arXiv subjects

Dirk Heberling

Publications and source records attributed to Dirk Heberling.

7 recordsLinked to original sources

arXiv2026

A 28-GHz Varactor-Based RIS With Continuous Phase Control: From Unit-Cell Modeling to Programmable Wavefront Control and Synthesis

This paper presents a 28 GHz varactor-based reconfigurable intelligent surface (RIS) platform with continuous phase control and establishes a unified device-to-system validation framework for programmable wavefront control and synthesis. The proposed RIS comprises 96 independently controlled elements, each employing a single varactor diode, with a board-integrated analog-bias control architecture. It builds on an experimentally validated unit-cell model providing approximately 300{\deg} of continuous reflection-phase tuning at normal incidence. An analytical framework incorporating measured horn illumination, finite phase availability, and unit-cell reflection losses consistently relates device-level characteristics to beamforming performance. It is evaluated via near-field-to-near-field characterization, near-field-to-far-field beam-steering, and far-field-to-far-field wireless-link experiments. The near-field-to-far-field results show close agreement among analytical predictions, full-wave simulations, and measurements, while the far-field-to-far-field response agrees with simulation and a first-order link-budget estimate. Accurate steering is demonstrated for all investigated angles within $\pm$45{\deg} across three azimuthal planes, with maximum deviation of approximately 2{\deg}. The complete prototype, including driver and bias network, draws only 0.85 W with an estimated full-aperture reconfiguration time of approximately 50 ms. Beyond beam steering, the same platform enables experimental investigation of 3-bit, 2-bit, and 1-bit phase quantization and programmable multi-beam wavefront synthesis using a common RF aperture and control architecture. Collectively, these results bridge realistic varactor behavior, analytical modeling, and programmable wavefront synthesis, providing a rigorous basis for developing and experimentally validating continuously tunable millimeter-wave RISs.

physics.app-ph↗

arXiv2025

Influence of Transmission Rank on EMF Exposure Measured With Provoked Data Traffic Around 5G Massive MIMO Base Stations

The introduction of 5G New Radio networks with massive MIMO technology has complicated electromagnetic field exposure assessments for radiation protection. Massive MIMO transmission enables beamforming, beam steering, and spatial multiplexing across multiple transmission layers, with the number of simultaneous transmission paths depending on the rank of the radio channel, further named 'transmission rank'. Since the total transmission power of a base station is shared among these layers, rank variations affect the measured exposure levels, e.g., when assessments use provoked traffic via user equipment. This study investigates the impact of the transmission rank on the measured maximum exposure in the 3.6 GHz (n78) band of a German 5G network employing massive MIMO technology. Field measurements were performed using a spectrum analyzer with isotropic probe, to capture maximum field strengths under full-load traffic conditions. The transmission rank was manipulated by artificially degrading the reception quality of the user equipment with a shielding bag, forcing a single transmission layer (rank-1). The results were compared with unshielded operation allowing up to the maximum number of four independent transmission layers (rank-4). The data reveal exposure differences ranging from 1.7 dB to 5.4 dB, with a median of 4.3 dB at the measurement points studied. These findings highlight the necessity of considering the transmission rank in exposure assessments to electromagnetic fields.

eess.SY↗

arXiv2024

Generative Adversarial Synthesis of Radar Point Cloud Scenes

For the validation and verification of automotive radars, datasets of realistic traffic scenarios are required, which, how ever, are laborious to acquire. In this paper, we introduce radar scene synthesis using GANs as an alternative to the real dataset acquisition and simulation-based approaches. We train a PointNet++ based GAN model to generate realistic radar point cloud scenes and use a binary classifier to evaluate the performance of scenes generated using this model against a test set of real scenes. We demonstrate that our GAN model achieves similar performance (~87%) to the real scenes test set.

cs.CV↗

arXiv2024

Theory of Seamless-Scanning Periodic Leaky-Wave Antennas based on $\mathcal{PT}$-Symmetry with Time to Space Mapping

