Radar Cross Section Reduction for Stealth UAV's

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

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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.

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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

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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

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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.

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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

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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.

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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.

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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

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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.

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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

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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.

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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

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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

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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.

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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.

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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

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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.

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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.

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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.

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