Radar Cross Section Reduction Techniques for Drones

Unmanned aerial vehicles (UAVs) are increasingly significant in modern warfare due to their versatility and capacity to perform high-risk missions without risking human lives. Beyond surveillance and reconnaissance, UAVs with jet propulsion and engagement capabilities are set to play roles similar to conventional jets. In various scenarios, military aircraft, drones, and UAVs face multiple threats while ground radar systems continuously monitor their positions. The interaction between these aerial platforms and radars causes temporal fluctuations in scattered echo power due to changes in aspect angle, impacting radar tracking accuracy. This study utilizes the potential radar cross-section (RCS) dynamics of an aircraft throughout its flight, using ground radar as a reference. Key factors influencing RCS include time, frequency, polarization, incident angle, physical geometry, and surface material, with a focus on the complex scattering geometry of the aircraft. The research evaluates the monostatic RCS case and examines the impact of attitude variations on RCS scintillation. Here, we ... Read More

Source

In the military field, studying the characteristics of radar cross section (RCS) of multi-rotor small UAVs is of great significance for UAV penetration and high-value target feature simulation. By studying the variation law of dynamic RCS of multi-rotor small UAV and combining deep learning technology, a dynamic RCS rapid estimation method based on Long Short-Term Memory (LSTM) is proposed, and its prediction effect is simulated and verified. This method can estimate the RCS of UAVs within a certain time range in the future during the flight of multi-rotor small UAVs, and provide data support for the optimal waveform design and target recognition of "low, slow and small" target detection, and then realize the accurate interception of multi-rotor small UAVs.

Source

Unmanned aerial vehicles (UAVs) are increasing in popularity in various sectors, simultaneously rasing the challenge of detecting those with low radar cross sections (RCS). This review paper aims to assess the current state-of-the-art in radar technology, focusing on multiple-input multiple-output (MIMO) and beamforming techniques, to address this growing concern. It explores the challenges associated with detecting UAVs in urban settings and adverse weather conditions, where traditional radar systems often do not succeed. This paper examines the existing literature and technological advancements to understand how these methodologies can significantly boost detection capabilities under the constraints of low RCS. In particular, MIMO technology, renowned for its spatial multiplexing, and beamforming, with its directional signal enhancement, are evaluated for their efficacy in the context of UAV surveillance and defense strategies. Ultimately, a comprehensive comparison is presented, drawing on a variety of studies to illustrate the combined potential of integrating these technologies,... Read More

Source

The purpose of this study is to analyze the variation of radar scattering cross-section (RCS) of UAVs, specifically focusing on the impact of propeller positions, polarizations, and frequencies. Models of UAVs with different propeller positions were constructed, and simulations were conducted using FEKO. Through the analysis of RCS, the following conclusions were drawn: Frequency has a significant impact on RCS, especially at 500MHz, and the trend of RCS increase and decrease of UAVs with different propeller positions remains stable. Changes in propeller positions and polarization directions lead to differences in RCS, and the relationship is nonlinear. The changes in RCS at 2GHz and 5GHz frequencies are more complex, but consistent trends can still be observed at specific locations and frequencies. The variations in maximum RCS and observation view are inconsistent, indicating that radar scattering behavior is affected by multiple factors. These results have important implications for the design and optimization of unmanned aerial systems and contribute to our understanding of elect... Read More

Source

This paper presents measurements of Radar Cross Section (RCS) of five Unmanned Aerial Vehicles (UAVs), comprising both consumer grade and professional small drones, collected in a semi-controlled environment as a function of azimuth aspect angle, polarization and frequency in the range 8.2-18 GHz.A first-order statistical analysis of the measured RCSs is firstly reported prior to assessing the radar detection performance on both measured and bespoke simulated data (leveraging the results of the developed statistical analysis), including, as benchmark terms, the curves for non-fluctuating and Rayleigh fluctuating targets.

