Millimeter-Wave High-Gain Dual-Polarized Flat Luneburg Lens Antenna with Reflection Cancellation
Round 1
Reviewer 1 Report
Millimeter-Wave High-Gain Dual-Polarized Flat Luneburg Lens Antenna with Reflection Cancellation
The following modifications are required before accepting this paper
1. Explain clearly the novelties of the current design compared to the reference papers mentioned.
2. Evaluate and include the figure related to the Equivalent Refractive index of the unit cell as a function of the width of the dielectric slab and s a function of the width of frequency.
3. Improve the quality of the figures in the paper
4. Explain elaborately conclusion of the research paper
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this article, a millimeter-wave dual-polarized flat Luneburg lens antenna (FLLA) with reflection cancellation following the transformation of optics is proposed and implemented using multilayer PCBs to improve its gain and bandwidth. The article is well-written and interesting, but should be improved by considering the following comments:
1. The author has stated that the proposed device is "high-gain", but it is unclear what it is being compared to in order to justify this claim.
2. It would be helpful if the experimental setup could be presented in more detail, particularly with regard to the measurement tools and procedures employed.
3. The conclusions drawn in the paper are incomplete, as they do not fully address the device's capabilities and functions for its intended purpose, including its bandwidth and other relevant parameters.
Author Response
Reviewer 2:
In this article, a millimeter-wave dual-polarized flat Luneburg lens antenna (FLLA) with reflection cancellation following the transformation of optics is proposed and implemented using multilayer PCBs to improve its gain and bandwidth. The article is well-written and interesting, but should be improved by considering the following comments:
Q1. The author has stated that the proposed device is "high-gain", but it is unclear what it is being compared to in order to justify this claim.
A1. Thanks. Typically, in antenna engineering, the antenna gain larger than 15 dBi is generally regarded as high gain comparing with the gain of single antenna element, which is usually 2-6 dBi. In the manuscript, the gain of the flat Luneburg lens is enhanced by around 2-3 dB comparing the that of previous works due to the introduced reflection cancellation method. Hence, the used ‘high-gain’ is to distinguish our achievement with others.
Q2. It would be helpful if the experimental setup could be presented in more detail, particularly with regard to the measurement tools and procedures employed.
A2. Thanks. The related measurement instruments and general procedures are added in ‘Section 4. Measurement and Discussion’. Generally, the S-parameter is measured with a Vector Network Analyzer and the far-field radiation patterns are measured in a far-field anechoic chamber. The corresponding measuring procedure is a standard one in antenna engineering.
Q3. The conclusions drawn in the paper are incomplete, as they do not fully address the device's capabilities and functions for its intended purpose, including its bandwidth and other relevant parameters.
A3. The purpose of the presented work is to enhance both the gain and the aperture efficiency of the flat Luneburg lens antenna. The obtained results shown in the comparison table (Table 1) demonstrate that the achieved gain and aperture efficiency are greater than previous works, in the millimeter wave band. The bandwidth is not included, as it is stated in Section 1. Introduction:
‘However, the radiation performance, in terms of both gain and beam scanning loss, is deteriorated drastically due to the reflection caused by the used high permittivity materials or structures. The low gain or low efficiency performance of such type of FLLs limits their applications.’
‘Then a flat LL antenna (FLLA) is designed using the reflection cancellation method to reduce the reflected wave and thus increase the gain and efficiency.’
Theoretically, the bandwidth is dominated by two factors: one is the number of adopted PCB layers in the lens, another is the reflection caused by the lens. The achieved bandwidth (17.6%) in our work is a little bit narrower than that (21%) reported in Ref. [20], but it does not mean the proposed design limits the bandwidth. Because the latter is designed in a lower frequency of 10 GHz with 17 PCB layers, and our work operates in 29 GHz and only 10 PCB layers can be used to adopt the lens due to the available thickness of PCB as well as the much smaller wavelength at 29 GHz. Thus, the bandwidth is mainly restricted by the number of layers at this time. In another words, the more layers, the wider bandwidth. Actually, we have also implemented a prototype at 10 GHz with 17 layers, and the achieved bandwidth is 30% due to the used cancellation method, which is not reported in this work.
