Wideband Multi-Layered Dielectric Resonator Antenna with Small Form Factor for 5G Millimeter-Wave Mobile Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper presents a wideband multi-layered dielectric resonator antenna for 5G millimeter-wave mobile applications, while reducing the height of the DRA compared to the converntional probe-fed RDRA. However, several aspects should be addressed to further strengthen the work.

1) I am wondering if some DRAs having been used in mobile applications or mobile phones.

2) What ahout the gain of the proposed DRA compared to the converntional probe-fed RDRA, due to the reduced height?

3）Actually, do DRAs need to be packaged in practical application?

4）Why didn't measure the 1x4 array? 

5) How to fix the DRA? Do you use the glue?

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. We have revised our manuscript according to the reviewer’s comments and recommendations. The changes that the authors made are in red in the manuscript. The replies to the recommendations and comments are as follows:

1. I am wondering if some DRAs have been used in mobile applications or mobile phones.

Reply: Thank you for this important question. While traditional DRAs have mainly been used in base stations and radar systems due to their size and packaging complexity, recent advancements in material miniaturization and packaging have enabled their use in mobile devices. For instance, An et al. [3] demonstrated a multi-stacked ceramic patch antenna on package for 5G millimeter-wave mobile applications. Additionally, Pan et al. [10] and Hong et al. [5] discussed DRAs integrated into MIMO antenna modules in mobile terminals.

In our case, the proposed low-profile CFPL-ML-RDRA, fabricated using multi-layered ceramic and adhesive polymer, is explicitly designed to address the size and manufacturability constraints of mobile devices.

As far as the authors know, DRA has not yet been applied to commercial mobile devices. However, we believe it can be applied in the near future, particularly because the thickness constraint of mobile devices strongly motivates low-profile antenna solutions.

2. What about the gain of the proposed DRA compared to the conventional probe-fed RDRA, due to the reduced height?

Reply: An excellent point. While antenna miniaturization often results in reduced gain, our design leverages a hybrid resonant mode formed by the capacitive-fed patch and DRA modes to maintain high gain over a wider bandwidth.

As shown in Figure 2(b) and detailed in Section 2.1, the realized gain bandwidth exceeding 4 dBi spans 5.4 GHz for the proposed CFPL-ML-RDRA—28.6% broader than that of the conventional PF-RDRA. Moreover, although the antenna height is reduced by 38.6%, the peak gain remains comparable, showing that the gain-bandwidth product is significantly improved.

3. Actually, do DRAs need to be packaged in practical application?

Reply: Yes, in most practical 5G applications, dielectric resonator antennas (DRAs) are typically integrated into antenna-in-package (AiP) modules or antenna-on-package (AoP) configurations to ensure mechanical stability and electrical integrity. Our proposed CFPL-ML-RDRA design is inherently package-compatible, thanks to the multi-layered ceramic structure and adhesive polymer layer that allow batch processing and integration onto PCBs.

4. Why didn’t you measure the 1x4 array?

Reply: We appreciate this insightful question. While the array was fully designed and simulated, fabrication and measurement of the 1×4 array were not conducted in this study due to limitations in prototyping facilities and time constraints. However, the unit antenna was fully fabricated and characterized, and its excellent agreement between simulation and measurement validates the simulation framework used for the array. The array design aims to demonstrate the scalability and array performance potential of the proposed antenna.

In future work, we plan to fabricate and characterize the antenna array to further validate system-level performance.

5. How to fix the DRA? Do you use the glue?

 Reply: Thank you for your practical question. Yes, the proposed CFPL-ML-RDRA uses a polymer layer with εr = 2.38 as an adhesive between the ceramic layers. For mounting onto the PCB, we use a soldering process for via connections, followed by an underfill process to enhance mechanical stability and adhesion. This ensures reliable integration onto the test board and is suitable for mass production.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors present a broadband, dual-polarized, capacitively fed, multilayer rectangular dielectric resonator antenna with reduced antenna height. The unit antenna was designed, simulated, fabricated, and characterized.

The proposed antenna is an interesting solution characterized by a wide operating band and stable energy gain over the entire operating range of at least 4 dB. The article is written clearly and presents the necessary simulations and measurements. Some inaccuracies may be noted in the drawings. Details below:

• in Fig. 1, the caption refers to Figs a), b) and c), and the figure only shows a) and b).
• Not fully understandable caption in Fig. 3.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. We have revised our manuscript according to the reviewer’s comments and recommendations. The changes that the authors made are in red in the manuscript. The replies to the recommendations and comments are as follows:

1. In Fig. 1, the caption refers to Figs (a), (b), and (c), and the figure only shows (a) and (b).

Reply: Thank you for pointing this out. As correctly noted, the current figure contains two sub-images within panel (b), which correspond to the originally intended (b) and (c). We have now split the second part of Figure 1 into (b) and (c) to improve clarity and match the caption.

