For radar applications, MIMO is often used. The problem is that the amount of available transmit- and receive channels is limited. If each channel is connected to a single antenna element, the effective aperture is small, and therefore the beamwidth is large and the angular resolution is limited. In this thesis, a novel scheme is proposed that circumvents this problem. More details are given in the full thesis. The result is an array that covers a reduced part of the visible space, with discrete beams that have improved beamwidth. The system gives the possibility to improve the angular resolution at the cost of field of view. A CST-model is made to verify this concept. In the specific example given in this thesis, the half-power beamwidth is improved from 8.4 degrees at broadside, to 5.7 degrees at broadside. At the same time the coverage is reduced from a theoretical ±90 degrees, to ±50 degrees.

With the emergence of new communication standards like Fifth-­Generation New Radio (5G NR), technologies are being developed to exploit millimeter­ wave (mm-­wave) frequency bands from 30­300 GHz, for their advantage of high bandwidth availability. Generation of carrier frequencies for these mm-­wave applications imposes a challenging specification of high spectral­ purity on the frequency synthesizers. Sub­sampling PLLs (SSPLLs) show a remarkable performance in terms of low­ power and good spectral purity, which are critical for such high­speed applications. However, due to their low lock­-in range, SSPLLs require the assistance of an additional frequency­-tracking loop (FTL) for an improved locking performance. These FTLs conventionally employ either high power consuming frequency dividers, or reference frequency multipliers. In this thesis, a novel implementation of an FTL which avoids the usage of high-­frequency dividers is proposed. The proposed FTL uses three sub­-Nyquist sampling rates, which are derived from three mutually co­prime integers, for an unambiguous VCO frequency estimation which helps in frequency error correction. Consequently, the proposed FTL eliminates the need of sampling rates higher than the Nyquist rate and the circuit limitations posed by such high sampling frequencies. The FTL employs a simple amplifier, counter and look­up table based VCO frequency estimation procedure which avoids the need of performing high complexity frequency estimation algorithms like Fast Fourier Transform (FFT). The FTL also features a speed optimization algorithm which helps in achieving low frequency­-locking times. The proposed FTL is designed in the 40­nm CMOS technology, targeting an output frequency locking range of 9.8­12.2 GHz. The post-­layout simulations show that the FTL is able to coarsely lock to any desired frequency in the wide­band locking range within an error of 3 MHz, in less than 3 휇s at start-up. Error injections as high as 1.5 GHz are efficiently detected and corrected in less than 3 휇s as well. The area consumed by the FTL is 0.35 푚푚2 and the active area of the total chip is 1.09 푚푚2 including the decoupling capacitors. The FTL consumes a maximum power of 1.56 mW when the PLL is in a locked state. A comparison with other state-­of-­the-­art frequency­-tracking loops demonstrates its clear advantage of wide­band frequency locking and low locking time, while consuming a similar amount of power. Analytically, the proposed FTL also exhibits competence in scaling to mm­wave frequencies.

