Advanced direct metal 3D printed passive components for wireless communications and satellite applications

Abstract

This thesis presents the design of advanced microwave passive filters, antennas, and antenna arrays using direct metal 3D printing technology. These work all incorporate the printing technology into the RF component design process, demonstrating the potential possibilities of direct metal 3D printing in the investigation and fabrication of passive microwave components with irregular shapes but attractive features. This thesis's works involved an extensive frequency range that starts with investigating S-band filters and then extends to C-band and Ku-band filters and antennas design. It is well known that in S- and C- band radio frequency (RF) applications that miniaturization is a critical factor for RF devices besides high performances. For this reason, the first project in this thesis proposed a novel compact waveguide loaded air slots resonator for designing inline bandpass filters. As a result, the designed filters not only have a smaller size than coaxial ones but also have controllable transmission zeros with inline structures. Since the air slots resonator is loaded inside the cavity, it is difficult to fabricate by conventional methods, but accessible by 3D printing technique with appropriate self-support structures. The fabrication quality was reflected by the mechanical and RF property measurements, which first demonstrated the advantage of using 3D printing technique to fabricate components with complex structures. The second project presents a compact high-Q fan-shaped folded waveguide resonator, which is applied to successfully design one C-band filter and filtering antenna. High performance RF properties and easy-to-print structures are always considered together. Accordingly, this work proposed and validated novel slots cross negative coupling topology of the filter and novel filtering antenna theory. Also, each of the designed components has better self-supported structures that can be printed with only two pieces, which highly reduced assembly processes and errors. Furthermore, the RF properties from measurement results further demonstrated that the reliability of the metal 3D printing technology for C-band RF applications. The concepts of the third project are extended from the second project but replaces the folded waveguide resonator with a metal strong coupling resonator (MSCR). The MSCR allows for even further compact dimensions while maintaining a high Q value of over 1000. It also allows producing mixed electrical-magnetic coupling by the curving coupling metal pairs intentionally. Except for the desired RF properties, the designed filter based on the MSCR can be printed as a whole even with complex inner circuits structures. Furthermore, the MSCR was integrated with the helical antenna using the proposed theory presented in the second project. Although the helical antenna belongs to the electrical-small antenna, the designed filtering antenna still has a high transmission efficiency of more than 95% and a 6 dBi realized gain concerning its less than quarter-wavelength. In addition, the filtering antenna has five helical radiation elements and one filter prototype but was printed with only three pieces, which showed the advantages of the direct metal 3D printing technology again. The fourth and the last project introduces a Ku-band slots antenna array application based on the sine corrugated waveguide resonator. Similar to previous projects, advanced RF performances were pursued in this project, in addition to demonstrating the use of 3D printing technology to fabricate compact and specific structures. The designed antenna array achieved a higher gain, wider band, and more simple feeding networks. The mode analysis method based on the EM software CST was applied to guide the design since no related formulas were available. The designed model was printed with two pieces and was measured thoroughly. The measured surface roughness, in-band responses, and radiation patterns showed promising results for the sine corrugated waveguide and 3D printing technology in satellite applications. In general, this thesis researched and proved the reliability and advantages of direct metal 3D printing technology in designing and fabricating advanced microwave passive components below the Ku-band. It should be mentioned that the designed passive components in this thesis can be easily re-designed/re-configured and applied on the 5G wireless base station and satellite communication systems.