Author Response File: Author Response.pdf
Reviewer 3 Report
The authors have presented design and implementation of a millimeter-wave dual-polarized flat Luneburg lens antenna (FLLA) with a reflection cancellation method for improving its gain and bandwidth. the paper is well written; however, some modifications should be considered in the manuscript as follows:
- The main problem of the manuscript is that the research objectives and contributions are unclear, which should be clarified. Also, it should be clarified that if the proposed reflection cancelation method is proposed by the author or the other research.
- The dimension details of the fabricated prototype are not provided.
- It is suggested to report the other important parameters in the flat Luneburg lens antenna (FLLA), such as side lobe level (SLL) and half power beam width (HPBW).
- Add more related works in the comparison table. Also, the fractional bandwidth is not significantly improved as author claimed in the abstract.
- The conclusion section needs improvement. The conclusion should summarize the main findings and contributions of the study effectively. However, it would be helpful to also discuss the limitations of the research and suggest future research directions in order to provide a more comprehensive understanding of the topic.
- There are some typos in manuscript, which should be corrected. For example, in the comparison table, in the gain row, the frequency is not written for ref[14]
The English level of the manuscript is fine
Author Response
Reviewer 3
The authors have presented design and implementation of a millimeter-wave dual-polarized flat Luneburg lens antenna (FLLA) with a reflection cancellation method for improving its gain and bandwidth. the paper is well written; however, some modifications should be considered in the manuscript as follows:
Q1. The main problem of the manuscript is that the research objectives and contributions are unclear, which should be clarified. Also, it should be clarified that if the proposed reflection cancelation method is proposed by the author or the other research.
A1. Thanks. The novelty of this work is to introduce the reflection cancellation method in the layered flat Luneburg lens, which can enhance the gain and aperture efficiency of the lens, as demonstrated in the comparison table. Our design prototypes in millimeter-wave band for 5G, and it shows superior performance than the related works operating in low frequency band. To further clarify the novelty, the corresponding statements in either Section 1. Introduction or Section 4. Measurement and Discussions are re-written in the revised manuscript. Detailed quantity descriptions are added to clear show the advances of our work.
The reflection cancellation phenomenon is not new, and it is widely used in optics to enhance the transmission. Here, this method is introduced to the flat Luneburg lens design by us, and following this concept, an optimal design is achieved in term of good gain and aperture efficiency.
Q2. The dimension details of the fabricated prototype are not provided.
A2. Thanks. The dimension of feed patch antenna is provided in the figure caption. The dimension of the used unit-cell is listed in the corresponding figure caption as well. The geometry size of the flat Luneburg lens is given in the related descriptions together with the information of the number of unit-cells and its arrangement. Since there are altogether 20×20×10 unit-cells contained in the lens, the dimension of each unit-cell cannot be provided one by one in the limited pages. Alternatively, the dimension of each unit-cell can be determined following the dimension-permittivity relation curve [see Fig. 5(a)] according to the required permittivity, which is a common way used in unit-cell based lens / transmit-array / reflect-array / meta-surface design or articles.
Q3. It is suggested to report the other important parameters in the flat Luneburg lens antenna (FLLA), such as side lobe level (SLL) and half power beam width (HPBW).
A3. Thanks. The SLL information is added in Section 4. Measurements, as follow:
‘The measured side lobe levels (SLLs) is smaller than -13 dB in E-plane and -15 dB in H-plane.’
The HPBW is already reported in the manuscript as a 3-dB beam-width, as
‘The measured 3-dB beam-widths in E- and H-plane are 17° and 16.5°, respectively.’
Q4. Add more related works in the comparison table. Also, the fractional bandwidth is not significantly improved as author claimed in the abstract.
A4. Thanks. Due to the limited space of the comparison table, one more related work is added.
