The different achievements of this thesis can be categorised into two main branches, which are the research and development of FMCW based 3D MIMO radar and OFDM based 3D MIMO radar architectures and algorithms, together with the design and im- plementation of novel receiver processing techniques and waveforms. Therefore, in order to fully describe the contributions and results, the thesis is organized as follows:
• Chapter 1: This chapter provides a general introduction to radar concepts, typolo- gies and state of the art, but also the applications and the motivation at the core of the research in this thesis.
• Chapter 2: Here, a theoretical background is introduced, with special focus on radar systems, radar equations and the ways that these systems operate. Addi- tionally the MIMO model and principles, the direction of arrival estimation, the time division multiplexing scheme and concepts regarding FMCW based radar systems are discussed. The information provided in this chapter is essential in or- der to understand the further two chapters, where complete FMCW based MIMO radar demonstrators are shown.
• Chapter 3: This chapter presents the first complete radar demonstrator which has been achieved: a 3D FMCW MIMO imaging radar system which operates with a 24x24 2D antenna array and integrates three FPGA boards for digital signal processing. The system architecture and an in depth description of the digital hardware and software processing is given. Moreover, the algorithms and tech- niques for the beam-forming and 3D radar image generation are here described. A calibration, timing and performance analysis on the overall radar system, espe- cially regarding its separation capabilities for the Azimuth angle, elevation angle and range resolution, is carried out. Several resulting radar 2D profiles, proving the high resolution of the reconstructed images, are here presented, for scenarios with static targets. Considering the achieved results, it can be understood that the radar demonstrator presented, is well suited in targeting applications, such as, the ground based surveillance of stationary wide-zones and high security or hazardous infrastructures. The portability and compact size factor aid in this, allowing the radar to be easily and flexibly moved.
• Chapter 4: In this section, the second complete radar demonstrator is shown. The system is a 16x16 2D antenna array based, 3D FMCW MIMO imaging radar, which represents the results of research and studies aimed at improving the architecture of
Chapter 1. Introduction 19 the radar presented in Chapter 3. A reduction is achieved in the size factor of both the RF front-end, obtaining a single board with TX and RX antennas integrated and a single board based receiver, and the digital hardware architecture, obtaining a single board as well, which is a ZYNQ based proprietary platform with 16 ADCs integrated. Furthermore, an implementation of a faster 3D-FFT based beam- forming processing, is also achieved. The MIMO radar demonstrator is tested and analysed in several scenarios. In an anechoic chamber and in outdoor test fields, for the detection of targets, both static and moving, represented by corner reflectors, UAVs and people. Additional concepts such as the utilization of an added camera sensor, scene imaging capabilities, target tracking algorithms and jamming applications are also discussed. Thanks to its size and fast sensing of 3D information from targets, a new range of applications can be addressed from this compact MIMO radar, as for example, all those situations where high-resolution 3D imaging sensors are required to have a small size factor, such as the situational awareness and autonomous operations in cars and flying platforms.
• Chapter 5: This chapter provides a general introduction to OFDM systems and a description of a new generation of radar system based on an OFDM architecture. Moreover, a description of a system concept architecture for an OFDM based radar is given, together with an in depth analysis of the parametrization of an OFDM radar waveform for a specific application connected to flying platforms.
• Chapter 6: In this chapter, the design, development and analysis of advanced MIMO OFDM waveforms, coding techniques and radar processing architectures is given. Several orthogonal waveforms based on LFM signals for MIMO OFDM radars are presented, in which various coding schemes, for achieving orthogonal- ity, are used: Golay complementary, Frank Zadoff Chu, Walsh-Hadamard, Space- Time, DFT and Costas based sequences. Moreover, a novel radar receiver pro- cessing based on a complex frame based multiplication in frequency domain be- tween transmit and received waveforms is presented, together with a unique 4D FFT beam-forming algorithm. The performance of the proposed waveforms is evaluated through the analysis their cross ambiguity functions and imaging capa- bilities, while the general performance of the radar’s receiver processing is shown through the use of multiple radar images, which show a full reconstruction of the range, Azimuth, elevation and speed of the targets. The flexibility in generating such orthogonal coded waveforms, the proposed general receiver’s architecture and the fast 4D-FFT beam-forming implemented, pave the way for an adaptive and real-time capable 3D MIMO OFDM radar.
• Chapter 7: In this section, a complete OFDM based 3D MIMO radar demonstra- tor is shown. The core of the hardware architecture is based on that of the 3D MIMO radar system introduced in Chapter 4. However, the digital processing is completely changed and adapted to be operating with the OFDM radar’s archi- tecture described in Chapter 6. The system operates with one of the novel LFM based OFDM waveforms discussed in Chapter 6, where the orthogonality between the transmit elements is achieved by means of a Walsh-Hadamard based coding scheme. The radar system is verified through measurements and the results are
Chapter 1. Introduction 20 presented, through radar image captures achieved outdoors. The proposed archi- tecture, paves the way for low cost, miniaturized and real-time capable, adaptive OFDM MIMO 3D radar systems.
• Chapter 8: This section summarizes the achieved results and introduces concepts for future works.
Chapter 2
Fundamentals of FMCW MIMO
Radars
2.1
Chapter’s Introduction
MIMO radar is an emerging technology that is an extension to the classical digital beam- forming radar. The main difference compared to a conventional radar is the capability of transmitting different signals on multiple TX antennas while keeping these signals separable at reception. Throughout this chapter, fundamental equations and parame- ters of radar systems are analysed, before introducing the concepts of MIMO radars, virtual arrays, angle of arrival estimation and, finally, the description of how FMCW MIMO radar systems operate and how the signals can be separated by means of time domain multiplexing.