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Increasing demands in radar sensor performance for automotive applications require reliable test solutions for the development and verification. In this paper, a modulation-based radar target simulator suitable for automotive settings is presented. A cost-effective circuit with low complexity is proposed that modulates the radar signal directly in the E-Band without an intermediate frequency stage. Models are derived for predicting the limitations of such radar target simulators due to hardware nonidealities. The introduced radar target simulator is analyzed with respect to the derived nonidealities in order to predict its performance based on the models. As a verification, radar measurements with the target simulator are conducted, and compared with the models' predictions., acceptedVersion

With modulation-based radar target simulators, complex traffic scenarios can be simulated for automotive radars at low costs. Yet the simulation principle relies on the timings of the chirp-sequence frequency modulated continous waveform. Since small timing variations can be purposely introduced on the radar's waveform e.g. for interference mitigation techniques, the assumption of ideal timings could be violated. Therefore, this paper investigates the influences of ramp timing deviations on the target simulation. A signal model for radar timing variations for modulation-based simulators is presented. Furthermore, the influence of ramp timings on the resulting signal-to-noise ratio of simulated target responses is derived and verified by measurements., acceptedVersion

A novel mechanically flexible filter integrated in a glass dielectric waveguide is presented for sensor applications at G-band (140–220 GHz). The use of laser-induced deep etching (LIDE) technology enables the production of via holes and thus the local modulation of the effective permittivity in a dielectric waveguide. This approach enables the implementation of a filter without the use of metal structures. In addition, extraordinary mechanical flexibility is achieved through meandering slots, which simultaneously perform the permittivity modulation. The RF performance was studied in full-wave simulations and validated by measurements of the manufactured bandstop prototypes. The experimental results of the implemented filter element show good agreement with the simulated values. At the center frequency of 156 GHz a notch depth below −14 dB in the measured stop band is achieved. Additional measurements show a stable filter characteristic at up to 8◦ bend angle applicable for the use as a low-loss waveguide under harsh environmental conditions, acceptedVersion

This paper presents novel data augmentation techniques for gesture recognition based on multistatic Doppler spectrograms. Contrary to intricate approaches such as generative models or simulations, the presented methods generate additional samples by manipulating data in time and Doppler frequency domain. Thus, they resemble well-known techniques from computer vision tasks, but produce physically plausible data. Moreover, based on a comprehensive dataset a thorough investigation of the impact of training data extent on cross-subject validation accuracy is conducted. It is demonstrated that accuracy tends to saturate with growing training sets, and that the techniques presented in this work can help to reach the accuracy at saturation with only half the number of measurements., acceptedVersion

In this work, a novel multi-feed synthesis for holographic leaky-wave (LW) antennas is presented that considers the angular dependence of each pixel structure. This approach of combining multiple single-beam holograms minimizes the impedance error w.r.t. each individual impedance hologram. A multi-feed antenna with two feeding points at 20GHz is fabricated and measured using this new design methodology. The simulation and measurement results show a good agreement. The fabricated LW antenna has a gain of 21.7 dBi and 22.1 dBi and a side lobe level (SLL) of 9.0 dB and 9.6 dB for both feeds., acceptedVersion

The repeatability of radar sensor tests is of high importance, in order to allow for a better comparability. Guaranteeing consistent test conditions is therefore essential. This article describes a radar target simulator able to simulate a traffic scenario for chirp-sequence frequency modulated continuous wave radar sensors, based on measurement data. First, the system setup is briefly presented, that is used to generate the targets, afterwards the major challenges and required signal processing steps are laid out. Finally, a comparison between the original measured scenario data and the replayed version is conducted., acceptedVersion

Multiple sensors in a radar network can be jointly evaluated to process the bistatic Doppler information of a target obtained under different aspect angles. This enables the estimation of the target’s vectorial velocity in a single snapshot. As a precursor to the joint evaluation, the monostatic and bistatic Doppler components need to be matched for each target in the range-Doppler map. In this work, a new approach for the target matching in the case of a radar-repeater network is presented. The matching is performed based on the correlation of monostatic and bistatic steering vectors extracted from the range-Doppler map for each receive channel of the radar. After validating the matched responses, the vectorial target velocity is determined. The approach is successfully tested with a 77 GHz radar and two repeaters by measurements of rotating cylinders., acceptedVersion

A wideband and robust design of a dielectric rod antenna at G-band (140 GHz–220 GHz) for short range radar applications in harsh environmental conditions is presented. The proposed antenna is based on a simple plug-in solution made of PEEK material (εr,PEEK =3.2), which enables the mechanically detachable integration into a glass-encapsulated millimeter wave radar sensor system. To further increase the antenna gain, an optically transparent biconvex lens is presented. The antenna performance has been investigated by full wave simulations and validated through measurements of the fabricated antenna prototype. The experimental results of the realized antenna element show excellent agreement to the simulated values. The rod antenna covers a 3 dB-beam width of 46° and achieves a maximum gain of 12.4 dBi. The additional use of the dielectric lens increases the gain to 30.4 dBi with a stable beam pattern over the entire modulation bandwidth of 20 GHz of the radar sensor. The measured 3D-radiation patterns at various frequencies across the operational band are provided., acceptedVersion

