Analysis and realisation of low-cost damped screened rooms

Radiated emission measurements in screened rooms suffer from the excitation of room resonances. Severe problems in measurement repeatability and difficulties in correlating emission measurements in a screened room to those on an open area test site occur as a result. One possible solution to this problem is by damping the room through the inclusion of small amounts of absorber. The effect of introducing resistive sheets in a screened room is examined using numerical modelling and experimental measurements. Results from the numerical model and the experimental measurements show that significant broadband damping may be achieved. The numerical model considered the frequency range of 30-500 MHz and comparison of the response in the room with the predicted free-space response shows that a screened room error of ±5 dB may be achieved over a broad frequency range. Experimental measurements were carried out on a screened room for the frequency range of 30-200 MHz and these show a reduction in variations in field levels from ±30 ds down to ±5 dB