Results: 486
Created on: Mon, 24 Jan 2022 07:21:48 +0100 in 0.0556 sec

Hofmann, Willi; Schwind, Andreas; Bornkessel, Christian; Hein, Matthias;
Bi-static reflectivity measurements of microwave absorbers between 2 and 18 GHz. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), insges. 6 S.

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.
Asghar, Muhammad Ehtisham; Bornkessel, Christian; Hein, Matthias; Köhler, Thomas; Köcher, Jens; Clauder, Philipp; Stöpel, Uwe;
Simulation and measurement of locomotive antennas in the installed state based on a scaled mockup. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), insges. 6 S.

Accurate characterization of locomotive antennas is key to safe and robust railway signaling and control communication. With the introduction of new technologies and the foreseeable migration from the GSM-R standard towards FRM CS, new wireless applications and specifications arise, and suitable antenna solutions need to be developed and tested. Moreover, the rooftops of modern locomotives present a dense and harsh environment; therefore, potential antenna mounting spaces should be carefully evaluated to avoid undesirable degradations of the antenna radiation patterns. Due to the electrically large and complex structure of locomotives, full-scale testing is challenging to perform, especially under laboratory conditions. Antenna measurements with geometrically scaled models present a powerful alternative to address this issue. In this paper, we present and discuss antenna measurement results of a scaled locomotive mockup. The mockup incorporates two different cabin geometries, one with a step-like rooftop contour, and one with a smooth slightly tilted geometry. First, the optimum scaling factor was identified and validated through numerical simulations. Afterwards, antenna measurements with a scaled locomotive mockup were carried out in our automotive antenna measurement facility VISTA. The measured results were compared with the numerical simulations, where a good correlation above 80 % was found. Secondly, the impact of the rooftop geometries, and superstructures on the roof has been investigated for a range of operational frequencies between 700 and 2600 MHz. The results reveal that the parasitic impact of the antenna environment becomes more pronounced at higher frequencies.
Berlt, Philipp; Bornkessel, Christian; Hein, Matthias;
Precise phase center localization of automotive LTE antennas in the installed state through phaseless LTE uplink measurements. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), insges. 5 S.

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.
Schwind, Andreas; Hofmann, Willi; Stephan, Ralf; Hein, Matthias;
Bi-static RCS variations of pedal and wheel movements on bicycles between 1 and 10 GHz. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), insges. 6 S.

One benefit of cooperative automated and connected driving lies in the fusion of multiple mobile wireless sensor and data transmission nodes, covering complementary technologies like radar, cellular and ad-hoc communications, and alike. Current developments indicate enormous potential to increase the environmental awareness through joint communication and radar sensing. In this respect, future channel models require knowledge of bi-static reflectivities of road users over a range of illumination and observation angles, both in the nearfield and in the far-field. To establish reference data and model such angle-dependent RCS variations, this paper deals with realistic pedal and wheel rotations of a bicycle based on electromagnetic simulations. In the simulation setup, idealized far-field conditions with plane-wave illumination and observation were assumed, while the angles covered the entire azimuth with 201 variations of the pedal and wheel positions. The fluctuation of the RCS is analyzed and discussed in terms of its probability density and cumulative distribution functions. Depending on the angular constellation, the range of the fluctuation varied between 1 dB and 14 dB, while the specular reflection and forward-scattering showed almost no fluctuation.
Mercier, Mathieu; Mioc, Francesca; Rutkowski, Kim; Scannavini, Alessandro; Nowack, Tobias; Bornkessel, Christian; Hein, Matthias;
Evaluation of automotive antenna over the air performance. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), insges. 2 S.

