W-Band FMCW MIMO radar demonstrator system for 3D imaging
One of the most dangerous situations when flying a helicopter is landing over dry sand or powder snow. The rotors swirl particles creating a dense cloud. With optical methods navigating through this cloud is impossible but for millimetre waves it becomes almost transparent. As a consequence millimetre waves are an outstanding choice for the development of imaging systems that can be used as a landing aid. Also smoke is transparent at this wavelength and thus imaging in case of fires is possible. The aim of this work is the three-dimensional imaging of static scenes with a large field of view, good resolution and high dynamics. In this thesis a demonstrator system is presented, which is based on the MIMO principle and works with FMCW radar modules in the millimetre wavelength range. The set-up of the demonstrator system is explained and the hardware components are described. The development of the electronics itself is not part of this work. An algorithm for image reconstruction is presented as well as a calibration routine. The arrangement of the individual transmitting and receiving antennas thereby determines the size of the unambiguously image able angular range, the resolution and the side lobe level. In addition, the arrangement is constrained by the spatial extent of the modules in which the single antennas are embedded. An optimized arrangement is presented that enables unambiguous imaging of the half-space in front of the aperture with good resolution and low side lobes. A heuristic algorithm is used for this optimization whereby valuable computation time is saved by preselecting an initial state. The acquisition of measurement data is realized with an FPGA. Major parts of the configuration of this FPGA is done within this work. Communication with a computer and data download is realized with Matlab that is also responsible for subsequent image reconstruction and calibration. A design for an FPGA program is presented that is aimed at image reconstruction inside of the FPGA to make the system capable of real-time operation. Various measurements illustrate three-dimensional imaging capabilities. The advantages of the optimized aperture can be demonstrated with images of large objects. In addition, the data acquisition rate is determined to be 130 images per second. This is an upper bound to the image repetition rate.
Freiburg/Brsg., Univ., Diss., 2017