Description
Satellite positioning systems have found widespread use in the private and industrial sector over the course of the last two decades. Some of the many applications are in logistics, vehicle navigation, aviation and marine navigation. However, satellite positioning systems are dependent on a direct line of sight to the satellites for reliable operation. High obstacles, such as urban canyons or stacked containers, can have a negative impact on positioning accuracy. These areas can be made accessible with the help of a local positioning system (LPS). This work deals with an LPS that is based on a frequency modulated continuous wave radar (FMCW). It is to provide centimeter accuracy and should allow the measurement of the angle of arrival as well. In addition, there shall be one mode for long range operation and another mode for high robustness against multipath propagation. For this the FMCW radar can be operated in two frequency bands: the 5.8 GHz ISM-Band and the unlicensed ultra-wide band range (UWB) 6.0 – 8.5 GHz. The RF-frontend is equipped with four channels to allow measuring the angle of arrival.
The objective of this work is to integrate as many of the FMCW radar components as possible in a single chip. The chip is fabricated in a 350 nm SiGe:C bipolar technology. The focus is on the frequency synthesizer for linear modulated frequency ramps. It is designed as a phase locked loop with variable division ratio. In order to allow for high robustness against multipath propagation and measurement accuracy, it must generate both broadband and as linear as possible frequency ramps with a frequency resolution in the single Hz range, thus putting high demands on the voltage controlled oscillator (VCO) in the regards of tuning range and linearity.
To meet the above mentioned requirements, a novel VCO with tuning linearization is presented and characterized by measurements in this work. This VCO achieves a continuous relative tuning range of 69.0 %; the tuning sensitivity KVCO varies by only ±20 % within a relative tuning range of 34.5 %. A method for measuring non-linearity that is based on short-time Fourier transform (STFT) is presented to analyze the linearity of the generated frequency ramps. The advantage of this method is that it is much more robust against noise in the measured signal in comparison to the phase-based methods often used in publications. The frequency synthesizer generates highly linear FMCW ramps. The maximum deviation from average is less than 1.1 kHz for a sweep bandwidth of 2 GHz.
Finally, the designed radar chip is embedded into a demonstrator system. The system achieves a standard deviation of only 2.7 cm in one-dimensional distance measurement in an environment with strong multipath propagation. The measurement error varies between -3° and 2° for the angle of arrival measurement. Thus, the LPS that is investigated in this work is ideally suited for a variety of applications.
Abschließend wird der entworfene Radarchip in ein Demonstratorsystem eingesetzt. In der eindimensionalen Distanzmessung erreicht das System eine Standardabweichung von nur 2,7 cm in einer Umgebung mit starker Mehrwegeausbreitung. Bei der Einfallswinkelmessung bewegt sich der Messfehler zwischen -3° und 2°. Das in dieser Arbeit untersuchte LPS ist damit für eine Vielzahl von Anwendungen hervorragend geeignet.
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