The reason why the fractional bandwidth is not improved is as follow: Theoretically the bandwidth is dominated by two factors: one is the number of adopted PCB layers in the lens, another is the reflection caused by the lens. The achieved bandwidth (17.6%) in our work is a little bit narrower than that (21%) reported in Ref. [20], but it does not mean the proposed design limits the bandwidth. Because the latter is designed in a lower frequency of 10 GHz with 17 PCB layers, and our work operates in 29 GHz and only 10 PCB layers can be used to adopt the lens due to the available thickness of PCB as well as the much smaller wavelength at 29 GHz. Thus, the bandwidth is mainly restricted by the number of layers at this time. In another words, the more layers adopted, the wider bandwidth achieved. Actually, we have also implemented a prototype at 10 GHz with 17 layers, and the achieved bandwidth is 30% due to the used cancellation method, which is not reported in this work.
It should be further clarified that the purpose of the presented work is to enhance both the gain and the aperture efficiency of the flat Luneburg lens antenna. The obtained results shown in the comparison table (Table 1) demonstrate that the achieved gain and aperture efficiency are greater than previous works, in the millimeter wave band. The bandwidth is not included, as it is stated in 1. Introduction:
‘However, the radiation performance, in terms of both gain and beam scanning loss, is deteriorated drastically due to the reflection caused by the used high permittivity materials or structures. The low gain or low efficiency performance of such type of FLLs limits their applications.’
‘Then a flat LL antenna (FLLA) is designed using the reflection cancellation method to reduce the reflected wave and thus increase the gain and efficiency.’
Q5. The conclusion section needs improvement. The conclusion should summarize the main findings and contributions of the study effectively. However, it would be helpful to also discuss the limitations of the research and suggest future research directions in order to provide a more comprehensive understanding of the topic.
A5. Thanks. The conclusion is re-written to further strength the main contribution, discuss the bandwidth limitation, as well as provide a perspective on the future work.
Q6. There are some typos in manuscript, which should be corrected. For example, in the comparison table, in the gain row, the frequency is not written for ref[14]
A6. Thanks. During the revision, the manuscript is thoroughly checked and revised.
Reviewer 4 Report
The topic is scientifically interesting; however, I have the following major and minor concerns:
- Proofreading is essentially required.
- Some figures (numbers, percentages, etc.) are required in the abstract to show the improvement value to the reader.
- The abstract and conclusion require improvement based on typical structure for better readability.
- Keywords require to be ordered alphabetically.
- The novelty, research gap, significance, and technical contributions of the proposal need to be highlighted concisely and clearly to show the importance of the work.
- The paper's organization and presentation must be improved for better readability.
- Please consider the MDPI template.
- It is highly recommended to restructure the sections of the paper as follows: introduction, Background, related work, Methodology, implementation, results, and conclusion.
- Essentially, expand your literature review of modern (6G) wireless communications and all the involved topics (e.g., the 6G infrastructure and terahertz frequencies) of this work for introduction and background sections by citing and adding the following references (Up-to-date wireless networks characteristics and performance, improving spectral and energy efficiencies, and your related objectives):
[1] H. W. Oleiwi and H. Al-Raweshidy, “Cooperative SWIPT THz-NOMA / 6G Performance Analysis,” Electronics, Vol. 11, No. 6, pp. 873, March 2022.
[2] H. W. Oleiwi and H. Al-Raweshidy, “SWIPT-Pairing Mechanism for Channel-Aware Cooperative H-NOMA in 6G Terahertz Communications,” Sensors, Vol. 22, No. 16, pp. 6200, Aug. 2022.
- Why could the article not adopt terahertz frequencies?
- Please avoid using abbreviations without writing the full form.
- It is (optionally) preferred if you could write a table for related works comparisons to emphasize the outperformance of their work over the state of the art.
- The contributions could be a concise paragraph and reflect only the added values to the field.
- The manuscript lacks mathematical analysis.
- Please add a table of parameters.
- The paper layout (organization) is missing or hidden behind the sections, please re-write it clearly at the end of the revised brief introduction section.
- An implementation (with set up) section is essentially required. The authors need to write the implementation separately in a separate clear section for better readability.
- Redraw the Figures with the highest quality, please. RESIZE the figures, axes labels, legends, and details, making them readable.
- The discussion and conclusion are different separated parts of any paper's structure. Please mind the typical structure.
- The conclusion is very concise!
- Future work is missing.
- Avoid too-long sections or sentences.
- Many references are old, please replace them with up-to-date references critically including the above-mentioned references.