Source

Purpose The purpose of his paper is to study the radar stealth performance of a Y-type quadrotor with coaxial rotors and parallel rotors. Design/methodology/approach This Y-type quadrotor is designed as an aerodynamic layout with parallel twin rotors at the front and coaxial twin rotors at the rear. The multi-rotor scattering (MRS) method based on multi-rotor dynamic simulation (MRDS) and electromagnetic scattering module (ESM) is presented. MRDS is used to simulate the complex rotation of parallel rotors and coaxial rotors. ESM is used to calculate the instantaneous radar cross-section (RCS) of the quadrotor. Findings For a single rotor, the minimum period of the RCS curve at a given azimuth is equal to the basic passage time of the blade, where increasing the speed can shorten this minimum period. When the elevation angle increases, the forward RCS fluctuation of the quadrotor increases, while the average RCS decreases. The change of the roll angle will affect both the mean and the maximum difference of the RCStime curve at the given lateral azimuth. The increase of the pitch angl... Read More

Source

Low observable techniques for stealth applications have become the need of the hour. RCS analysis for airborne platforms in military bands is the stringent requirement. Techniques such as shaping of aircrafts and use of absorbers suppresses radar echoes. This paper discusses about the use of special absorber techniques such as multi-layered Radar Absorbing Techniques with and without FSS to cater the reduction of echoes in the X-Band. The RCS analysis with and without absorber for Unmanned Combat Aerial Vehicle has been compared and analysed. The target tracking for the UCAV has also been covered in hostile environment condition using Altair Feko.

Source

This paper studies radar cross section (RCS) of small-target at low altitude and slow velocity. Choosing civil small multi-rotor unmanned aerial vehicle (UAV), research on its monostatic RCS simulation was carried out based on theory and commercial software. In the research, 10GHz, 30GHz and 60GHz electromagnetic waves were used to incident on 4-axis and 8-axis multi-rotor UAVs with different polarizations, and the model of blended wing body (BWB) and the model of all physical components as target were built. By choosing a simulation scheme based on combination of theoretical analysis and bottom algorithm of commercial software, the simulation results of monostatic co-polarization RCS were obtained.

Source

In order to study the optimal sweepback angle when a variant unmanned aerial vehicle (UAV) exhibits a low radar cross-section (RCS) indicator during phase flight, an auto sweep scheme based on electromagnetic scattering evaluation and an improved particle swarm optimization algorithm was presented in this article. An aircraft model with variable swept wings was built, and high-precision grids were used to discretize the target surface. The results showed that the optimal sweep angle did not change with the increase in the initial azimuth angle when the observation field was horizontal and the ending azimuth was 90. While the increase in the elevation angle affected the optimal sweepback angle of the aircraft under the given conditions, when the observation initial azimuth angle was 90, the auto sweep scheme could reduce the mean and some minima of the RCS indicator curve of the aircraft and could provide the aircraft with an optimal sweep angle under different observation conditions. The presented method was effective in learning the optimal sweep angle of the aircraft when low sca... Read More

Source

One platform that is currently highly developed as an air defense technology is the Unmanned Combat Aerial Vehicle (UCAV) which is a UAV system equipped with a weapon system or has combat capabilities. In this study, the UCAV concept was developed with the aim of having a stealth or low observability aspect by being shown to have a low Radar Cross Section (RCS) value. And in this paper the UCAV model developed is a generic UCAV configuration developed by the NATO STO/AVT-161 task group, namely SACCON UCAV. The SACCON UCAV is also goal-oriented typical of low observability with a combination of high agility and high Angle of Attack (AoA) capabilities. The results of the SACCON UCAV design were then analyzed by the RCS value using the SBR method using the Ansys HFSS software. And the results of the RCS calculation show that the SACCON UCAV model has a low RCS value and the RCS value can be reduced again by shaping the UCAV configuration.

