Truncation error mitigation in free-space automotive partial spherical near field measurements

Antennas installed in modern cars are often highly integrated. In such cases, the entire vehicle is contributing to the radiated field, in particular at lower frequencies such as VHF. The complete characterization of the full vehicle is thus typically required. For frequencies down to 70 MHz, a widely accepted and cost effective solution is a multi-probe spherical Near Field (NF) system in which the scanning area is truncated below the horizon to minimize system dimensions. In order to emulate a proper freespace condition in the lower hemisphere, the ground floor is covered with absorbing material [1]. The partial NF acquisition of such systems leads to truncation errors if standard Near Field to Far Field (NF/FF) transformation is applied [2-3]. The mitigation of truncation error in general measurement scenarios by different post-processing techniques are described in the literature [4-9]. In this contribution, the mitigation capabilities of two techniques are investigated by experiment for an automotive scenario for the first time. The measurements have been performed on a 1:12 scaled vehicle-mounted antenna in a full-sphere multi-probe system. The scaled system and vehicle is representative of a real size system in the frequency range 70-400 MHz. Both truncated and full 3D measurements are performed for comparison.