An evaluation of using small biconical antennas in normalized site attenuation measurements

Validation of radiated emission measurement sites is usually performed through normalized site attenuation (NSA) measurements in 30 MHz to 1 GHz using broadband antennas, as established in such standards as ANSI 63.4 and CISPR 16-1-4. By the standard method, it is typical to use a biconical antenna in the 30 MHz to 200 MHz range and a log-periodic dipole antenna in the 200 MHz to 1 GHz range. Meanwhile, we see cases of using a small biconical antenna in NSA measurements over the entire frequency range Therefore, we, VCCI decided to conduct a series of experiments to evaluate the feasibility of using small biconical antennas in NSA measurements, as contrasted to typical Bicon/LPD antennas. Prior to a series of experiments, we conducted NSA antenna factor calibration, and found small biconical antennas would require an NSA measuring system being able to ensure a wide dynamic range of 140dB or more due to their large antenna factors. Also we experimented the differences of antenna impedance and radiation patterns of each antenna. NSA measurements in this evaluation were conducted at three 3 m SACs and twe 10 m SACs of each antenna. As the results, we found that, although there were little differences from the standard method below 200 MHz, differences were apparent above 200 MHz by the difference of antenna radiation patterns and above 500 MHz by the effect of reflections from the antenna mast.