Project M04 - 3D Reflectometric Material Characterization using Co-located MIMO Radar
In this project a measurement concept for novel MIMO radar sensors is developed in order to characterize and identify the geometric and electromagnetic properties of typical inroom objects, such as woods, concrete and plastics in the sub-mmWave regime. The field of electromagnetic material characterization comprises a very large area of microwave metrology and has been subject to various kinds of theoretical and practical research. However, research on a fusion of electromagnetic material characterization with the field of radar imaging in order to obtain spatial information on the distribution and properties of different media is still very rare. This fusion will be one of the key goals that are addressed during this Collaborative Research Centre. The high centre frequency of the targeted measurement system, operating at 260 GHz to 400 GHz, allows for high absolute bandwidths, which result in a very high spatial resolution. This comes with the drawback that the roughness of the characterized surface has a major impact on the measurement quality, since the wavelength of the probing signals as well as the surface variations are in the same range. Thus, the amount of diffusely scattered signal power increases compared to specular reflections. This effect has to be compensated by knowledge about the geometry of the measured object, which will be identified by radar imaging algorithms.
Since the MIMO system will be under development (C03) in the first years of the Collaborative Research Centre, the measurements are – in a first step – done using existing 250 GHz radar systems with up to 60 GHz bandwidth and sub-mmWave extensions to network analyzers. The MIMO system is set up by a virtual array, using one transmit and one receive channel that are operated on 3D positioning units. By using a MIMO approach to cope with the measurement problem, beamforming concepts can be utilized that allow SFB/TRR 196 - Mobile Material Characterization and Localization by Electromagnetic Sensing 120 optimization of the illumination of the material under test. Furthermore, a 3D image of the measurement domain is obtained by investigating appropriate synthetic aperture and focusing algorithms, based on the back-projection algorithm, for example. The quality of these images benefits significantly from the large bandwidth that can be obtained by sub-mm wave radar. In order to achieve optimum performance, different array geometries for the MIMO system will be evaluated, since the resolution and measurement dynamic of the resulting image will depend heavily on the point spread function of the arrays.
For the purpose of accurate material characterization, adequate methods for the calibration of the material measurement system have to be developed to take the internal and external error sources into account. Additionally, self-calibrating concepts will be investigated to utilize information from the scene under test itself in the process of calibration. The innovative approach of enabling a calibrated, spatially resolved material characterization at submmWave frequencies and utilizing compact MIMO radar modules make this project a main contributor to the vision of the CRC. Thus it is strongly related with other projects in terms of models, hardware and exchanging results.