Design of Dielectric Resonator Antennas with Dielectric Paste


Student thesis: Doctoral Thesis

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Award date20 Aug 2021


Dielectric resonator antennas (DRA) have been a research topic for the past 3 decades. Owing to their advantageous features, such as wide bandwidths, ease of excitation, lower ohmic losses especially at higher frequencies and relative compactness, they can be an attractive choice for wireless applications. Nevertheless, one of their major drawbacks is that their manufacturing process is typically more complicated as compared to other antennas, such as dipoles, microstrip patch antennas or other printed circuit board-based (PCB) antennas, as well as their lack of integration with PCB technology. For instance, in many cases DRAs need to be reshaped from blocks of ceramic materials, which can cause tolerance related issues because the manufacturing tolerance of the dielectric blocks is limited. This becomes increasingly problematic, when the operating frequency of the antenna is increased because the antenna size is drastically decreased for higher frequencies such as in the millimeter wave range. Furthermore, owing to material tolerance related issues, reliable DRA manufacturing is overall more challenging as compared to conductor or PCB-based antennas.

For higher frequencies substrate integrated DRAs (SIDRA), which solely rely on printed circuit board materials and manufacturing methods, have been developed. Even though such approaches can solve the aforementioned manufacturing and material-related issues since standard PCB materials and manufacturing methods can be deployed, SIDRAs suffer from limited material choice. Owing to the restricted choice of different available PCB substrates and the restrictions of the PCB manufacturing process itself, the variety of structures, which can be realized in SIDRA technology, is limited. Hence, many design techniques developed for DRAs that are shaped from ceramic blocks are not applicable in SIDRA technology. In particular, designs deploying different dielectric constants cannot be replicated with SIDRA technology. Furthermore, as the variety of different PCB substrates and available substrate thicknesses is limited, the design of SIDRAs or even PCB-based low profile DRAs is much more challenging.

In this thesis solutions to both, manufacturing related issues of DRAs shaped from ceramic materials and SIDRAs/PCB-based DRAs, which are limited by manufacturing methods and material choice of the PCB process, are investigated.

In the first chapter of this thesis state-of-the-art DRA technologies are reviewed and current research trends are analyzed with an emphasis on their issues as explained in the previous two paragraphs

In the second chapter of this thesis, dielectric vias are introduced and analyzed for the first time. Dielectric vias consist of cylindrical holes drilled into a PCB substrate and are subsequently filled with barium strontium titanate (BST) nanoparticle-sized powder, exhibiting a dielectric constant different to that of the PCB substrate. An effective medium is constructed inside the PCB substrate and the dielectric constant of the dielectric vias loaded PCB substrate material can be controlled. Using an effective media approach, a simple model of the dielectric vias is generated and a multi-ring SIDRA with wide bandwidth is designed to demonstrate the dielectric vias technique. After the feasibility of the technique is confirmed, an improved design is proposed and characterized.

To further explore the dielectric vias technique, single and dual polarized low profile and wideband antennas are investigated in the third chapter. The antennas utilize PCB materials only, which make them an attractive choice for practical applications. A combination of dielectric and air vias is used to control the antenna performance of both antennas, leading to compact, low profile, wideband antennas. A single port antenna is studied first and the working mechanism is elaborated in detail. A prototype is constructed and characterized. The design technique is extended to a dual polarized antenna. Besides wide impedance bandwidth, the dual polarized antenna features high port isolation without the need for a complex feeding scheme or feeding circuit.

A dielectric paste consisting of BST nanoparticle sized powder and a silicone rubber is investigated in the fourth chapter of this thesis. The paste is characterized and its dielectric constant can be adjusted freely by controlling the BST content of the dielectric paste with respect to the silicone rubber content. After the paste is inserted into a mold and solidified, an effective DRA is obtained, which can replace the ceramic block required for traditional DRA manufacturing. To demonstrate the technique, a circularly polarized menger sponge fractal DRA with wide bandwidth is designed and characterized.

Chapter 5 summarizes the work presented in this thesis. A future outlook for further investigations into the presented research areas is given.