EUT directivity and other uncertainty considerations for GHz-range use of TEM waveguides

Over the past several years, there has been an increasing trend to identify and minimize measurement uncertainties in most types of EMC testing. This paper describes various uncertainty influence quantities that may affect direct voltage-based or correlated E-field radiated emissions tests in most TEM waveguides, and specifically in the GTEM cell. Most TEM-waveguide emissions testing is based on the measurement of EUT total radiated power. To clarify directivity and EUT loading influences, total radiated power and field strengths measured from canonical loop antenna and slotted and raised-lid box EUTs in GTEM cells in the 30-2000 MHz frequency range is presented. Measured results from various GTEM multi-position conversion-to-free-space or -OATS schemes are compared. The intent is to describe an analysis framework and raise awareness so that operators can begin to recognize and minimize uncertainty sources, and to contribute to better understanding of correlation effects in GTEM.