Annual Report 2023

In September 2023, Dr. Tim Freialdenhoven successfully defended his doctoral thesis titled »Frequency-Controlled Polarizers for Polarimetric Radar Applications« at the Institute of High Frequency Technology (IHF) of RWTH Aachen University. His doctoral supervisor was Prof. Dr.-Ing. Dirk Heberling, with guidance from Junior Prof. Dr.-Ing. Thomas Dallmann at the institute. 

Dr. Tim Freialdenhoven pursued his studies in Electrical Engineering, Information Technology, and Computer Engineering with a focus on Information and Communication Technology at RWTH Aachen University, completing his master‘s degree in 2015. Subsequently, he spent two years working at an SME specializing in sensor and industrial automation technology. However, he realized his inclination towards intensifying scientific aspects alongside practical work. Through Prof. Heberling and Junior Prof. Dallmann, whom he worked with for his master‘s thesis at IHF, he established contact with Fraunhofer FHR. From 2017, he spent nearly 6.5 years at the institute, initially as a research associate in the then Research Group Aachen and eventually as the Aachen site manager within the Industrial High-Frequency Systems (IHS) department. 

The idea of pursuing a Ph. D. occurred to Dr. Freialdenhoven soon after completing his master‘s degree. Upon learning about the establishment of the Research Group Aachen and the opportunities for doctoral studies at Fraunhofer FHR, he recognized it as his path forward. The topic of his research stemmed from the project he was involved in: PERFOM, an internally funded Fraunhofer FHR project aimed at developing polarization-modifying structures for radar polarimetry across departments. He was so passionate about the topic that he wished to continue researching it after the project concluded. 

Dr. Freialdenhoven‘s doctoral thesis revolves around polarimetric radars utilizing orthogonal electromagnetic polarizations to enable reliable target characterizations and classifications. A non-polarimetric, frequency-modulated radar can be extended to a polarimetric system using the frequency-dependent and polarization-rotating Reflect- and Transmitarrays presented in his work. These introduced polarizers consist of specially designed compact unit cells optimized either for preserving or rotating linear polarization in two closely adjacent frequency bands, manufacturable with printed circuit board technology. The influence of manufacturing tolerances and calibration methods are discussed and evaluated with measurements from fabricated samples. 

»What fascinated me most about my research topic was the additional information a radar system can acquire by evaluating the polarization of the electromagnetic wave, and that this can be achieved with structures mounted in front of a radar,« says Dr. Freialdenhoven. The greatest challenges during his Ph. D., which commenced in October 2017, lay in defining the topic and the practical realization of the developed structures. Balancing this with project work was not always easy, but he succeeded, partly due to the freedom and financial resources granted for his research. »The excellent training opportunities provided by the Fraunhofer Society, which allowed me to build interdisciplinary qualifications, were also very helpful. I am very grateful for the opportunities provided at Fraunhofer FHR.« 

He also acknowledges the support of his colleagues and particularly appreciates the guidance from Junior Prof. Dallmann. »Collaborating in a friendly team and the great working atmosphere in the Research Group Aachen, as well as the close contact with IHF at RWTH Aachen University, were highlights of my Ph. D. experience. I look back very positively on my time pursuing my doctorate at Fraunhofer FHR, and I hope that polarimetry will contribute to making radar sensors even more powerful in the future,« concludes Dr. Freialdenhoven.