Electromagnetic Modelling of Microwave Absorbers (EMMA)

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The relevance of testing radio components and systems in virtual environments, for instance and especially for automated and connected driving, is rapidly increasing. The installation of virtual electromagnetic environments usually relies on pyramid absorber lined shielded chambers. Specifically shaped absorbers at walls, ceiling, and floor attenuate the reflections of electromagnetic waves incident from different angles over a wide range of frequencies and thus minimise the reaction of the test environment on the measurement. The resulting degree of reaction eventually determines the basic usability, quality, and accuracy of the measurements and thus the comparability of the virtual environment with real field tests. Therefore, it is of utmost importance to precisely characterise the electromagnetic field distribution in anechoic chambers. For frequencies above 100 MHz, ray optical methods exhibit advantages compared to electromagnetic full-wave simulations and are therefore preferred. Remarkably, however, until to date there exists no suitable absorber model which describes the physical functional principles of pyramid absorbers comprehensively. Such a model has to be broadband (400 MHz to 80 GHz), angular dependent, and fully polarimetric. Accordingly, the main object of this project is the conceptualisation, implementation, and exploration of such a model.The work plan is divided into three main work packages (WP1000, 2000, and 3000). In WP1000, various experimental techniques to accurately measure the absorber reflectivity and its spatial variation over volume are studied. Important input parameters such as the electrical size of the absorber, angles of incidence and reflection, as well as polarisation are taken into account. By combining the measured results with the numerical and semi-analytical descriptions of WP2000, a mutual validation and extension of the distinctly different approaches is achieved. The results and experiences accumulated are fed into WP3000 and used to identify and describe the constituting factors and physical mechanisms of reflection and absorption. Based on these findings, eventually, a powerful absorber model suitable for ray tracing simulations will be developed, which effectively reproduces the electromagnetic properties of the absorbers. This model will be verified by computing the wave propagation in the semi-anechoic chamber VISTA: Virtual Road - Simulation and Test Area at the Technische Universität Ilmenau, and by comparing the results with measured data.The absorber model explored in this project represents an efficient and valuable tool to predict the wave propagation in electromagnetic virtual test environments and thus provides a significant contribution to the research of modern wireless transmission systems.