example the coupling coefficient and the electrical antenna parameters) on the conditions for de-tuning compensation are calculated.