News

This week, we will be giving three presentations at the International Conference on Microwaves for Intelligent Mobility. The first of our presentations will take place on Tuesday at 2:10 pm in Session 2, the other two on Wednesday starting from 9:20 am in Session 4.

In the research training group KoRaTo, UAV-based radar systems for the analysis of structures in the subsurface are developed. Recently, a team of the Institute of Microwave Engineering has sucessfully recorded cryospheric measurement data for the first time. For this campaign, we were in Switzerland and worked at the high-altitude research station Jungfraujoch at 3500m.

We are contributing five papers to the European Conference on Antennas and Propagation, which takes place in Glasgow in the upcoming week. Our three talks are in session CS21 (Wednesday), A11 (Thrusday), and CS12a (Friday). The two posters are in poster session PA6 (Wednesday) and PA3 (Thursday), respectively.

Pirmin defended his dissertation on the topic "Konzepte der Radarzielsimulation für komplexe Mehrzielszenarien". Congratulations!

Curious about the impact of uncoupled references on PMCW radar networks? And how to overcome these effects? David Werbunat's latest paper, published in T-MTT, presents an innovative approach to synchronize PMCW radars using digital signal processing techniques. This research addresses effects such as sample and carrier frequency offsets, as well as uncorrelated phase noise, and presents recovery methods to mitigate them. The effectiveness of the concept has been confirmed through successful validation using a 77-GHz radar demonstrator, with very favourable results.

Paper: On the Synchronization of Uncoupled Multistatic PMCW Radars

How could you gather enough radar data for autonomous driving to successfully apply machine learning? This question is investigated by Nicolai Kern and Pirmin Schöder in their latest article, by presenting a new way to generate training data for neural networks. Real test drives are virtually augmented by simulated gesturing pedestrians with a hardware radar target simulator. The generated dataset enables a neural network to successfully identify traffic gestures in-the-wild without ever having seen a real human! Hence, the proposed approach allows to speed up the development of autonomous driving for the future!

Paper: Virtually Augmented Radar Measurements With Hardware Radar Target Simulators for Machine Learning Applications

Tobias Chaloun receives the Best Paper Prize 2022 of the Journal of Microwaves for his paper "Electronically Steerable Antennas for Future Heterogeneous Communication Networks: Review and Perspectives". Congratulations!

Matthias Linder has been recognized as Outstanding Reviewer by the IEEE Journal of Microwaves. Congratulations!

In this article, Adrian Diepolder presents a novel measurement and calibration method for quasi-optical material characterization. It is based on the rotation of the sample around its own axis to vary the angle of incidence at which the sample is illuminated. This method does not require any calibration standards; instead, the sample itself is used to calibrate the system. A highly accurate beam model takes into account a large number of transmitting antennas. Measurements in the frequency range from 220 GHz to 330 GHz of a known aluminum oxide sample verify the calibration method.

Paper: A Novel Rotation-Based Standardless Calibration and Characterization Technique for Free-Space Measurements of Dielectric Material

In the field of autonomous driving, high-precision radar images of the environment are essential for accurate trajectory planning and obstacle detection. In his new journal article, Timo Grebner presents a possibility for synthetic aperture radar (SAR) processing without relying on external localization systems. The relative localization, which must be known with millimeter accuracy in the frequency range of 77 GHz, is carried out exclusively on the basis of the radar data itself. This not only saves costs with regard to the installation of high-precision localization systems such as GNSSs or IMUs, but also enables the algorithm to be used in parking lots or tunnels where GNSS is not or only poorly available. Hence, the work is a breakthrough for cost-effective autonomous driving with the support of radar sensors employing SAR.

Paper: Simultaneous Localization and Mapping (SLAM) for Synthetic Aperture Radar (SAR) Processing in the Field of Autonomous Driving

The paper presents a signal model applicable to low-frequency coupled and uncoupled MIMO radar networks. Additionally, signal processing methods enabling coherent processing in the range, velocity, and angular domain are introduced. We are able to show that phase noise is an insignificant factor in the process of establishing coherency in low-frequency coupled and uncoupled MIMO radar networks for the automotive sector. The presented signal model and proposed signal processing are verified by measurements with MIMO radar networks using CS-FMCW. The network operates at 76 GHz and is composed of two or three radar sensors, corresponding to 768 and 1728 virtual channels, respectively.

