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Drone RCS Statistical BehaviorPavel Sedivy & Ondrej Nemec

psedivy@retia.cz; onemec@retia.cz

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Outline

˃ Introduction˃ Radar Cross-Section, RCS˃ Drone RCS Measurement˃ Drone Observation Scenario˃ Drone RCS Behavior˃ Conclusion

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Introduction

˃ Drones/UAVs/RPASs˃ Same equipment

A TOY (market) vs. a PLANE (law) vs. a WEAPON (threat)

˃ Often Violate The Rules of Flying - Rough drones(Unaware/Careless/Intentional)

˃ Rules must be enforced˃ Surveillance tools needed

˃ Primary radar – the most powerful tool for non-cooperative surveillance

˃  Challenges for Radar Detection ˃  Low flying˃  Slow ˃  Small 

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Radar Cross Section, RCS 

˃ Radar Cross-Section RSC is the Cross-section of equivalent isotropic reflector ˃ Received power proportional to RCS

˃ Determined by material and shape ˃ General (bistatic, general polarization)

RCS˃  Monostatic, co-polarized RCS ˃  Need of UAS RCS measurements 

˃ Demand for more exact meaning of “Small” 

˃ Radar performance estimation ˃ Opportunity for classification

Bistatic RCS

Monostatic RCS

σ(f,θI,φI,polarI,θR,φR,polarR)

σ(f,θ,φ,polarVV)

σ(f,θ,φ,polarHH)

σ(f,θ,φ,polarCP)

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Published results on UAVs RCS 

˃ DJI Phantom RCS measurement ˃ Single plane cut˃ Single Frequency˃ Often single number (0.02 sqm) 

˃ DJI Phantom RCS simulation ˃ Sometimes limited relevance of model

e. g. propellers “made of” Aluminium instead of plastic

˃ No validation against real RCS measurement˃  Missing information 

˃ Meaning of figures (mean vs median, etc.) ˃ Detailed behaviour (frequency dependence)

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RCS Measurement˃ Near Field – hard to perform

˃ Small size - mandatory wide band measurement ˃ Antenna radiation pattern compensation not feasible

(frequency dependence)- inaccuracy 

˃  Far Field setup (Indoor/Outdoor) ˃ Relative measurement (calibration  400 mm s. steel ball)˃ DUT (Drone Under Test) on turntable ˃ VNA based measurement (s21 measurement, VNA ports

connected to two horn antennas, wideband sweep)˃ Time gating (post-processing, implementation of Time

Domain Reflectometry)

˃ Observation elevation  by UAV tilt or antenna height

Cross-talk UAVChamberparts

Chamberparts

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Radar Observation of UAVs

˃ UAV operation principle impacts observation scenario

˃ Lift generated by at least 4 rotary propellers ˃ Mutual compensation of reactive moments ˃ Manoeuvres performed by

unbalancing propellers speed/thrust ˃ Rotation by imbalance clockwise/counter

clockwise˃ Tilt by imbalance left/right or front/rear ˃ Tilt converts part of lift into thrust

Movement or wind compensation

˃ Statistics obtained by analysis of real flight logs

Multi-copters Operation Principle

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Radar Observation of UAV 

˃ Analysis of real flight logs ˃ UAVs observed often slightly from bottom/top˃ Roll/Pitch same behaviour

˃ RCS measurement for different ELEVATION˃ At least few

degrees 

Multi-copters Operation Principle

Roll cumulative density function

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Measured UAVs RSC

˃ Measured set of drones ˃ Consumer ˃ DIY 

˃ Even big drone small RCS ˃ VV polarization˃ HH polarization (only

some)˃ Median VV RCS listed˃ X-band about 9 GHz

Yuneec MANTIS Q(0.007 sqm)

Pelican GAMA 2100(0.010 sqm)

Parrot (0.004 sqm)

ROBODRONE Hornet(0.101 sqm)

ROBODRONE Super Hornet(0.130 sqm)

ROBODRONESparrow(0.090 sqm)

DJI Phantom 4 (0.019 sqm)

DJI F550 (0.029 sqm)

ROBODRONEKingfisher(0.092 sqm)