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.
Spira, Steffen; Blau, Kurt; Thomä, Reiner; Hein, Matthias;
Agile multi-beam front-end for 5G mm-wave measurements. - In: International journal of microwave and wireless technologies, ISSN 1759-0795, Bd. 13 (2021), 7, S. 740-750

The 5th generation new radio (5G NR) standards create both enormous challenges and potential to address the spatio-spectral-temporal agility of wireless transmission. In the framework of a research unit at TU Ilmenau, various concepts were studied, including both approaches toward integrated circuits and distributed receiver front-ends (FEs). We report here on the latter approach, aiming at the proof-of-principle of the constituting FEs suitable for later modular extension. A millimeter-wave agile multi-beam FE with an integrated 4 by 1 antenna array for 5G wireless communications was designed, manufactured, and verified by measurements. The polarization is continuously electronically adjustable and the directions of signal reception are steerable by setting digital phase shifters. On purpose, these functions were realized by analog circuits, and digital signal processing was not applied. The agile polarization is created inside the analog, real-time capable FE in a novel manner and any external circuitry is omitted. The microstrip patch antenna array integrated into this module necessitated elaborate measurements within the scope of FE characterization, as the analog circuit and antenna form a single entity and cannot be assessed separately. Link measurements with broadband signals were successfully performed and analyzed in detail to determine the error vector magnitude contributions of the FE.
Singh, Jasmeet; Altinel, Berk; Bornkessel, Christian; Stephan, Ralf; Hein, Matthias;
V2V communication performance of conformal plastic-embedded side-mount antennas investigated with field-operational tests. - In: 2021 IEEE 93rd Vehicular Technology Conference (VTC2021-Spring), (2021), insges. 5 S.

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.
Bornkessel, Christian; Kopacz, Thomas; Schiffarth, Anna-Malin; Heberling, Dirk; Hein, Matthias;
Determination of instantaneous and maximal human exposure to 5G massive-MIMO base stations. - In: Focus on linking antennas and propagation with the automotive and 5G industries, (2021), insges. 5 S.

The roll-out of the 5G standard with novel functionalities brings with it the urgent need to evaluate the human exposure to massive-MIMO base stations. This paper discusses concepts for the measurement of instantaneous and maximal exposure in the sub-6 GHz frequency range (FR1). The concepts have been implemented with the NARDA SRM-3006 selective radiation meter. For instantaneous exposure, the Safety Evaluation mode with an averaging over multiple frequency sweeps has been identified appropriate. First results with provoked data traffic revealed exposures below 0.25 % of the ICNIRP 1998 power density reference levels. For maximal possible exposures, the exposure to the synchronization signal and physical broadcast channel block (SSB) should be measured in the Level Recorder mode and extrapolated to the signal bandwidth considering a measurement point-specific gain difference between traffic and broadcast beams. As another outcome of our studies, we argue that code-selective devices for SSB measurements are urgently needed.
Hasnain, Syed N.; Stephan, Ralf; Brachvogel, Marius; Meurer, Michael; Hein, Matthias;
Performance testing of a distributed automotive satellite navigation array with jammer in virtual environment. - In: Focus on linking antennas and propagation with the automotive and 5G industries, (2021), insges. 5 S.

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.
Altinel, Berk; Bornkessel, Christian; Hein, Matthias;
Wave-physical factors determining the link quality in ITS-G5 studied with field-operational tests. - In: Focus on linking antennas and propagation with the automotive and 5G industries, (2021), insges. 5 S.

Even though vehicular communication systems have been rolled out in road, they remain a prominent field of research and development. The functional and operational safety of vehicle-to-X system demands reliable and efficient methods for verification and validation, based on their functional principles and underlying wave-physical phenomena. To test such systems in virtual environment, we have undertaken empirical studies of the communication channel, to analyze parameters like distance and sight conditions in a rich multipath environment. This paper describes the results and conclusions derived from a set of field-operational tests along a track, with modules operating with ITS-G5. While the results confirm the expectation that field-operational tests aren't reproducible on a quantitative level, we have gained insight into fundamental constraints on the channel parameters and approaches towards emulation in virtual environment. Employing omni-directional roof-mounted antennas, we have observed reliable communication links for ranges up to 250 meters, independent of sight conditions.