Rapid Prototyping of Reduced-Height Dielectric Lens with One-Take 3D Printing for Antenna Directivity Enhancement
Round 1
Reviewer 1 Report
In this manuscript, the authors have presented a dielectric lens with reduced height for increasing the antenna's directivity. The lens can be easily manufactured using resin SLA technology with high accuracy. The manuscript presents a satisfactory level of background in the introduction and analysis of the proposed design. Additionally, all the simulated results are confirmed with experimental ones.
However, there are some points regards the proposed design which would be better to be discussed and investigated:
1. Can the authors discuss the results of the similar final lens (model 3) but without the holes, so like model 1 but fixing all the parameters of model 3 (so here, you will not have the improvement in reducing the height)? For dielectric constant, you can try both 2 and 2.5, would you obtain similar radiation patterns directivity enhancement, and if so, what are the benefits of this modified lens shape, is it only the 15% reduction in height?
2. In the introduction when the authors show an improvement of about 7dB in directivity, it would be good to present some other state-of-the-art dielectric lenses used for the same purposes and compare their performance. For example, the 3rd section in the proposed design is a hemisphere, and it is known that a similar lens (hyperhemispherical as in [1]) can provide an enhancement in the directivity of about 20dB. But this is under the cost of a bulky height of about 6 wavelengths. So even if your proposed lens provides worse directivity improvements, it still provides a compact design, hence, such advantages and disadvantages for the design would be helpful for readers that can later choose your design to extend the work depending on their applications.
[1] E. García-Muñoz, et al. "Photonic-based integrated sources and antenna arrays for broadband wireless links in terahertz communications." Semiconductor Science and Technology 34.5 (2019): 054001.
3. In Fig. 1 d, the max value can be read from the figure is around 12dBi and in the text, it is claimed that the directivity is 14.6dBi, please comment on this, for example, is the Figure presents the gain, not the directivity!
4. Fig. 4 presents the experimental study for estimating the dielectric constant with specific holes distention and size, it would be helpful to add future explanations for how can you estimate the dielectric constant before manufacturing in form of tables with some numbers like with x holes and D size we have this dielectric constant and so on as it can be seen in this lens design [2].
[2] S. Zhang, R. Arya, S. Pandey, Y. Vardaxoglou, W. Whittow, and R. Mittra, "3D‐printed planar graded index lenses." IET Microwaves, Antennas & Propagation 10.13 (2016): 1411-1419.
5. On page 1, lines 40-42, when the authors discussed the plating of 3D printed antennas and said that it would affect only the higher frequencies, this is not technically true in all cases. In the 1st part, yes, at higher frequencies, the surface roughness will cause losses and this effect will increase with increasing frequency. However, similarly, there is another important factor which is the effect of metal resistive losses on the gain [3] which will increase with decreasing the frequencies. And will be dominant at lower frequencies where the skin depth of the plating layer can be larger than its achieved thickness unless multiple metal-plating processes are involved to guarantee a thick metal layer.
[3] E. R. Brown, K. A. Abdalmalak and W. Zhang, "Effect of Metal Resistive Losses on the Gain of a THz Planar Spiral Antenna," 2020 14th European Conference on Antennas and Propagation (EuCAP), 2020, pp. 1-4, doi: 10.23919/EuCAP48036.2020.9135409.
6. Quantitative comparisons with some other dielectric lenses in form of a table in the last section would be helpful to highlight the contribution of the proposed lens. You can include the main terms like lens diameter, length (in terms of the wavelength), improved gain (or the obtained one), and ease of manufacturing.
Author Response
We appreciate the reviewer's invaluable comments to revise this manuscript. We've tried our best to address all the reviewer's comments accordingly in the response letter and the revised manuscript. Please see the attached PDF.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Motivation and impact for using high loss material 3d printing on getting such small improvement is interesting, however not big achievement in the field. 3d itself is over value technique, and results are quite obvious for engineers. All recent lens studies are not reviewed. I cannot see high benefits in general to read this paper, but it presents common level demonstrator and engineering work.
Author Response
We appreciate the reviewer's invaluable comments to revise this manuscript. We've tried our best to address all the reviewer's comments accordingly in the response letter and the revised manuscript. Please see the attached PDF.
Author Response File: Author Response.pdf
Reviewer 3 Report
See the attachment
Comments for author File: Comments.pdf
Author Response
We appreciate the reviewer's invaluable comments to revise this manuscript. We've tried our best to address all the reviewer's comments accordingly in the response letter and the revised manuscript. Please see the attached PDF.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors successfully addressed all the comments by highlighting the contribution with the added quantitative comparisons and the modified studies. Hence, I believe that the paper level is enhanced significantly after the revision and I recommend the acceptance. Only some final minor edits are needed such as in Fig. 4 and Table 1 where they are split into 2 pages.
