A Single Antenna Method for Characterizing Absorber Effectiveness at Low Frequency

Abstract

Measurements in anechoic chambers do not provide reliable results below a cut-off frequency defined based on the absorber reflectivity. Such a parameter should be assessed in order to further develop data-processing techniques for removing multipath effects at low frequencies. In this paper we propose a single antenna method for characterizing absorber effectiveness by measuring the reflection coefficient at the antenna input over a set of distances between the measuring antenna and the reflecting wall. We used as a probe a low-profile, bowtie antenna and a mobile, controlled platform. In order to improve the directivity, we applied an end-fire type weighting on the measured data. The contribution of the wall reflection at the antenna input, was extracted through a differential method based on computing an estimate of the S11 parameter in a reflectionless environment by using the distance averaging method. The technique was successfully demonstrated in an anechoic chamber normally designed to operate over 700 MHz.