Triple-Band Uniform Circular Array Antenna for a Multi-Functional Radar System
Round 1
Reviewer 1 Report
While I find the presented antenna array design interesting and worthy of publication, I am missing the section in introduction, which would clearly state the novelty of the proposed array structure, or distinguish the difference of this array with regards to the state of the art. I highly encourage the authors to amend the introduction such that the comparison of their work with respect to previous antenna arrays is provided.
As for the results and conclusion sections, I am missing section "future work". Currently, the array antenna elements are fed in-phase, is there any plan for the future to incorporate electronic steering of main lobe/adaptive beamforming capability?
Please find my detailed notes in the attached pdf file.
Thank you.
Comments for author File: 
Comments.pdf
Author Response
Reviewer 1
While I find the presented antenna array design interesting and worthy of publication, I am missing the section in introduction, which would clearly state the novelty of the proposed array structure, or distinguish the difference of this array with regards to the state of the art. I highly encourage the authors to amend the introduction such that the comparison of their work with respect to previous antenna arrays is provided.
Response) The authors appreciate the reviewer for the comments. As the reviewer suggested, we have included more comprehensive comparison in the introduction part. The introduction part has been changed to deal with the limitation of the previous works and the advantages of the proposed array antenna. The added explanation to the introduction part is provided below:
“The use of the floating antenna may be disadvantageous in terms of providing low profile and stubborn structure [7]. The multi-layer radiating elements are restricted to achieve the desired radiation characteristics for all radiating elements [6]. The utilization of the multi-layered design involves in the complication of the fabrication process with increasing the mass of the entire structure [5, 6, 9].”
“In this paper, ~. The radiating parts are placed on the top layer for realizing efficient radiation characteristics while feed network for each frequency band is implemented on the top and bottom layer. The adoption of the common ground for antenna and feed line is greatly helpful to derive the low-profile two layered design and reduce the interaction between different frequency bands.”
(The changes made in the main text are indicated as yellow highlights)
As for the results and conclusion sections, I am missing section "future work". Currently, the array antenna elements are fed in-phase, is there any plan for the future to incorporate electronic steering of main lobe/adaptive beamforming capability?
Response) The authors are planning to continue this research to build the complete array design with diverse beam configurations. It will be interesting to see the beam steering capability for the different frequencies. The research plan in future is added to the manuscript, and the following sentences are also included in the discussion part (page 5).
“This work primarily highlighted the aspect of achieving the multi-band array antenna. In future, comprehensive antenna design including electronic steering mechanism will be presented for creating diverse beam configurations at each frequency band. In addition, the size reduction technique such fractal-shaped design can be applied to the patch element design to reduce the entire size of the array antenna.”
Author Response File: Author Response.pdf
Reviewer 2 Report
An interesting design is presented in this paper—a very straightforward but effective design approach. The antenna providing three stable bands is simulated and the measurement results are reasonably in good agreement. All in all, the paper is well pieced together and provides a good contribution. However, some aspects need clarifications/improvements
Materials and Methods Section (Page 2) line 66 to 70:
It is mentioned that the spacing between neighboring elements is carefully chosen as 0.8 λ in order to avoid the appearance of the grating lobe in the radiation pattern. By neighboring elements, the authors mean elements of each array? Please clarify it.
The introduction of the paper should include more recent techniques. For example, a recent method in designing multi-functional antennas, such as multi bands, is based on artificial intelligence algorithms as explained by Boursianis in " Multiband Patch Antenna Design Using Nature-Inspired Optimization Method. IEEE Open Journal of Antennas and Propagation,", IEEE Open Journal of Antennas and Propagation, 2020. And In this method of design, a simulation-driven approach based on a nature-based optimization is used to design the antenna device. Different optimization algorithms, such as particle swarm optimization as explained in Directivity improvement of a Fabry-Perot cavity antenna by enhancing near field characteris ”, a neural network that explained in “Socialization of industrial robots: An innovative solution to improve productivity”, ant colony ( https://doi.org/10.1587/transinf.E96.D.2309) that can be used for this purpose. This recent avenue of research needs to be included in the introduction.
How the authors came up with 0.8 lambda for the spacing? Any strategy? What is the logic behind that?
There is some mistach in the case of C-band between the simulated and measured S22? What is the reason? Is it because of the feed? Please comment.
