Functionality Investigation of the UAV Arranged FMCW Solid-State Marine Radar

Round 1

Reviewer 1 Report

Thank you for the great work. Paper is very nicely written and I have enjoyed reading it. It is rare nowadays to see a paper with such an extensive hardware component.

I appreciate your in-depth analysis of the observed interference. EMI/EMC can be quite a problem in a complex system, such as your UAV radar.

I agree that the radial interference is most likely due to the ground interference (e.g. transmitters operating close to your radar frequency). As for the ring-shaped interference, I would like to suggest the influence of the rotors. Namely, your aircraft rotors are in the nearfield of the antenna and are capable of producing additional reflections/Doppler shifts in the radar echo, to which FMCW radar can be sensitive. It would be interesting to see if there is any correlation of the apparent ring range to the frequency of the rotors (RPM) or its harmonics. I have included few papers on the topics of interference of the rotors on the rotor-craft based GPS/GNSS receivers:

• Griffith KA, Gupta IJ: “Inclusion of rotor blade modulation in hardware-in-the-loop testing of RF systems”, IEEE Transactions On Aerospace and Electronic Systems. 47: 1580-1593. DOI: 10.1109/Taes.2011.5937251
• Gupta IJ, Griffith KA: “Simulations of antennas mounted on rotorcrafts”, 21st International Technical Meeting of the Satellite Division of the Institute of Navigation, Ion GNSS 2008. 3: 1271-1276.
• O'Brien AJ, Hayhurst K, Gupta IJ: “Effects of rotor blade modulation on GNSS receiver measurements”, 22nd International Technical Meeting of the Satellite Division of the Institute of Navigation 2009, Ion GNSS 2009. 2: 1150-1159.

This is not exactly the same situation, but it may give you an idea for further direction to explore.

It would be nice to include radar antenna radiation pattern plot, if available. Maritime radars tend to have fan-beam patterns to accommodate ship’s roll and surge. I’m especially interested if there are any sidelobes that could open a signal path from unwanted direction.

I would recommend a minor grammar /spelling correction (e.g. comma before “which”). Other than that, I have no additional requests about the presented material.

Author Response

1 comment

The influence of the rotors. Namely, your aircraft rotors are in the nearfield of the antenna and are capable of producing additional reflections/Doppler shifts in the radar echo, to which FMCW radar can be sensitive. It would be interesting to see if there is any correlation of the apparent ring range to the frequency of the rotors (RPM) or its harmonics. I have included few papers on the topics of interference of the rotors on the rotor-craft based GPS/GNSS receivers. This is not exactly the same situation, but it may give you an idea for further direction to explore.

We have provided an answer on page 16 of the paper in red coloured text.

We sincerely thank the reviewer for suggesting possible sources of interference and for providing papers on similar topics. During the experiments detailed in our paper, no correlation between the apparent rings and the frequency of the rotors or their harmonics was observed, thus the possibility of the rotors causing additional reflections and/or Doppler shifts was ignored. No changes of the first ring’s radius during various stages of flight were observed, only the appearance of the additional rings due to the higher intensity of harmonics at higher altitudes.

2 comment

It would be nice to include radar antenna radiation pattern plot, if available. Maritime radars tend to have fan-beam patterns to accommodate ship’s roll and surge. I’m especially interested if there are any sidelobes that could open a signal path from unwanted direction.

The radar‘s antenna‘s technical data and a reference to its source were provided on page 2 of our paper with additional 21 reference.

It is important to mention that, according to the directivity diagram data of the Simrad 4G FMCW marine radar‘s antenna, which is presented in the radar‘s brochure, the sidelobe level of the radar‘s Tx and Rx antenna is below -18 dB when within ±10° and below –24 dB outside ±10°, the vertical beamwidth (–3 dB) is 25° ±20% and the horizontal beamwidth (–3 dB) is ) 5.2° ±10%.

4 comment

would recommend a minor grammar /spelling correction (e.g. comma before “which”). Other than that, I have no additional requests about the presented material.

We have additionally checked and corrected a lot of grammar and spelling errors.

Reviewer 2 Report

The manuscript just-1325747 entitled: Functionality Investigation of the UAV arranged FMCW solid-state marine radar, presents very interesting scientific aspects given the context of application to UAVs. Overall, the manuscript is very informative and the experimental activities conducted are innovative and interesting. We ask a small effort to the authors to revise the article according to the formatting requirements of the JMSE journal. References on Author Contributions are missing and the bibliography is too small and should be extended and improved. As for the discussion paragraph, a comparison with other radar systems should be reported to bring out the advantages and possibly the limitations of the system tested. If possible, the conclusions should include indications of future perspectives and above all possible applications of the UAV + Radar system in concrete and defined contexts should be mentioned. The manuscript, therefore, requires minor revisions to be accepted.

Author Response

1 comment

We ask a small effort to the authors to revise the article according to the formatting requirements of the JMSE journal

The MDPI latex template was used in the paper. We would be grateful if more information on the appropriate template or any existing formatting errors was to be supplied.

2 comment

References on Author Contributions are missing and the bibliography is too small and should be extended and improved.

The information on author contribution was provided following the requirements of MDPI during the submission of the paper. The bibliography was created from the list of sources used in this research and was extended according to the reviewers‘ comments.

3 comment

As for the discussion paragraph, a comparison with other radar systems should be reported to bring out the advantages and possibly the limitations of the system tested.

We have provided an answer on page 16 of the paper in red coloured text.

The UAV’s radar has a rotating antenna inside its radome. It allows for rapid scanning at the cost of additional weight and volume of the rotator and circular radome. In this paper, the performance of the radar such as angular resolution and the range was prioritized over the speed, flight duration and range of the UAV. Using a relatively small UAV with a mass of several tens of kilograms the antenna diameter was limited to 0.5 m with an angular resolution of 5° due to weight. Initial experiments were performed using a 2 m long antenna on a rotorcraft UAV where scanning was done by rotating the aircraft. This concept can be implemented in a fixed-wing UAV for which the antenna is integrated into the wing as presented in the patent application WO/2019/003194.

4 comment

If possible, the conclusions should include indications of future perspectives and above all possible applications of the UAV + Radar system in concrete and defined contexts should be mentioned

We have provided an answer on page 17 of the paper in red coloured text.

The radar on the UAV can be used for the identification of vessels as a back-up option in case the AIS system fails. It can also be used for border control, anti-piracy measures, anti-drone systems, ice monitoring and in other applications.