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Schiffarth, Anna-Malin; Julian Ta, Thanh Tam; Schilling, Lisa-Marie; Bornkessel, Christian; Hein, Matthias; Heberling, Dirk
Characterization of typical instantaneous exposure and usage scenarios in the vicinity of 5G massive-MIMO base stations. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), insges. 5 S.

A recurring discussion is whether it is useful to specify a typical exposure in addition to the theoretical maximum exposure for massive-MIMO systems, but currently no reliable method exists. Therefore, typical 5G use cases are investigated, grouped according to their throughput, and three typical data rates are derived. To evaluate the reproducibility of data rates and corresponding exposures, three measurement runs have been performed at four measurement points (MP) with different cell utilization by other users, while a 5G UE generated the typical data rates in the vicinity of the MP. Furthermore, temporal variations have been considered by evaluating three different averaging times. The results demonstrate that the exposure values are reproducible within typical measurement uncertainty across different averaging times and even across different measurement runs. Therefore, this method is considered to be capable of providing reproducible measurements of the typical exposure in addition to the maximum possible exposure.
Struck, Tobias; Schilling, Lisa-Marie; Hofmann, Willi; Bornkessel, Christian; Hein, Matthias
Hybrid antenna measurement and post-processing for 5G small cell exposure assessment with site-specific mounting conditions. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), insges. 5 S.

Ongoing mobile radio small cell deployment requires detailed analysis of the electromagnetic exposure which is dependent on the installation environment. To facilitate site-specific small cell exposure analysis, a hybrid exposure assessment approach is utilized which combines antenna nearfield measurement and post-processing. An equivalent current antenna model is investigated under virtually varying installation conditions, considering three real applications of small cell installation. The equivalent current antenna model's results are in good agreement with reference measurements and geometry-based simulations. Antenna pattern deviations vary between 0.9 dB and 2.9 dB, depending on the installation environment selected. This highlights the advantages of using the hybrid exposure assessment approach which adequately captures and reflects changes in the installation surroundings. Additionally, it yields comparable results to established methods and provides extensive flexibility for virtual exposure estimations by taking into account varying installation environments.
Bornkessel, Christian; Pikushina, Alena; Schilling, Lisa-Marie; Struck, Tobias; Hein, Matthias
Reproducibility studies of instantaneous and 6-minute average exposure measurements around 5G massive-MIMO base stations. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), insges. 5 S.

Measurements of RF exposure to mobile radio base stations are important for risk communication. We measured instantaneous exposure with a focus on 5G with an exposimeter on an identical route on three afternoons to study the reproducibility. Due to different walking speeds, the relationship between time and place was not identical for the measurements, so time is not suitable as a reference for comparison. When the distance walked was used as reference, accuracy problems of the exposimeter's internal GPS system occurred, resulting in a mismatch between the actual location and the GPS location. This problem was successfully corrected by using the gradient descent with momentum method. The three measurements show a variation in maximum measured exposure of up to 5.4 dB for a selected section of the route, which is reduced to 2.8 dB when averaged over 6-minute intervals, which is acceptable given typical measurement uncertainties of ±3 dB.
Pikushina, Alena; Centeno, Luis Fernando; Stehr, Uwe; Jacobs, Heiko O.; Hein, Matthias
Electrical lengths and phase constants of stretchable coplanar transmission lines at GHz frequencies. - In: Flexible and printed electronics, ISSN 2058-8585, Bd. 9 (2024), 1, 015005, S. 1-12