Source

A new method is proposed to reduce the radar cross-section (RCS) by generalizing and combining phase cancellation and polarization conversion methods. In the proposed technique, similar to the polarization conversion method, only one unit-cell is used. The surface of the RCS reducer consists of arrays of this unit-cell in which each array is rotated 90 degrees relative to its side arrays. Unlike previous RCS reduction methods wherein the cells (in a periodic arrangement) either do not rotate the polarization of the reflected wave or rotate it 90 degrees, in the proposed generalized method, the unit-cells can rotate the polarization of the reflected wave arbitrarily. For this purpose, no symmetry is considered in the design of the unit-cell. The theory of the proposed RCS reduction method has been developed mathematically. Then, as a proof of concept, a unit-cell was designed using a pattern optimization method based on the pixelization of the cell's surface and applying a binary particle swarm optimization algorithm. The simulation results show that a 10-dB monostatic RCS reduction b... Read More

Source

This paper deals with Radar Cross Section (RCS) measurements of five small Unmanned Aerial Vehicles (UAVs) in a semi-controlled environment as a function of azimuth aspect angle, polarization, and frequency in the range 8.2-18 GHz. The experimental setup and the data pre-processing, which include coherent background subtraction, range gating procedures, and calibration, are presented. Then, a thorough statistical analysis of the measured RCSs is provided by means of the Cramrvon Mises (CVM) distance and the KolmogorovSmirnov (KS) test.

Source

The expediency of creating a passive multi-position radar based on a grouping of unmannedaerial vehicles is substantiated. The variant of building of such radar is proposed, the main technicalproblems of the sonar developing are evaluated and possible ways to overcome them areconsidered. It is shown that for detecting aerial targets and determining their coordinates fromthe radio emission of on-board equipment, the difference-rangefinder method is the most promisingas it does not depend on signal modulation and is potentially resistant to interference. Forsmall-sized UAV for transmitting information over open radio channels, the typical frequencyranges are 2.4 and 5.0 GHz. A block diagram of a passive multi-position radar has been developed,including digital shapers of the quadrature components of the received signal, blocks fordetecting and determining the coordinates of the target. The main parameters are calculated andanalytical expressions of digital signal processing algorithms for detecting and determining thecoordinates of the target are given. A stroboscopic effect is used in... Read More

Source

As Unmanned Aerial Vehicles (UAVs) have become widespread in defense industry, the radar technology that can detect them has also improved. These improvements cause UAVs to be detected more easily, which limits their effectiveness in military usage. Although the reduction of the radar cross-section (RCS) can provide a solution to this issue, the studies regarding that is insufficient in the literature. In this study, a shaping method is recommended to reduce the RCS of UAVs, and it is shown the method is effective to address the problem. Firstly, using a simulation tool, an UAV model is designed from simple shapes and the model is validated by comparing it with the ones in literature. Secondly, RCS values are measured using vertical and horizontal polarization throughout 360 degrees by incrementing the aspect angle by one degree in X-Band using the CST Studio Suite environment. Then, considering the hardware and aerodynamic requirements as well as limitations of the UAV model, a shaping technique is applied to the body, legs and the hollow parts of the UAV model with parametric simul... Read More

Source

In this study, detection of unmanned aerial vehicles (UAV), determination of radar cross-section (RCS) values, and range estimation were performed using a commercial off-the-shelf (COTS) millimeter-wave Frequency Modulated Continuous Wave (mmWave FMCW) radar system in the 77-81 GHz frequency band. The measurements were carried out in a laboratory environment using a single transceiver antenna without the need for an anechoic chamber. RCS values of different vertically and horizontally positioned UAVs were measured experimentally along the 360^o aspect angle, and the simulated results obtained from computational tool were compared with the experimental results. The measurement and simulation results, together with the range estimation, matched with high accuracy.

Source

The radar cross section (RCS) of an object is reduced by using an active cancellation strategy, with a microstrip patch antenna used to radiate a cancelling signal. By using a square patch with two feeds, it is possible to eliminate the scattering from the object for an incident wave of arbitrary polarization, for a given frequency and fixed angle of incidence.

