Radar surveillance of unmanned aerial vehicles (review)
Keywords:unmanned aerial vehicle, UAV detection radar, technical requirements, noise jamming, passive interference, signs of recognition, rotor modulation
AbstractRadar surveillance of unmanned aerial vehicles (UAVs) is actively developing area of scientific research. This article provides a review and analysis of publications in recent years devoted to the methods and radar systems of detection and recognition of classes and types of UAVs. It is noted that the most difficult targets for radar detection are low-sized, low-speed small UAVs (drones) flying at low and extremely low altitudes. If large and medium-sized UAVs can be detected by modern radar systems, then for the detection of small UAVs it is advisable to create specialized highly efficient, highly mobile, portable and inexpensive active UAV detection radars. The technical requirements for such radars are defined and recommendations for their implementation are provided. High-performance protection systems based on adaptive lattice filters are offered to protect UAV detection radars from noise jamming and passive interference. It is shown that the research on the methods of recognizing UAV classes and types is a development of the existing theory and technology of radar recognition of air targets.
S. Vishnevsky, L. Beylis, V. Klimchenko, “Potential capabilitys of radiotechnical troops radars to detect operational-tactical and tactical unmanned air vehicle,” Sci. Technol. Air Force Ukr., no. 2(27), pp. 92–98, 2017, doi: https://doi.org/10.30748/nitps.2017.27.18.
G. V. Eremin, A. D. Gavrilov, I. I. Nazarchuk, “Small-Sized Drones as a New Challenge for Air Defense,” Armeiskii Vestn., 2015, uri: https://army-news.org/2015/02/malorazmernye-bespilotniki-novaya-problema-dlya-pvo/.
S. I. Makarenko, A. V. Timoshenko, A. S. Vasilchenko, “Counter Unmanned Aerial Vehicles. Part 1. Unmanned aerial vehicle as an object of detection and destruction,” Syst. Control. Commun. Secur., no. 1, pp. 109–146, 2020, doi: https://doi.org/10.24411/2410-9916-2020-10105.
A. E. Ananenkov, D. V. Маrin, V. M. Nuzhdin, V. V. Rastorguev, P. V. Sokolov, “To the question of small-sized UAVs surveillance,” Tr. MAI, no. 91, 2016, uri: http://trudymai.ru/eng/published.php?ID=75662&eng=Y.
A. Laučys et al., “Investigation of detection possibility of UAVs using low cost marine radar,” Aviation, vol. 23, no. 2, pp. 48–53, 2019, doi: https://doi.org/10.3846/aviation.2019.10320.
B. Taha, A. Shoufan, “Machine Learning-Based Drone Detection and Classification: State-of-the-Art in Research,” IEEE Access, vol. 7, pp. 138669–138682, 2019, doi: https://doi.org/10.1109/ACCESS.2019.2942944.
C. Clemente, A. Balleri, K. Woodbridge, J. J. Soraghan, “Developments in target micro-Doppler signatures analysis: radar imaging, ultrasound and through-the-wall radar,” EURASIP J. Adv. Signal Process., vol. 2013, no. 1, p. 47, 2013, doi: https://doi.org/10.1186/1687-6180-2013-47.
J. S. Patel, F. Fioranelli, D. Anderson, “Review of radar classification and RCS characterisation techniques for small UAVs ordrones,” IET Radar, Sonar Navig., vol. 12, no. 9, pp. 911–919, 2018, doi: https://doi.org/10.1049/iet-rsn.2018.0020.
S. A. Musa et al., “A review of copter drone detection using radar systems,” Def. S&T Tech. Bull., vol. 12, no. 1, pp. 16–38, 2019, uri: http://psasir.upm.edu.my/id/eprint/80464/.
A. I. Godunov, S. V. Shishkov, N. K. Yurkov, “Complex for Detection and Combating Small-Sized Pilotless Aircraft Vehicles,” Reliab. Qual. Complex Syst., no. 2, pp. 62–69, 2014, uri: https://nikas.pnzgu.ru/page/20187.
G. V. Eremin, A. D. Gavrilov, I. I. Nazarchuk, “System Organization for Combating Small-sized UAVs,” Arsenal Otechestva, no. 6, 2014, uri: https://arsenal-otechestva.ru/article/389-antidrone.