Elastic, bendable and stretchable electronics establish a new and promising area of multi-physics engineering for a variety of applications, e.g. on wearables or in complex-shaped machine parts. While the area of metamorphic electronics has been investigated comprehensively, the behavior at radio frequencies (RFs), especially in the GHz range, is much less well studied. The mechanical deformation of the soft substrates, for instance, due to stretching, changes the geometrical dimensions and the electrical properties of RF transmission lines. This effect could be desirable in some cases, e.g. for smart devices with shape-dependent transmission or radiation characteristics, or undesirable in other cases, e.g. in feed and distribution networks due to the variable electrical lengths and thus phase variations. This contribution describes the results of a systematic study of the broadband RF properties of coplanar transmission lines on Ecoflex® substrates, based on numerical simulations and experimental data. Two types of stretchable transmission line structures were studied: Meander- and circular ring-segmented lines. Modeling and simulation were performed combining a 2D circuit simulation software with electromagnetic full-wave simulations. The experimental part of the work included the fabrication of metamorphic substrates metallized with thin copper layers and systematic measurements of the electrical lengths and phase constants of coplanar waveguides in the frequency range from 1 to 5 GHz based on vector network analysis for different stretching levels. With the given substrate technology, we succeeded in demonstrating stretchability up to a level of 21%, while the theoretical limit is expected at 57%. The meander- and circular-shaped line structures revealed markedly different sensitivities to the stretching level, which was lower for circular structures compared to the meander structures by approximately a factor of three.
Berlt, Philipp;
Messkonzepte für Funksysteme bei Mobilfunk-basierter Fahrzeugkommunikation. - Ilmenau : Universitätsbibliothek, 2023. - 1 Online-Ressource (ii, 171 Seiten)
Technische Universität Ilmenau, Dissertation 2023

Die vorliegende Arbeit beschäftigt sich in interdisziplinärer Weise mit Fragestellungen und anhand von over-the-air Tests mit Lösungsansätzen zur Antennenmesstechnik und Funkkanalemulation sowie mit Testverfahren bei LTE-basierter Mobilkommunikation im Kontext vernetzter Automobile. Die Herausforderung besteht darin, dass der Speisepunkt der Antennen aufgrund des Einbauzustandes im Fahrzeug sowie der fortschreitenden Integration von Antennen und Empfängern nur schwer oder gar nicht zugänglich ist. Durch Nutzung modulierter Kommunikationssignale gelingt es, direkt und ohne komplexe Algorithmen dreidimensionale Gewinn- und Phaseninformation von Fahrzeugantennen im Einbauzustand aus einfachen Leistungsmessungen zu ermitteln. Kenntnis des Phasendiagramms der Antennen ist insbesondere bei der Übertragung mit mehreren Antennen essenziell und wird außerdem für die Bestimmung der Position von Antennen anhand ihres Phasenzentrums benötigt. Nach der Charakterisierung der Strahlungseigenschaften der Antennen werden diese als Teil einer Funkumgebung betrachtet und in der Funkkanalnachbildung berücksichtigt. Für die Bestimmung der Leistungsfähigkeit von Fahrzeugantennen durch die Emulation drahtloser Ausbreitungskanäle wurden im Rahmen dieser Arbeit mittels programmierbarer Funkmodule Alternativen zu etablierten Kanalemulatoren sowie die Zahl und Anordnung von Beleuchtungsantennen für die Nachbildung räumlicher Eigenschaften erforscht. Im Bereich realer und virtueller Fahrtests mit vernetzten Automobilen bestehen die Ergebnisse dieser Arbeit aus einem Messkonzept für virtuelle Fahrtests mit dem Ziel der Nachbildung relevanter Ausbreitungseffekte aus realen Fahrtests. Als relevantes Testszenario wurden die Grenzbereiche zwischen Mobilfunkzellen, bzw. die Nachbarbasisstation als größter Störeinfluss, identifiziert. Anhand gezielter Regelung von Nutz- und Störsignalpegeln im virtuellen Test kann das Verhalten des Testgeräts an den kritischen Stellen in Nähe der Zellränder mit Schwankungen < 5 % nachgebildet werden. Dieses Konzept ermöglicht einen einfachen Test, ohne notwendigerweise detaillierte Kenntnis des Funkkanals haben zu müssen, indem der Fokus auf der Nachbildung von für die Übertragung kritischen Szenarien anstelle der Nachbildung eines spezifischen Funkkanals liegt.
Hein, Matthias; Saccardi, Francesco
Automotive antenna measurements at VISTA. - In: Reviews of electromagnetics, ISSN 2709-4057, Bd. 2 (2023), S. 17-18
Enthalten in Roadmap paper: Antenna measurement challenges and opportunities, guest editors: Olav Breinbjerg and Manuel Sierra-Castañer
Stehr, Uwe; Hasnain, Syed N.; Bieske, Björn; Brachvogel, Marius; Meurer, Michael; Hein, Matthias
LO and calibration signal distribution in a multi-antenna satellite navigation receiver. - In: Engineering proceedings, ISSN 2673-4591, Bd. 54 (2023), 1, 23, S. 1-10

