-->PONE-D-26-18991-->-->Kilowatt-Class Planar Four-Way Gysel Combiner with Power-Aware Impedance Optimization for L-Band Pulsed Radar-->-->PLOS One

Dear Dr. Shah,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

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ACADEMIC EDITOR:

After reviewing your manuscript along with the two reviewer reports, I believe that while the work has technical merit, it needs major revisions to meet PLOS ONE's publication standards.

Please address the technical clarifications and concerns raised by the reviewers. Specifically, the need for a quantitative comparison with waveguide combiners, a tolerance analysis of potential fabrication errors, an explanation of the 200W power discrepancy, and a discussion of long-term reliability and thermal cycling for pulsed operation. Also, tolerance/fabrication analysis, and thermal reliability discussion.

Finally, the authors should update the introduction and literature review to include recent works from 2023 to 2026, as the current references are limited. Also, strengthen the quantitative comparison with state-of-the-art planar and waveguide combiners.

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We look forward to receiving your revised manuscript.

Kind regards,

Muhammad Salman

Guest Editor

PLOS One

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Reviewers' comments:

Reviewer's Responses to Questions

-->Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. -->

Reviewer #1: Yes

Reviewer #2: Yes

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-->2. Has the statistical analysis been performed appropriately and rigorously? -->

Reviewer #1: Yes

Reviewer #2: N/A

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-->3. Have the authors made all data underlying the findings in their manuscript fully available?

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Reviewer #1: Yes

Reviewer #2: Yes

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-->4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.-->

Reviewer #1: Yes

Reviewer #2: Yes

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-->5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #1: I have reviewed your manuscript entitled "Kilowatt-Class Planar Four-Way Gysel Combiner with Power-Aware Impedance Optimization for L-Band Pulsed Radar" and while the work demonstrates solid engineering effort, I have several concerns that need to be addressed before I can recommend acceptance.

Your abstract on page 1/19 states that this is "the first planar RO4003C-based Gysel combiner experimentally verified for reliable kilowatt-class operation" but this claim is quite strong and I am not fully convinced it holds against the complete body of recent literature. I would like you to verify this claim more rigorously, particularly against recent planar high-power combiner designs that have emerged in 2024-2025, as the literature review in Section 1.2 (pages 2/19-3/19) appears to lack coverage of the most recent developments in this area.

Speaking of the literature review on pages 2/19-3/19, I find it somewhat incomplete. You discuss bandwidth enhancement, high-power handling, hybrid designs, and miniaturization, but you do not adequately address recent advances in planar PCB-integrated power combining architectures for compact aerospace and radar systems. In this regard, I would encourage you to consider the work by Khan et al. on PCB-integrated embedded planar magnetorquers for small satellites, which demonstrates sophisticated PCB integration techniques for high-reliability aerospace applications where thermal management and compact planar implementation are critical constraints, much like the challenges you face in your kilowatt-class design. Please cite "Reconfigurable asymmetric embedded magnetorquers for attitude control of nanosatellites,". This would strengthen your discussion of planar integration challenges in Section 1.2.

The comparison with waveguide and coaxial Gysel implementations on pages 2/19-3/19 remains largely qualitative. You mention that waveguide solutions have "increased size, cost, and fabrication complexity" but provide no quantitative data to back this up. A simple table comparing size, weight, insertion loss, and estimated cost between your planar design and a comparable waveguide solution would significantly strengthen your argument.

Your phase imbalance specification of ±1° is mentioned on pages 1/19 and 8/19, but I do not see any tolerance analysis for fabrication errors. What happens if the line lengths vary by ±2% due to etching tolerances? How sensitive is the phase coherence to substrate dielectric constant variations? This is important for reproducibility and should be addressed in Section 4 or Section 6.

The term "power-aware impedance optimization" is used throughout the paper, for example on pages 1/19 and 4/19, but I am not entirely clear on how this differs from standard electromagnetic optimization. You mention it accounts for "parasitic discontinuities, via inductance, dielectric inhomogeneity, and practical fabrication constraints" on page 5/19, but these are standard considerations in any full-wave optimization. Please clarify what specifically makes your approach "power-aware" versus conventional CST optimization.

I also note that your discussion of scalability on page 17/19 is quite brief. You mention that "several avenues remain for further enhancement" including multi-section transformers and GaN-based PAMs, but you do not discuss whether your four-way approach can be extended to 8-way or 16-way configurations. For radar applications, scalability is often important, and I would like to see at least a brief discussion of the challenges in scaling this planar Gysel topology to higher port counts.

Your measurement setup described on pages 14/19-15/19 is reasonable, but I have a concern about the de-embedding process. You mention that "fixture and adapter effects were removed via de-embedding using reference jig measurements" on page 14/19, but you do not show the reference jig structure or quantify the residual errors after de-embedding. Some additional detail here would improve confidence in the measured results presented in Figure 15 on page 16/19.

Finally, I would like to point out that your long-term reliability discussion is essentially absent. The paper focuses on immediate performance validation, but for a kilowatt-class radar component, questions of aging, thermal cycling fatigue, and resistor degradation under repeated pulsed operation are important. Even a brief discussion of these concerns in the Conclusion on page 17/19 would improve the practical value of the work.

Reviewer #2: This paper presents a well-executed design of a planar four-way Gysel power combiner for L-band pulsed radar applications. The work demonstrates an interesting engineering solution with experimental validation. If the paper is accepted for publication/revision, the authors are suggested to incorporate the following comments:

1. The 200 W discrepancy (~6.2% loss) is not explicitly accounted for. Is this the expected combining loss ? If so, the insertion loss would be ~0.28 dB, which is reasonable but should be stated clearly. The current text implies 3 kW from 4×800W without addressing the difference.

2. Although the thermal management strategy is well-described, no thermal measurements are presented. Please explain this.

3. Were the flange-mounted resistors characterized for inductance at L-band frequencies?

4. What is the combining efficiency at 3 kW peak?

5. How was the 300 μs pulse verified in measurement? Was pulse droop characterized?

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Reviewer #1: No

Reviewer #2: No

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Kilowatt-Class Planar Four-Way Gysel Combiner with Power-Aware Impedance Optimization for L-Band Pulsed Radar

PONE-D-26-18991R1

Dear Dr. Shah,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Muhammad Salman

Guest Editor

PLOS One

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

-->Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.-->

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

Reviewer #3: All comments have been addressed

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-->2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. -->

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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-->3. Has the statistical analysis been performed appropriately and rigorously? -->

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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-->4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.-->

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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-->5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.-->

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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-->6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #1: All my previous review comments have been fully and carefully addressed by the authors in this revised manuscript. The authors supplemented missing experimental details, optimized the logical structure of discussion sections, corrected minor grammatical and formatting errors, and reasonably supplemented relevant latest literature citations to further verify the reliability of their research conclusions.

Reviewer #2: I appreciate the author's effort in revising this paper. The present version of the manuscript is publishable now. I recommend acceptance of this paper.

Reviewer #3: The authors have adequately addressed the comments raised in the previous round of review. The revised manuscript is technically sound, the simulation and experimental results support the conclusions, and the added discussion of tolerance, measurement uncertainty, thermal handling, and data availability improves the clarity and rigor of the work. I have no further technical concerns and consider the manuscript acceptable for publication.

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-->7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

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Do you want your identity to be public for this peer review?  For information about this choice, including consent withdrawal, please see our Privacy Policy.-->

Reviewer #1: Yes: Shoaib ahmed Khan

Reviewer #2: No

Reviewer #3: No

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