A Reconfigurable Analog Beamformer for Multi-Frequency, Multiantenna GNSS Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This article addresses the challenges of multipath and interference in multi-frequency, multi-antenna GNSS applications by designing and testing a reconfigurable analog beamformer. The key work involves implementing analog weighting for up to 14 channels through digitally controlled attenuators and phase shifters managed by PC software, analyzing relative errors, and applying a simple calibration for constant errors. Finally, the performance of the designed beamformer was evaluated experimentally. However, several issues should be addressed before the manuscript can be considered for publication:

(1) A brief summary of similar works in the existing literature should be provided to clarify the positioning of this study.
(2) The introduction should explicitly summarize the key contributions of this paper.
(3) In the performance analysis, the designed beamformer should be compared with existing beamformers to better highlight its advantages or novelty.
(4) The formatting of the references should be checked and consistently aligned with the journal’s style guidelines.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors presented the reconfigurable analog beamformer for GNSS systems. However, I cannot find strong research motivation or details about previous studies. Additionally, there are limited measured data and analysis for each output, such as temperature and radiation patterns. Therefore, the submitted manuscript has some critical issues for publication. The authors carefully revised the manuscript.

1. The abbreviated journal names in the reference sections need to be used.
2. The authors need to provide in detailed analysis for previous studies about the analog beamforming techniques for GNSS applications in the Introduction section because the description is too simple.
3. I cannot find any research motivation for the desired idea for a reconfigurable analog beamformer for GNSS applications.
4. In Figure 4, the two small Figures in (a) and (b) for the bottom sides are similar to each other for the data output phase.
5. Why did the authors show there are two examples in Figure 6? The authors could show more cases.
6. What units do those values in Table 1 ? dB?
7. In Figures 8 and 9, the measured radiation patterns are too simple to be shown. Are there any data for different multi-band and multi-frequency ranges?
8. The authors do not show some detailed specifications for the beamformer board as shown in Figure 2.
9. Why did the authors use such temperature ranges only for −35◦C to 40◦C?
10. The authors need to provide a detailed setup for the anechoic chamber measurement.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript presents a well-designed and experimentally validated 14-channel reconfigurable analog beamformer for GNSS applications. The work is technically solid, relevant for multipath mitigation and interference suppression, and supported by real measurements, which significantly strengthens the contribution. The simplified calibration strategy is particularly valuable from a practical engineering perspective.

Before acceptance, however, several points should be improved to enhance clarity and completeness:

 

1. Expand the technical description of the control software

Although the RF hardware is well detailed, the software responsible for generating and loading the excitation weights is only briefly described. Please clarify:

--- how users specify weight vectors (phase-only? amplitude/phase pairs?),

--- how discretization errors are handled,

--- latency and timing of SPI communication,

--- whether the software performs any optimization or is purely a control interface.

 

2. Provide more quantitative metrics in the Validation section

Figures 8 and 9 clearly show qualitative improvement after calibration, but quantitative indicators would strengthen the claims:

--- depth of the null before and after calibration (in dB),

--- deviation between optimized and achieved weights,

--- measured beamwidth or gain differences.

 

3. Improve figure clarity

Some figures (e.g., temperature plots in Figures 4, 5 and 6) use extremely small font sizes that are difficult to read in the PDF. Please enlarge axis labels, legends, and titles. Figure captions could also be made more descriptive.

 

4. Discuss the 3 dB amplitude drift over temperature

Section 4.2 reports up to 3 dB amplitude variation across −35°C to 40°C. Although the relative variation between channels is small, please comment on whether this absolute drift has implications for the beamformer’s use in long-term outdoor operation.

 

5. Clarify the calibration workflow

The concept of measuring a full reference channel and only one state per remaining channel is interesting, but the workflow is not fully clear. Please add:

--- a block diagram of the calibration process or lookup table generation,

--- some statistics on systematic offsets (e.g., mean ± standard deviation),

--- a brief discussion of limitations (e.g., non-linearities not corrected).

 

6. Minor language/typo corrections

Some examples: “dependance” → “dependence”, “ouput” → “output”, “stucture” → “structure” due to PDF artefact. Please revise the manuscript for small grammatical and typographical errors.

Comments on the Quality of English Language

The manuscript is generally clear and easy to follow, but several minor grammatical issues and typos should be corrected. Examples include incorrect word forms (“ouput”, “dependance”), missing commas, and occasional awkward phrasing. Figure captions also contain some formatting artefacts. A light proofreading pass is recommended to improve clarity and flow, but no major rewriting is required.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors revised the manuscript according to the questions so the paper can be accepted as it is.