Time-domain evaluation of anechoic environments up to 325 GHz

In this paper we describe measurements performed a) to obtain the broadband attenuation of absorbing material and b) for anechoic chamber performance evaluation up to 325 GHz. The measurements were taken in frequency-domain using the latest vector network analyzer (VNA) technology available. We take advantage of the large dynamic range of a 50 GHz four-port VNA and multiple broadband frequency converters. After a time-domain transform of the measured frequency response data the obtained signal response in time-domain is evaluated for several setups like a metal reflector, anechoic material samples, and several inhomogeneity in anechoic chambers such as edges, doors, light installations etc. Both S₁₁ and S₂₁ measurements are performed in anechoic chambers which give some insight into the imponderabilities of S-VSWR measurements. These have been proposed as a figure of merit of the total chamber performance, but in some laboratories users may have used equipment or setups which do not describe the absorber installation performance adequately. Some, but not all of the drawbacks are addressed by the latest CISPR standards up to 18 GHz. One example is the undersampling due to the given spacing of field strength samples which becomes already obvious below 18 GHz. This sampling procedure may not be useful at higher frequencies at all as the wavelength becomes smaller and smaller. This paper is a contribution to the understanding of how to evaluate anechoic chamber performance up to mm-wave frequencies.