Fast irregular antenna field transformations above perfectly conducting ground planes

Near-field measurements above a perfectly electrically conducting ground plane require an appropriate consideration of ground effects in the subsequent reconstruction of equivalent sources for the device under test and the transformation into the far-field. In this paper, the fast irregular antenna field transformation algorithm is enabled to handle this kind of near-field measurements. For this purpose, the image principle is applied to the spectral plane wave representations of the equivalent sources on the various levels of the octree in order to incorporate the ground effects into the multilevel plane wave based field transformation operator. The octree for the spatial organization of the sources is, thus, not even extended below the ground and a high computational efficiency together with the known flexibility of the hierarchical field translations to arbitrarily located near-field measurement points above the ground plane is achieved. Results of the transformation approach are presented for numerical examples and show its applicability to automotive antenna tests.