→ The figure has been updated in the revised manuscript, and the caption now reads:.

Figure 1. Geometry and dimensions of the proposed capacitive-fed patch-loaded multi-layered rectangular dielectric resonator antenna (CFPL-ML-RDRA): (a) 3D and top views, (b) detailed top view of the capacitive-fed patch with critical parameters, and (c) side cross-sectional view of the layered antenna structure.

2. Not fully understandable caption in Fig. 3.

Reply: We appreciate this observation. The previous caption for Figure 3 was ambiguous and did not clearly convey the comparison being made. We have now revised the caption of Figure 3 as follows to more accurately describe its content:

Figure 3. Comparison of the height and performance characteristics between the conventional probe-fed RDRA (PF-RDRA) and the proposed capacitive-fed patch-loaded multi-layered RDRA (CFPL-ML-RDRA), highlighting the reduction in antenna height and enhancement in gain bandwidth.

This revised caption provides better context for the figure and aligns with the explanation in Section 2.1 of the manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This paper proposes a novel antenna design: a Capacitive-Fed Patch-Loaded Multi-Layered Rectangular Dielectric Resonator Antenna (CFPL-ML-RDRA). The methodology involves stacking two high-permittivity ceramic substrates with an adhesive polymer layer in between. A key innovation is the integration of a metallic patch on the top surface of the bottom ceramic substrate, which is capacitively fed by probe-fed strips for dual-polarization. This structure excites two distinct resonant modes: the fundamental TE mode of the RDRA and a hybrid mode combining the RDRA's TE mode with a patch-like TM mode. The strategic merging of these two modes, confirmed through E-field analysis and parametric studies, achieves a wide impedance bandwidth of 5.5 GHz while simultaneously reducing the antenna's physical height by 38.5% compared to a conventional probe-fed DRA.

The methodology presents a novel contribution. While the use of stacked DRAs and capacitive feeding techniques are known concepts individually, their specific integration to create a hybrid resonant mode for the explicit purpose of simultaneously enhancing bandwidth and reducing profile is innovative. The paper clearly demonstrates that the second resonance is not a pure DRA higher-order mode but a hybrid mode, a phenomenon directly enabled by the unique capacitive-fed patch-loaded multi-layered structure. This distinct approach to bandwidth enhancement differentiates it from prior work.

The paper presents a significant and well-executed study with clear potential impact for 5G mmWave mobile applications. The work is technically sound, featuring a clear problem statement, a novel proposed solution, comprehensive simulation studies (including field analysis and parametric investigations), and experimental validation that strongly correlates with the simulated results. Its practical relevance is further enhanced by the expansion to a 1×4 array simulation.

To improve the quality of the paper, it would be beneficial to address some useful issues. Overall, it is recommended for acceptance with minor revisions pending:

1. Comparison with a conventional PF-RDRA is useful; however, a comparison with one or two other recent, compact wideband DRA designs would more clearly demonstrate the proposed architecture's superiority and competitive advantage.
2. There is a lack of clarity in the description of the gain measurement system (“custom-designed gain measurement system”). The method (e.g., comparison, near-field to far-field transformation) should be briefly discussed.
3. For mmWave systems, it would be beneficial to explicitly report the simulated and measured radiation efficiency of the antenna element.
4. It appears that the caption of Figure 3, “This is a figure. Schemes follow the same formatting,” is merely a placeholder instruction for the authors and should be revised.
5. The unit for volume should be mm³ (cubic millimeters). Fix the statement “The volume of the fabricated CFPL-ML-RDRA measures85 × 1.85 × 2.15 mm3”.

Comments for author File: Comments.pdf

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. We have revised our manuscript according to the reviewer’s comments and recommendations. The changes that the authors made are in red in the manuscript. The replies to the recommendations and comments are as follows:

1. Comparison with a conventional PF-RDRA is useful; however, a comparison with one or two other recent, compact wideband DRA designs would more clearly demonstrate the proposed architecture’s superiority and competitive advantage.

Reply: Thank you for this valuable suggestion. To better highlight the advantages of our proposed design, we have added a comparative discussion referencing two recent wideband and compact DRA designs:

Chair et al., Electron. Lett., 2006 [12]

Fang et al., IEEE Antennas Wireless Propag. Lett., 2020 [13]

These works utilize high-order modes or perforated dielectric structures to widen bandwidth, but either result in higher profiles or more complex fabrication processes. In contrast, our CFPL-ML-RDRA achieves broad bandwidth, low profile, and structural simplicity via hybrid mode excitation from a capacitive-fed patch in a stacked ceramic format.