Source

To take benefit from the wide bandwidth operation of the ridged horn antennas and to overcome its limitation of wider beamwidth performance at low frequencies, we propose two techniques that are used to reduce the H-plane beamwidth of the ridged horn antenna from 2 GHz to 12 GHz. For Unmanned Aerial Vehicles (UAVs) based in-situ characterization and measurement of radars, it is usually desired that the probe has narrow beamwidth as well as overall symmetric radiation patterns so that the antenna performance is not degraded due to the back-scattering from the drone structure. This is verified from the measured results that at low frequencies, when the beamwidth is wider, the fields strongly interact with the drone platform thus induces ripples in the co-polar patterns and also increases the cross-polarization levels, especially in the H-plane. To overcome this limitation, two techniques are discussed in this work. The first technique involves the integration of a wideband multi-layer dielectric lens structure with a ridged horn antenna. In the second technique, corrugations are introd... Read More

Source

Abstract In this study, spatial separation of the radar transmitter and receiver units is considered, as a means of reducing the masking effect in noise radars. A bistatic radar system is constructed, with emphasis on a lightweight transmitter unit that can be mounted on a commercial Unmanned Aerial Vehicle (UAV). The system uses pseudorandom noise, generated digitally at the receiver and transmitter units. Correlation losses, due to nonlinearities in the transmitter and receiver units, are measured to 0.1 dB. This study shows that by separating the transmitter and receiver unit the masking effect is significantly reduced, compared to a monostatic setup. This reduction is enough for the system to detect a slow flying UAV. Thus, bistatic separation should be considered as a practical tool to reduce the masking effect. By processing clutter with an extended CLEAN algorithm, the correlation noise floor is further suppressed.

Source

This article presents measurements of radar cross section (RCS) of five unmanned aerial vehicles (UAVs), comprising both consumer grade and professional small drones, collected in a semicontrolled environment as a function of azimuth aspect angle, polarization, and frequency in the range 8.218 GHz. The experimental setup and the data preprocessing, which include coherent background subtraction and range gating procedures, are illustrated in detail. Furthermore, a thorough description of the calibration process, which is based on the substitution method, is discussed. Then, a first-order statistical analysis of the measured RCSs is provided by means of the Cramr-von Mises (CVM) distance and the KolmogorovSmirnov (KS) test. Finally, radar detection performance is assessed on both measured and bespoke simulated data (leveraging the results of the developed statistical analysis), including, as benchmark terms, the curves for nonfluctuating, and Rayleigh fluctuating targets.

Source

The continuous improvement and development of military application devices have led to the analysis of their stealth characteristics. The Radar Cross Section (RCS) is the calculation of a target reflective power. The reduction of the RCS of military aircraft allows its late detection to capitalize on elements of security. The RCS of a military vehicle has thus become an extremely significant design element for security, effort and survival. Accurate RCS estimation and RCS reduction are therefore extremely essential for such type of vehicle. Numerous factors affect RCS, such as the target's form, orientation, operating frequency, aspect angle, the medium's permittivity and permeability, and the pulse's transmitted power. This paper aims to provide an overview of the theoretical history and engineering approach to the RCS estimation and reductions for such applications.

Source

In the paper, radar cross section (RCS) reduction method for slot-loaded UAV based on characteristic mode theory (CMT) is proposed. Firstly, the strong characteristic current distribution positions of UAVs in different modes are obtained through characteristic mode analysis (CMA). Then, the slot-loaded technology is carried out on the overlapping position to achieve the purpose of RCS reduction of UAV. The experimental results show that RCS is reduced in different incident directions of plane waves. UAV can achieve RCS reduction with the peak of 8dBsm within 2~3 GHz. The proposed method can provide a new design idea for stealth technology of UAV.

Source

Quadcopter is very popular as a consumer electronics, but recently it is also being used on military purpose. To the defence side, detecting the quadcopter is a first priority, and to the offense side, reducing its detectability is important, and both are related to its radar cross section (RCS). We simulate the RCS of a typical quadcopter using the multi-level fast multi-pole method (MLFMM), and then try to reduce its radar cross section by modifying its external shape into a disk type. The results indicate such modification indeed can reduce its RCS to -10 dBsm when the radar wave is incident at horizontal direction, but less effective at other radar wave incident direction.