Radar simulations of human targets can be deployed to reduce the measurement effort linked to dataset generation for tasks such as gesture or activity classification. However, simulations require realistic human motion data in order to capture the dynamics of the simulated activities. For this purpose, this paper proposes a stereo camera-based system that enables simultaneous recording of radar data and the corresponding human pose ground truth. By introducing a camera-radar calibration procedure, the 3D human poses and the radar system are synchronized both in time and space. Thus, the system enables the one-by-one re-simulation of the captured measurements for the investigation of simulation quality or sensor studies. The performance of the calibration procedure and the feasibility of direct re-simulations is shown with measurements of an exemplary gesture. In addition, the straightforward extension of the proposed approach to radar sensor networks is demonstrated., acceptedVersion

In autonomous driving, the detection of all relevant road users is a key requirement for the sensors. In order to improve the detection capability and to increase the signal to noise ratio, transmit (Tx) beamforming can be applied. In this paper, the possibility of adaptive Tx beamforming in a multiple-input multiple-output radar imaging system using state-of-the-art radar transceivers is analyzed both in theory and by measurements. The imaging performance is shown for an exemplary intersection scenario, using an antenna system with a high virtual channel count exceeding the state-of-the-art. For the first time, high-resolution radar images are shown both with and without Tx beamforming. To enable the detection of a pedestrian in the proximity of a strong target, such as a car, the target response and side lobes of the strong target can be weakened by more than 11 dB, even at a large incident angle., Beim autonomen Fahren ist die Erkennung aller relevanten Verkehrsteilnehmer eine zentrale Anforderung an die Sensoren. Um die Erkennungsfähigkeit zu verbessern und das Signal-Rausch-Verhältnis zu erhöhen, kann sendeseitiges (Tx) Beamforming angewendet werden. In diesem Beitrag wird die Möglichkeit adaptiven Tx-Beamformings in einem bildgebenden Multiple-Input-Multiple-Output-Radarsystem mit modernen Radartransceivern sowohl theoretisch als auch messtechnisch untersucht. Die Leistungsfähigkeit der Bildgebung wird für ein beispielhaftes Kreuzungsszenario gezeigt, bei dem ein Antennensystem mit einer hohen virtuellen Kanalzahl verwendet wird, die den Stand der Technik übertrifft. Zum ersten Mal werden hochauflösende Radarbilder sowohl mit als auch ohne Tx-Beamforming gezeigt. Um die Erkennung eines Fußgängers in der Nähe eines starken Ziels, z. B. eines Autos, zu ermöglichen, können die Zielantwort und die Nebenkeulen des starken Ziels um mehr als 11 dB abgeschwächt werden, selbst bei einem großen Einfallswinkel., acceptedVersion

In order to test and verify radar based systems for advanced driver assistance systems (ADAS), radar target simulators offer a test environment for reproducible dynamic automotive scenarios. This article presents a system capable of generating multiple targets with individual ranges and velocities for chirp-sequence frequency modulated continuous waveform (CS-FMCW) radars. The novel approach allows to generate targets without prior knowledge about the radar sensor by estimating the radar���s waveform parameters. The proposed simulator offers high flexibility at low costs by performing the estimation on undersampled data. Finally, an automotive scenario of a spacially extended target is simulated for a radar sensor with the proposed system., acceptedVersion

Although the beginning of research on automotive radar sensors goes back to the 1960s, automotive radar has remained one of the main drivers of innovation in millimeter wave technology over the past two decades. Today, millions of sensors are produced each year, which was made possible by inexpensive and mature millimeter wave technology. The technology maturity, in turn, enables research to be carried out on systems that are considerably more complex and powerful than was possible just a few years ago. The focus of research has thus shifted from purely hardware-oriented and device-level topics to sophisticated millimeter wave systems and RF signal processing topics. This opens up new research topics such as digital modulation schemes, radar networks, radar imaging, and machine learning. In this review paper, we sketch the path from the very beginning through the state of the art with sophisticated multiple-input multiple-output (MIMO) antenna arrays and mature assembly and interconnect concepts to today’s key research topics of automotive radar., publishedVersion

Due to its noise-like signal property, digital orthogonal frequency-division multiplexing (OFDM) radars are often assumed to be robust against interference. While a lot of research has been carried out for interference between different modulation schemes, the mechanisms of interference from OFDM to OFDM radars have been barely addressed. This paper provides a thorough analysis of mutual OFDM to OFDM interference based on radar measurements using a 4x4 77 GHz multiple-input multiple-output (MIMO) OFDM radar prototype. The effects of interference are described both qualitatively and quantitatively for cyclic-prefix and stepped-carrier OFDM. Second, it is shown that conventional mitigation methods in the spectrogram are not suitable due to the random coding of cyclic-prefix OFDM. As an alternative, the application of adaptive beamforming is proposed and two realization possibilities are provided. Finally, new mitigation strategies in the modulation domain are proposed. They allow to shape interference to specific range-Doppler cells, yielding an interference-free range-velocity map for the area of interest. Additionally, the method may be used as the basis to enable simple conventional interference mitigation strategies., publishedVersion

In this paper a thorough system analysis to evaluate the overall imaging performance of millimeter wave radar systems is presented. All relevant noise influences and their influence on the system performance are considered. A comparison of two imaging radar systems at 160 GHz with different hardware architectures is discussed, one of which is based on monolithic microwave integrated circuits (MMICs) optimized for low phase noise. Radar measurements are performed to evaluate the achievable imaging performance with both realized radar demonstrators. It is shown that the optimization of the phase noise of a single MMIC is not necessarily advantageous when used for multi-channel radar systems., acceptedVersion