Publications

The increasing complexity and sensitivity of wireless communication systems enforce the requirements for test environments such as anechoic chambers. The minimum achievable level of interference between desired signal and scattered copies is essentially determined by the reflectivity of the installed absorbers, emphasizing the importance of thoroughly characterizing the scattering behavior of absorbers. In this paper, the scattering off absorbers with different geometric shapes, namely convoluted, pyramidal, wedge, and flat, is investigated using a numerical unit-cell model. To verify the simulation model, the angle-dependent reflectivity of the convoluted absorbers was measured at different angles-of-incidence between 2GHz and 18GHz. The numerical results agree well with the measured reflectivity at representative angles-of-incidence, validating the numerical model and revealing the expected increase in reflectivity for increasing beam tilts. Further, it becomes apparent that the performance of all shapes decreases similarly at oblique incidence. These results contribute to build a comprehensive database on the angle- and frequency-dependent reflectivity of absorbers, in order to develop a consistent data body, e.g., for modelling anechoic environments.

Progressing towards highly automated and connected vehicles, radar systems have evolved into reliable assistance systems for environmental perception, for a wide spectrum of traffic scenarios, and with them, accurate angle-dependent descriptions of reflectivities and scattering centers of traffic participants and road users. Depending on the electrical size of the radar object, the influence of possibly unwanted ground reflections can be significant in radar cross-section measurements. This paper presents an analytical model based on the transmitter, receiver, and single or multiple scattering center positions, that takes into account the geometric reflections at the ground floor and calculates the resulting interference. Considering also the bi-static crosstalk between the transmit and receive antennas, six different propagation paths are obtained, which differ in path delay and attenuation. Subsequent validation measurements in a semi-anechoic automotive antenna test facility confirm the analytical approach very well. Existing discrepancies between the single scattering center model and the measurements with a metal sphere could be corrected by a closer look at the position of the scattering center. Final measurements on realistic bicyclist dummies show that the model is also reliably applicable to extended radar targets.

Safety assurance of intended functionality through rigorous testing is a key to large-scale homologation and deployment of automated driving. It is therefore imperative to transfer real world tests into efficient and quantifiable virtual testing procedures and environments without compromising reliability. In earlier work, we presented a fully operational over-the-air vehicle-in-the-loop test system for automotive millimeter-wave radar, where we generated a virtual electromagnetic environment with physically realistic radar target echoes. We evaluated the performance of the implemented test system with an exemplary scenario parameterised with analytically pre-defined vehicle manoeuvres. In this work, we significantly proceed with the performance evaluation through re-simulation of scenarios based on real driving data and traffic manoeuvres. We have measured a standard Euro-NCAP scenario, namely, the Car-to-Pedestrian Longitudinal Adult on a proving ground and re-simulated the ground truth parameters in the test bed. We compare the consistency of the test results at several data abstraction levels using parameter trajectories. Additionally, we introduce and evaluate quality metrics such as difference and root mean square error. For a driving scenario approximately 20 seconds long, we achieved promisingly low root mean square errors in range, azimuth and RCS of 0.3 m, 0.5˚ and 2 dB, respectively.