Introduction

Whereas at lower frequencies from DC to several tens of Mega Hertz voltages and currents are typical quantities at higher frequencies we will use very often power quantities. It is necessary to measure the effective power between a generator to a load to determine the energy transport. This measurement can be derived from a voltage measurement across a known impedance in the lower frequency range. However, at higher frequencies this method is not longer applicable with the required accuracy. Looking to a theoretical, ideal matched circuit with a fixed geometric dimension: 1) At lower frequencies the power level can be easily determined by doing voltage measurements across a line or an impedance because the voltage level is nearly constant over the line which is much shorter compared to the wavelength. 2) At higher frequencies the wavelength becomes shorter what results in a distance dependent voltage. At different positions on the line, we will measure different voltage levels..