Kalibrierung von Magnetfeldantennen mittels kontaktloser vektorieller Netzwerkanalyse

The increasing amount of power electronics in combination with decreased switching times of power semiconductors in daily life products as well as industry applications gives the necessity to qualify unintended cablebound and field coupled disturbances even for frequencies below 80 MHz. As radiated measurements within this frequency range are performed under nearfield conditions, the coupled power is mainly provided by the magnetic field. Thus in this frequency range magnetic loop antennas are mainly used for qualification of radiated emissions. In [CHS11] and [IF14] investigations on these calibration methods are presented and it is stated, that in some cases large variations of the resulting antenna factors occur. A more detailed investigation of the calibration methods has shown, that all of these are based on the generation of an analytical describable magnetic field. As no qualification measurement based on a national standard can be performed, the measurement chain can not be seen as traceable and thus also these calibration methods can not be seen as traceable, too. The error caused by boundary conditions is always hard to quantify, especially when generating an analytical describable field for antenna calibration. That leads to the objective of this work to develop a traceable calibration routine for magnetic loop antennas based on a contactless vectorial network analysis procedure. The principle of the contactless vectorial network analysis is presented in [Jun09] as the in situ calibration of current probes. Using this analytical failure term model allows the determination and correction of the current probes complete scattering parameters. Interpreting the loop antenna as a two-port network, where one port is represented by the antennas port at the feed point network and the other port is realized by clamping the current probe over the antennas shielding gap, the scattering parameters of the complete measurement setup can be measured using a vector network analyser. During postprocessing the error terms caused by the current probe are corrected to obtain the real scattering parameters of the loop antenna. Finally the antenna factor can be calculated using these scattering parameters, which already consider all parasitic coupling of the antenna and used measurement cables with the electromagnetic environment. A good match between the resulting antenna factors of the different calibration routines can be stated under laboratory conditions.