Multipath mitigation in pattern measurement of small directive antennas based on the singularity expansion method (SEM)

Many antenna ranges are limited in operation by the effects of multipath propagation due to reflection from adjacent structures. Such structures include buildings, range walls, floors, and ceilings. Diffraction fences and absorber provide the classic methods for reducing these effects. With modern processing capabilities, new methods can be incorporated to reduce multipath effects. In this paper, we review the results of Davis and Licul´s approach [1] that push the limits of an antenna range due to multipath from unavoidable adjacent scatterers. Their approach only considered boresight interaction. The radiation pattern of a 4 GHz Yagi-Uda antenna was measured inside an anechoic chamber with a metal plate present to introduce a multipath environment. A time gating approach based on the singularity expansion method (SEM) was used to mitigate the multipath effects and to estimate the radiation pattern in free space environment based on the boresight SEM poles. The results showed that some complex poles of a test antenna might not be excited strongly at certain angles, as with the use of boresight poles in the previous work. To resolve the problem, combined poles were extracted from multiple angles to remove the multipath effects and obtain non-distorted radiation patterns.