Dual-Element Wideband CP Slot-Integrated MIMO Antenna with X-Notch Square AMC for DSRC Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. In Fig. 6, increase the linewidth for “Second layout”, not properly visible. Check Figs. 9, 11 too. 

 2. In Table 2, how is “Center frequency” calculated? It is not the center frequency for the given frequencies.  

 

Author Response

A point-by-point response to the reviewer’s comments has been included in the PDF file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have presented good work, I have following recommendations.

1) Improve the figure quality. All figures should be revised.

2) The authors should include parametric modeling of atleast two physical parameters

3) Merge Fig. 15 and 16.

4) You should mention which modes are dominant in abstract.

5) Last two sentences in abstract should be removed.

6) The authors should compare the proposed work with following.

a) https://doi.org/10.1016/j.aeue.2024.155302
b) 10.1109/ACCESS.2021.3077844

c) https://doi.org/10.32604/cmc.2020.011057

Author Response

A point-by-point response to the reviewer’s comments has been included in the PDF file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear authors,

This paper presents a dual-element, wideband, circularly polarized MIMO antenna featuring an 8×8 array of X-notch square AMC units. The antenna is constructed from two FR-4 substrate layers, each 1.6 mm thick, separated by an air gap. The upper layer incorporates two CPW-fed slot antennas along with an I-shaped defected ground structure (DGS) to reduce mutual coupling between the elements. Circular polarization is achieved through Characteristic Mode Analysis (CMA) by exciting two orthogonal modes, J5 and J6. The antenna demonstrates a return loss bandwidth of 32% (4.72 to 6.61 GHz), an axial ratio bandwidth of 21.18% (5.2 to 6.45 GHz), isolation above 19 dB, a gain of 8.6 dBic at 5.9 GHz, an envelope correlation coefficient below 0.003, and diversity gain exceeding 9.98 dB. This design is well-suited for DSRC and V2X communication applications.

I have several suggestions that could help improve the manuscript:

1. The introduction requires a thorough revision to enhance focus and clarity. It currently contains some redundant and overly detailed explanations. Trimming verbose sections and avoiding repetition would make it more concise. Additionally, providing a more critical and detailed comparison with closely related prior work will help to clearly identify the research gap. Emphasizing the motivation and novelty of your approach in relation to existing literature will strengthen this section significantly.

2. Some paragraphs in the design and related work sections are lengthy and dense. Breaking these into smaller, more digestible sections and refining figure captions will enhance readability. For example:

• In the Introduction and Related Work sections (pages 2–4), paragraphs covering previous MIMO antennas with AMC reflectors often address multiple concepts at once. These could be split into shorter paragraphs, each focusing on a single study or theme.
• Similarly, in the Antenna Evolution Process (section 2.2), the paragraphs describing the three layouts of the single-element antenna (around Figures 2–6) contain dense technical content that would benefit from being divided and summarized with bullet points or tables.

3. Some figure captions are minimal and would benefit from more descriptive details. For instance, Figures 3, 4, and 5 present CMA results but do not clearly highlight the key takeaways of each subplot (modal significance, phase difference, current distribution, radiation patterns). Adding brief clarifications such as “(a) Modal significance showing modes J5 and J6 with MS > 0.9 at 5.9 GHz, indicating potential for CP radiation” would aid reader understanding.
4. It appears that the label "(c)" is missing under the third subplot of both Figures 2 and 6. Including these labels will improve clarity.
5. The current distribution plots (subplot c) in Figures 3, 4, and 5 are not very clear. The color scales and directional arrows are difficult to interpret. Improving the resolution and clarity of these visuals would help readers better follow the modal current behaviors.
6. Table 2 compares various MIMO antennas with different reflector types, showing that the proposed antenna achieves the highest gain (8.6 dBic), good isolation (>19 dB), and very low envelope correlation coefficient (<0.003) within the DSRC frequency band (~5.9 GHz). While some designs offer wider bandwidths or smaller sizes, these often come at the expense of gain or isolation, reflecting inherent design trade-offs. To enhance this section, I recommend including practical factors such as physical size, fabrication complexity, cost, and installation constraints alongside electromagnetic performance metrics wherever possible. Emphasizing these trade-offs—between bandwidth, size, gain, and isolation—will provide readers with clearer insight into how different antennas balance these factors depending on specific application requirements.

