Calculation of absorption cross section of lossy objects used when measuring antennas in reverberation chambers

Abstract

Reverberation chambers can be used to measure radiation efficiency and input impedance of small antennas. In particular, they can be used to measure these characteristics for small antennas located close to lossy objects, such as a mobile phone antenna located in different positions relative to a head phantom. It is therefore of interest to know the absorption cross section of different lossy objects used when measuring antennas in reverberation chambers. We show how the absorption cross section of a lossy sphere and a lossy cylinder can be calculated from the scattered far field by using the forward scattering theorem and the moment method. The results are in agreement with mean absorption cross sections of a lossy cylinder found from the measured mean transfer level of a reverberation chamber used for measuring small antennas close to a cylinder. They validate the formula that relates the net average transfer level of a reverberation chamber to the mean absorption cross section of a lossy object (see Hill, D.A. et al., IEEE Trans. on Electromagnetic Compatibility, vol.36, no.3, p.169-78, 1994). The absorption cross section of the cylinder varies with angle of incidence. This is important to know, as it may affect the accuracy of measured radiation efficiencies in reverberation chambers.