Enhancement of Phase Dynamic Range in Design of Reconfigurable Metasurface Reflect Array Antenna Using Two Types of Unit Cells for E Band Communication

Round 1

Reviewer 1 Report

The paper presents the simulation results of a reflectarray antenna for E-band. A mechanical tuning scheme is also investigated.
Although, it seems that the Authors have done their best to write this paper, the quality, scientific soundness and novelty are low. Moreover, the paper is inconsistent and not very well-structured, and some parts seems more like something from an undergraduate student report than an actual scientific paper. In the end, the validity of the simulation results are questionable as the claimed efficiency is far more than what you would expect for such a structure. This likely stems from a misconception of the used materials, where either the losses are highly underestimated or not considered at all.

Major comments

- There is an ongoing switch between introduction to literature and structure, which I found confusing (pp. 1-5). This actually continues on in Section 2, which made me unsure about the design was a reflectarray with or without feed.

- Although, Rogers 5880 is commercially available, the dielectric constant and loss tangent of the substrate at the frequencies the reflect array is designed for, and used for the simulations, must be specified in the text. To my knowledge, Rogers has only specified these values at 10 GHz and below that. Moreover, has the ohmic losses in the metal been considered?

- Obtaining a reflection coefficient of 1 at all phases would indeed be 'superior electromagnetic properties' as mentioned on line 166, however this is never the case. Particularly not at 80 GHz. Therefore, the results for the magnitude of the reflection coefficient must be shown. Moreover, these simulations must include the appropriate losses in the dielectric and metals.

- In addition, the Authors mention that a reflection coefficient of 1 is obtained for all phases in Ref. [33]. This is very unlikely since Varactor diodes introduce losses, and thus must be taken into account (see e.g. 10.1109/TAP.2009.2037697). At 28 GHz (and 80 GHz), I expect high losses and thus the reflection coefficient will not be 1 as mentioned on line 138. 

Minor comments

- Abstract: 
-- Claim ‘demonstration’, but no experiment. Thus, the design is ‘proposed’.
-- Specifies a loss of 1 dB, but this is not mentioned in the main text of the paper.
-- Mentions gain of 30 dB, but Fig. 10 shows directivity.

- Not all symbols found in the text and figures are used consistently. For example, x_i vs X_i and F vs f.

- Symbol font size varies in equations. Moreover, the sinusoidal function should be non-italic.

- I am unsure what part of Fig. 1 that the Authors refer to on line 79: (see Fig. 1 BOTTOM).

- What does ‘lossless’ mean on line 110?

- I have never seen 'F' being used as a symbol for frequency. Normally, it is 'f' (line 217). Moreover, on line 222, it is specified to be F = 80 mm.

- Are Fig. 1 and 2 taken from previous published papers? Then this must be specified.

The are several errors in the text and confusing sentences.

Author Response

We extend our sincere thanks to the reviewer for his invaluable comments on this article. The manuscript underwent extensive revisions in response to these comments, and we are confident that we have addressed them effectively.

Regarding the reviewer's major comments:

We have restructured pages 1 to 5 of the article to enhance clarity and coherence, minimizing potential confusion. Additionally, we have introduced a reference to experimental research [35], which validates the applicability of parameters listed in the Rogers 5880 datasheets for design purposes, even at frequencies as high as 115 GHz.

The dielectric constant and loss tangent of Rogers 5880 have been included in the article (line 176).

Figure 7 has been added to the article, illustrating the reflection coefficient of unit cells A and B. Simulation results, accounting for all losses, indicate a reflection coefficient close to 1.

In reference [33], the reflection coefficient is approximately -1 dB, reflecting a value close to 1. This adjustment has been made to line 166.

Regarding the reviewer's minor comments:

Antenna gain is calculated by multiplying directivity by radiation efficiency. Given that the reflection coefficient of the metasurface approaches 1, and the efficiency is close to 100%, the gain or directivity of the metasurface approaches the same value.

 Consistent symbols have been used throughout the text and illustrations.

The figure caption of Figure 1 has been revised.

The term "lossless" now exclusively refers to an ideal unit cell.

Symbol "f" now denotes frequency, while symbol "F" denotes the focal distance of the metasurface.

Figure 1 is an original illustration crafted specifically for this article, while Figure 2 has been sourced from a previously published article, with appropriate reference added.

Author Response File: Author Response.pdf

Reviewer 2 Report

See attached file.

Comments for author File: Comments.pdf

See attached file.

Author Response

We extend our sincere thanks to the reviewer for his invaluable comments on this article. The manuscript underwent extensive revisions in response to these comments, and we are confident that we have addressed them effectively.

