The Open Area Test Site - Still the Key to Radiated Emission Testing

For years, the preferred method for determining compliance with radiated electric field emission limits has been to use test sites with one reflective surface - the ground plane. This implies that any site or enclosed facility like an absorber-lined shielded room must replicate a test site with only the one (ground plane) conducting surface. Further, regulatory agencies and Postal Telephone and Telegraph (PTT) authorities generally agree that any audit of radiated emissions from products in the frequency range 30-1000 MHz or more will be done on a site with one conductive ground plane. Such sites are called open area test sites (OATS) (the term open field site is now obsolete) with a conducting ground plane made out of metal. The latest draft revisions of IEC/CISPR Publications 16 and 22 include requirements for such sites. Yet, how much is known about constructing such sites, especially if they are to be enclosed by a non-conducting all weather protective cover? This paper will review the basic principles in constructing, and most importantly, maintaining a good OATS. This topic is described in the well-known American National Standards Institute document C63.7-1988 entitled, "Guide for Construction of Open Area Test Sites for Performing Radiated Emission Measurements".¹ This document has been revised in 1992 and includes new material highlighted in this paper along with the basic principles in the original document.