High Radar Cross Section Research Articles

An online frequency allocation strategy for multi‐carrier radar against spot jammer

AbstractSpot jamming poses a significant threat to radar detection due to its ability to rapidly intercept radar signals and emit high‐power interference. A novel Cognitive Multi‐Carrier Radar (CMCR) is proposed, which utilises a detection waveform comprising multiple narrow bands to reduce the disruption from the spot jammer. Additionally, it can analyse the target’s Radar Cross‐Section (RCS) characteristics and proactively select frequencies with high RCS for detection, thereby enhancing target detection capability. The online frequency allocation problem of CMCR is a Multi‐Armed Bandit (MAB) problem with a combinatorial action space. To tackle the challenge from the huge action space, an efficient aDaptive Accept Reject (DART) method is employed, which significantly reduces the regret of CMCR in the detection task. Moreover, a slide‐window change point indicator is proposed to monitor the change of target’s RCS, which enables CMCR to be applicable in scenarios where target’s RCS varies. Finally, the effectiveness and robustness of CMCR are through extensive numerical experiments.

Enhancement of Small Ship Detection Using Polarimetric Combination from Sentinel−1 Imagery

Speckle noise and the spatial resolution of the Sentinel−1 Synthetic Aperture Radar (SAR) image can cause significant difficulties in the detection of small objects, such as small ships. Therefore, in this study, the Polarimetric Combination-based Ship Detection (PCSD) approach is proposed for enhancing small ship detection performance, which combines three different characteristics of polarization: newVH, enhanced VH, and enhanced VV. Employing the Radar Cross Section (RCS) value in three stages, the newVH was utilized to detect Automatic Identification System (AIS) -ships and small ships. In the first step, the adaptive threshold (AT) method was applied to newVH with a high RCS condition (>−10.36 (dB)) for detecting AIS-ships. Secondly, the first small ship target was detected with the maximum suppression of false alarms by using the AT with a middle RCS condition (>−16.98 (dB)). In the third step, a candidate group was identified by applying a condition to the RCS values (>−23.01 (dB)), where both small ships and speckle noise were present simultaneously. Subsequently, the enhanced VH and VV polarizations were employed, and an optimized threshold value was selected for each polarization to detect the second small ship while eliminating noise pixels. Finally, the results were evaluated using the AIS and small fishing vessel tracking system (V-Pass) based on the detected ship positions and ship lengths. The average matching results from 26 scenes in 2022 indicated a matching rate of over 86.67% for AIS-ships. Regarding small ships, the detection performance of PCSD was 42.27%, which was over twice as accurate as the previous Constant False Alarm Rate (CFAR) ship detection model. As a result, PCSD enhanced the detection rate of small ships while maintaining the capacity for detecting AIS-equipped ships.

Dual Resonance Behavior and Enhanced Microwave Absorption Performance of Fe3O4@C@MoS2 Composites with Shape Magnetic Anisotropy.

Ternary hierarchical Fe3O4@C@MoS2 composites and binary hierarchical Fe3O4@C composites were successfully fabricated by a modified mixed solvothermal method, a self-oxidation polymerization method, and a hydrothermal process. Their magnetic properties and microwave absorption performance were investigated. Dual resonance behavior was observed in the Fe3O4@C@MoS2 composites. One of the resonances was attributed to natural resonance with a resonance frequency of 2.58 GHz, which was much higher than that for Fe3O4 bulk (1.5 GHz). The other originated from the superparamagnetic/ferromagnetic relaxation with a resonance frequency of 12.45 GHz. The minimum reflection loss (RLmin) reached -64.30 dB with a matched thickness of 2.24 mm at 11.64 GHz, and the maximum effective absorption bandwidth (EABmax) covered 6.39 GHz with a matched thickness of 1.89 mm. In addition, the maximum Radar cross section (RCS) reduction value reached 31.90 dB m2 at a scattering angle of 0°. Electron holography analysis confirmed a dense magnetic absorption network in the Fe3O4@C@MoS2 composites. The boost in microwave absorption performance was caused by the synergistic effects of magnetic and dielectric properties owing to the ternary hierarchical structure, shape magnetic anisotropy, and incorporation of 1T/2H MoS2. Besides, the binary hierarchical Fe3O4@C composites also exhibited good absorbing performance caused by natural resonance, with an RLmin of -52.90 dB at 5.80 mm, an EABmax of 5.98 GHz at 3.38 mm, and a relatively high RCS reduction value of 13.04 dB m2 at θ = 20°. This work paves the way for designing multicomponent hierarchical absorbers with broadband and intensive microwave absorption.

