Project C01 - UWB Phase-Locked Loops with Highest Phase Stability

Principal Investigator: Prof. Dr. Thomas Musch, RUB EST

For fulfilling future requirements of electromagnetic measurement systems based on the radar principle in terms of spatial resolution and precision, the enlargement of the utilized bandwidth of today’s systems is essential. Especially the determination of material properties and precise indoor localization, which are the dominant goals of this Collaborative Research Centre, require an extremely high phase resolution and phase stability of the electromagnetic measurement signal. The only possible way for significantly increasing the absolute bandwidth is to shift the centre frequency to a higher region. However, the demands concerning phase stability increase with the center frequency. This especially holds true for the widespread Multiple Input Multiple Output (MIMO) systems used in a heterodyne concept. These systems benefit significantly if the phase jitter of the synthesized signals is reasonably low. MARIE aims at systems working in the range of 250 GHz up to 4 THz, which corresponds to signals exhibiting a time jitter in the order of only a few femtoseconds. However, due to slow time (e.g. temperature) and short time (e.g. noise) drifts this cannot be achieved using a free-running wideband oscillator. Such phase stability can only be achieved if the oscillator is controlled by a Phase-Locked Loop (PLL). Promising PLL concepts will be investigated within this project to ensure that the synthesized signals achieve highest phase stability. Electronic pulsed systems use extremely narrow pulses with very high bandwidth, but due to their low transmit power they are inapplicable for the intended measurement distances. In contrast to pulsed systems, frequency modulated continuous wave (FMCW) systems employ continuous signals and can therefore use significantly more transmit power. However, the FMCW system must exhibit a highly linear frequency modulation for the required precision. Thus, the key question of this project is how to reach the aforementioned phase stability while maintaining a highly linear frequency modulation over a relative bandwidth of 30%. This project aims at synthesizing signals with highest phase stability for the application in radar systems working at frequencies of 250 GHz up to several THz.

This project aims at the synthesis of microwave signals with a hitherto unattained combination of phase noise performance, bandwidth and linearity. Therefore, innovative synthesizer concepts will be investigated by means of research on binary direct digital synthesis, minimizing in-loop division factors and combining sapphire and yttrium iron garnet based oscillators. A reference source with the outstanding characteristic mentioned here is key to high-precision electromagnetic MIMO measurement systems in the THz regime.