Angle-dependent reflectivity of microwave absorbers at oblique wave incidence. - In: IEEE Xplore digital library, ISSN 2473-2001, (2022), S. 233-236
For frequencies in the GHz-range, anechoic chambers are usually evaluated using ray-tracing techniques to locate disturbing reflections off the chamber walls. Most approaches reduce this wave-absorber interaction to a specular reflection, although the absorbers may extend over several wavelengths in size and display a rough surface. In order to develop more realistic ray-tracing models, the reflection characteristics of absorbers must be evaluated based on physical wave phenomena. In this paper, a measurement method is proposed which extends the established NRL-arch to measure the angle-dependent reflectivity for non-specular cases. First measurement results of commercial pyramidal absorbers in the frequency range between 1GHz and 10GHz indicate that the assumption of specular reflections is not justified, as power is reflected over a wide angular range with approximately the same intensity. This effect is, to our knowledge, currently not implemented in ray-tracing methods. These results contribute to a better understanding of the properties of RF absorbers to improve the efficiency of their use.
Impact of small-cell deployment on combined uplink and downlink RF exposure compared to the status quo in mobile networks. - In: IEEE Xplore digital library, ISSN 2473-2001, (2022), S. 618-621
As new cellular technologies are introduced in mobile networks nowadays, more and more small cells and mobile road side units are being deployed to upgrade the performance of the wireless communication network. With regard to the overall human RF exposure, the question arises to what extent the exposure is affected by the deployment of such small cells compared to macro cells as the status quo. In an attempt to answer this important question, this paper proposes a method to measure and evaluate the combined uplink and downlink exposure in terms of the specific absorption rate of a mobile phone user at recently installed small cell locations. The comparison between the small cell and macro cell scenarios revealed a reduction of the total exposure when the user equipment was logged into the investigated LTE small cells, although the downlink exposure increased. The main reason for this encouraging result is the reduction of the uplink transmission power due to the improved link conditions across the small cell. In contrast, the total exposure in a macro cell scenario is dominated by the uplink exposure. In order to minimise the total exposure, a balance must be sought between downlink and uplink exposure.
A data-driven approach for stochastic modeling of automotive radar detections for extended objects. - In: IEEE Xplore digital library, ISSN 2473-2001, (2022), S. 80-83
Radar sensors play an important role in automated driving technologies. However, the rising number of sensors deployed to enable autonomous driving functions leads to enormous validation efforts. While simulations are a possible approach to accelerate the validation process, the development effort for realistic sensor models increases significantly. Data-driven sensor models offer the possibility to replicate sensor data accurately and efficiently. Using real measurement data, the sensor output can be simulated without the detailed parametric modeling of the wave propagation and sensor effects. In this paper, the radar signatures of a passenger vehicle under a constant aspect angle are analyzed in real measurements. Then, a data-driven approach for stochastically modeling the radar target detections is presented. The model is trained with real sensor data to achieve a high degree of realism. A qualitative comparison between the simulated and measured detections reveals promising results.
Concept for virtual drive testing on the basis of challenging V2X and LTE link scenarios. - In: IEEE Xplore digital library, ISSN 2473-2001, (2022), insges. 5 S.
Virtual drive tests using the over-the-air/vehicle-in-the-loop method are becoming an essential part of testing vehicular radio systems. Different approaches address the question which link scenarios and channel environments are relevant, and should be tested. Up to now, this question has not been fully answered. This paper deals with the identification of challenging scenarios for the wireless transmission standards LTE and ITS-G5 based on jointly performed drive tests, and how these can be transferred into a virtual test concept. In the case of LTE, the focus is on the transition region between different mobile radio cells (cell edge). We have reproducibly observed that the achievable data throughput drops significantly at cell edges compared to the cell centers. For ITS-G5, the communication limit was examined as a function of the distance and visibility conditions between two communicating vehicles.
Analysis of instantaneous and maximal RF exposure in 4G/5G networks with dynamic spectrum sharing. - In: IEEE Xplore digital library, ISSN 2473-2001, (2022), insges. 5 S.