E. Filin, R. Kirichek, “Approaches to the detection micro air vehicle based on the analysis of the electromagnetic spectrum,” Telecom IT., vol. 6, no. 2, pp. 87–93, 2018, uri: https://elibrary.ru/item.asp?id=35269062.
M. Jahangir, C. Baker, “Persistence surveillance of difficult to detect micro-drones with L-band 3-D holographic radarTM,” in 2016 CIE International Conference on Radar (RADAR), 2016, pp. 1–5, doi: https://doi.org/10.1109/RADAR.2016.8059282.
W. Zhang, C. Tong, Q. Zhang, Y. Zhang, X. Zhang, “Extraction of Vibrating Features With Dual-Channel Fixed-Receiver Bistatic SAR,” IEEE Geosci. Remote Sens. Lett., vol. 9, no. 3, pp. 507–511, 2012, doi: https://doi.org/10.1109/LGRS.2011.2172974.
K. Kim, M. Uney, B. Mulgrew, “Estimation of Drone Micro-Doppler Signatures via Track-Before-Detect in Array Radars,” in 2019 International Radar Conference (RADAR), 2019, pp. 1–6, doi: https://doi.org/10.1109/RADAR41533.2019.171375.
V. P. Riabukha, V. V. Tsisarzh, Y. A. Katiushyn, V. I. Zarytskyi, “Estimation of potential efficiency of interperiod processing of coherent batch radio pulses against background of clutter in pulse-Doppler radars with medium frequency of probing,” Radioelectron. Commun. Syst., vol. 61, no. 12, pp. 529–546, 2018, doi: https://doi.org/10.3103/S0735272718120014.
J. Farlik, M. Kratky, J. Casar, V. Stary, “Multispectral detection of commercial unmanned aerial vehicles,” Sensors, vol. 19, no. 7, p. 1517, 2019, doi: https://doi.org/10.3390/s19071517.
R. L. Sturdivant, E. K. P. Chong, “Systems Engineering Baseline Concept of a Multispectral Drone Detection Solution for Airports,” IEEE Access, vol. 5, pp. 7123–7138, 2017, doi: https://doi.org/10.1109/ACCESS.2017.2697979.
G. J. Mendis, T. Randeny, J. Wei, A. Madanayake, “Deep learning based doppler radar for micro UAS detection and classification,” in MILCOM 2016 - 2016 IEEE Military Communications Conference, 2016, pp. 924–929, doi: https://doi.org/10.1109/MILCOM.2016.7795448.
M. Jian, Z. Lu, V. C. Chen, “Drone detection and tracking based on phase-interferometric Doppler radar,” in 2018 IEEE Radar Conference (RadarConf18), 2018, pp. 1146–1149, doi: https://doi.org/10.1109/RADAR.2018.8378723.
G. Galati et al., “Visibility trials of unmanned aerial vehicles (Drones) by commercial X-band radar in sub-urban environment,” in 2017 AEIT International Annual Conference, 2017, pp. 1–6, doi: https://doi.org/10.23919/AEIT.2017.8240554.
J. Ochodnicky, Z. Matousek, M. Babjak, J. Kurty, “Drone detection by Ku-band battlefield radar,” in 2017 International Conference on Military Technologies (ICMT), 2017, pp. 613–616, doi: https://doi.org/10.1109/MILTECHS.2017.7988830.
W. Zhang, G. Li, “Detection of multiple micro-drones via cadence velocity diagram analysis,” Electron. Lett., vol. 54, no. 7, pp. 441–443, 2018, doi: https://doi.org/10.1049/el.2017.4317.
P. Zhang, L. Yang, G. Chen, G. Li, “Classification of drones based on micro-Doppler signatures with dual-band radar sensors,” in 2017 Progress in Electromagnetics Research Symposium - Fall (PIERS - FALL), 2017, pp. 638–643, doi: https://doi.org/10.1109/PIERS-FALL.2017.8293214.
C. J. Li, H. Ling, “An Investigation on the Radar Signatures of Small Consumer Drones,” IEEE Antennas Wirel. Propag. Lett., vol. 16, pp. 649–652, 2017, doi: https://doi.org/10.1109/LAWP.2016.2594766.
L. Fuhrmann, O. Biallawons, J. Klare, R. Panhuber, R. Klenke, J. Ender, “Micro-Doppler analysis and classification of UAVs at Ka band,” in 2017 18th International Radar Symposium (IRS), 2017, pp. 1–9, doi: https://doi.org/10.23919/IRS.2017.8008142.
