Due to the evolutions in wireless communication systems, antenna engineers have been confronting a number of challenges regarding improving the performance of antennas, miniaturizing the size as well as considering the fabrication simplicity. Although dielectric resonator antennas typically suffer from exhibiting low gain, they have been thoroughly under investigating as they are being excellent candidates to be utilized to fulfill contemporary communication systems requirements and specifications, especially at high-frequency ranges. The reason behind this solicitude is because they have several advantageous features, including but not limited to the simplicity of the used excitation mechanism and fabrication easiness.
One of the well-known methods to improve the gain is by arraying additional individual DRAs. However, one major obstacle evokes when designing the array to operate at a higher frequency. Spurious radiations from the feeding network are considerable and unfavorably influence the overall array performance. Moreover, it is mandatory to have several quarter-wavelength transmission lines and power dividers which, in turns, lead to high configuration complexity.
The substantial intention of this dissertation is to explore dielectric resonator array antenna designs where the concept of standing waves is utilized. In contradictory to corporate-fed traveling-wave array antennas designs, the need to utilize microstrip discontinuities such as quarter-wave transformers or power dividers is eliminated while having a single feeding port to excite the entire array structure. Consequently, undesired spurious coupling and radiations can be exceedingly minimized especially when operating at very high-frequency bands.
The dissertation proposes two novel dielectric array configurations based on the concept of standing-wave. In the first configuration, vertical and horizontal low-profile dielectric bridges have been employed to connect 3x3 dielectric array elements. The top surface of each bridge is covered by a metallic patch to prevent unfavorable radiations coming out of the bridges. The array structure is fed using a single coupling aperture resides symmetrically underneath the center element only. When exciting waves are coupled to the center element, these waves can be transferred to other array elements via the introduced dielectric bridges. Therefore, the entire structure resonates at the resonant frequency as a whole. The proposed design provides a realized gain of about 15 dBi at the boresight. The return loss is about -20 dB possessing about 35.7% useful impedance bandwidth. The experimental results show excellent agreement with those obtained by simulation.
The second proposed configuration consists of four dielectric resonator antennas forming a linear array. On the top surface of the substrate and between the array elements, there are three metallic patches which are employed to excite the array elements. These patches are slightly extended under the slabs to allow sufficient coupling. Under each dielectric slab, there is one metallic patch reside symmetrically at the center to enhance the wave coupling in both directions toward the array elements. The single feeding coaxial probe is attached to the center patch, and its location was optimized to provide excellent impedance matching. The maximum observed gain is 15 dBi at the boresight. The array structure is well matched and the return loss is measured to be -45 dB.
The validity and versatility of both designs are realized and illustrated. One powerful advantageous feature is that the feeding network was extremely simplified to a single port to excite the entire array structure. Another advantage is that both designs were partially fabricated using 3D printing technology. Therefore, it can be said that the proposed configurations are easy to fabricate since the complexity of designing feeding networks was obviated.
Choon Sae Lee
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Althuwayb, Ayman, "Standing-Wave Dielectric Array Antennas" (2018). Electrical Engineering Theses and Dissertations. 21.
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