A Multiple-Input Multiple-Output Antenna with Metamaterial Enhancement for 5G Channel Sounding in the Upper 6 GHz Band

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper is interesting. However, some clarifications are necessary

The font in some figures, such as Figure 6 and Figure 8, is not sufficiently large for comfortable reading.

Figure 12: The authors should provide more technical explanations for the significant differences between S11, S11 measured, and S11 with SSR, especially in the frequency range of 5.8–6.4 GHz.

Table 2 should be updated to include a comparative analysis with previous studies on antennas designed for the same frequency band.

Table 2: I suggest adding new columns for the Fabrication Technology and Realization Technique.

Enrich the references by adding new related works on antennas designed for the same frequency band.

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

Line 35: change 4x4 to 2x2

Line 73 – 77 can be eliminated. Referring THz without using that frequency range make the introduction confusing.

 

Line 105: change letter to paper

Fig 1b and others. Do not mix “mm” and “cm” on the same drawing.

 

The analyzed structure (Fig. 2) is not a SRR. No split is present in the structure, but a sequence of concentric rings are reported/presented/used/analyazed.

 

Section starting line 155:

the name of the SW is “Suite” non “studio”;

insert references for eq. (1)-(4);

Described where ports 1 and 2 are. They are different with respect to the indicated port numbering in the previous figures.

Cancel the square brackets in Eq. (2);

I eq. (1). Are S_ij complex numbers? In case (S12 is) Cos^{-1} can be complex. Please clarify.

 

Section starting line 178: Why losses correspond to positive and negative values of the imaginary part of the two considered material parameters. Please clarify.

 

Section starting line 192 is not connected to the rest of the manuscript. It reports important considerations, but no logical connection with the previous paragraph is immediate.

 

Increase readability of Fig. 6, 8, 9, 10.

 

Ref. 17 and ref 18 has the same author, but the name is written differently. Pls check and be coherent.

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

I really enjoyed this article—it is well-written and highly informative!

Minor Suggestions:

1. The sentence "To address these challenges, this work proposes..." could be moved to a separate section titled "Research Overview" or "Aims and Contributions" for better structure.
2. Please provide further explanation for Figure 4b, particularly regarding the statement "obtained confirm that both the real parts of permittivity, R."
3. Figures 9 and 10 could be explained in greater detail and presented more clearly.
4. The statement "are intended for a different frequency band but have been used as a reference" could be elaborated further. Is there no available bandwidth antenna within this GHz range?
5. Lastly, please add a brief sentence in Section 5 outlining potential future directions for this study.

Author Response

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Reviewer 4 Report

Comments and Suggestions for Authors

I have some comments

1) Please cite a link or a paper for the framework of the World Radio communication Conference (WRC-23). 

2) Section 2.1 is not clear. You should give more details about how to design this structure, and provide the elements' S parameters and radiation patterns.  

3) The structure in Fig.2 is unclear. I still do not know how it is placed.

4) The simulation setup to extract MTM permittivity is unclear.

5) You need to give a citation for the eq.(1) - (4).

(6) when you want to say the structure can enhance the gain and improve isolation, you have to make a performance comparison between the antennas with and without MTM.  (line 192 to linr 198.) 

(7)  Combing questions (2) and (6), I suggest you discuss antenna performance in Section 2.1 and discuss antenna with MTM performance in Section 2.2. Reflection coefficients should be given along with mutual coupling.  The 3D radiation pattern is important. But the 2D cuts for co-cross polarizations are also important to show.

(8) When it comes to 3.2. Antenna Prototype and Measurements, the measured mutual coupling should be given. The measured radiation pattern should be given.

 

(9) Section 2.3 should be discussed after the section 3.2. To justify it becoming better in the sounder system, you should show some measured results with the proposed MIMO and make a comparison with the old ones. Or you do not need to compare the channel measurements. You can only compare the antenna performance with old antennas or the published papers.

I suggest authors take a look at other sounder antenna design paper.  The whole story is not smooth to read. 

 

 

Comments on the Quality of English Language

Written English should be improved. The antenna community terms need to be used carefully.

Author Response

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Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I would prefer to use 2x2 array. It would be more correct.

Author Response

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Reviewer 4 Report

Comments and Suggestions for Authors

Thanks for your reply to my comments. However, I am not happy with the revision. I still have some comments:

1) The mutual coupling measurement results 'must' be shown along with the measurement setup. Fig.11's simulation curve must be marked as 'simulated' S_11.

2) The measured S11 should indicate whether it is the one with CRR or not.

3) The measured radiation patterns 'must' be shown along with simulated ones. (E-plane and H-plane). It is 'necessary' to show the one without CRR for comparison.

4) ECC calculations are based on S-parameters and/ or radiation patterns. Therefore, before Fig.7, they should be shown.

5) I am still not happy with the article's writing structure. It is not clear. 

6) A side view of the antenna PCB board should be given.

7) Where is the feed point of the antenna element (as shown in Fig. 1(a))? The reason why you design the structure like Fig.1(a) should be given.

8) I do not quite understand why the authors the '2x2' to '4x4' MIMO since there are only 4 elements in total. Offline beamforming (maybe MRC?) will be used to obtain the array gain if I understand correctly.

9) I still do not know why permittivity characterization is important and is introduced. I guess the authors do not need them when designing CRR. Or if they are needed, the authors must show how to use them to design. The simulation boundary shown in [20] is 'unit cell'. However, the authors only have a 'single' element. Citing [20] is not suitable.  I think the authors should give the working principle of the CRR.

In total, the new measurements and antenna analyses must be given in this article before acceptance.

 

 

Author Response

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Round 3

Reviewer 4 Report

Comments and Suggestions for Authors

Thanks again for the improvements to the paper. I still have some questions.

Mutual coupling measurements are not very hard to implement.  Two-port VNA with 2 matching loads can do this. Or four-port VNA can measure the complete S-parameter matrix. I think you have such devices in the lab since you have the VNA to build the channel sounders.  Mutual coupling is very important here.  I know a good fabricated antenna can have similar results of simulations with measured ones. However, you only have the measured S11. No other measured data. Therefore, your measured results cannot prove you can have good practical results as you want to achieve by simulations.  You mentioned in the paper that you have a gain improvement with CRR. However, you do not have any measured results to prove this. From my understanding, when I see the antenna pattern with and without CRR, the gain improvements may result from the ripples since the antenna without CRR does not have any ripples. This is why I want to see the 2D plot (E-plane or H-plane) to check how the gain is improved. 

Sometimes, we cannot get the expected antenna gain and efficiency improvements for practical antennas. Therefore, I suggest the authors provide more measurement results (radiation pattern and mutual coupling).  

More time can be asked from the editors.  If no more measurement results, sorry, I cannot accept this paper. 

 

 

 

 

Author Response

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