Major revision
Author Response
Reviewer 4
The topic is scientifically interesting; however, I have the following major and minor concerns:
Q1. Proofreading is essentially required.
A1. Thanks. As suggested, a through proofreading is made during the revision.
Q2. Some figures (numbers, percentages, etc.) are required in the abstract to show the improvement value to the reader.
A2. Thanks. As suggested, a quantity description (with numbers) is used in the abstract to show the improvement.
Q3. The abstract and conclusion require improvement based on typical structure for better readability.
A3. Thanks. The corresponding parts are revised accordingly.
Q4. Keywords require to be ordered alphabetically.
A4. Thanks. The keywords are reordered in an alphabetical way.
Q5. The novelty, research gap, significance, and technical contributions of the proposal need to be highlighted concisely and clearly to show the importance of the work.
A5. Thanks. The novelty of this work is introducing the reflection cancellation method in the layered flat Luneburg lens, which can enhance the gain and aperture efficiency of the lens, as demonstrated in the comparison table. Our design prototypes in millimeter-wave band for 5G, and it shows superior performance than the related works operating in low frequency band. To further clarify the novelty, the corresponding statements in either Section 1. Introduction or Section 4. Measurement and Discussions are re-written in the revised manuscript. Detailed quantity descriptions are added to clear show the advances of our work.
Q6. The paper's organization and presentation must be improved for better readability. Please consider the MDPI template. It is highly recommended to restructure the sections of the paper as follows: introduction, Background, related work, Methodology, implementation, results, and conclusion.
A6. Thanks. The template is referred during the revision.
Q7. Essentially, expand your literature review of modern (6G) wireless communications and all the involved topics (e.g., the 6G infrastructure and terahertz frequencies) of this work for introduction and background sections by citing and adding the following references (Up-to-date wireless networks characteristics and performance, improving spectral and energy efficiencies, and your related objectives):
[1] H. W. Oleiwi and H. Al-Raweshidy, “Cooperative SWIPT THz-NOMA / 6G Performance Analysis,” Electronics, Vol. 11, No. 6, pp. 873, March 2022.
[2] H. W. Oleiwi and H. Al-Raweshidy, “SWIPT-Pairing Mechanism for Channel-Aware Cooperative H-NOMA in 6G Terahertz Communications,” Sensors, Vol. 22, No. 16, pp. 6200, Aug. 2022.
A7. Thanks. The suggestion is constructive, but it is believed that both the 6G and THz are out of scope of the current manuscript for the following reasons:
In our manuscript, the designed Luneburg lens aims to millimeter-wave applications, with a targeted frequency band of 27-32 GHz. Thus, THz is not covered. The proposed design provides a solution for the planarized design of Luneburg lens with a high aperture efficiency and a corresponding high gain, providing a promising solution for 5G antennas with advances of low weight, flat form-factor, ease of installation, etc. Though multibeam antennas, including lens-based antennas, are expected to be a promising technique for 6G, the concept, system infrastructure, as well as research trends for 6G cannot be included in such an article which already has 13 pages. We will focus the topic of 6G and THz in our future work.
Meanwhile, as you advised, we add some related paper as references to fully introduce the research background of multibeam antennas, lens antennas, and 5G millimeter-wave communications.
Q8. Why could the article not adopt terahertz frequencies?
A8. The proposed work aims providing a flat Luneburg lens with low weight, low profile, and ease of installation properties for the boosting mobile communication in millimeter wave band, which is a significant part of 5G.
Actually, the size of spherical Luneburg lens is not a big issue in THz frequencies due to the wavelength is too small, only several micro meter or even smaller, thus they do not require to be flattened.
Q9. Please avoid using abbreviations without writing the full form.
A9. Thanks. Revised as suggested.
Q10. It is (optionally) preferred if you could write a table for related works comparisons to emphasize the outperformance of their work over the state of the art.
A10. Table I is already given to show the comparison between our work and other related works, which can demonstrate that in our work, a good gain and aperture efficiency are achieved.
Q11. The contributions could be a concise paragraph and reflect only the added values to the field.