2. There is a lack of clarity in the description of the gain measurement system (“custom-designed gain measurement system”). The method (e.g., comparison, near-field to far-field transformation) should be briefly discussed.

Reply: We thank the reviewer for pointing out this ambiguity. The “custom-designed gain measurement system” refers to a standard gain comparison method using a reference horn antenna in an anechoic chamber setup. This system is optimized for mmWave frequencies and allows precise boresight gain measurement using a GSG RF probe.

We have revised the description in Section 3 to clarify the gain measurement approach:

“A standard gain comparison method using a calibrated horn antenna and an anechoic chamber was employed to characterize the antenna gain. The measurement setup included a GSG RF probe station and VNA to capture the boresight realized gain.”

3. For mmWave systems, it would be beneficial to explicitly report the simulated and measured radiation efficiency of the antenna element.

Reply: An excellent point. We have now included the simulated radiation efficiency, calculated using CST Studio Suite, and discussed it in Section 3. The simulated efficiency of the CFPL-ML-RDRA exceeds 85% across the operating band. Due to limitations in the measurement setup, measured radiation efficiency could not be directly obtained, but the consistency between measured and simulated gain suggests minimal loss.

We have added the following sentence in section 3.

“The simulated total radiation efficiency of the proposed antenna exceeds 85% over the operating band (24–30 GHz), demonstrating high-efficiency performance due to low-loss ceramic materials and optimized feeding. Direct measurement of radiation efficiency was not feasible due to equipment limitations.”

4. It appears that the caption of Figure 3, “This is a figure. Schemes follow the same formatting,” is merely a placeholder instruction for the authors and should be revised.

Reply: We appreciate the reviewer for catching this oversight. The caption for Figure 3 has been revised as follows:

Figure 3. Comparison of the physical height and gain bandwidth performance between the conventional probe-fed RDRA and the proposed CFPL-ML-RDRA, showing the benefits of height reduction and wider operational bandwidth.

5. The unit for volume should be mm³ (cubic millimeters). Fix the statement “The volume of the fabricated CFPL-ML-RDRA measures 1.85 × 1.85 × 2.15 mm3”.

 Reply: Thank you for this correction. We have revised the sentence in Section 3:

“The volume of the fabricated CFPL-ML-RDRA is 1.85 × 1.85 × 2.15 mm³, corresponding to 0.15 λL × 0.15 λL × 0.17 λL, where λL is the free-space wavelength at 24 GHz.”

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Dear authors,

congratulations on your paper multi-layered dielectric resonator antenna. Your studies regarding such an antenna led to a better and performant structure. I would have some suggestions on improving your article:

-please include a paragraph in Section 1 presenting what is described in each of the other sections

-in Figure 2 please place (a) and (b) under the figures

-you talk at raw 107 about "all three antennas", I think you wanted to write "two"

-please rephrase the name of Figure 3....or consider it  as a table

-in Figure 4 my first observation is that the legend should be included for each representation

-the second observation regarding Figure 4 is that I would consider it as a table or maybe split it in three different figures 

-please highlight more your contributions in the conclusions

-include more recent references.

 

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. We have revised our manuscript according to the reviewer’s comments and recommendations. The changes that the authors made are in red in the manuscript. The replies to the recommendations and comments are as follows:

1. Please include a paragraph in Section 1 presenting what is described in each of the other sections.

Reply: Thank you for the helpful suggestion. We have added a paragraph at the end of Section 1 summarizing the structure of the paper and briefly describing the content of each subsequent section. The following paragraph was added.

“The rest of the paper is organized as follows: Section 2 introduces the design, simulation, and mode analysis of the proposed antenna. Section 3 presents the fabrication process and measured results. Section 4 provides the array simulation performance. Finally, Section 5 concludes the paper with a summary of the contributions and key findings.”

2. In Figure 2 please place (a) and (b) under the figures.

Reply: Thank you for this formatting suggestion. We have revised Figure 2 to place the sub-labels (a) and (b) under each corresponding figure. This improves visual clarity and figure comprehension.

3. You talk at raw 107 about "all three antennas", I think you wanted to write "two".

Reply: You're absolutely correct. This was a typographical error. We have corrected the sentence from:

“all three antennas were designed...” to “both antennas were designed...”

