Short-range leakage cancelation in FMCW radar transceiver MMICs

Todays cars are equipped with radar sensors, which provide precise information about the distance, speed and angle to surrounding objects on the road. This information is essential for modern driver assistance systems such as adaptive cruise control or brake assistance systems. Further, it enables future autonomous driving features. Most importantly, however, the accuracy and range of the radar sensors are critical for the safety of the car occupants as well as other daily road users. This is of particular significance since around 90 percent of all rear-end collisions with personal injuries occur due to human mistakes. Assuming all cars on the road to be equipped with emergency brake systems, up to 72 percent of these collisions could be prevented. For reasons of car appearance as well as protection of the device itself, the radar sensors are often mounted right behind the bumper. This, however, causes unwanted signal reflections from such. Particularly, the reflections yield so-called short-range (SR) leakage, which superimposes reflections of true objects that have to be detected most precisely. Together with the phase noise (PN) inherently present in the frequency modulated continuous wave (FMCW) transmit signal, the bumper reflections limit the achievable sensitivity and accuracy of the radar sensor severely. As a consequence, driver assistance systems may react delayed in critical situations. In this thesis, novel concepts that aim to cancel the SR leakage in the automotive application are proposed. These are the first known solutions of their kind that can be integrated holistically within a monolithic microwave integrated circuit (MMIC) operating at 77 GHz. The concepts make use of an artificial on-chip target (OCT), which mimics an object reflection on the chip. The tight design constraints regarding implementation in the MMIC are circumvented by employing sophisticated statistical signal processing. Simulation as well as measurement results from the developed hardware prototype show that the sensitivity can be more than doubled by applying the proposed concepts. Besides SR leakage cancelation, also the issue of PN power spectral density (PSD) estimation is addressed. Different to existing on-chip PN PSD estimation techniques, the input signal is considered as a linear FMCW signal rather than a pure continuous wave (CW) signal. Two methods to obtain estimates of the PN PSD are proposed. Both make use of the artificial OCT, and are evaluated with simulations as well as measurements. The proposed techniques not only allow for a fast characterization after production of the chip, but also enable continuous monitoring of the PN during normal operation of the radar for the first time.submitted by Alexander MelzerZusammenfassung in deutscher SpracheUniversität Linz, Dissertation, 2017OeBB(VLID)197111