Paper: Signal Model for Coherent Processing of Uncoupled and Low Frequency Coupled MIMO Radar Networks

A novel radar network system that enables high-resolution radar imaging by combining a 4x4 OFDM radar with multichannel repeaters! This innovative network configuration presented by David Werbunat in T-MTT creates an extended aperture that provides detailed radar imaging - Without the cost and inflexibility drawbacks associated with large MIMO sensors! The success of the system is evident not only in systematic measurements, but also in automotive scenarios with multiple road users.

Paper: Multichannel Repeater for Coherent Radar Networks Enabling High-Resolution Radar Imaging

In his new journal article, Thomas Frey presents a novel full tensorial synthesis method for holographic-based leaky wave antennas. In order to extract the impedance tensor of an arbitrarily shaped pixel geometry, an angular-dependent nonlinear system of equations is created and solved. A 3D-tensor database is created, resulting in a very accurate realization of the anisotropic impedance tensor. This leads to a significant improvement of the polarization purity and the antenna gain. Based on the full tensorial synthesis method, an anisotropic holographic-based leaky wave antenna prototype is realized on a fused silica wafer for an operation frequency of 160 GHz. The article appears in the IEEE Antennas and Wireless Propagation Letters and is now available in the Early Access.

Paper: A Full Tensorial Synthesis Method for Holographic-Based Leaky Wave Antennas

We congratulate Elias Ruopp on receiving the first prize of the Argus Award 2023 for his outstanding bachelor thesis "Combining Compressed Sensing and Backprojection for UAV-based SAR".

This week we are at the International Conference on Electromagnetics in Advanced Applications in Venice. Our three paper presentations are on Wednesday October 11 in "Session 31: Micro- and mmWave Sensors in Advanced Applications".

In the coming week, the European Microwave Week takes place in Berlin. We contribute seven paper presentation talks, one poster and two workshop presentations.

You will find us in the following conference sessions: EuMC05, EuRAD04, EuMC/EuRAD03, EuRAD12, EuRAD13, EuRAD14, EuRAD15, EuRAD12, WF2 und WF4.

In the field of autonomous driving, high-precision radar images of the environment are essential for accurate trajectory planning. In his new journal article in IEEE Sensors Letters, Timo Grebner shows that with conventional automotive radar sensors (77 GHz) not only the detection of obstacles and other road users is possible, but also the detection of lane markings. By employing the synthetic aperture radar (SAR) technique, lane markings are captured with such a high quality that allows their automated extraction from the resulting SAR image via digital image processing techniques. Due to the high integration gain of SAR, this method enables the detection of lane markings without having to add additional reflective particles to the paint, which enables the algorithm to be used for existing lane markings.

Paper: Detection of Optical Road Markings With Automotive Radar Sensors

We are presenting one paper about reflectarrays at the IEEE Antennas and Propagation Symposium in Portland in the upcoming week.

Join us in session "WE-SP.2P: Millimeter-Wave and THz-Wave Antennas with Beam-Scanning and Multi-Beam Functions".

Semi-analytical models for predicting the far-field pattern of reflectarrays are of great advantage to save computationally expensive full-wave simulations. In her latest journal article in the IEEE Transactions on Antennas and Propagation, Susanne Brandl presents a novel modeling technique for reflectarrays. This method allows to predict the effects of specular reflections, which usually appear in offset-fed reflectarrays, by fitting a model parameter based on a full-wave simulation of an array row.

Paper: Modeling Offset-Fed TE Reflectarrays for Far-Field Pattern Prediction at Upper mm-Wave Frequencies

We have one paper presentation about UAV-based GPSAR at the International Geoscience and Remote Sensing Symposium in Pasadena this week.

You will find us in session "FR2.R9: UAV/Mobile-Mapping SAR Systems and Applications II".

By electronically tuning varactor diodes, the increased phase sensitivity of biomimetic arrays can be controlled in direction-of-arrival and the strength of the biomimetic effect becomes adjustable. In her latest journal article to be published in the Open Journal of Antennas and Propagation, Ines Dorsch discusses the requirements, describes a design process, and presents multiple demonstrators of tunable biomimetic antenna arrays in the 77 GHz range. Such arrays can adaptively adjust their characteristic depending on target parameters, allow for multi-step angle estimation, and improve the detectability of weak radar targets.

Paper: Tuning the Angular Characteristics of Biomimetic Antenna Arrays

Patrik has defended his PhD thesis entitled "Biomimetische Antennensysteme für kompakte hochauflösende Radarsensoren". We congratulate Patrik on completing his doctorate!

