A method for determining attenuation of electromagnetic waves impacting an electromagnetic shield. A reference amplitude is provided. A signal exhibiting a first frequency is converted to a converted signal exhibiting a second frequency higher than the first frequency. Electromagnetic waves corresponding to the converted signal are transmitted from a first antenna toward a second antenna with the electromagnetic shield positioned between them. Attenuated remnants of the electromagnetic waves received by the second antenna are converted to a corresponding signal exhibiting a third frequency that is lower than the second frequency. The amplitude of the corresponding signal is compared to the reference amplitude.