Analyzing broadband, free-field, absorber measurements

The authors present and analyze a method for the free-field evaluation of a broadband absorber in a nonideal testing environment. Using broadband, short-impulse TEM horns, a frequency-rich spectrum (equivalent pulse length <0.5 ns) illuminates a sample of the material under test and the reflections are recorded. Unwanted reflections from the sample edges, room environment, antenna and other systematic events are mathematically removed by a combination of time gating, background subtraction and systematic deconvolution. The result is an estimate of the reflection characteristics of the center at the sample. The authors also present an uncertainty analysis of the measurement technique.