New method to validate the performance of SACs from 200 MHz to 1000 MHz

An improved method is proposed to adequately validate the performance of a semi-anechoic chamber (SAC) from 200 MHz to 1000 MHz, by replacing the transmit antenna (Tx) from a log-periodic dipole array (LPDA) antenna with a mini-biconical antenna. SACs are widely used to make radiated emission (RE) measurements, and for each SAC, after newly construction or after several years, a validation must be made to make sure it is good enough to make RE measurements. However, in present standard such as CISPR 16-1-4:2012 or ANSI C63.4:2014, a directive antenna, e.g. LPDA is always used as the Tx from 200 MHz / 300 MHz to 1000 MHz. This is based on a questionable assumption that the RE from an equipment under test (EUT) is directional over this frequency band. Comparisons are made by measuring SACs with a LPDA and a mini-biconical antennas as the Tx, respectively. The measured results show that for a good SAC, the performance is slightly degraded once the Tx is changed from a LPDA into a mini-biconical antenna; however, for a compact SAC, the change is fairly larger. This shows the improved method is more sensitive to the real performance of a SAC.