Wideband Patch-Integrated Dielectric Resonator Antennas

Abstract

Dielectric resonator antennas (DRAs) and microstrip patch antennas are essential radiating elements in contemporary wireless systems. While patch antennas offer a low profile and facilitate easy planar integration, DRAs deliver high radiation efficiency and possess an inherently wide impedance bandwidth. Combining these attributes in a single design is challenging, especially given the rigorous demands of 5G, beyond-5G, and 6G technologies, which necessitate compact, low-profile antennas capable of wideband, high-gain performance to support multi-gigabit data rates, low latency, and dense connectivity. This study addresses this challenge by experimentally demonstrating wideband patch-integrated DRA configurations that leverage both the bandwidth and efficiency of DRAs alongside the integrability of patches, thereby mitigating traditional bandwidth-gain-profile trade-offs. The resulting designs provide valuable physical insights and practical design guidelines for patch-integrated wideband DRAs aimed at 5G, 6G, and future wireless platforms, where high efficiency, broad bandwidth, and stable gain are critical for compact base stations, Internet of Things (IoT) devices, and millimetre-wave (mmW) systems.

This thesis presents a comprehensive study that explores the integration of patch antennas with DRAs, with a particular focus on the geometric placement of the patch within various wideband DRA designs to enhance performance. This study establishes a new paradigm for high-performance wideband antennas. The first work introduces a parasitic patch that fully covers the top surface of a wide aperture-fed DRA. While this patch does not introduce any additional resonance, it significantly reduces the antenna profile without impacting the existing slot and dielectric modes. The second work demonstrates the use of a DRA to excite a patch antenna, differing from the conventional method that employs a patch to excite the DRA. This configuration effectively merges the patch mode with the dielectric mode, resulting in an expanded impedance bandwidth while maintaining a compact form factor. The third work investigates an integrated patch positioned between a dielectric patch and a dielectric block, creating a DRA-patch-DRA structure. This arrangement successfully mitigates gain drops associated with higher-order modes and equalises the gain contributions of all dielectric modes, thereby achieving the widest impedance and gain bandwidth of the three designs.

The second chapter introduces a wideband DRA designed for operation in the mmW band. It is fed through a wide aperture connected to a substrate-integrated waveguide (SIW) network. The DRA utilises a relatively low permittivity material (_εr = 6.45), which is significantly lower than the conventional value of around 10. This design promotes strong coupling between the slot and dielectric modes, effectively broadening the bandwidth. The wide aperture, which matches the dimensions of the DRA base, further excites higher-order modes to enhance bandwidth. Additionally, a parasitic metallic patch, which is the same size as the DRA’s top surface, is placed on the upper face. This patch significantly reduces the antenna height by more than 40%, while maintaining the existing modes. To address the severe path loss associated with the mmW spectrum, a 4 × 4 array based on this element is implemented, achieving an impedance bandwidth of 35.5%, a peak gain of 18.5 dBi, and stable radiation patterns across the entire operating band. This design skilfully combines the wide-aperture coupling technique with metallic-patch loading to achieve both wideband performance and a compact structure.

The third chapter demonstrates a wideband patch antenna fed by a DRA, designed for operation in the microwave band. A high-permittivity ceramic DRA (_εr = 20.5) is fed by a microstrip line using aperture coupling, where the high permittivity allows the DRA to reduce its final antenna profile to just 0.1λ_o, where λ_o represents the free-space wavelength at the centre frequency of the antenna. A metallic patch with a significantly larger surface area is placed above the DRA to integrate both the dielectric and patch modes. This patch not only enhances the bandwidth by incorporating the patch mode but also improves the impedance matching at the high frequencies, allowing effective integration with the slot mode generated through the microstrip line aperture coupling. Compared to traditional aperture-coupled single DRAs, this patch configuration reduces the DRA’s thickness (technique introduced in the second chapter) and eliminates the gain drop associated with the higher even-order modes. Additionally, a wide slot is etched at the centre of the metallic patch, which plays a crucial role in controlling the impedance matching across all operating modes and eliminates the out-of-phase current introduced by the high permittivity DRA beneath. This design outperforms traditional patch-integrated DRA configurations, which utilise a metallic patch with a central aperture to excite the DRA. This is particularly evident in terms of bandwidth and the stability of radiation patterns. The final prototype demonstrates an impressive overlapping bandwidth of 45% for both the 10 dB impedance and 3 dB gain criteria. It achieves a peak gain of 9.95 dBi, with stable radiation patterns maintained throughout its entire operating range. Remarkably, this is the first instance of using a DRA to excite a patch antenna, with measurements confirming its effectiveness.

The fourth chapter investigates a wideband stacked DRA-patch-DRA configuration designed for operation in the microwave band. Initially, a traditional large dielectric block with a permittivity of 10.2, which is fed by a microstrip line through a wide aperture coupling (technique introduced in the second chapter). This design effectively reduces reactance at high frequencies, allowing for the use of multiple higher-order modes within a single structure. An air gap is incorporated within the DRA, creating a stacked configuration where a dielectric patch with a larger surface area is placed above the dielectric block, supported by a thick air substrate. This arrangement significantly lowers the quality factor (Q-factor) of the dielectric modes, enabling wideband operation using only three resonant modes. However, conventional wideband DRAs often face inter-mode gain drops when higher-order modes are involved. To address this issue, a metallic patch larger than the dielectric block and smaller than the dielectric patch is placed between them. This metallic patch helps align the higher-order modes more closely with the frequency of the fundamental mode, effectively eliminating inter-mode gain drop and equalising the gain contributions of all dielectric modes. As a result, the DRA-patch-DRA structure provides stable gain across the entire operating band. The fabricated prototype achieves an impressive 80% impedance bandwidth and a 60% 1-dB gain bandwidth, all while maintaining stable radiation patterns across the operating range. This structure highlights the crucial function of the metallic patch in mitigating unwanted gain variations and balancing the gain contributions of dielectric modes in wideband DRA designs. Consequently, it offers the broadest overlapping bandwidth among the three works presented in this thesis.

In summary, this thesis presents a comprehensive study and experimental validation of a unified family of patch-integrated DRA architectures. It demonstrates how strategic metallic patch placement can simultaneously achieve wide impedance bandwidth, a compact profile, and stable gain—performance characteristics that are seldom found together in traditional DRAs or microstrip patches alone. By systematically investigating three distinct configurations across microwave and mmW bands—a parasitic patch–loaded wide-aperture fed DRA, a low-profile DRA-excited patch antenna, and a stacked DRA-patch-DRA structure featuring equalised modal gain—this work establishes a coherent design framework. This framework focuses on tightly coupling and reshaping dielectric and patch modes to address long-standing trade-offs among bandwidth, gain, and profile, offering both theoretical insights and practical design guidelines for next-generation wireless communication systems.

Date of Award	16 Jun 2026
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Hang WONG (Supervisor)