Autonomous driving is a new emerging technology that will enhance traffic safety. Automotive radars are essential to attaining autonomous driving since they can function in adverse weather conditions and are used for detection, tracking, and classification in traffic settings. However, the dramatic growth in the number of radar sensors used for automotive radars has raised concerns about spectral congestion and the coexistence of radar sensors. The mutual interference between multiple radar sensors downgrades the sensing performance of automotive radar and needs to be mitigated. Moreover, automotive radars have limited processing power, preventing them from using computationally heavy techniques to countermeasure interference. This thesis aims at developing, evaluating and verifying a robust waveform with required processing steps suitable for automotive radars to boost the coexistence of multiple radar sensors. To achieve this task, phase-coded frequency modulated continuous wave (PC-FMCW) and necessary processing steps are studied. The first step is taken by investigating the sensing properties of the PC-FMCW waveforms and possible receiver strategies in Chapter 2. It is demonstrated that the ambiguity function of the code is sheared after frequency modulation. Moreover, different binary phase codes are examined with the PC-FMCW waveforms, and their sensing performance is compared in terms of integrated sidelobe level. Subsequently, two receiver approaches based on the dechirping process to decrease the sampling demands of the PC-FMCW waveforms are examined. The sensing performance of the investigated receiver approaches is compared, and the trade-offs between the sensing performance and the code bandwidth are analyzed. Moreover, the PC-FMCW waveform is applied to a real scenario, and the sensing performance of the investigated receiver structures is validated experimentally. Chapter 3 investigates the beat signal spectrum widening due to coding and explores the smoothed phase-coded frequency modulated continuous wave (SPC-FMCW) to improve the sensing performance in the limited receiver analogue bandwidth. The abrupt phase changes seen in binary phase-coded signal is analyzed, and a phase smoothing operation to reduce the spectral broadening of the coded beat signals is proposed. The introduced SPC-FMCW waveforms are analyzed in different domains and compared with the binary phase coding. It is shown that the proposed smoothing operation decreases the spectral broadening of the coded beat signal and improves the sensing performance of the waveform. In Chapter 4, the limitation in the group delay filter receiver approach is investigated, and the appropriate receiver strategy with low computational complexity is designed to process the PC-FMCW waveforms. The impact of the group delay filter on the coded beat signal is examined in detail, and a phase lag compensation is proposed to enhance decoding performance. It is demonstrated that performing phase lag compensation on the transmitted code eliminates the undesired effects of the group delay filter, and the beat signal is recovered properly after decoding. Then, the properties of the resulting waveforms are theoretically examined, and the sensing performance improvement over the existing approach is demonstrated. Moreover, both sensing and cross-isolation performance of the introduced waveforms with proposed processing steps are validated experimentally. Chapter 5 studies the PC-FMCW waveforms for a coherent multiple-input-multiple-output (MIMO) radar. To this end, the MIMO ambiguity functions of the PC-FMCW waveform with different code families are investigated for their separation capability and compared with the PMCW waveform. It is illustrated that the PC-FMCW ambiguity function outperforms the PMCW one in terms of range resolution, Doppler tolerance, and sidelobe level for the identical types of codes. Afterwards, the developed phase lag compensated waveform with a single transmitter-receiver approach is performed to a coherent MIMO radar, and a novel PC-FMCW MIMO structure is proposed in Chapter 5. The introduced MIMO structure jointly utilizes phase coding in both fast-time and slow-time to achieve low sidelobe levels in the range-Doppler-azimuth domains while maintaining high range resolution, unambiguous velocity, good Doppler tolerance and low sampling requirements. The sensing performance of the introduced MIMO structure is evaluated and compared with the state-of-the-art techniques. Moreover, the proposed MIMO structure's practical limitations are investigated and demonstrated. In addition, the sensing performance of the developed approach with the simultaneous transmission is verified experimentally. Finally, the interference resilience and communication capabilities of the developed PC-FMCW radar have been studied in Chapter 6. First, the automotive radar interference problem between various types of continuous waveforms is examined. The interference analysis formulation is extended to PC-FMCW waveforms, and a generalised radar-to-radar interference equation is proposed. The introduced equation can be utilised to quickly and accurately derive the numerous interference scenarios discussed in the literature. In addition, the proposed equation's validity to characterise the victim radar's time-frequency distribution is demonstrated experimentally using the commercially available off-the-shelf automotive radar transceivers. Afterwards, the robustness of the developed PC-FMCW radar against different types of FMCW interference cases is examined, and an improvement in the sensing performance over the conventional FMCW waveform is demonstrated. Moreover, the communication performance of the PC-FMCW with dechirping receivers is compared, and the trade-off between the bit error rate and the code bandwidth is investigated. This thesis shows that the developed PC-FMCW radar structure can provide high mutual orthogonality to enhance the functioning of multiple radars within the same frequency bandwidth while sustaining the low sampling demand and good sensing performance. Consequently, the introduced approach can be effectively utilized by automotive radars to mitigate mutual interference between multiple radar sensors and improve the sensing performance of simultaneous MIMO transmission. Although the focus is on the application in an automotive radar context, the developed approach can also be used in other radar fields.@en