Is there any way to reduce the size of the antenna, basically the L band? One possible approach is to adopt the modified Minkowski Fractal geometry on the larger array as explained in “Microstrip hairpin bandpass filter using modified Minkowski fractal-shape for suppression of second harmonic, IEICE” . is it applicable in the case of your antenna? Please comment on potential ways to achieve a smaller size?
Please include cross-polarization results if available and comment on them accordingly.
Author Response
Reviewer 2
An interesting design is presented in this paper—a very straightforward but effective design approach. The antenna providing three stable bands is simulated and the measurement results are reasonably in good agreement. All in all, the paper is well pieced together and provides a good contribution. However, some aspects need clarifications/improvements
Materials and Methods Section (Page 2) line 66 to 70:
It is mentioned that the spacing between neighboring elements is carefully chosen as 0.8 λ in order to avoid the appearance of the grating lobe in the radiation pattern. By neighboring elements, the authors mean elements of each array? Please clarify it.
Response) The spacing between neighboring elements is the one between elements of each array. As the reviewer indicated, the expression ”neighboring” used in the paper may provide confusion to readers. The authors have removed the expression “neighboring”, instead, we have used the expression “inter-element spacing”, which may be more adequate for the intended purpose
The introduction of the paper should include more recent techniques. For example, a recent method in designing multi-functional antennas, such as multi bands, is based on artificial intelligence algorithms as explained by Boursianis in " Multiband Patch Antenna Design Using Nature-Inspired Optimization Method. IEEE Open Journal of Antennas and Propagation,", IEEE Open Journal of Antennas and Propagation, 2020. And In this method of design, a simulation-driven approach based on a nature-based optimization is used to design the antenna device. Different optimization algorithms, such as particle swarm optimization as explained in Directivity improvement of a Fabry-Perot cavity antenna by enhancing near field characteris ”, a neural network that explained in “Socialization of industrial robots: An innovative solution to improve productivity”, ant colony ( https://doi.org/10.1587/transinf.E96.D.2309) that can be used for this purpose. This recent avenue of research needs to be included in the introduction.
Response) The authors appreciate the reviewer for the comment. We have included all of the recent research activities for the introduction part.
How the authors came up with 0.8 lambda for the spacing? Any strategy? What is the logic behind that?
Response) The authors have used 0.8 λ in terms of the minimum distance preventing collapse of the elements. The minimum inter-element spacing may be helpful in terms of reducing the appearance of grating lobes. The authors have properly changed the explanation in the manuscript. The reviewer may find the changed part which is indicated with yellow highlights in page 2 (line 26).
There is some mistach in the case of C-band between the simulated and measured S22? What is the reason? Is it because of the feed? Please comment.
Response) The connector effect was not included in the simulation, but it was included in the measurement. Based on a target design frequency of 5.8 GHz, the measured S22 (C-band) is upshifted by 2.2%. Nevertheless, the measured S22 results in good impedance matching below -14dB within the C-band. The authors have commented on the reasons for the resonant frequency shift in page 5 (line 8).
Is there any way to reduce the size of the antenna, basically the L band? One possible approach is to adopt the modified Minkowski Fractal geometry on the larger array as explained in “Microstrip hairpin bandpass filter using modified Minkowski fractal-shape for suppression of second harmonic, IEICE” . is it applicable in the case of your antenna? Please comment on potential ways to achieve a smaller size?
Response) The authors appreciate the reviewer for the comments. The proposed antenna includes the patch antenna design without any miniaturization technique. We think that the use of fractal-shape may be helpful to reduce the size of the entire array antenna even though there will be some reduction of antenna gain due to the smaller aperture size. The miniaturization of the proposed array antenna can be one of research topics in future, and we have commented on this in the discussion part (page 5).
Please include cross-polarization results if available and comment on them accordingly
Response) Unfortunately, only simulated cross-polarization results is available at this moment. Considering the hemisphere in the broad side direction, the cross-polarization level is below -41 dB in S-band, below -23 dB in C-band, and below -16 dB in X-band in terms of each co-polarization level. The authors have included comment on the cross polarization in page 5, line 23. Since only simulated result is available, we could not incorporate the simulation results in figure 5.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thank you for addressing my concerns.
Reviewer 2 Report
The paper has been improved and I think it is now qualified for publication
