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Item type:Publication, Access status: without files , Parametric modeling of cardiac radar signatures via symbolic regressionDue to its contactless nature, vital-sign monitoring using radar has gained increasing attention. The complex relationship between cardiac motion and radar signals makes signal analysis and the development of reliable heartbeat detection algorithms challenging. This work presents a symbolic regression approach for deriving analytical expressions of the phase and magnitude of radar heartbeat signatures, trained on measurements from 30 adults. Similar heartbeat morphologies are clustered prior to learning compact parametric formulas incorporating the heart rate frequency and sinusoidal components representing its harmonics, along with subject-specific scaling parameters. The models enable accurate signal reconstruction of the training data and synthetic heartbeat generation for arbitrary heart rate trajectories, supporting scalable data augmentation to train machine learning models without extensive measurement campaigns.Publicationtype: Conference Paper - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , On embedded radiation pattern effects in MIMO radar and their mitigation using dummy antennasIn antenna arrays, mutual coupling and different electromagnetic boundary conditions cause distortions of the radiation patterns of the antennas, also referred to as embedded radiation pattern. These individual patterns differ in gain and phase and, thus, distort the array manifold. This contribution investigates the effect of the embedded radiation pattern in colocated multiple-input multiple-output MIMO radar, where this distortion affects array signal processing techniques and degrades the system performance. Dummy antennas placed at the edges of dense arrays provide a simple and effective means to equalize the electromagnetic boundary conditions. As a result, dummy antennas reduce pattern deformation and mitigate distortions in the array manifold. Numerical results for direction-of-arrival (DOA) estimation and beamforming demonstrate that performance degradation can be effectively mitigated by incorporating dummy antennas.Publicationtype: Conference Paper - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Reduction of radar channel spatial variability in medical radar applications by means of large antenna arraysIn radar-based vital-sign sensing, the radar sensor operates in the near field of the human body, which is an electrically large target at millimeter-wave frequencies. Consequently, already small-scale random variations of the relative position may lead to severe power level fading and phase variation, thereby potentially impeding the retrieval of vital sign information. To mitigate the spatial variability, this contribution analyzes the application of large antenna arrays rather than single low-directivity antennas. By exploiting spatial diversity, the radar channel variability can be significantly reduced. The simulative predictions are confirmed by scattering measurements with a human-like target at 24 GHz.Publicationtype: Conference Paper - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Simulation framework for the evaluation of the radar channel transfer function in the near field of electrically large targets(Cambridge University Press, 2026-10-05); ; ; ; A simulation framework to evaluate the radar channel transfer function in the near field of electrically large targets is presented in this article. The framework is based on the concepts known from physical optics adapted to the near-field conditions. The impact of the radar antenna characteristics on the scattering, which is non-negligible in the target near field, is incorporated by means of the antenna’s far-field radiation patterns. The inputs of the simulation framework are an STL-file-based model of the target and the gain and phase patterns of the antenna. The required sampling density of the target surface is examined in the context of convergence. The framework accounts for absorption effects due to dielectric or ohmic losses. Because the framework relies on direct evaluations without the need to solve equations, it exhibits a low computational effort, leading to fast computations. The applicability of the simulation framework is validated by measurements with different antennas at 24 and 61 GHz.Publicationtype: Journal Article36 183 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Digital predistortion of power amplifiers for quantum computing(Institution of Engineering and Technology (IET), 2026-09-01); ; ; Power amplifiers (PA) are essential for microwave-controlled trapped-ion and semiconductor spin based quantum computers (QC). They adjust the power level of the control signal and therefore the processing time of the QC. Their nonlinearities and memory effects degrade the signal quality and, thus, the fidelity of qubit gate operations. Driving the PA with a significant input power back-off reduces nonlinear effects but is neither power-efficient nor cost-effective. To overcome this limitation, this letter augments the conventional signal generation system applied in QCs by digital predistortion (DPD) to linearize the radio frequency (RF) channel. Numerical analysis of the qubit behavior based on measured representative control signals indicates that DPD improves its fidelity.Publicationtype: Journal Article16 5 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Electrical and morphological properties of tollens-deposited silver on photopolymer resin relevant to 3D-printed microwave componentsThis work presents the first systematic investigation of the fundamental electrical and morphological properties of