Analysis and Design of an Imaging Ultra-Wideband Frequency Modulated Continuous Wave Primary Radar System operating in S, C, X and Ku Band

Research and development of modern radar systems has recently become the center of attention through the rise of various new applications. This results in more demanding requirements for radar systems such as high frequency agility, high range resolution and high radar range at the same time while generating low-noise radar images with a high amount of details. This multi dimensional optimization problem can be translated to specific research challenges. Accord- ingly, future radar systems require a high system bandwidth, high frequency chirp bandwidth while transmitting a frequency chirp at a low center frequency, high linearity and with low phase noise.

The presented work discusses the research and design process, from a custom signal generator ASIC to the final UWB FMCW imaging primary radar system. This is achieved from the ground up and does not use any previously available radar-specific components.

First, a novel consideration of non-linearities within an UWB FMCW primary radar transceiver is derived. This analysis identifies the critical spurious attenuation components of the down-conversion mixer to avoid ghost targets in the distance spectrum.

The commonly known topology of a cross-coupled LC tank oscillator is im- proved regarding its tuning range capability. Based on this research, a state-of- the-art UWB VCO ASIC achieving a record relative continuous frequency chirp bandwidth at a low center frequency combined with a very low phase noise is presented.

Furthermore, existing tuning range expansion techniques are studied and an innovative tuning range expansion concept is derived. Based on this concept a novel signal generator ASIC is presented, greatly increasing the tuning range of the single oscillator covering a frequency range from 3.1 GHz to 22.5 GHz while maintaining superior frequency chirp bandwidth and phase noise performance. The record figures of merit for both systems, the single VCO ASIC with 215 dB and the expanded signal generator ASIC with 217 dB confirm the validity of the derived concepts.

The signal generator ASIC is then employed in a closed-loop UWB frequency synthesizer. The analysis and design of the required loop filter is emphasized con- sidering the targeted high bandwidth. A UWB receiver and further supporting systems like the transmit power amplifier, digital control system and power supply system are presented. A power supply noise filtering system is adapted and designed for the noise sensitive RF components and its influence on the resulting phase noise is investigated. Finally, a compact and low weight FMCW primary radar is built. The typical EIRP of the designed system is 30.2 dBm and the typical power consumption amounts to 6.7 W while transmitting and receiving. This researched and designed novel imaging UWB FMCW primary radar sys- tem operates in the S, C, X and Ku frequency bands. Guided by the identified research challenges, the presented radar achieves a superior combination of a very high relative system bandwidth of 143 %, a very high relative frequency chirp bandwidth of 79 %, a low center frequency of 10.85 GHz and a low typical phase noise of −105 dBc/Hz at 1 MHz offset. Non-imaging radar measurements show the achieved very high range resolution of 2 cm for distant radar targets. Subsequently, the radar is expanded to an imaging SAR measuring various radar images of complex open field measure- ment scenarios illuminating a downrange of more than 100 m and a crossrange of 50 m. The SAR is further expanded towards a PolSAR system utilizing polarime- try. This system is deployed for a measurement series to monitor the effects of environmental factors on vegetation in a forest. The superior performance enables the radar system to dissolve the existing compromise between a high range resolution and a high radar range. Both desired performance parameters are achieved at the same time without degrading the resulting phase noise and therefore allows low-noise radar images. Furthermore, the presented primary radar offers an extremely high frequency flexibility allowing it to adapt to respective frequency restrictions and to operate as multi band, multi application system. Consequently, the presented concept can replace several narrowband and application specific radar systems with only one single radar front end. This reduces the overall cost, size, complexity and power consumption of future radar systems while enabling new fields of applications.