Real free space antenna factors for validating completely absorber lined chambers?

The validation of a completely absorber lined chamber (CALC) turned out to be difficult. The first attempt was made with antennas calibrated on an open area test site (OATS). In this case a correction factor was necessary, this factor is related to the ground reflection and thus to the antennas. The validation started with determining the real free space antenna factors (AF_FS). These real free space antenna factors were used for new site attenuation measurements in the CALC. The goal has been to validate the CALC by means of practical measurements. As a result the CALC can meet the normalized site attenuation (NSA) requirements. Because of near field effects and mutual coupling a minor problem area below 80 MHz remains, this problem was not dealt with. In our opinion the CALC should replace the OATS as the reference site. In conclusion, a CALC is the best test site for compliance testing for both immunity and emission, and all radiated EMC-measurements should be normalized to free space