Tollens-deposited silver on stereolithography (SLA) 3D-printed polymers. Instead of examining specific waveguides or components, the goal is to establish reliable superordinate process-property relationships for the Tollens-based metallization. Therefore, planar specimens were fabricated to allow quantitative characterization of the metallization. Fundamental process parameters: immersion time, temperature, surface cleaning, and surface pretreatment were systematically varied, and additional influencing factors including ultrasonic assistance, water purity, surface contamination, and repeated metallization were assessed. The characterization included measurements of layer thickness, electrical conductivity, sheet resistance, surface roughness, as well as morphological analysis by scanning electron microscopy and optical microscopy. Depending on the combination of process parameters, the conductivity and layer thickness show significant variations from 27.9 to 6.6 MS/m and 164 to 77 nm, respectively. The best result for a single metallization, 27.9 MS/m and 164 nm, was achieved using deionized water and ultrasonic assistance. The deposited silver thickness is markedly smaller than the surface roughness, and the silver layer is overlain by an island-like layer of irregular silver agglomerates, resulting in an atypical multilayer structure. The findings of this work establish a quantitative basis for the future assessment and optimization of loss and propagation characteristics in microwave components based on 3D-printed, Tollens-metallized photopolymers.Publicationtype: Journal Article23 3 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Determination of the radar channel transfer matrix in the near field of electrically large targets based on physical optics principlesThis contribution deals with the determination of the radar channel transfer matrix in short-range radar applications. In these, the radar antennas are often located in the near field of an electrically large target, in which the scattering properties, in contrast to far-field relationships, depend on distance as well as the antenna. Based on physical optics and the antenna radiation pattern, a bistatic complex-valued transfer function between the feed of a transmit antenna and the output port of a receive antenna is derived. For multiple antennas, it extends to a channel matrix, which allows to predict the radar response of multiple-input multiple-output (MIMO) systems as well as antenna arrays. Measurements of the channel matrix in the case of a disk target conducted with horn and open-ended waveguide antennas at 24 GHz prove the validity of the proposed approach. It accurately predicts near-field effects such as power level fading and nonlinear phase distortion for MIMO radar configurations.Publicationtype: Conference Paper29 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A novel concept for a wake-up receiver for LoRa communication with improved selectivityThis work presents a novel approach for the implementation of a wake-up receiver for LoRa communication. It is designed to exploit the LoRa modulation based on chirp spread spectrum and is inherently less susceptible to false wakeups caused by interfering signals. The theory of the concept is presented indicating key parameters. For validation, a proof-ofconcept implementation is developed with exemplary measurement results.Publicationtype: Conference Paper34 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Impact of prediction delay and machine learning model complexity on the performance of near-real-time CW radar heartbeat detectionContactless vital-sign measurement has gained increasing attention across a variety of sectors, including medical and automotive applications as well as sleep monitoring. Radar-based systems enable the detection of heartbeat-induced microvibrations on the skin surface. This work investigates two key aspects of machine-learning-based near-real-Time heartbeat detection in radar signals: The influence of a prediction delay relative to an electrocardiography (ECG) reference signal and the impact of model complexity. For a systematic analysis, 153 gated recurrent unit (GRU) models have been trained and evaluated. At a delay of 200 ms, F1 scores above 92.7% and interbeat interval (IBI) mean absolute errors (MAEs) of less than 40 ms can be achieved. With increasing delay, the error reduces further, reaching an F1 score of 95.9% and IBI MAE of 23.4 ms at 1300-ms delay. In model complexity analysis, the preferrable combination of model depth, width, and prediction delay strongly depends on the metric of interest.Publicationtype: Conference Paper44 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Feedback-receiver-based compensation of nonlinearities in trapped ion qubit gate signaling(IEEE, 2026-03); ; ; ; This paper presents an analog microwave frontend designed to downconvert and feed back the control signal for trapped ion qubits, which are frequency-multiplexed by the magnetic gradient induced coupling (MAGIC) principle. Shorter gate durations require a higher excitation signal power, increasing distortion caused by nonlinear components. The proposed feedback receiver serves the purpose of coupling out a portion of the generated qubit control signal to feed it back into the signal generation hardware. This enables closed-loop signal processing techniques to compensate for nonlinearities in signal generation, thus improving the idle fidelity of untargeted qubits. The characterization of a manufactured prototype is performed, followed by an active cancellation of spurious tones based on the downconverted qubit control signal to demonstrate the capability for qubit fidelity improvement.Publicationtype: Conference Paper32