Due to the low signal power of global navigation satellite signals, the receivers are prone to radio frequency interference. Employing multi-antenna arrays is one method to mitigate such effects, by incorporating spatial processing techniques. The large size of the uniform rectangular arrays prevents their use in applications where installation space is limited. Therefore, we proposed a new approach, namely to split one full array into a number of smaller, spatially distributed, sub-arrays to reduce their size and exploit available installation spaces. This concept challenges the distribution of the local oscillator and calibration signals to the respective sub-arrays. This paper compares qualitatively different design concepts for a satellite navigation receiver with two two-element sub-arrays, installed multiple wavelengths apart from each other, in support of establishing an optimal choice for our intended applications in the automotive sector in terms of electrical performance and required hardware and software efforts. In general, weighing the pros and cons of the different concepts, as discussed in the paper, will assist in optimizing the system design approach for a specific application.
Tayyab, Umais; Kumar, Ashish; Petry, Hans-Peter; Robbani, Md. Golam; Wack, Thomas; Hein, Matthias
Circularly polarized patch antenna array for 5G automotive satellite communications. - In: 2023 53rd European Microwave Conference, (2023), S. 794-797

5G low-earth orbit (LEO) satellite communication plays a crucial role in enhancing the reliability and coverage of wireless connectivity for automated and connected driving. Compactness of user equipment antennas presents a key requirement for automotive mass-market applications offering non-terrestrial connectivity in addition to terrestrial mobile communications. Latest studies reveal the potential for moderate-gain antenna terminals for such applications. We present a circularly polarized 4 × 4 patch antenna array operating at a center frequency of 2S GHz in the 5G new-radio band n257 suitable for LEO satellite communications. The antenna is feasible for integration into the rear spoiler of a car, roof-top shark-fin antenna, or other plastic-covered antenna mounting locations. The embedded array offers 12 dBi measured realized gain and 4 GHz of -10 dB impedance bandwidth. It offers a 3-dB axial-ratio bandwidth of 900 MHz, demonstrating its circular polarization purity along the broadside direction. Realistic link budget calculations predict an uplink data rate of 6 Mbit/s, promising for various automotive mobility applications.
Aust, Philip; Hau, Florian; Dickmann, Jürgen; Hein, Matthias
Numerical synthesis of radar target detections based on measured reference data. - In: 2023 20th European Radar Conference, (2023), S. 26-29

Virtual validation methods strive to reduce the testing efforts of automated driving functions significantly. However, assuring the fidelity of deployed sensor models based on objective criteria remains an unsolved challenge, especially for radar target detection point clouds, since they are subject to major stochastic fluctuations.This work focuses on the scenario-based derivation of requirements for synthetic radar target detections, which are deduced from sensor data recorded in real-world test drives. Based on these reference data, deviations between the radar point clouds from different recordings are quantified using metrics for both point clouds from single measurement cycles and relative probability distributions for accumulated point clouds. Finally, the suitability of the calculated reference values as adequate metrics of deviations between recorded and simulated sensor data is evaluated.
Scialacqua, Lucia; Foged, Lars J.; Berlt, Philipp; Altinel, Berk; Bornkessel, Christian; Hein, Matthias; Hoppe, Reiner; Hager, Thomas; Soler Castany, Jordi
Combination of measurement and simulation for fast virtual drive testing. - In: 2023 IEEE International Symposium on Antennas and Propagation (and USNC-URSI Radio Science Meeting), (2023), S. 25-26

Virtual Drive Test (VDT) is an area of great interest for both scientific research and industry. The objective of VDT is to emulate a real-world communication testing by approximation of defined conditions. VDT can be performed in measurement facilities with over-the-air approaches and channel emulation techniques [1] [2], by simulation-based software-in-the-loop tests [3] or by combining measurement and simulation [4]. For all possible solutions, the challenge of the scientific community is to look for an automated, controllable, repeatable, and reliable procedure, which can considerably reduce testing time and costs. In this paper we present a new VDT technique to evaluate the V2X communications performances based on the combination of measurement and simulation. In particular, the radiation performance of a DUT representing the antenna under test installed on a vehicle is tested in a measurement facility, the radiation pattern (vehicle equipped by the antenna) is integrated in a simulation of a realistic scenario to reproduce a real-world communication testing. The accuracy of the method is validated by comparison with results of measured data from Field Operational Test (FoT) of LTE links [5] [6].