J. Drozdowicz et al., “35 GHz FMCW drone detection system,” in 2016 17th International Radar Symposium (IRS), 2016, pp. 1–4, doi: https://doi.org/10.1109/IRS.2016.7497351.
V. Semkin et al., “Analyzing Radar Cross Section Signatures of Diverse Drone Models at mmWave Frequencies,” IEEE Access, vol. 8, pp. 48958–48969, 2020, doi: https://doi.org/10.1109/ACCESS.2020.2979339.
S. Dogru, L. Marques, “Pursuing Drones With Drones Using Millimeter Wave Radar,” IEEE Robot. Autom. Lett., vol. 5, no. 3, pp. 4156–4163, 2020, doi: https://doi.org/10.1109/LRA.2020.2990605.
P. Hugler, M. Geiger, C. Waldschmidt, “77 GHz radar-based altimeter for unmanned aerial vehicles,” in 2018 IEEE Radio and Wireless Symposium (RWS), 2018, pp. 129–132, doi: https://doi.org/10.1109/RWS.2018.8304965.
Á. D. de Quevedo, F. I. Urzaiz, J. G. Menoyo, A. A. López, “Drone detection and radar-cross-section measurements by RAD-DAR,” IET Radar, Sonar Navig., vol. 13, no. 9, pp. 1437–1447, 2019, doi: https://doi.org/10.1049/iet-rsn.2018.5646.
D. I. Lekhovytskiy, D. S. Rachkov, A. V. Semeniaka, V. P. Ryabukha, D. V. Atamanskiy, “Adaptive lattice filters. Part I. Theory of lattice structures,” Appl. Radio Electron., vol. 10, no. 4, pp. 380–404, 2011, uri: https://openarchive.nure.ua/bitstream/document/4699/1/380-404.pdf.
D. I. Lekhovytskiy, “Adaptive lattice filters for systems of space-time processing of non-stationary Gaussian processes,” Radioelectron. Commun. Syst., vol. 61, no. 11, pp. 477–514, 2018, doi: https://doi.org/10.3103/S0735272718110018.
D. I. Lekhovytskiy, V. P. Riabukha, G. A. Zhuga, V. N. Lavrent’ev, “Experimental investigations of MTD systems based on ALF in pulse radars with transverse wobbling of probing periods,” Appl. Radio Electron., vol. 7, no. 1, pp. 11–24, 2008, uri: https://openarchive.nure.ua/bitstream/document/6228/1/MRF_T1_Ch1_2008-rus-105-108.pdf.
V. P. Riabukha, A. V. Semeniaka, Y. A. Katiushyn, V. I. Zarytskyi, O. O. Holovin, “Digital adaptive system of radar protection against masking clutter on the basis of adaptive lattice filter,” Weapons Mil. Equip., vol. 24, no. 12, pp. 32–40, 2019, uri: https://journal.cndiovt.com.ua/issue/view/28.
C. E. Muehe, M. Labitt, “Displaced-phase-center antenna technique,” Lincoln Lab. J., vol. 12, no. 2, pp. 281–296, 2000, uri: https://archive.ll.mit.edu/publications/journal/pdf/vol12_no2/12_2displaced.pdf.
V. P. Riabukha, “Adaptive radar noise jamming protection systems. 2. Quasi-Newton correlation self-compensators. Adaptive lattice filters,” Appl. Radio Electron., vol. 15, no. 2, pp. 88–99, 2016, uri: https://openarchive.nure.ua/handle/document/12114.
D. I. Lekhovitskiy, V. P. Riabukha, A. V. Semenyaka, E. A. Katyushin, V. M. Grytsenko, “Adaptive radar noise jamming protection systems. 5. Exploratory model of a jamming protection system,” Appl. Radio Electron., vol. 16, no. 3, 4, pp. 95–102, 2017, uri: https://nure.ua/wp-content/uploads/2018/Scientific_editions/are_1_2.pdf.
D. I. Lekhovytskiy, Y. S. Shifrin, “Statistical analysis of ‘superresolving’ methods for direction-of-arrival estimation of noise radiation sources under finite size of training sample,” Signal Process., vol. 93, no. 12, pp. 3382–3399, 2013, doi: https://doi.org/10.1016/j.sigpro.2013.03.008.
