Analysis of shielded-room error for screened rooms and its application to low-frequency emission measurements from electrically small sources

Screened rooms are an alternative to open area test sites for radiative emission measurements. The cost of screened anechoic rooms by comparison is considerable, especially for low-frequency operation. The paper considers the use of screened rooms operated below resonance in obtaining low-frequency emission measurements from electrically-small sources. The screened room is modelled as a lossless rectangular cavity using a rapidly convergent Green´s function formulation. This is used to establish the shielded-room error for electric and magnetic current sources and examine the main coupling mechanisms between the source and observation point in a screened room. Emission measurements are presented for a self-contained electrically-small test source. Comparison with open-air measurements and emission measurements from a TEM cell show agreement to within ±5 dB