Source

Small Unmanned Aerial Vehicles (UAV) have evolved from an entertainment 3C product into a real military application recently. Because of their relative low cost compared to traditional military aerial vehicles, they are used to cause destruction in battle fields and civilian infrastructure facilities, and the defense against UAV attracts more studies. In this article we use Ray-Launching Geometrical-Optics (RL-GO) algorithm to simulate the monostatic radar cross section (RCS) of a typical quadcopter in 3, 10, and 28 GHz at $\theta = 105^{\circ}$ and 135 radar wave incidence angles. We found their RCS is indeed closed to the generally accepted RF stealth level of 20 dBsm, and are generally higher as frequency increases, but not in a significant way. As the radar transmitter output power usually decrease at 28 GHz, this means more transmitters are needed to increase the detection possibility at 28 GHz.

Source

Scattering center is one of the key contents in the study on electromagnetic scattering of radar targets, while it is based on the rapid calculation of radar cross section (RCS). Characteristic mode (CM) method expands the surface current on the target with a set of CMs as the global basis functions. It can reduce the unknowns in the method of moments (MoM) and speed up the iteration process. Combining the broadband CM method and with the monostatic/bistatic approximation method, the monostatic RCS can be calculated approximately by the bistatic RCS in the vicinity of incident angle, which decreases the angle to be simulated in the angle sweeping process. Thus, the time consumption of the iterations and angle sweeping process can be greatly reduced. At the same time, the scattering center can also be extracted accurately and quickly. Numerical results are presented to demonstrate the accuracy and efficiency of this method.

Source

It is difficult to achieve the effect of raid target because of the large Radar Cross Section (RCS) of Unmanned Aerial Vehicle (UAV) group when carrying out military missions. This paper proposes a method to reduce RCS of UAV linear array. Based on the principle of array scattering pattern synthesis, this paper calculates the RCS of a linear array UAV group and optimizes the posture of the UAV through a multi-objective evolutionary algorithm so that the RCS of the UAV group is significantly reduced within the viewing angle. The simulation results show that the reasonable arrangement of UAVs significantly reduces the RCS of the group within the specified viewing angle range.

Source

Chapter Contents: 9.1 Introduction 9.2 Review of UAV and bird radar signatures research 9.3 Target motion models 9.4 Fully polarimetric, multiple observation angle laboratory measurements of UAV target 9.5 Bistatic and multistatic radars used to gather bird and drone data 9.5.1 NetRAD 9.5.2 NeXtRAD 9.6 NetRAD bird and drone S-band measurements 9.7 NetRAD drone payload experiments 9.8 NeXtRAD L- and X-band drone and birds measurements 9.8.1 Drone filtering 9.9 Concluding remarks Acknowledgements References

Source

Abstract An analytical method for electromagnetic scattering characteristics of complex unmanned aerial vehicle targets by using hybrid multilevel fast multipole algorithm (MLFMA)-physical optics (PO) and short-time fourier transformation (STFT) is proposed in this paper. By constructing accurate electromagnetic models of unmanned aerial vehicle (UAV) target with inlet, the aspect and polarization characteristics of radar cross section (RCS) and time-frequency representation (TFR) are studied. To validate the influence of the inlet, the monostatic and bistatic RCS at specific angles, RCS statistical characteristics and TFR correlation are simulated and compared. It is concluded that the inlet should be sufficiently considered to calculate the accurate scattering characteristics.

Source

With the increase in small unmanned aerial vehicle (UAV) applications in several technology areas, detection and small UAVs classification have become of interest. To cope with small radar cross-sections (RCSs), slow-flying speeds, and low flying altitudes, the micro-Doppler signature provides some of the most distinctive information to identify and classify targets in many radar systems. In this paper, we introduce an effective model for the micro-Doppler effect that is suitable for frequency-modulated continuous-wave (FMCW) radar applications, and exploit it to investigate UAV signatures. The latter depends on the number of UAV motors, which are considered vibrational sources, and their rotation speed. To demonstrate the reliability of the proposed model, it is used to build simulated FMCW radar images, which are compared with experimental data acquired by a 77 GHz FMCW multiple-input multiple-output (MIMO) cost-effective automotive radar platform. The experimental results confirm the models ability to estimate the class of the UAV, namely its number of motors, in different operat... Read More