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Measured Drone RSCs

Drone type Size Statistics [sqm] VV polarization

Statistics [sqm] HH polarization

max median 10th percentile max median 10th percentile

DJI Phantom 4 350 mm 0.213 0.019 0.002 0.129 0.018 0.002

DJI F550 600 mm 0.237 0.029 0.005

YUNEEC Mantis Q 170 mm 0.03 0.004 0.001

PELICAN Gama 2100 2,000 mm 0.120 0.010 0.002

Parrot 400 mm 0.045 0.004 0.001

ROBODRONE Hornet 450 mm 0.198 0.101 0.049

ROBODRONE Super Hornet 850 mm 0.730 0.130 0.012 0.059 0.007 0.002

ROBODRONE King Fisher 1,000 mm 0.600 0.092 0.045 0.468 0.046 0.010

ROBODRONE Sparrow 1,200 mm 3.231 0.090 0.036 1.790 0.039 0.009

˃ Pd=90% indication 10th percentile (median RCS insufficient)

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Measured Drone RSCsYUNEEC Mantis Q˃ Measurement of rolled/pitched UAV

˃ RCS generally slightly higher "off the main the plane"˃ Low RCS turntable (balsa wood, low density PUR foam)˃ Mean slightly above median˃ Extremely low fluctuation with frequency

Scenario

RCS [sqm]

max median mean10th

percentile

main 0.03 0.004 0.006 0001

5 deg. from the top

0.05 0.006 0.008 0.001

Pitch29 deg.

0.06 0.006 0.008 0.001

Roll 25 deg. 0.03 0.005 0.006 0.001

RCS [dBsm]

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DJI Phantom RCS details

˃  DJI Phantom 4 RCS ˃ Roll/pitch impact ˃ Probability density ˃ Vertical polarization˃ 400 mm diagonal

size propellers

ϑ [deg]

RCS [sqm]

max median mean 10th percentile

-2.6 0.27 0.030 0.05 0.005

-1.4 0.15 0.017 0.03 0.004

+1.4 0.23 0.022 0.04 0.003

+2.6 0.25 0.034 0.05 0.005

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ROBODRONE Kingfisher RCS details

˃ Glass fibre composite hexacopter

˃ Size about 1m˃ Large hexacopter, quite small

RCS˃ Flat surface – mirror effects˃ RCS - random variable behaviour

ϑ [deg]

VV polar RCS [sqm] HH polar RCS [sqm]

max median 10th percentile

max median 10th percentile

-3.6 0.3 0.036 0.009 0.436 0.024 0.006

0 0.533 0.056 0.012 0.468 0.046 0.010

RCS cumulative distribution function

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ROBODRONE Super Hornet

˃ Carbon composite UAV design˃  +1.3 deg. (from radar)

extreme difference VV-HH˃ OTHER elevation in between,

close to each other˃ RCS UAV design dependent˃ "stealth" design (flat lower deck

HH polarization)

VV vs. HH comparison

ϑ [deg.]

VV polar RCS [sqm] HH polar RCS [sqm]

max median 10th percentile

max median 10th percentile

-3.6 0.245 0.025 0.004 0.184 0.016 0.003

+1.3 0.677 0.088 0.017 0.059 0.007 0.002

+1.3 deg.

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Small vs Huge UAV

˃  DJI Phantom 4  - a consumer drone (gimbal+camera only)˃ 1,400 g MTOW˃ 350 mm diagonal size˃ 9.4" propellers˃ plastic

˃ ROBODRONE Sparrow˃ 5 kg payload˃ 11 kg MTOW˃ 27" propellers˃ Composite

˃ Similar behaviour˃ RCS - small difference

˃ 1.7 dB (median)˃ 1.8 dB (P10)

DJI Phantom 4 & DJI Sparrow

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Diversity Gain

˃ Dual frequency observation increases detection probability˃ Fluctuation UAV size dependent (bigger, higher gain)˃ Limited impact – bandwidth limitations˃ Classification opportunities

Small vs. Medium and large UAV

DJI Phantom 4MANTIS Q ROBODRONE Kingfisher

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Conclusion

˃ RCS of UAVs˃ RCS behaves as random variable˃ Very small figures (median) - few thousands or hundreds of sqm in X band˃ VV and HH polarization very similar˃ Extremally small figures for 10th percentile (more relevant for Pd=0.9)

˃ Slightly higher RCS for tilted (flying) multicopter UAVs˃ Weak fluctuation with frequency (small frequency diversity gain)

˃ Research outlook˃ Use RCS behaviour for classification˃ Analyse bird RCS (based on radar data)

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