3-D Printed microwave and tetrahertz passive components

This thesis presents the design of microwave and terahertz filters, fabricated using different types of 3-D printing technology. The work demonstrates the potential of using 3-D printing in the fabrication of microwave and terahertz passive components. The first project introduces a compact coaxial cavity resonator filter which was fabricated using stereolithography 3 D printing process. The size and volume of this filter reduced by almost half, by fitting one resonator inside another resonator. This filter is ideal for fabrication by 3 D printing, as such a complex structure cannot be made easily by other methods. This project demonstrates the advantage of using 3-D printing in fabrication of components with complex structures. The second project introduces three waveguide bandpass filters operating at centre frequency of 90 GHz, which were fabricated using the micro laser sintering process. The filters were the highest frequency metal 3-D printed filters reported at the time of publication. The third project introduces two waveguide filters operating at centre frequency of 180 GHz, which were also fabricated using the micro laser sintering process. These are the world highest frequency waveguide filters fabricated by a metal 3-D printing process. The capability of reproducibility of the micro laser sintering process is also discussed in this thesis. The fourth project introduces a hybrid coaxial bandpass filter with two symmetrical transmission zeros, which was fabricated using stereolithography 3-D printing process. In this project the main-line couplings and input/ output coupling were realized using PCB lines, the idea of using PCB lines instead of coupling irises or probes is to allow different topologies to be designed easily by altering the PCB layout. Finally, the fifth project introduces a terahertz waveguide bandpass filter with embedded H plane waveguide bends. This filter is being fabricated using 3-D screen printing

Review of 3D Printed Millimeter-Wave and Terahertz Passive Devices

The 3D printing technology is catching attention nowadays. It has certain advantages over the traditional fabrication processes. We give a chronical review of the 3D printing technology from the time it was invented. This technology has also been used to fabricate millimeter-wave (mmWave) and terahertz (THz) passive devices. Though promising results have been demonstrated, the challenge lies in the fabrication tolerance improvement such as dimensional tolerance and surface roughness. We propose the design methodology of high order device to circumvent the dimensional tolerance and suggest specific modelling of the surface roughness of 3D printed devices. It is believed that, with the improvement of the 3D printing technology and related subjects in material science and mechanical engineering, the 3D printing technology will become mainstream for mmWave and THz passive device fabrication

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

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

3-D printing quantization predistortion applied to sub-THz chained-function filters

This paper investigates physical dimension limits associated with the low-cost, polymer-based masked stereolithography apparatus (MSLA) 3-D printer, with 50 μm pixels defining the minimum print feature size. Based on the discretization properties of our MSLA 3-D printer, multi-step quantization predistortion is introduced to correct for registration errors between the CAD drawing and slicing software. This methodology is applied to G-band 5th order metal-pipe rectangular waveguide filters, where the pixel pitch has an equivalent electrical length of 8.5° at center frequency. When compared to the reference Chebyshev filter, our chained-function filter exhibits superior S-parameter measurements, with a low insertion loss of only 0.6 dB at its center frequency of 182 GHz, having a 0.9% frequency shift, and an acceptable worst-case passband return loss of 13 dB. Moreover, with measured dimensions after the 3-D printed parts have been commercially electroplated with a 50 μm thick layer of copper, the re-simulations are in good agreement with the S-parameter measurements. For the first time, systematic (quantization) errors associated with a pixel-based 3-D printer have been characterized and our robust predistortion methodology has been successfully demonstrated with an upper-millimeter-wave circuit. Indeed, we report the first polymer-based 3-D printed filters that operate above W-band. As pixel sizes continue to shrink, more resilient (sub-)THz filters with ever-higher frequencies of operation and more demanding specifications can be 3-D printed. Moreover, our work opens-up new opportunities for any pixel-based technology, which exhibits registration errors, with its application critically dependent on its minimum feature size

Antenna Systems for Wideband Direction Finding and Spectrum Sensing

Antenna systems for direction finding (DF) and spectrum sensing remain vital to modern engineering; civilian and defense sensing requires wideband systems meeting rigorous requirements across the spectrum. Wideband DF systems can be examined as wide absolute bandwidth or wide relative bandwidth. The challenges at mm-wave frequencies are the large impact of small features and controlling pattern shape over wide absolute (>30GHz) bandwidths. At microwave frequencies the challenge is establishing ripple-free beam shape over wide relative (>3:1) bandwidth. Typical DF at high frequencies uses poorly controlled pattern shape, while at low frequencies allow low efficiencies and strong pattern ripple, reducing accuracy and range. More rigorous goals require analytical evaluation of DF antennas, and pattern and mode control. A theory is developed analyzing DF with ideal cosine, sinc, or gaussian radiation patterns. This theory models many realistic antenna beams, and shows a fundamental link between beam shape and pointing angle, and three DF system parameters: field of view (FOV), minimum FOV gain, and minimum DF function slope. Utilizing this framework, realistic system goals are established, antennas can be evaluated analytically, guiding design for DF. This analysis is validated by design of three antennas. A curved aperture horn is designed for wide absolute bandwidth W-band Sensing, and substantial pattern control over frequency, enabling frequency insensitive DF. Multiple manufactured configurations show agreement with simulation. A dual polarized TEM horn is developed for wide relative bandwidth L to C-band operation, integrated with loop and bowtie antennas to achieve miniaturization through spherical modes engineering. High efficiency, dual polarization, and DF operation are obtained. Measurements show agreement of pattern shape and validate design, but are impacted by modeled and actual absorber loss. A dual polarized LPDA antenna is designed from L to C-band for consistent gain and match. Development includes integrated tapered line matching network. Performance impacts of geometric parameters are discussed. Finally, 3D Printing is investigated for self-supporting, low-loss coaxial lines. A High Q resonator is designed to investigate surface roughness. Wideband filters and diplexers are demonstrated, incorporating novel coaxial junction geometry to compensate for parasitic loading. Manufactured devices achieve significant miniaturization and agreement with simulation

