Low-frequency RF absorber performance with in situ and moveable sample techniques

The purpose of this paper is to describe two free-space measurement systems, developed at NIST for the evaluation of RF absorbers, and to demonstrate capabilities using measurement examples. The first consists of a moveable measurement system that performs in situ measurements of the reflectivity of a selected section of absorber wall in a chamber. The second is a fixed measurement system, deployed in conjunction with a moveable sample of absorbing material to be tested. Normal incidence results are presented for the in situ measurement system, and both normal and oblique incidence scattering results are shown for the moveable sample system. Typical Type-A measurement uncertainties are also shown for both systems