Untersuchung von frequenzstabilen Radar-Sendesignalen für FMCW-Anwendungen im GHz-Bereich

Fractional-N PLL-synthesizers offer the possibility to generate highly stable frequencies and with the use of digitally modulated divider ratios they are suitable to be used as signal sources for FMCW-radar applications. Thereby the linearity of the ramp is important for distance resolution and to differ between multiple targets. Hence, it is a key parameter in designing FMCW-radars. If the ramp is not ideal, phase errors occur in the intermediate frequency. On the one hand, this may cover targets and on the other hand, clutter (virtual targets) could arise. In this thesis, a new method to characterize the linearity of frequency chirped signals will be presented. To analyze the impacts on the ramp linearity of a PLL-stabilized VCO-design, a frequency synthesizer has been realized, which is able to generate frequency ramps at about 8 GHz and 16 GHz. Nowadays, measuring the linearity of chirped signals with conventional measurement equipment is not possible. Therefore, a measurement setup has been designed, performing time-domain analysis of the intermediate frequency signal. Using a graphical programming language, computer software has been developed, which synchronizes data acquisition to frequency ramps. Several FMCW-signal sources have been characterized and com-pared against each other, using the presented measurement setup. As a result, it has been shown that the linearity of a chirped signal generated by Fractional-N PLL synthesizers is excellent compared to other signal sources, especially when addressing the GHz domain. With the frequency synthesizer, which has been developed in the context of this work, the generation of ultra-linear frequency ramps is possible. It has been shown, that the frequency of the phase frequency detector as well as the design of the loop-filter are crucial to achieve best performance in terms of linearity