Source

An efficient electromagnetic (EM) optimization technique for radar cross section (RCS) reduction is proposed to achieve stealth. At first, two optimization models, namely coarse and fine models, are constructed to describe the scattering problem. More specifically, the coarse model of shooting and bouncing ray (SBR) method provides worse accuracy results than the fine model of the method of moment (MoM). However, less computational resources are needed for the coarse model when compared with the fine model. Then the SBR method is implemented into the Hummingbird optimization algorithm to obtain the solution of the coarse model. Third, the solution of the coarse model is verified for the fine model by using the MoM. Noted that the impedance boundary condition is applied to accelerate the calculation. At last, the trust region aggressive space-mapping (TRASM) algorithm is used to find the optimal solution between the SBR and MoM methods. By building the mapping relationship between these two models, the optimization efficiency can be significantly improved with high accuracy. Numerical... Read More

Source

In this study, a quantitative radar cross section (RCS) analysis of different unmanned aerial vehicle (UAV) models were accomplished by means of a series of RCS simulations. The simulations were carried out by high-frequency RCS simulation and analysis tool called PREDICS. To quantify the RCS features of the UAV model, both the anglevariation and frequency-variation simulations for all polarization excitations were performed. The results of the simulations suggested that RCS values were dramatically varying with respect to look angle with some special angles providing the large values of RCS. Generally, the RCS values of the UAV model was increasing with frequency as expected. A quantitative radar detection range analyses were also accomplished to assess the visibility of both the military-type and civil-type UAV models. The outcome of these studies has suggested that large-size UAV model can be easily detected by a high-sensitive radar on the ranges of tens of kilometers while these numbers reduce to a few kilometers for a civilian UAV model that is much smaller than the its militar... Read More

Source

This paper studies the monostatic radar cross section (RCS) simulation of a popular Unmanned Aerial Vehicle (UAV), DJI Phantom 2 Vision Plus in UHF band. The RCS () is evaluated when the plane wave is horizontally and vertically polarized. First, for a constant ( = 90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"></sup> ) and a varying (0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"></sup> 90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"></sup> ), the results show that hh is higher than the other polarizations, its highest value is found when = 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"></sup> or = 90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"></sup> , meaning when the excitation is in front of the center of the blades. Second, for constant ( = 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="ht... Read More

Source

This article presents a radar cross section (RCS) reduction method using antennas with circulators and phase shifters. In this method, an antenna connected to a circulator with a phase shifter and an amplifier in its circulation path is utilized, and the amplitude and phase of the antenna mode scattered field, which is the reradiated field of the antenna, are controlled to cancel out the structural mode scattered field. This article proposes array RCS synthesis methods for antenna RCS minimization and for broadening RCS reduction bandwidth and angular range. In addition, a measurement method to determine the amplitude and phase of the antenna mode of each antenna element and the structural mode of the array is proposed for deterministic RCS reduction. The effectiveness of the proposed method is confirmed experimentally in a monostatic case using an eight-element array antenna with circulators and digital phase shifters.

Source

The radar cross section (RCS) of sea-skimming unmanned aerial vehicle (UAV) can be influenced by the sea surface scattering under different sea conditions. In this paper, a composite model of the rough sea surface and sea-skimming UAV is established. A hybrid algorithm based on the application of physical optics (PO) method and improved multilevel fast multipole algorithm (PO-IMLFMA) for solving the RCS of the composite model based on four-path model (FPM) is proposed. Compared with multilevel fast multipole algorithm (IMLFMA) and PO and method of moment (PO-MOM), PO-IMLFMA has the advantages of less memory consumption (about 295 MB) and faster solution speed (about 768 s) for solving the composite model. Furthermore, in view of the influence of sea surface on the RCS of sea-skimming UAV, a compensation scheme based on back propagation (BP) neural network for the RCS of UAV is proposed. The compensation scheme is analyzed for the monostatic RCS of sea-skimming UAV under different sea conditions. The compensation results show that the compensation errors under 1-scale, 3-scale and 5-s... Read More

Source