Periodic Leaky-Wave Antennas (P-LWA) offer highly directive and space-scanning radiation. Unfortunately, they have been plagued by the ``broadside issue'', characterized by a degradation in gain when the antenna's main beam is steered across broadside. While this issue has been addressed by circuit and network approaches, a related fundamental and general electromagnetic theory has been lacking. This paper fills this gap. We first show that a P-LWA is a $\mathcal{PT}$-symmetric system, whose even- and odd-mode coupling in the complex space of temporal frequencies leads to the characteristic pair of two-sheet Riemann surfaces. We observe that the branch cuts of these surfaces, which form the well-known $\mathcal{PT}$-symmetric double pitchfork spectrum, correspond to the ``balanced frequency'' condition, while the branch point at the junction of the pitchforks, is an exceptional point that corresponds to the ``$Q$-balanced'' condition, two conditions that where previously shown to be the conditions for eliminating the broadside issue. In order to acquire an independent and rigorous interpretation of this spectrum, we further transform the coupled complex temporal eigenfrequencies into complex spatial eigenfrequencies. We identify the resulting spatial frequencies as coupled forward-backward modes, with frequency-independent imaginary parts (leakage factors), a condition for P-LWA equalization across broadside. Finally, we derive the scattering parameters of the P-LWA and show that matching is achieved only at one of the two ends of the P-LWA structure. This work both provides a solid foundation to the theory of P-LWAs and represents an original contribution to the field of $\mathcal{PT}$-symmetry.

physics.app-ph↗

arXiv2024

Landmark-based Vehicle Self-Localization Using Automotive Polarimetric Radars

Automotive self-localization is an essential task for any automated driving function. This means that the vehicle has to reliably know its position and orientation with an accuracy of a few centimeters and degrees, respectively. This paper presents a radar-based approach to self-localization, which exploits fully polarimetric scattering information for robust landmark detection. The proposed method requires no input from sensors other than radar during localization for a given map. By association of landmark observations with map landmarks, the vehicle's position is inferred. Abstract point- and line-shaped landmarks allow for compact map sizes and, in combination with the factor graph formulation used, for an efficient implementation. Evaluation of extensive real-world experiments in diverse environments shows a promising overall localization performance of $0.12 \text{m}$ RMS absolute trajectory and $0.43 {}^\circ$ RMS heading error by leveraging the polarimetric information. A comparison of the performance of different levels of polarimetric information proves the advantage in challenging scenarios.

cs.RO↗

arXiv2023

Exceptional Point Perspective of Periodic Leaky-Wave Antennas

Over the past decade, the issue of gain degradation at broadside in periodic leaky-wave antennas (P-LWAs) has been resolved, using a circuit modeling approach, by introducing proper asymmetry in the unit cell of the antenna structure. This paper provides a more fundamental and insightful perspective of the problem by showing, using a simple coupled-mode analysis, that the optimal level of structural asymmetry corresponds to an exceptional point of the coupling parameter between the two eigenmodes of the P-LWA. This contribution represents a key step towards the development of a full electromagnetic resolution of the broadside issue.

physics.app-ph↗

arXiv2017

Broadside Dual-channel Orthogonal-Polarization Radiation using a Double-Asymmetric Periodic Leaky-Wave Antenna

The paper demonstrates that double unit-cell asymmetry in periodic leaky-wave antennas (P-LWAs), i.e. asymmetry with respect to both the longitudinal and transversal axes of the structure -- or longitudinal asymmetry (LA) and transversal asymmetry (TA) -- allows for the simultaneous broadside radiation of two orthogonal modes excited at the two ports of the antenna. This means that the antenna may simultaneously support two orthogonal channels, which represents an interesting polarization diversity characteristics for wireless communications. The double asymmetric (DA) unit cell combines a circularly polarized LA unit cell and a coupled mode TA unit cell, where the former provides equal radiation in the series and shunt modes while the latter separates these two modes in terms of their excitation ports. It is also shown that the degree of TA in the DA unit cell controls the cross-polarization discrimination level. The DA P-LWA concept is illustrated by two examples, a series-fed line-connected patch (SF-LCP) P-LWA and a series-fed capacitively-coupled patch (SF-CCP) P-LWA, via full-wave simulation and also experiment for the SF-LCP P-LWA case.

physics.class-ph↗