Improving the Reproducibility of Radiated Immunity Tests Through the Use of the CMAD

The use of the Common Mode Absorption Device (CMAD) for improving the reproducibility of radiated immunity tests carried out according to the standard IEC 61000-4-3 is here investigated. Electromagnetic field simulation software is used to analyze several test setups in the frequency range from 30 MHz to 200 MHz, where the CMAD is designed to be effective in reducing resonances of the common mode current along cables. Both vertical and horizontal polarizations of the electric field are investigated. The cable transfer impedance is accounted for by the simulations in order to quantify interference induced in inner circuits. The measured S-parameters of a commercial CMAD, complying with the requirements of the standard CISPR 16-1-4, are effectively integrated in the numerical computation. It is demonstrated that the use of the CMAD on cables leaving the test volume significantly damps the peak of resonances of the induced interference in the full frequency range from 30 MHz to 200 MHz.