Simple Planar Microstrip Crossover Coupler with Independent Control over Bandwidth and Selectivity
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
The manuscript presents a compact hexagonal microstrip crossover design for 2.4 GHz applications, combining Sierpinski fractals, Defected Ground Structures (DGS), and reactive loading stubs. This combination is potentially innovative, as it offers significant miniaturization while allowing independent control of selectivity and fractional bandwidth. The topic is relevant and timely for microwave and RF integrated circuit design. The design and simulation results appear promising; however, the manuscript has several issues that need to be addressed before it can be considered for publication.
1- The manuscript should explain why a Rogers substrate was selected (e.g., low loss tangent, stable dielectric constant over frequency, mechanical considerations) and must list the complete substrate parameters in the design section: relative permittivity (εr) with tolerance, loss tangent (tan δ), substrate thickness (h), and also copper thickness. Please add these details to enable reproducibility.
2- Please state explicitly which EM tool was used for design and simulation (for example, Ansys HFSS, CST Microwave Studio, Keysight ADS), and based on the type of the simulator, provide key solver settings: frequency range, mesh settings, convergence criteria, boundary conditions, and port excitation type. This is necessary for validation and reproducibility.
3- Figure 1 caption is incorrect and needs rewording:
Current caption: “Figure 1. Classical hexagonal crossover. (a). Topology, (b). Electric field intensity plot at 2.4 GHz. when the input is at port.”
Suggested corrected caption to use in the manuscript:
Figure 1. Classical hexagonal crossover: (a) topology; and (b) simulated electric field intensity distribution at 2.4 GHz when the input is applied to Port 1.
3- In Figure 2, the S-parameter definitions are inconsistent: the same label (S14) appears twice. Please correct the S-parameter labels so each transfer is uniquely identified (e.g., S11, S12, S13, S14) and make sure index order follows the port numbering used in the text and figures.
4- The unit should be written as mm² (with the superscript 2)
5- Wherever a technical term or definition is used for the first time (e.g., “circular Sierpinski fractals,” “phase imbalance,” “amplitude imbalance”), include a brief explanation or cite a reference that introduces the concept. This makes the paper accessible to readers outside the immediate subfield and supports reproducibility.
6- All density or field-distribution plots must include a colorbar (with units), and it is strongly recommended to mark the maximum and minimum values on the image (e.g., with crosses and numeric labels). The caption should state the plotted quantity (e.g., |E| in V/m or normalized field intensity) and the scale range.
7- Major: The dimensional information presented in Table 1 (and on the figures) is insufficient for reconstruction. Provide a complete set of dimensions and clearly annotate these dimensions on the geometry figures.
8- At line 190 the text references a 2.9 GHz feature (likely a new transmission zero), whereas the caption of Figure 5 references 2.4 GHz. This is confusing. Please verify it and correct all statements and captions so that frequencies are consistent and accurate throughout the manuscript.
9- For quick and unambiguous reading, label port numbers on every schematic and measurement figure (e.g., Port 1or P1, Port 2 or P2, Port 3 or P3, Port 4 or P4). This avoids confusion when referring to Sij in text.
10- Section 3.2 is titled “VIA,” but Figure 7 (mentioned nearby) only comments on a 0.3 mm gap and does not show via details. Please include explicit figures showing via locations, via diameters, plating type, and how the via(s) relate to the claimed operating mode. If the vias are intended to be “grounded via holes,” show them on the PCB layout.
11- The resolution of Figures 12 and 13 is poor, making numeric values and plot detail very hard to read. If re-running the simulation is not possible, at minimum regenerate higher-resolution underlying numeric data and numbers.
12- Major: For the measured results, present a clearer image of the network analyzer screen and sketches of the measurement setup, including calibration cables, connectors, and port connections.
13- Table 3 includes a list of parameters but lacks definitions. Add a short definition for each parameter below the table or in a caption, and reference the measurement or simulation standard where appropriate. If any parameter is taken from a specific standard or prior work, please provide a citation.
14- Major: Figure 15 must show both simulated and measured S-parameter results together for direct comparison. Without this, the results lack scientific validity and cannot confirm the proposed model. Please include the measured data from the VNA alongside the simulation curves, and provide a photo of the VNA screen with the calibration method. Without such comparison, the manuscript is an incomplete experiment and can only be considered a simulation/design study.
Comments for author File: 
Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsA microstrip crossover coupler consisting of a modified hexagonal structure with Sierpinski fractals, four open-circuit shunt stubs, and defected ground structures (DGSs) is proposed in this paper. The following items needs to be addressed for clarity and completeness of the paper.
- The first paragraph in introduction (lines 26 to 34) should be removed. This is the same as template.
- It would be better if coupler is added after crossover in the title. It is somewhat confusing. In addition, the definition of the crossover coupler needs to be added for explantion.
- Detailed geometry of Sierpinski fractal structure should be provided with geometric parameters. In addition, Sierpinski carpet would be more accurate for the name of Sierpinski fractal structure because there are many different types of Sierpinski fractal structures such as triangle or carpet.
- Relative permittivity and loss tangent of Rogers 4003 substrate should be provided.
- Pls. add some reference for the classical hexagonal crossover coupler.
- What would be the reason for using the hexagonal patch instead of a square or circular patch?
- ‘1’ is missing in the caption for Figure 1. In addition, the scale for the colors in Figure 1(b) should be added.
- In Figure 2, the legend for the solid line should be ‘dB(S(3,1))’ not ‘dB(S(4,1))’.
- Some design guideline for deciding the dimensions of Sierpinski carpet structure and the DGS should be provided.
- Pls. add some reference for the open-circuit shunt stubs and grounded via holes.
- Equivalent circuit for the proposed microstrip crossover coupler needs to be provided.
English needs to be improved.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript reads as if it were AI-generated, as evidenced by the introduction, raising doubts about its originality.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThank you for your revisions. However, the manuscript still does not provide credible experimental validation, and the key concerns regarding the measurement results remain unresolved. Therefore, the manuscript does not meet the requirements for publication and cannot be accepted in its current form. I encourage the authors to conduct proper fabrication and measurement and to include reliable experimental results in a future submission.
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsAccept.
Comments on the Quality of English LanguageEnglish needs to be improved.
Author Response
We thank the reviewer for his precious time and efforts.
Reviewer 3 Report
Comments and Suggestions for AuthorsI have no further comments.
Author Response
We thank the reviewer for his precious time and efforts.
Round 3
Reviewer 1 Report
Comments and Suggestions for AuthorsDear author,
The experimental results are not sufficient to support your claims, and the circuit has not been properly measured; it has only been constructed without any real evaluation. Therefore, I recommend rejection.
