PhD Oral Defence - Essa Mujammami, Electrical and Computer Engineering
When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
Generating multi-beams along with having broadband and beam steering capability in mmWaves band are of crucial importance for diverse applications such as remote piloted vehicles, satellites, collision-avoidance radars, and ultra-wideband communications systems. Besides, the propagation environment at millimeter wave (mmWave) frequencies—suggested for the next generation of wireless networks (5G)—lends itself to a beamforming structure wherein antenna arrays are required in order to obtain the necessary link budget and to overcome the associated poor signal attenuation. Therefore, design of high gain antennas (to focus the directive beam to a user) and beamforming networks (to reduce interference) are essential and needed to address many challenges associated with 5G wireless communications.
Rotman lens has been widely used in many microwave beamforming applications, and recently in mmWave with focus mainly on the phase error performance, while a few number of publications focus on the amplitude performance. Moreover, there is a lack of publications on Rotman lens-based beamforming network implemented with the ridge gap waveguide (RGW) in its metal form, printed (PRGW), or metalized 3D-Printing (3DP-RGW). Few related publications are found in the open literature with simulation results and without experimental verification. For these reasons, this thesis deals with developing high gain, wideband antennas and beamforming networks. The proposed work addresses both the amplitude and the phase error while, at the same time, determining the design parameters of the proposed Rotman lens-based beamforming network implemented with the printed circuit board (PCB) and RGW technologies.
This work addresses the design and development of high-performance Quasi-Yagi antenna and Rotman lens-based beamforming networks. Accordingly, several issues are addressed in this thesis. Firstly, the design of a thin dielectric lens antenna (DLA) is implemented in order to improve the propagation characteristics of a dielectric slab waveguide (DSW) in front of a planar Quasi-Yagi antenna. Secondly, the construction of a wideband beamforming network—based on Rotman lens in the printed circuit board (PCB) technology—capable of steering the beam within a reasonable scanning angle. Thirdly, implementing the beamforming network using the RGW technology to overcome partially dielectric and radiation losses associated with the microstrip technology. Lastly, implementing the beamforming network using the printed version of the RGW (PRGW)—that is, as a compromise solution—where it possesses the ease of fabrication with the PCB technology, which is in addition to the advantage of the wave propagation in the air only as of the metal RGW.
A single element Quasi-Yagi antenna with a perturbed dielectric lens of broadband and high gain is designed, optimized, fabricated and tested at 30 GHz. The antenna provides 95% aperture efficiency with a measured gain of 15.5 dBi as well as a radiation efficiency of ~90% at 30 GHz and a broadband (24-40 GHz) for S11<-15. The designed end-fire antenna, with its low-profile and compact size, is a good candidate for many applications in mmWave band.
An optimum and accurate methodology for designing Rotman lens-based mmWave analog beamforming network (BFN) is presented. The simulation and measurement results showed good beamforming capabilities as well as a scanning range of 80 degrees in the azimuth plane, and, also, good matching at the array-ports. The maximum phase error is ±6.6°, and the main beam of the proposed BFN points at seven different angular directions that cover the range of ±40°. The maximum achieved realized gain is 14 dBi at 28 GHz for the center beam.
An analog Rotman lens-based BFN using RWG technology, integrated with the excitation ports and the antenna array elements, is designed, simulated, manufactured, and measured. The proposed integrated system is realized using the metallized 3D-Printing technology, in order to reduce the implementation cost of the full metal RGW Rotman lens. The measured results demonstrate that the system scan range equals ±39.5º over a wideband 27.5-37 GHz decreases to 30º in the band 37-40 GHz. The antenna bandwidth for VSWR < 2 is larger than 38% and is limited by the bandwidth of the radiating part and its beamwidth as well. Aiming to reduce the implementation cost, the printed version of the RGW (PRGW) is proposed and simulated. The PRGW Rotman lens-based BFN shows a good amplitude and phase performance in the band 26.5 GHz to 40 GHz. The maximum phase error is 6º with about 1 dB insertion loss improvement compared to microstrip (MS) Rotman lens-based beamforming network are achieved.