D. I. Lekhovytskiy, D. V. Atamanskiy, V. P. Riabukha, D. S. Rachkov, A. V. Semeniaka, “Combining target detection against the background of jamming signals and jamming signal DOA estimation,” in 2015 International Conference on Antenna Theory and Techniques (ICATT), 2015, pp. 1–5, doi: https://doi.org/10.1109/ICATT.2015.7136777.
B.-K. Kim et al., “Drone Detection with Chirp-Pulse Radar Based on Target Fluctuation Models,” ETRI J., vol. 40, no. 2, pp. 188–196, 2018, doi: https://doi.org/10.4218/etrij.2017-0090.
A. Herschfelt et al., “Consumer-grade drone radar cross-section and micro-Doppler phenomenology,” in 2017 IEEE Radar Conference (RadarConf), 2017, pp. 0981–0985, doi: https://doi.org/10.1109/RADAR.2017.7944346.
A. B. Blyakhman, V. N. Burov, A. V. Myakinkov, A. G. Ryndyk, “Detection of unmanned aerial vehicles via multi-static forward scattering radar with airborne transmit positions,” in 2014 International Radar Conference, 2014, pp. 1–5, doi: https://doi.org/10.1109/RADAR.2014.7060334.
H. D. Griffiths, N. R. W. Long, “Television-based bistatic radar,” IEE Proc. F Commun. Radar Signal Process., vol. 133, no. 7, p. 649, 1986, doi: https://doi.org/10.1049/ip-f-1.1986.0104.
A. P. Kondratenko, “Role and function of unconventional radio location in the airspace control system,” Zbirnyk Nauk. Pr. KhVU, no. 1, pp. 87–90, 2002.
A. Kondratenko, P. Kovalenko, I. Dobrinin, “Principles and variants of construction of the radio-location system with the use of radiation of mobile communication,” Inf. Process. Syst., no. 4, pp. 71–78, 2006, uri: http://www.hups.mil.gov.ua/periodic-app/article/5093/eng.
Y. Liu, X. Wan, H. Tang, J. Yi, Y. Cheng, X. Zhang, “Digital television based passive bistatic radar system for drone detection,” in 2017 IEEE Radar Conference (RadarConf), 2017, pp. 1493–1497, doi: https://doi.org/10.1109/RADAR.2017.7944443.
B. Knoedler, R. Zemmari, W. Koch, “On the detection of small UAV using a GSM passive coherent location system,” in 2016 17th International Radar Symposium (IRS), 2016, pp. 1–4, doi: https://doi.org/10.1109/IRS.2016.7497375.
A. D. Chadwick, “Micro-Drone Detection using Software-Defined 3G Passive Radar,” in International Conference on Radar Systems (Radar 2017), 2017, doi: https://doi.org/10.1049/cp.2017.0419.
D. Solomitckii, M. Gapeyenko, V. Semkin, S. Andreev, Y. Koucheryavy, “Technologies for Efficient Amateur Drone Detection in 5G Millimeter-Wave Cellular Infrastructure,” IEEE Commun. Mag., vol. 56, no. 1, pp. 43–50, 2018, doi: https://doi.org/10.1109/MCOM.2017.1700450.
X. Yang, K. Huo, W. Jiang, J. Zhao, Z. Qiu, “A passive radar system for detecting UAV based on the OFDM communication signal,” in 2016 Progress in Electromagnetic Research Symposium (PIERS), 2016, pp. 2757–2762, doi: https://doi.org/10.1109/PIERS.2016.7735118.
E. Vinogradov, D. A. Kovalev, S. Pollin, “Simulation and Detection Performance Evaluation of a UAV-mounted Passive Radar,” in 2018 IEEE 29th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), 2018, pp. 1185–1191, doi: https://doi.org/10.1109/PIMRC.2018.8580940.
T. Martelli, F. Murgia, F. Colone, C. Bongioanni, P. Lombardo, “Detection and 3D localization of ultralight aircrafts and drones with a WiFi-based Passive Radar,” in International Conference on Radar Systems (Radar 2017), 2017, doi: https://doi.org/10.1049/cp.2017.0423.