We have thoroughly revised the article to improve the quality of the English language used. This involved careful review and adjustments to enhance readability and clarity throughout.

The caption for Figure 1 has been modified as per the feedback.

Figure 6 has been split into two separate figures, Figure 6 and Figure 7. In Figure 7, the reflection magnitude of the unit cell has been incorporated. Corresponding updates have been made to the text of the article to reflect these changes.

Abbreviations used in lines 152 and 154 have been clarified for better understanding.

Unnecessary capital letters have been corrected throughout the article.

The references have been reorganized to eliminate duplicate citations, ensuring a more streamlined citation format.

Arrows have been added to Figure 7 to indicate the parts of the ground (GND) created by type A and type B unit cells.

Preliminary results indicate successful radiation focusing at approximately 80 mm, as anticipated. However, further enhancements are required for the measurement system to ensure precise and high-quality measurements.

The description of Figure 9 has been enhanced to elucidate how the beam is deflected using Piezoelectric benders.

A graph illustrating the magnitude of reflection for both types of unit cells is included to demonstrate minimal attenuation. Additionally, an explanation and reference [35] have been added to confirm the validity of the parameters listed in the datasheet of the Rogers 5880 substrate for millimeter wave ranges.

In the designed metasurface, the electric field of the incoming wave must be aligned parallel to the surface. Additionally, an explanation has been provided on how the angle of incidence influences beam deflection, with reference [4] providing a detailed discussion of this effect.

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper focuses on the optimization and innovation of metasurface reflect array antenna, which requires a lot of engineering and optimization work.
1. The innovative reconfigurable metasurface reflect array antenna proposed in this paper has the advantages of simple structure, large dynamic phase range, low loss, high gain and high novelty.
2. The format of the contents in Line 167 parentheses is different from that in Line 12 and Line 149.
3. The unit format of parameter t in Line 174 is different from that of other parameters in this section (Line 172-Line 184).
4. The units after “290” in paragraph (Line 191-Line 201) are confused and need to be consistent.
5. The contents of paragraphs (Line 191-Line 201) are partially repeated and need to be integrated and improved.
6. The two images in Figure 6 need to be placed left and right.
7. Formula 1 (Line 250) in the legend in Figure 7 (Line 249-Line 251) does not correspond to the previous example (Line 247).

Author Response

We extend our sincere thanks to the reviewer for his invaluable comments on this article. The manuscript underwent extensive revisions in response to these comments, and we are confident that we have addressed them effectively.

Below, you will find our responses to your comments according to the numbering provided in your review of the article:

1. We thank the reviewer for his comments and suggestions.
2. Unfortunately, the line numbers you commented on are different from those of the paper we have. We do not see parentheses in line 12.
3. We have changed the parameter t units so now it is given in mm.
4. A phase threshold of 290 degrees was selected to determine the choice between type A and type B unit cells, as clarified in the paper.
5. The paragraph has been substantially revised to enhance clarity and readability while avoiding confusion.
6. Figure 6 has been divided into two separate figures, now referred to as Figures 6 and 7, as per your request. The images are positioned on the right and left sides as specified.
7. We assert that the MS structure depicted in that figure corresponds to the application of Equation 1. Could you please clarify your statement?

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I would like to thank the Authors for making these considerable improvements to the manuscript. My comments have been addressed and the many of the needed modifications have been made. However, I have a few minor comments:
- On page 7, lines 179-188, it is stated that permittivity of the used Roger substrate is approximately constant with up to at least 115 GHz. To my knowledge, this perhaps applies to the real part (dielectric constant), but this should not be the case for the loss tangent. For normal dielectric, in the spectrum where the dielectric constant is slowly decreasing, the loss tangent is always growing. However, perhaps it is not significant in your case.
- Regarding the losses, have the (finite) conductivity of copper been considered in your simulations? This should be clarified in the manuscript, and must be taken into account when estimating the efficiency of the design.
- Metasurface reconfigurabilities are discussed on page 4, where several methods are covered. However, I think you should mention the aspect of using liquid/water to reconfigure metasurfaces. I suggest to read and refer to the following review of water-based devices (including metasurfaces):
Rasmus E. Jacobsen, Samel Arslanagić, Andrei V. Lavrinenko; Water-based devices for advanced control of electromagnetic waves. Appl. Phys. Rev. 1 December 2021; 8 (4): 041304. https://doi.org/10.1063/5.0061648

For future paper revisions, I would recommend to make your reply to Reviewers' comments as as point by point with the comments included in the reply letter.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

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Comments for author File: Comments.pdf

See attached file.

Author Response

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Author Response File: Author Response.pdf