Field perturbations due to accessories used in radiated emission tests

Radiated emission measurements are usually performed in a facility that meets the normalized site attenuation (NSA) requirements of standards such as CISPR 22 and ANSI C63.4. These NSA measurements are taken in the absence of necessary accessories, such as the 80 cm support table on which test samples must lie. Additionally, the standards offer only vague guidance on the materials and construction methods used to create test accessories. This paper presents a technique for measuring the far-field signal perturbations that result from inserting test accessories into the measurement environment, along with data showing how various accessories perform.