V. G. Nebabin, V. V. Sergeev, Radar Detection Methods and Technology, [in Russian]. Moscow: Radio i Svyaz’, 1984.
A. Farina, A. Visconti, “Classification of radar targets by means of multiple hypotheses testing,” in Proceedings of the International Conference Radar-87, 1987, pp. 73–78, uri: https://ui.adsabs.harvard.edu/abs/1987rapr.conf...73F/abstract.
A. L. Gorelik, Y. L. Barabash, O. V. Krivosheev, S. S. Epshtein, Selection and Detection Based on Radar Data, [in Russian]. Moscow: Radio i Svyaz’, 1990.
A. L. Gorelik, V. A. Skripkin, Some Issues in Constructing Recognition System, [in Russian]. Moscow: Sov. Radio, 1974.
J. Martin, B. Mulgrew, “Analysis of the theoretical radar return signal form aircraft propeller blades,” in IEEE International Conference on Radar, 1990, pp. 569–572, doi: https://doi.org/10.1109/RADAR.1990.201091.
N. E. Chamberlain, E. K. Walton, F. D. Garber, “Radar target identification of aircraft using polarization-diverse features,” IEEE Trans. Aerosp. Electron. Syst., vol. 27, no. 1, pp. 58–67, 1991, doi: https://doi.org/10.1109/7.68148.
V. M. Koshevoi, I. I. Makarova, “Synthesis and efficiency assessment of algorithms for multialternative classification of radar objects with due regard for the specified restrictions under exposure to interference,” Zarubezhnoe Voen. Obozr., no. 10, pp. 61–69, 1992.
Y. D. Shirman, S. A. Gorshkov, S. P. Leshchenko, G. D. Bratchenko, V. M. Orlenko, “Radar recognition methods and their simulation,” Zarubezhnaya Radioelektronika, no. 11, pp. 3–62, 1996.
Y. D. Shirman, Computer Simulation of Aerial Target Radar Scattering Recognition, Detection and Tracking. Norwood, MA: Artech House, 2002.
A. G. Ivakhnenko, Ed., Perceptron as an Image Recognition System, [in Russian]. Kiev: Naukova Dumka, 1975.
I. Jouny, F. D. Garber, S. C. Ahalt, “Classification of radar targets using synthetic neural networks,” IEEE Trans. Aerosp. Electron. Syst., vol. 29, no. 2, pp. 336–344, 1993, doi: https://doi.org/10.1109/7.210072.
Y. D. Shirman, S. T. Bagdasaryan, A. S. Malyarenko, D. I. Lekhovitskii, Radio Electronic Systems. Principles of Construction and Theory. Reference Book, [in Russian]. Moscow: Radiotekhnika, 2007.
A. L. Gorelik, V. A. Skripkin, Recognition Techniques. Textbook, [in Russian]. Moscow: Radio i Svyaz’, 1984.
Y. D. Shirman, S. A. Gorshkov, S. P. Leshchenko, G. D. Bratchenko, Radar Recognition. Textbook on Theoretical Basics of Radiolocation Course, [in Russian]. Kharkov: Kharkov Military University, 1994.
X. Bai, M. Xing, F. Zhou, G. Lu, Z. Bao, “Imaging of Micromotion Targets With Rotating Parts Based on Empirical-Mode Decomposition,” IEEE Trans. Geosci. Remote Sens., vol. 46, no. 11, pp. 3514–3523, 2008, doi: https://doi.org/10.1109/TGRS.2008.2002322.
F. Su, M. Jiu, “ISAR Imaging of Target with Micro-motion Parts Based on SSA,” in 8th European Conference on Synthetic Aperture Radar, 2010, uri: https://ieeexplore.ieee.org/document/5757441.
V. C. Chen, F. Li, S.-S. Ho, H. Wechsler, “Micro-doppler effect in radar: phenomenon, model, and simulation study,” IEEE Trans. Aerosp. Electron. Syst., vol. 42, no. 1, pp. 2–21, 2006, doi: https://doi.org/10.1109/TAES.2006.1603402.
A. Solodov, A. Williams, S. Al Hanaei, B. Goddard, “Analyzing the threat of unmanned aerial vehicles (UAV) to nuclear facilities,” Secur. J., vol. 31, no. 1, pp. 305–324, 2018, doi: https://doi.org/10.1057/s41284-017-0102-5.