Analysis and Design of Low-Cost Waveguide Filters for Wireless Communications

The area of research of this thesis is built around advanced waveguide filter structures. Waveguide filters and the waveguide technology in general are renowned for high power capacity, low losses and excellent electromagnetic shielding. Waveguide filters are important components in fixed wireless communications as well as in satellite and radar systems. Furthermore, their advantages and utilization become even greater with increase in frequency, which is a trend in modern communication systems because upper frequency bands offer larger channel capacities. However, waveguide filters are relatively bulky and expensive. To comply with more and more demanding miniaturization and cost-cutting requirements, compactness and economical design represent some of the main contemporary focuses of interest. Approaches that are used to achieve this include use of planar inserts to build waveguide discontinuities, additive manufacturing and substrate integration. At the same time, waveguide filters still need to satisfy opposed stringent requirements like small insertion loss, high selectivity and multiband operation. Another difficulty that metal waveguide components face is integration with other circuitry, especially important when solid-state active devices are included. Thus, improvements of interconnections between waveguide and other transmission interfaces are addressed too. The thesis elaborates the following aspects of work: Further analysis and improved explanations regarding advanced waveguide filters with E-plane inserts developed by the Wireless Communications Research Group, using both cross coupled resonators and extracted pole sections (Experiments with higher filter orders, use of tuning screws, degrees of freedom in design, etc. Thorough performance comparison with competing filter technologies) - Proposing novel E-plane filter sections with I-shaped insets - Extension of the E-plane filtering structures with metal fins to new compact dual band filters with high frequency selectivity and miniaturized diplexers. - Introduction of easy-to-build waveguide filters with polymer insert frames and high-performance low-profile cavity filters, taking advantage of enhanced fabrication capabilities when using additive manufacturing - Developing new substrate integrated filters, as well as circuits used to transfer signals between different interfaces Namely, these are substrate integrated waveguide to metal waveguide planar transitions that do not require any modifications of the metal waveguides. Such novel transitions have been designed both for single and orthogonal signal polarizations

Emerging Trends in Techniques and Technology as Applied to Filter Design

In the last decade, the filter community has innovated both design techniques and the technology used for practical implementation. In design, the philosophy has become "if you can't avoid it, use it", a very practical engineering approach. Modes previously deemed spurious are intentionally used to create in-line networks incorporating real or imaginary transmission zeros and also reduce the number of components and thus further miniaturize; spurious responses are re-routed to increase the passband width or stopband width, frequency variation in couplings is used to create complex transfer functions, with all of these developments using what was previously avoided. Clever implementations of baluns into passive and active networks is resulting in a new generation of noise-immune filters for 5G and beyond. Finally, the use of a diakoptic approach to synthesis has appeared an evolving approach in which small blocks ("singlets", "doublets", etc.) are cascaded to implement larger networks, (reducing the need for very complex synthesis), with this new approach promising a large impact on the implementation of practical structures. Filter technology has migrated towards "observe it and then adapt it", pragmatically repurposing tools not specifically originally intended for the applications. Combinations of surface wave and bulk wave resonators with L-C networks are improving the loss characteristics of filters in the region below 2 GHz. Lightweight alloys and other materials designed for spacecraft are being used in filters intended for space, to provide temperature stability without the use of heavy alloys such as Invar. Fully-enclosed waveguide is being replaced in some cases by planar and quasiplanar structures propagating quasi-waveguide modes. This is generically referred to as SIW (Substrate Integrated Waveguide). Active filters trade noise figure for insertion loss but perhaps will offer advantage in terms of size and chip-level implementation. Finally, the era of reconfiguration might be approaching, as the basic networks are evolving, perhaps lacking only the appearance of lower-loss, higher-IP solid-state tuning elements

Additive Manufacturing of RF Waveguide Components

The exponential growth of publications, in the last years, on the use of additive manufacturing (AM) technologies in the microwave field proves the increasing interest of research institutions and industries in these techniques. Some advantages of AM with respect to conventional machining are weight reduction, design flexibility, and integration of different functionalities (electromagnetic, thermal, and structural) in a single part. This chapter presents the most employed AM technologies for the manufacturing of RF waveguide components. First, an overview of the AM processes is discussed with particular care on material properties and post-processing. Then, an extensive survey on microwave-guided components fabricated by AM processes published in literature is shown