Understanding and Selecting Antennas for Measuring in Congested Electromagnetic Environments

It is not uncommon for electromagnetic compatibility (EMC) engineers who conduct surveys of electric and magnetic fields in some commercial, industrial, power plant, and healthcare facilities to encounter congested areas where challenges are presented in selecting the appropriate survey antenna. Site surveys and laboratory experiments conducted by the EMC Group at EPRI Solutions have been conducted with a variety of antennas in efforts to compare techniques and measurement results. This paper presents two examples of electromagnetic field measurements, one conducted in an open area test site (OATS) and the second conducted in a doubly- isolated shielded enclosure (DISE) in comparing electromagnetic field measurements using a biconical log periodic dipole (BLPD) the radiated antenna and two antennas: the biconic and discone as the receiving (or antennas under test) antennas. Comparison of the laboratory data to the OATS data clearly shows that the reflections that do occur may attenuate or amplify the signal from an interferer at the point of installation. Considering this phenomena, it is important not only to consider a survey when a new piece of equipment is installed, but it may be necessary to perform a survey to determine the change in the electromagnetic environment when structural metallic objects are present at the site.