X. Li, B. Deng, Y. Qin, H. Wang, Y. Li, “The Influence of Target Micromotion on SAR and GMTI,” IEEE Trans. Geosci. Remote Sens., vol. 49, no. 7, pp. 2738–2751, 2011, doi: https://doi.org/10.1109/TGRS.2011.2104965.
C. Clemente, J. J. Soraghan, “Vibrating Micro-Doppler signature extraction from SAR data using Singular Value Decomposition,” in Proc. 9th European Conference on Synthetic Aperture Radar EUSAR 2012, 2012, uri: https://ieeexplore.ieee.org/document/6217013.
V. C. Chen, W. J. Miceli, B. Himed, “Micro-Doppler analysis in ISAR - review and perspectives,” in Proc. of 2009 International Radar Conference “Surveillance for a Safer World” (RADAR 2009), 2009, uri: https://ieeexplore.ieee.org/document/5438505.
B. Li, J. Wan, K. Yao, Y. Wang, L. Ci, J. Lu, “ISAR based on micro-doppler analysis and Chirplet parameter separation,” in 2007 1st Asian and Pacific Conference on Synthetic Aperture Radar, 2007, pp. 379–384, doi: https://doi.org/10.1109/APSAR.2007.4418631.
C. Clemente, J. J. Soraghan, “Vibrating Target Micro-Doppler Signature in Bistatic SAR With a Fixed Receiver,” IEEE Trans. Geosci. Remote Sens., vol. 50, no. 8, pp. 3219–3227, 2012, doi: https://doi.org/10.1109/TGRS.2011.2180394.
B. Torvik, K. E. Olsen, H. Griffiths, “Classification of Birds and UAVs Based on Radar Polarimetry,” IEEE Geosci. Remote Sens. Lett., vol. 13, no. 9, pp. 1305–1309, 2016, doi: https://doi.org/10.1109/LGRS.2016.2582538.
B. K. Kim, H.-S. Kang, S.-O. Park, “Experimental Analysis of Small Drone Polarimetry Based on Micro-Doppler Signature,” IEEE Geosci. Remote Sens. Lett., vol. 14, no. 10, pp. 1670–1674, 2017, doi: https://doi.org/10.1109/LGRS.2017.2727824.
M. Ritchie, F. Fioranelli, H. Griffiths, B. Torvik, “Micro-drone RCS analysis,” in 2015 IEEE Radar Conference, 2015, pp. 452–456, doi: https://doi.org/10.1109/RadarConf.2015.7411926.
A. V. Khristenko et al., “Magnitude and Spectrum of Electromagnetic Wave Scattered by Small Quadcopter in X-Band,” IEEE Trans. Antennas Propag., vol. 66, no. 4, pp. 1977–1984, 2018, doi: https://doi.org/10.1109/TAP.2018.2800640.
M. Ritchie, F. Fioranelli, H. Borrion, H. Griffiths, “Multistatic micro-Doppler radar feature extraction for classification of unloaded/loaded micro-drones,” IET Radar, Sonar Navig., vol. 11, no. 1, pp. 116–124, 2017, doi: https://doi.org/10.1049/iet-rsn.2016.0063.
X. Guo, C. S. Ng, E. de Jong, A. B. Smits, “Micro-Doppler Based Mini-UAV Detection with Low-Cost Distributed Radar in Dense Urban Environment,” in Proc. of 2019 16th European Radar Conference (EuRAD), 2019, uri: https://ieeexplore.ieee.org/document/8904760.
M. Ritchie, F. Fioranelli, H. Borrion, H. Griffiths, “Classification of loaded/unloaded micro-drones using multistatic radar,” Electron. Lett., vol. 51, no. 22, pp. 1813–1815, 2015, doi: https://doi.org/10.1049/el.2015.3038.
D. A. Brooks, O. Schwander, F. Barbaresco, J.-Y. Schneider, M. Cord, “Temporal Deep Learning for Drone Micro-Doppler Classification,” in 2018 19th International Radar Symposium (IRS), 2018, pp. 1–10, doi: https://doi.org/10.23919/IRS.2018.8447963.
S. Bjorklund, “Target Detection and Classification of Small Drones by Boosting on Radar Micro-Doppler,” in 2018 15th European Radar Conference (EuRAD), 2018, pp. 182–185, doi: https://doi.org/10.23919/EuRAD.2018.8546569.