 

Comments on the Quality of English Language

The manuscript is generally well-written and the English is understandable. However, some sections could benefit from clearer sentence structure and smoother phrasing to improve readability. A few sentences are overly long or complex, which might make them harder to follow. Simplifying these sentences and enhancing the flow would help make the paper more accessible to a broader audience. Additionally, there are minor grammatical and punctuation errors scattered throughout the manuscript. For example:

1. Missing commas in complex sentences, such as in “The antenna design consists of two substrate layers separated by an air gap,” where adding a comma after “layers” would improve clarity.
2. Inconsistent verb tense usage, with past and present tense sometimes mixed closely together, which can confuse readers. For example, “The antenna achieves wide bandwidth and gain, and measurements confirmed its performance.”
3. Subject-verb agreement errors, like “The results shows” instead of “The results show.”
4. Some repetitive phrasing such as “the upper layer features... while the lower layer comprises...” could be simplified to improve clarity and conciseness.

Author Response

A point-by-point response to the reviewer’s comments has been included in the PDF file.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript by Musika et al. reports on a wideband circularly polarized MIMO antenna employing an artificial magnetic conductor (AMC).  The proposed antenna consists of two layers separated by an air gap: the top layer features a dual-element coplanar waveguide-fed antenna, while the bottom layer integrates an artificial magnetic conductor (AMC). This configuration is well-suited for dedicated short-range communications in Vehicle-to-Everything (V2X) applications. The simulation results clearly illustrate the optimization process and justify the design decisions. Furthermore, the experimental measurements show excellent agreement with the simulated performance, validating the effectiveness of the proposed design.

This is an excellent research paper which strongly adheres to the scope of the journal Technologies.

I propose the following minor revisions:

• The introduction effectively presents the relevant state of the art by discussing slot-integrated antennas and subsequently slot-integrated antennas combined with AMC structures. However, this section could be further strengthened by also considering slot-integrated antennas incorporating metasurfaces functioning as partial reflectors, which represent an important extension in the field (10.1080/02726343.2023.2276428 10.1109/LAWP.2025.3557941).
• For the sake of completeness, please specify the operating bandwidth at line 126.
• It is recommended to add axes in Fig. 1(a) to improve clarity. Please enlarge the axis labels in Fig. 1(b)–(d) to enhance readability.
• In Fig. 1(b), the parameters h_a and h_s are difficult to distinguish. It is suggested to reposition these labels onto a white background to improve legibility.
• Please specify in Section 2.1 that the geometry of the AMC structure is described in a later section of the manuscript.
• The description of the antenna evolution process (lines 163–185) could be rephrased for clarity and conciseness. The current text contains redundant phrasing (e.g., "first stage" vs. "first step") and somewhat disjointed sentence structure. A more logically connected description is recommended.
• Please indicate the frequency at which the current distributions and radiation patterns in Figs. 3, 4, 5(c), and 7 are plotted. Also, the color scale bars in these figures are difficult to read and should be made clearer.
• The use of the artificial magnetic conductor (AMC) in place of a conventional metal ground plane should be justified in the text. Typically, AMCs allow for closer placement to the radiating element due to their near-zero phase reflection, enabling more compact antenna structures. At 6 GHz, the wavelength is approximately 5 cm, while the chosen separation is 3.6 cm. Please justify this design choice. Additionally, as shown in Table 2, the antenna demonstrates high thickness compared to referenced works, due to this aspect. Consider discussing possible strategies to mitigate this limitation in future designs.

Author Response

A point-by-point response to the reviewer’s comments has been included in the PDF file.

Author Response File: Author Response.pdf