Dynamic radar jamming metasurface with amplitude and phase modulation

In this paper, a one-bit coding metasurface comprised of 20 columns is proposed to achieve amplitude and phase modulation. Each column is dynamically controlled by p-i-n diodes to modulate the incident electromagnetic waves. By synthesizing the code sequence, the radar cross section (RCS) of the surface can be reduced to specific values. With shift coding and inverse code sequence, the metasurface can also achieve phase modulation function with almost the same amplitude responses. A metasurface prototype is fabricated and measured, showing an obvious RCS reduction in a 35.2% bandwidth from 7 to 10 GHz. Specifically, a high RCS reduction of 23 dB can be achieved at 8.5 GHz. In addition, the metasurface exhibits the capability of phase modulation with responses of and , while the amplitude responses are almost the same. Overall, the proposed dynamic metasurface is useful for radar jamming, which is expected to further improve the stealth performance of the target.

Toward improved urban flood detection using Sentinel-1: dependence of the ratio of post- to preflood double scattering cross sections on building orientation

High-resolution synthetic aperture radar (SAR) sensors are now commonly used for flood detection. Automated detection tends to be limited to rural areas owing to the complicated backscattering mechanisms occurring in urban areas. Flooding can be identified in urban areas by searching for increased SAR backscatter in a postflood image due to double scattering between water and adjacent buildings, compared with a preflood image where double scattering is between unflooded ground and buildings. For co-polarized data, if φ is the angle between the building wall and the satellite direction of travel, double scattering is strongest for φ = 0 deg and falls off as φ increases. Theoretical studies estimating the ratio of flooded-to-unflooded double scatterer (DS) radar cross section (RCS) using X-band SAR data, found that the ratio was high at φ = 0 deg but only small at φ > 10 deg. Ostensibly, this implies that few DSs might be detected in an urban area. However, experiments on real images have called into question the veracity of the modeling. We describe an empirical study to examine the relationship between the flooded-to-unflooded DS RCS ratio and φ in Sentinel-1 (S-1) C-band data. We use high-resolution light detection and ranging and aerial photographs so that φ can be measured accurately and is based on S-1 images from flood events that occurred in the United Kingdom during the storms of winter 2019 to 2020. Results indicate that vertical–vertical polarization is better than vertical–horizontal at distinguishing flooded from unflooded DS; that the theoretical model used underestimates the number of DS with high RCS ratios in the φ range 10 deg to 30 deg; and that sufficient DS ground heights can be determined to estimate an accurate local average flood level, although in high density housing there are less of these due to the presence of adjacent buildings.

Illuminator scheduling method for passive radar sea surface target detection based on RCS characteristic

ABSTRACT In order to improve the signal-to-clutter-noise ratio (SCNR) of received signal, this letter studies the illuminator scheduling problem in the detection process with the aim of maximizing SCNR time series. In order to use the illuminator with long detection time as much as possible and get high SCNR in the detection process, we propose a neighbourhood search illuminator scheduling method. Firstly, we study the characteristics of radar cross-sections (RCS) of target and sea surface under different incident directions and polarizations, and analyse the regions of high target RCS and low sea surface RCS. Then the coordinate transformation method is used to get the scheduling sequence within the detection range. Based on the global scheduling sequence, the neighbouring frames are searched to obtain the illuminator sequence of the randomly appearing target. Simulation results show that the proposed method can effectively improve the received signal SCNR 15 dB on average.

Metasurface Radome to Achieve a Wideband High Gain, Low RCS, and Low SLL Antenna

A Phase- and amplitude-adjustable metasurface radome (PAMR) is proposed to achieve a wideband high gain and low radar cross-section (RCS) antenna with arbitrary sidelobe levels (AS-PGMA) at a 9.8 GHz operating frequency. The proposed PAMR is a special multilayer phase gradient metasurface lens whose amplitude distribution is modified based on the Dolph-Tschebyscheff technique. The AS-PGMA simulation results indicate that a high gain, low RCS, and low sidelobe level (SLL) antenna can be achieved over a broad impedance frequency bandwidth of 9.25–10.1 GHz with in-band average values of 17 dB, −7.5dBsm, −20 dB/−27 dB for gain, RCS, and E-/H-plane SLL, which are measured at 9.8 GHz as 17.4 dB, −9dBsm, and −23.02 dB/−27.91 dB, respectively. Additionally, a novel analytical method for calculating the RCS of the proposed PAMR and AS-PGMA is described and verified by measurement and simulation findings. Measurement results show that the E-/H-plane SLL of the AS-PGMA is improved by 12.2 dB/5.1 dB at the operating frequency, respectively, while its gain and RCS reduction are reduced by 1.6 and 2.1 dB, respectively. Moreover, RCS of the AS-PGMA is reduced over an ultrawide bandwidth of 1–20 GHz for orthogonal polarizations. The analysis, simulations, and measurements are all in good agreement.

