Using Computational Methods to Insert Ground Planes and Dielectric Half-Space in the Presence of Measured Antennas

It is well-known that any structure in the proximity of a radiating antenna will affect its radiation pattern. This is one of the reasons that a vehicle-mounted antenna tends to be tested while mounted onto the actual vehicle. There is a current discussion regarding how the vehicle should be tested. Traditionally, metallic turntables are used, with the tested vehicle resting on this conductive half-space. Several new spherical near field (SNF) ranges elevate the vehicle over a floor treated with RF absorber to obtain a quasi-free-space pattern. Discussions regarding which method is better are on-going. One of the arguments in favor of the free-space SNF range approach is that, using computational methods, the equivalent radiating currents that radiate the measured near fields, be it over a spherical surface or a non-canonical surface, can be computed. The equivalent radiating currents computed on a triangular element mesh are then imported onto a quadrilateral element mesh on a higher order basis function method of moments (HOBF-MoM) package. Once imported into the HOBF-MoM these currents can be used as excitations to obtain the far field. Within the HOBF-MoMit it is possible to place these equivalent currents in the presence of a metallic (PEC) using symmetry. A new development that allows for the use of an arbitrary Green's function hence it is possible to get the far field from the computed equivalent currents in the presence of a dielectric half-space. Thus, the theoretical radiation pattern of the vehicle mounted antenna can be computed when the vehicle is on concrete, dirt, or even salt water. In this paper the authors present the latest work performed using this approach to place free space measured antennas over a PEC or dielectric half-space. Results show the potential of this approach. The higher order basis functions allow for the modeling of large structures with reduced number of unknowns. Thus, the antenna under test can be then placed in proximity to not only various half-space materials, but also to towers, buildings, or spacecraft.