Inverse Source Solutions and Antenna Field Transformations Above Lossy Dielectric Halfspace via Exact Sommerfeld Integral Representation of the Green's Functions

Automotive near-field (NF) antenna measurements above a dielectric, possibly lossy halfspace enable an accurate characterization of the antenna radiation especially for frequencies below around 300 MHz, where mutual interactions between the automobile with integrated antenna and the ground become relevant. In order to correctly consider these effects, an inverse source solver with exact Sommerfeld integral representation of the pertinent Green's functions is presented. The Sommerfeld integrals are numerically evaluated for a mixed-potential integral representation of the fields with real-axis integration and quasistatic image extraction. As such, the inverse source operator is pre-computed as a system matrix, in order to allow for an efficient iterative solution of the inverse source problem and the related antenna field transformation. The accuracy of the approach is demonstrated for hemispherical observation data of a backlight broadcast antenna on a metallic car body.