In the field of autonomous driving, high-precision radar images of the environment are essential for accurate trajectory planning and obstacle detection. Timo Grebner proves in his new journal article the feasibility of probabilistic SAR (synthetic aperture radar) processing. The advanced algorithm allows a high-resolution and amplitude-independent probabilistic SAR processing of the environment, resulting in a final image that represents a direct complex-valued occupancy probability. This presents an enormous advantage over conventional SAR processing schemes, which can only handle amplitude and phase information lacking suitable occupancy information. Hence, the work is a milestone for autonomous driving with the support of radar sensors employing SAR.

Paper: Probabilistic SAR Processing for High-Resolution Mapping Using Millimeter-Wave Radar Sensors

David Werbunat has received the International Microwave Symposium Advanced Practice Paper Award for his paper "An All-Digital Carrier Synthesis for Stepped OFDM Radars". Congratulations!

We have two paper presentations at the International Microwave Symposium in San Diego in the coming week. You will find us in session "Tu3E: Advanced High-Frequency Mixed-Signal Circuits and Systems" and "We1G: Automotive and MIMO Radar".

Accurate knowledge of the mounting orientation of radar sensors is essential for precise environmental sensing and obstacle detection. In his latest journal article in the Transactions on Aerospace and Electronic Systems, Timo Grebner presents a new method to estimate the mounting orientation of distributed radar sensors based solely on radar data. Furthermore, the algorithm functions with arbitrary targets, unconstrained sensor positioning, and random vehicle trajectories.

Paper: Self-Calibration of a Network of Radar Sensors for Autonomous Robots

Compared to existing methods, UAV-based ground-penetrating synthetic-aperture radars (GPSAR) offer significant advantages due to their highly adaptable flight trajectories. At heights of a few meters above ground, refraction effects at the surface must be considered for high-resolution imaging. Often, the surface is therefore assumed to be horizontal. In a new journal article in Transactions on Geoscience and Remote Sensing, Alexander Grathwohl investigates the influence of uneven surfaces on the detection of buried objects in theory, and using simulations and measurements. It is concluded, that surfaces can be considered locally horizontal for shallowly buried objects.

Paper: Detection of Objects Below Uneven Surfaces With a UAV-Based GPSAR

We are contributing four papers to the Radar Conference taking place in San Antonio, where we are presenting work on radar target simulation, gesture recognition, array design and interference avoidance.

Susanne Brandl's conference paper "A Flexible Measurement Setup for Far-Field Characterization of Reflectarrays above 200 GHz" has been selected as an Honorable Mention. Congratulations!

A novel synthesis method for holographic multi-feed antennas, which allows to combine all sub-holograms into an angular-dependent shared holographic aperture, is proposed by Thomas Frey in a new article in the Open Journal of Antennas and Propagation. For a very accurate implementation of the analytical impedance tensor hologram, an eigenvector approach taking all tensor components into account is introduced. The holographic multi-feed antenna prototype is realized on a fused silica wafer and is intended for the integration into a 2D-monopulse radar system for the automotive frequency range.

Paper: Angle-Dependent Synthesis Method for Holographic Multi-Feed Antennas

The combination of synthetic aperture radar (SAR) with bistatic measurement geometries creates an opportunity to improve imaging significantly. A repeater element can be used for bistatic imaging to circumvent the need for highly accurate synchronization. In a new article in the Journal of Microwaves, Alexander Grathwohl and Benedikt Meinecke show simultaneous mono- and bistatic SAR imaging with an airborne UAV-based radar system and a stationary repeater element in a practical measurement scenario.

Paper: UAV-Based Bistatic SAR-Imaging Using a Stationary Repeater

We are contributing three papers to the conference European Conference on Antennas and Propagation (EuCAP) taking place end of March in Florence. We are presenting our work in the following sessions: Wide-Scanning Antenna Array Concepts for Millimetre-Wave Application (CS53), Innovative Lens Antennas I (A10), Frequency-Selective Surfaces (E04).

We congratulateHasan Iqbal on completing his doctorate on the topic "Synthetic Aperture Radar (SAR) Imaging and Polarimetric Clutter Analysis Using Automotive Radars".

A highly-efficient calibration procedure for radar sensors enables the simultaneous storage of several measurement points by employing active radar targets. This is demonstrated by measurements in the near-field of the sensor. The results are presented by Matthias Linder in the Open Journal of Antennas and Propagation, now available in IEEE Early Access.