A11. Thanks. The contribution of this work is further clarified in Section 1. Introduction and the conclusion part.
Q12. The manuscript lacks mathematical analysis.
A12. Thanks. The design formula is derived in a cylindrical coordinate, and added in the revision.
Q13. Please add a table of parameters.
A13. Thanks. The parameters are already provided in an alternative way as: The dimension of feed patch antenna is provided in the figure caption. The dimension of the used unit-cell is listed in the corresponding figure caption as well. The geometry size of the flat Luneburg lens is given in the related descriptions together with the information of the number of unit-cells and its arrangement. Since there are altogether 20×20×10 unit-cells contained in the lens, the dimension of each unit-cell cannot be provided one by one in the limited pages. Alternatively, the dimension of each unit-cell can be determined following the dimension-permittivity relation curve [see Fig. 5(a)] according to the required permittivity, which is a common way used in unit-cell based lens / transmit-array / reflect-array / meta-surface design or articles.
Q14. The paper layout (organization) is missing or hidden behind the sections, please re-write it clearly at the end of the revised brief introduction section.
A14. Thanks. As suggested, the paper organization is added in the end of Section 1. Introduction.
Q15. An implementation (with set up) section is essentially required. The authors need to write the implementation separately in a separate clear section for better readability.
A15. Thanks. The information of implementation as well as measurement setup is added.
Q16. Redraw the Figures with the highest quality, please. RESIZE the figures, axes labels, legends, and details, making them readable.
A16. Thanks. In the revision, all the figures have been updated, and a high-resolution PDF file is generated for review.
During the first submission, we only uploaded the word file, and during the conversion to a PDF file for review, a low resolution (default) setup is used by the manuscript system. In the revision, we provide a PDF file which is converted with a high resolution to improve the figure quality
Q17. The discussion and conclusion are different separated parts of any paper's structure. Please mind the typical structure. The conclusion is very concise! Future work is missing.
A17. The discussion and conclusion are re-arranged and re-written in the revision.
Q18. Avoid too-long sections or sentences.
A18. Thanks. Checked during the revision as suggested.
Q19. Many references are old, please replace them with up-to-date references critically including the above-mentioned references.
A19. Thanks. The reference list is renewed as suggested, and now over 50% references are publicized in recent 5 years, i.e. 2018-2023.
Reviewer 5 Report
The design is very interesting and the prototype design for the actual measurement is imaginative. In the conclusion you write that the antenna has promising prospects for use in 5G networks and other multi-band systems. In which specific systems will you find applications with your prototype? What kind of transmission powers can a lens made of these materials withstand?
Author Response
Reviewer 5
The design is very interesting and the prototype design for the actual measurement is imaginative. In the conclusion you write that the antenna has promising prospects for use in 5G networks and other multi-band systems.
Q1. In which specific systems will you find applications with your prototype?
A1. The proposed Luneburg lens can be used in millimeter-wave mobile communication systems. For instance, the lens can be equipped in small cells, and its multi beams can provided several continuous small sectional coverages with high-dense system capacity in terms of both number of connectivity and throughputs for scenarios of stadium or concert hall full of people.
Q2. What kind of transmission powers can a lens made of these materials withstand?
A2. The maximum transmission power of the proposed flat Luneburg lens is mainly determined by the used PCB substrate in terms of its maximum electrical strength and maximum operating temperature. The used Rogers RO4003C has a maximum electrical strength of 31.2 KV/mm, and highest operating temperature of 150 ºC, as given in the datasheet. Theoretically, the substrate can bare a maximum power of around 60-80W, depending of the detailed structures of both transmission line and patch. If a larger power is expected, an open waveguide is suggested to be used as the feed for the Luneburg lens.
Round 2
Reviewer 3 Report
The authors have addressed all of my comments and the paper can now be accepted.
The English level of the manuscript is good for publication.
Author Response
Thanks for your review.
Reviewer 4 Report
The authors need to stick to the reviewers' notes and convince them, professionally and ethically!
Moderate
Author Response
In the updated response letter, all the comments from reviewers are replied in a one-by-one manner, especially for the comments from Reviewer 4.
If there is any comment need to be further clarified or the reviewer has further comment, please let us know.