From mid of 2020 to mid of 2021, the 3G mobile radio network in Germany was gradually replaced by the successor technologies 4G and 5G. Therefore, dynamic spectrum sharing (DSS) was introduced in the 2100 MHz band, which allows a parallel operation of 4G and 5G. There is an increasing need of public information with regard to a possible change in human RF exposure associated with 5G and DSS. Hence, investigations were carried out to study the instantaneous and maximal exposure of persons to base stations in the 2100 MHz band. Our study shows, that the instantaneous exposure has remained comparable before and after the introduction of 4G/5G with DSS. Regarding the maximal RF exposure, code-selective measurements of 3G and 4G with DSS show no significant change in exposure. To analyze the maximal exposure to 5G with DSS, code-selective measurements have been applied for the first time and compared with the 4G exposure in the same band. The results show no significant difference in maximal exposure between 4G and 5G. Furthermore, the need of code-selective measurements in comparison with the frequency-selective method for 5G is demonstrated if different parts of the electromagnetic field that contribute to exposure have to be assigned to selected base stations.
Robustness testing of a compact distributed automotive GNSS array in virtual environment. - In: IEEE Xplore digital library, ISSN 2473-2001, (2022), insges. 5 S.
To develop a compact distributed array for safe and robust automotive satellite navigation, considerable work on testing prototypes is in progress. Before scheduling resource-hungry outdoor tests, functionality and robustness of a Galileo-compatible compact distributed 4-element L-shaped array receiver has been tested against interference in a virtual environment at E5a frequency band. Such an array consisting of compact quarter wavelength sub-arrays distributed over many wavelengths, fed with a decoupling network, mounted in side mirrors of a mock-up car was measured and evaluated with and without a jammer. The effects of automotive mounting location and robustness of the receiver against the jammer have been analyzed in terms of measured radiation patterns and achieved carrier-to-noise-density ratio of the received satellite signals.
Automotive antenna measurements in the installed state under variable boundary conditions. - In: IEEE Xplore digital library, ISSN 2473-2001, (2022), insges. 4 S.
Automotive antenna measurements are typically performed in an anechoic (free-space) or semi-anechoic (reflective ground) environment. Even though measurements under these conditions provide sufficient knowledge about antenna performance, the automotive industry often desires to evaluate installed automotive antennas under practical road conditions. This requires a combined approach to test and qualify vehicular antennas; however, facilities deploying variable boundary conditions for measurements are challenging to devise. Alternatively, numerical simulations can be used to perform such investigations; nevertheless, it is essential to verify such simulations through measurements. In the Virtual Road Simulation and Test Area (VISTA) of the Thuringian Center of Innovation in Mobility at the Technische Universität Ilmenau, a new approach to provide variable boundary conditions for antenna measurements is realized to evaluate the impact of different electromagnetic boundary conditions and to bridge the gap between numerical simulations and measurements. It consists of a modular and mechanically robust plastic frame carrying a customizable fabric substituting a ground plane. This paper presents and discusses the initial measurement results of a reference antenna and an installed automotive antenna performed over the conducting fabric. The convincingly good correlation of more than 74% between the measured data and numerical simulations shows the validity of the proposed method.
Analysis of microwave absorber scattering using ray-tracing and advanced measurement techniques. - In: IEEE Xplore digital library, ISSN 2473-2001, (2022), insges. 5 S.
Ray-tracing methods can be applied to evaluate the wave propagation in anechoic electromagnetic environments, in order to improve measurement concepts, or to address the increasing demands on test concepts for new radio wireless transmission functionalities. The accuracy of the data obtained from such a chamber model depends crucially on the modeling of the microwave absorbers. Often the scattering off the absorbers is simplified by specular reflections, ignoring the actual direction-dependent scattering properties of the absorbers resulting from their geometry, arrangement, and material. As this may cause significant misconceptions, improved ray-tracing models of absorbers based on their scattering character are needed. In this paper, the scattering of two types of 18″ absorbers with pyramidal and wedge geometries is analyzed and expected scattering patterns are described. Based on an existing shooting-and-bouncing-rays software, a simulation approach is introduced and used to relate the analytical findings with results of measurements of the angle-dependent reflectivity. In addition to the primarily specular reflection for wedge absorbers and scattering in many directions off the pyramidal absorbers, the results show that nearfield effects influence this scattering pattern, as eventually confirmed by the simulations.
Evaluation of integral quantities of over the air automotive antenna measurements. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), S. 1954-1955
This document outlines the Over the Air (OTA) testing methodology which is currently employed for full automotive antennas and provides a pertinent Figure of Merit.
Plastic-embedded patch antenna array for automotive satellite communication in the Ka-band. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), S. 1-4