Paper: Highly Efficient Calibration of Antenna Arrays by Active Targets in the Near-Field

We congratulate Mario Müh on completing his doctorate on the topic "A Terahertz Sensor Platform for the Detection of African Trypanosomes".

Last summer, our research project about detection of land mines with the aid of radar sensors mounted on an UAV was presented in a TV report for the science program "nano". In this project, we collaborate with Urs Endress Foundation and Fondation suisse de déminage (FSD). The video is now available on the Youtube channel of FSD.

Video: Detecting Mines using High-Tech Drones

A new signal model for arbitrary radar array configurations and beamformers is derived by Pirmin Schöder in his new journal article. With the new model, the capabilities of flexible direction-of-arrival simulations can be extended beyond existing methods. The generation of targets for radars with different antenna configurations is presented utilizing different approaches. The article appears in Transactions onAerospace and Electronic Systems and is now available in IEEExplore Early Access.

Paper: A Unified Model of Coherent Direction-of-Arrival Simulation for Radar Target Simulators

The connection of mechanically flexible dielectric waveguides without the use of mode converters is now possible directly via an interface in a glass package. In his new journal article, Thomas Galler compares galvanically coupled and electromagnetically coupled approaches above 150 GHz. The article appears in Transactions on Microwave Theories & Techniques and is now available in IEEExplore Early Access.

Paper: MMIC-to-Dielectric Waveguide Transitions for Glass Packages Above 150 GHz

Marco Veit received the VDE-Prize for his master thesis about a tunable multilayer fishnet metamaterial lens at millimeter-wave frequencies. Congratulations!

Radar-based gesture recognition algorithms can work without a single measured sample for training! In a new journal article by Nicolai Kern, this is demonstrated by one-to-one re-simulation of a comprehensive real dataset, thus pointing out both the potential and the challenges of simulation-based data augmentation. The results are presented in the Transactions on Microwave Theories & Techniques’ special issue on AI for Microwaves, now available in Early Access.

Paper: Learning on Multistatic Simulation Data for Radar-Based Automotive Gesture Recognition

We congratulate Pirmin Schöder on receiving the EuRAD Young Engineer Prize for his paper “A Modulation-Based Target Simulator and Its Hardware Nonidealities”.

Multicopter UAVs offer unmatched flexibility, which allows for new ways for close-proximity ground-penetrating radar imaging without requiring traversable terrain. There is a large variety of applications that could benefit from these systems. In a new magazine article, Alexander Grathwohl and Michael Stelzig provide an overview of the requirements for high-quality imaging, current state-of-the-art applications and future possibilities. The system prototype is even featured on the IEEE Microwave Magazine's cover.

Paper: Taking a Look Beneath the Surface: Multicopter UAV-Based Ground-Penetrating Imaging Radars

We congratulate André Dürr on completing his doctorate on the topic of radar systems for high-resolution imaging

We are contributing seven papers and two workshops presentations to the conference taking place end of September.

A new MIMO Radar with 1728 Virtual Channels for high-resolution 4D imaging is presented by Dominik Schwarz in his new journal article. The system is composed from 12 radar MMICs, exceeding the channel count of modern automotive radars by a factor of 10, has a new multilayer PCB concept to seperate RF circuitry and antennas, and features beamwidths of 0.78° (azimuth) and 3.6° (elevation). The article is already available on IEEExplore and will be published in the Journal of Microwaves.

Paper: System Performance of a 79 GHz High-Resolution 4D Imaging MIMO Radar With 1728 Virtual Channels

The institute contributes a paper about Interference of Automotive Radars in Complex Traffic Scenarios to the conference in Gdansk.

Neural networks can reliably recognize real-world traffic gestures from multi-perspective radar target lists as input. Hence, the gesture recognition algorithm presented by Nicolai Kern in his article for the Transactions on Aerospace and Electronic Systems is particularly suitable for autonomous driving in strongly scattering environments, helping vehicles to safely interact with pedestrians. The article is already available on IEEExplore Early Access.

Paper: PointNet+LSTM for Target List-based Gesture Recognition with Incoherent Radar Networks

Martin Geiger was awarded a prize for his outstanding dissertation, donated by the Ulmer Universitätsgesellschaft. Congratulations! Martin wrote his dissertation about a flexible waveguide probe for MMIC-based radar systems at 300 GHz.