Investigation of wave diffusers to scatter the unstirred radiation of an antenna in a reverberation chamber

In a reverberation chamber the direct (unstirred) path between two antennas is the aggregation of the line-of-site path and a number of unstirred specular wall reflections. Ideally these latter reflections should be eliminated in order to control the direct path for multi-path radio simulation applications (Pirkl et al., 2011). This work describes an experimental programme undertaken to investigate the hypothesis that the contribution of the specular wall reflections to the unstirred energy in a reverberation chamber can be reduced by wave diffusers placed around the specular reflection points on the chamber walls. The wave diffusers will scatter the reflected energy over a wide angular spectrum and increase the energy that is stirred by the chamber’s stirrer. Periodic wave diffusers were used optimized for a frequency of 3GHz. The method is based on a past research method for increasing the mode density in a reverberant screened room. That study found that the electromagnetic field was scattered in many directions by the use of binary pseudo-random phase reflection gratings on the wall of the screened room, while in the absence of the gratings the field was concentrated in particular directions (Clegg et al., 1996). The suggested approach in the present research is to create a grating formed by a binary sequence diffuser which causes diffuse reflection. Experiments were initially conducted in an anechoic and then in a reverberation chamber. The technique was tested while varying the antennas’ heights, polarization and elevation angles, and additionally the orientation of the grating. Furthermore, the power of the line-of-sight component was measured in the anechoic chamber by placing absorbers on the grating and was then subtracted from the total received signal, toleave the scattered components remaining. The power of the signal reflected from the grating could thus be calculated and compared at the receiving antenna with the power in specular reflection which is observed by using a plane reflector. In the reverberation chamber the research was based on the effect of the diffusers on the unstirred energy. For this reason the transmitting signal between two biconical antennas was measured, with and without the diffusers placed around the specular reflection points of the room. Parameters like the heights, the polarization and the distance of the antennas as well as the orientation of the diffusers were tested. Measurements in time domain showed significant reduction in the unstirred energy of the cavity.