Digital Theses Archive


Tesi etd-09092019-103911

Type of thesis
Challenges in implementation of Microwave Photonics systems for Radar Applications
INGEGNERIA - Ph.D. Programme in Emerging Digital Technologies (EDT)
Presidente Prof.ssa BOGONI, ANTONELLA
  • Auto-regressive algorithm
  • Beam forming network
  • Microwave Photonics
  • MIMO radars
  • Photonic integrated circuits
  • Radars
  • Via-less rectangular waveguides
Exam session start date
In the past two decades, microwave photonics has emerged as a potential solution to the technical challenges faced by conventional CMOS electronics. Integrated electronic circuits have long served the society with innovative technological solutions. Today, the very fabric of human civilization is weaved with excellence in electronic and optical engineering. The pinnacle of mankind’s ingenuity is reflected in the technological marvels, extending from intercontinental fiber optic connectivity to the endeavors beyond the edge of our solar system. The boom of information technology has pushed the conventional electronic devices to the maximum of their physical limit in-terms of data rate, operating frequency and supply power. The electronic industry is currently looking for solutions which can meet the ever growing need for high-speed, efficient and cost-effective devices. A possible answer to conventional limitations of electronics comes from the field of optics. The optical devices operate at 100s of THz and are immune to interference and bandwidth limitations (in comparison with microwave devices). The photonic principles can be applied for the generation, processing and detection of microwave signals using cost-effective optical components. The possibility of amalgamation of both worlds i.e. optical and electronic, seems more realistic with the recent introduction of silicon based optical devices. Silicon based technologies for electronic device fabrication has matured over the course of several decades. The consonance of optical and electronic devices using same base material has opened the possibility to realize systems with unprecedented operating frequencies, data rates and functionalities.<br>This doctoral work is focused on the realization of microwave photonic (MWP) based sub-systems suitable for modern radar applications. Radar systems being the second most used application of wireless systems, have bottle necks such as resolution, range, operating frequency and power. The technological breakthroughs in the field of MWP have ushered a new design era for radar systems. The research work presented here is an effort to realize necessary sub-systems such that it can catalyze the development of a fully functional radar system with advanced features such as vary fast beam steering, active target lock and tracking, frequency agility and MIMO functionality. The interdisciplinary research has been conducted to search for solutions from different electrical engineering fields e.g. signal processing, photonic integrated circuits, microwaves and advanced packaging. Various sub-systems are realized using different technologies ranging from integrated circuits to coherent distributed networks. The research work has been conducted in collaboration with industrial partners such as Elettronica Spa and Ericsson AB. The industrial oversight has assured that the designed sub-systems are in-line with the needs of modern radar systems. <br>A detailed and thorough study of MWP systems have revealed various possibilities to answer the technical challenges faced by today’s radar systems. An analysis into radar systems revealed that electronic based systems suffer from bandwidth discretization, limited flexibility in terms of operating frequency, and poor beam steering capability at very high frequencies. Moreover, the lack of phase coherence among microwave signals has limited the number of deployed transceivers across the radar scene . The presented research work is a humble effort to answer the identified limitations of today’s radar technology.<br>Digital signal processing techniques inspired from synthetic aperture radars (SARs) have been utilized to stitch the sparse spectral profile of a multiband radar system. Using the inherent property of coherence among RF signals (generated using photonics), an auto-regressive algorithm has been tailored to interpolate among sparse sub-bands, thereby avoiding the detrimental effects of bandwidth discretization. Furthermore, an innovative UWB receiver is implemented using optical frequency comb generation. It was demonstrated that the receiver can support a bandwidth of 0-30 GHz with channel spacing of 1GHz. The UWB receiver was realized and tested to meet the specifications set by the industrial partner. An innovative beam forming network (BFN) is also implemented using a combination of silicon photonics and microwave techniques. It was experimentally verified that the designed BFN can provide a phase shift of 360° with an unprecedented switching speed of &lt; 1nsec. It was also demonstrated that the operating frequency of the system is flexible and is limited only by the RF interface. In order to further push the amalgamation of photonics and electronics, a via-less planar technique is presented. The contactless rectangular waveguides realized using bed of nail architecture can answer the long standing fabrication challenges of Indium-Phosphide (InP), thereby providing the possibility to realize a system-on-chip (SoC). <br>Finally, an innovative and first of its kind radar over fiber (RaoF) system is presented. The ability of an optical network to transport RF carrier to 100s of kilometers with minimum signal degradation has been utilized to envision a new kind of radar system. Instead of single transmitter and receiver, a coherent distributed network of radar transceivers is deployed across the radar scene. The acquired radar echo across multiple transmitting/receiving nodes, is processed using a novel coherent signal processing technique. The added spatial information has made it possible for a radar system to synthesize targets not only in range but also in the cross-range. A 2×4 coherent MIMO radar network is realized and tested in an industrial radar test range for its performance. The possibility of a coherent distributed radar network has opened a barrage of new applications and possibilities for radar systems.<br>This doctoral thesis highlights the importance of interdisciplinary research conducted over the past three years. The various engineering challenges solved using inspired techniques from different fields have provided a road map for implementing a robust, agile and cost-effective radar system. The presented sub-systems are not limited only to radar applications but also can be utilized for wireless communications. <br>