Uncertainties and Limitations of Shielding Measurement with Two Antenna Method

The measurement of the shielding performance of material samples with two antennas is a good method to evaluate, if the material is suitable for the construction of a housing with good shielding properties. This method uses a transmitting antenna outside a shielded room and a receiving antenna, which is inside. In the wall of the shielded room a material sample is fixed in an aperture for measurement. The method has several uncertainties and limitations. The investigation of the impact of the sample size to the measured results showed, that from a certain frequency the sample size has no impact, below this frequency the measured shielding effectiveness is underestimated. The connection of the sample with the wall of the shielded room is crucial for the measurement method. With no or insufficient connection the shielding performance is strongly underestimated. Finally, the measurement of the connection method between a metallic shielding material and the wall of the shielded room was investigated by numerical simulations. From the results of the numerical simulations it can be observed that the measurement of the connection can be performed with different sample size too, because the shift of the shielding result can be predicted and thereby the result corrected.