Publikationen

In anechoic chambers, the level of spurious reflections is determined by the reflectivity of the installed absorbers and is usually estimated using ray-tracing methods. But since the basic assumption of a purely specular reflection in most of these ray-tracing methods can lead to insufficient results, the reflectivity of the absorbers must be analyzed for oblique incidence and over a broad range of observation angles. In this paper, a bi-static measurement setup is proposed, which overcomes angular limits of the NRL-arch method and allows to analyze the scattering behavior of absorbers in an extended angular range. Using this setup, and applying the radar cross-section method, the reflectivity of two types of pyramidal absorbers was analyzed with respect to different illumination and observation angles for parallel and perpendicular polarization between 2 and 18 GHz. While the measurement results for normal incidence agree well with the specifications, additional non-specular reflections of similar strength were detected in the time-domain at different observation angles. Especially for the case of oblique wave incidence, it becomes apparent that the highest reflectivity does not necessarily occur for specular reflection. These findings help to improve the understanding of the scattering behavior of absorbers in general, as more comprehensive analyses become possible with this method.

With the event of integrated and multi-standard wireless links, phaseless antenna measurements are attracting more and more interest in research. Especially in the context of connected and automated driving, antennas, frontends, and digital signal processing units merge into telematic units and require new methods for performance evaluation in the installed state. The measurement of the phase diagram and the exact absolute positioning of electrically large antennas, i.e., antennas interacting with the car body, present challenges for safety-relevant applications and reliable test methods. This paper describes a way to determine the position of automotive antennas in the installed state with sub-wavelength precision from phaseless measurements. Realistic L TE uplink signals were used as test signals as they would be transmitted by an active device in a real-world scenario. The localization algorithm is based on orthogonal power measurements of the transmitted signal on a cylinder surface and a non-linear optimization. By comparison with a conventional localization based on spherical far-field data, an accuracy of the approach of less than 1 cm was achieved, which is less than N16 at the considered frequency of 1870 MHz.

This document outlines the measurement methodology currently employed to evaluate wireless technology on vehicles. Near Field Over the Air measurement results are provided and the Figure of Merit developed to assess the performance is reviewed. Simulation results of a more complex measurement scenario are also presented.

Car-to-car communication has wide-ranging applications in the fields of traffic safety and optimization as well as minimization of emissions. For a seamless and reliable communication between the cars and their road environment, as may be evaluated through packet delivery ratio and received power measurements, an appropriate antenna placement is necessary. Accordingly, the field test discussed in this paper compares the performance of three different antenna placements on a test vehicle: 1. Roof-mounted monopole antenna pair contained in a shark fin housing, 2. Patch antenna pair embedded in the front-left B-column, and 3. Combination of two patch antennas with one in the front-left and the other in the front-right B-column. The concurrent use of three V2V modules allowed us to evaluate the performance of the three antenna set-ups simultaneously in a single run through a mixed terrain, allowing for straightforward performance comparisons. The power received by the roof-top monopole antennas was, on average, 8 dBm higher than the front-left/right B-column patch antenna combination and 13 dBm higher than the front-left B-column patch antenna pair. The reasons for these and other differences are appropriately addressed in the paper. While the roof-top monopole antenna combination performed overall better, we argue that using an appropriate amplifier could raise the performance of the B-column antennas to the same or even higher levels.

State-of-the-art antenna arrays require a significant installation area when envisaged for compact passenger cars, whose footprint area can be reduced by splitting the full array into two smaller, spatially distributed sub-arrays. The challenge of grating lobes develops while arranging the sub-arrays several wavelengths apart mounted on distant parts of a car. As a consequence, spatial sampling of the incident waves leads to ambiguous direction-of-arrival estimation. An inhomogeneous L-shaped orthogonal arrangement can, however, mitigate such drawbacks to some extent while allowing easier installation. The performance of such an array needs to be tested in a virtual electromagnetic environment in the course of the development process, even long before homologation. An example of such distributed array mounted on a conventional passenger car for satellite navigation is shown in this paper, and the array performance is tested in terms of positioning accuracy in presence of a jammer in our automotive antenna test facility.