4. Please rephrase the name of Figure 3… or consider it as a table.

Reply: Thank you for pointing this out. We have revised the caption of Figure 3 to clearly describe its contents as a graphical comparison rather than a placeholder or table. The updated caption reads:

“Figure 3. Comparison of the physical height and gain bandwidth performance between the conventional probe-fed RDRA and the proposed CFPL-ML-RDRA, showing the benefits of height reduction and wider operational bandwidth.”

We believe the figure remains appropriate in its current graphical form, rather than as a table, as it conveys visual information about structure and performance characteristics.

5. In Figure 4, my first observation is that the legend should be included for each representation.

 Reply: Thank you for the observation. To improve clarity, we have revised the caption of Figure 4 to explicitly indicate which side corresponds to the PF-RDRA and which side corresponds to the CFPL-ML-RDRA, as well as to explain the meaning of the color scale and field arrows. This ensures that the figure can be clearly interpreted without modifying the figure layout. The updated caption is below.

Figure 4. Simulated cross-sectional field distributions of the conventional probe-fed RDRA (left) and the proposed capacitive-fed patch-loaded multi-layered RDRA (right) at (a) 25 GHz and (b) 29 GHz. The color scale represents the electric field intensity, while arrows indicate the magnetic field distribution.

6. The second observation regarding Figure 4 is that I would consider it as a table or maybe split it in three different figures.

Reply: We appreciate the reviewer’s suggestion. While we agree that clarity is important, we believe that presenting the results in a single composite figure with clear labeling provides the most effective comparison between the PF-RDRA and CFPL-ML-RDRA. To address the reviewer’s concern, we have enhanced the caption of Figure 4 to explicitly describe the content of each subfigure and to indicate the comparison format (left: PF-RDRA, right: CFPL-ML-RDRA). This allows readers to clearly distinguish the results without fragmenting the figure into multiple parts.

The revised caption reads:

Figure 4. Simulated cross-sectional field distributions of the conventional probe-fed RDRA (left) and the proposed capacitive-fed patch-loaded multi-layered RDRA (right) at (a) 25 GHz and (b) 29 GHz. The color scale represents the electric field intensity, while arrows indicate the magnetic field distribution.

By strengthening the caption in this way, we ensure clarity and consistency while retaining the side-by-side visual comparison that highlights the differences between the two antenna structures.

7. Please highlight more your contributions in the conclusions.

Reply: Thank you for this excellent suggestion. We have revised the Conclusion section (Section 5) to more explicitly state the novelty and key technical contributions of the paper. The following sentences were added

“The key contributions of this study include the development of a novel capacitive-fed patch-loaded multi-layered RDRA that excites a hybrid resonant mode, enabling significant bandwidth enhancement while achieving a low-profile structure. This configuration supports dual polarization, efficient performance, and compact integration, making it well-suited for next-generation 5G mmWave mobile platforms. Additionally, the proposed antenna demonstrates robustness to ground plane size reduction and scalability to array configurations.”

8. Include more recent references.

Reply: Thank you for this valuable suggestion. We agree that incorporating more recent references will strengthen the paper by situating our work within the latest advancements in dielectric resonator antenna research. In the revised manuscript, we have added four new references published between 2023 and 2025, covering compact DRAs, dual-band filtering features, UWB MIMO array designs, and optimization techniques for wideband performance. These recent works provide a broader context for comparison and highlight the novelty and competitive advantage of our proposed CFPL-ML-RDRA.:

The following references have been added as [29]–[32] in the updated manuscript:

[29] Rai, H.T.; Mu, G.W.; Lu, R.Q. Integrated Dielectric Resonator Antenna to Traditional Antenna for Better Bandwidth and Gain. Natl. J. Antennas Propag. 2024, 6(2), 9–16.

[30] Bizan, M.S.; Naseri, H.; Pourmohammadi, P.; Melouki, N.; Iqbal, A.; Denidni, T.A. Dual-Band Dielectric Resonator Antenna with Filtering Features for Microwave and Mm-Wave Applications. Micromachines 2023, 14, 1236.

[31] Tirado-Méndez, J.A.; Jardón-Aguilar, H.; Linares-Miranda, R.; Flores-Leal, R.; Vasquez-Toledo, A.; Gomez-Villanueva, R.; Perez-Miguel, A. Compact Four-Port Axial Symmetry UWB MIMO Antenna Array with Bandwidth Enhancement Using Reactive Stub Loading. Symmetry 2025, 17, 1285.

[32] Cepeda, L.E.; Garza, L.A.; Panduro, M.A.; Reyna, A.; Zuñiga, M.A. Thinned Eisenstein Fractal Antenna Array Using Multi-Objective Optimization for Wideband Performance. Appl. Sci. 2025, 15, 5584.

Author Response File: Author Response.pdf