High capacity chipless RFID tags for biomass tracking application

AbstractThe design of a low-cost, flexible, miniaturized, and a high code density chipless radio-frequency identification (RFID) tag is presented as a solution for tracking the transportation of biomass fuel pellets. The performance of the tag is presented and demonstrates the applicability of the design for different material systems, while maintaining a compact size of 5.06 cm2. The tag consists of nested concentric hexagonal elements and a central spiral resonator suitable for ID encoding. The tag presented demonstrates code density of 3.6-bits/cm2, possesses angular stability up to 60°, and high radar cross section (RCS). The tag performance was also observed for tracking 5 kg of fly-ash biomass. Additionally, as the tag mass mostly consists of FR4, PET, or Taconic TLX-0 with a minute mass of either copper, gold, or silver, the tag can be easily combusted and disposed of during biomass combustion. The novel features of this tag are the combination of hexagonal and spiral shape slots for maximum space utilization thereby achieving high RCS signatures along with high code density. All these properties of the proposed chipless RFID tag provide a pioneering pathway for a real-time biomass tracking application.

Fe nanoparticles decorated in residual carbon from coal gasification fine slag as an ultra-thin wideband microwave absorber

Microwave absorbing materials are widely used in the defense and telecommunications industries, as means for enhancing battlefield penetration rate and improving the protection of precision instruments. The magnetic-dielectric Fe@ residual carbon from coal gasification fine slag (Fe@RC) nanocomposites were fabricated via a chemical coprecipitation and thermal annealing method, in which involve a reduction process from the Fe3O4 to Fe metal. The structure, morphology, compositions and electromagnetic parameters of the as-prepared Fe@RC materials were characterized. The obtained nano-micro scale Fe@RC shown adjusting electromagnetic parameters and outstanding microwave absorbability. The optimized reflection loss value of −47.1 dB was attained at 5.5 GHz for Fe@RC, and the effective bandwidth is 5.3 GHz (12.4–17.7 GHz) at a matching thickness of 1.5 mm. Benefit from good impedance match, special space architecture and synergistic effect between the dielectric loss from RC component and magnetic loss from Fe component, this Fe@RC materials are expected to be a potential microwave absorber. The simulated radar cross section (RCS) results prove that the Fe@RC can efficaciously reduce the microwave scatterings of the perfect electric conductor substrate at different degrees in C-, X-, and Ku-bands via adjusting the Fe@RC coating thickness. The low-cost carbon-based magnetic nanocomposites display an ultra-thin wideband microwave absorption ability and high RCS reduction performance, promoting resource utilization of the RC from coal gasification fine slag.

A low-profile FSS-based high capacity chipless RFID tag for sensing and encoding applications

AbstractThis paper presents a polarization-independent 11-bit chipless RFID tag based on frequency-selective surface which has been designed for encoding and relative humidity (RH) sensing applications. The 10 exterior U-shaped resonators are used for item encoding whereas Kapton has been incorporated with the interior resonator for RH sensing. This radio-frequency identification (RFID) tag operates in S- and C-frequency bands. The proposed design offers enhanced fractional bandwidth up to 88% with the density of 4.46 bits/cm2. Both single- and dual-layer tags have been investigated. The simulated results are in good agreement with measured results and a comparison with existing literature is presented to show the performance. Simple geometry, high code density, large frequency signature bandwidth, high magnitude bit, high radar cross-section, and angular stability for more than 75° are the unique outcomes of the proposed design. In addition, RH sensing has been achieved by integrating the Kapton on the same RFID tag.

Dual wideband, polarization, angle-insensitive diffusion electromagnetic surfaces for radar cross section reduction

In this paper, we introduce an effective technique for designing diffusion electromagnetic (EM) surfaces with polarization and angle-insensitive characteristics over multiple wide bands. The proposed EM surface consists of a random pixelated metal structure in the middle of double substrate layers and a metallic ground at the bottom. Phase cancellation for radar cross section (RCS) reduction is achieved by different propagation paths generated by the pixelated metallic layer. The theoretical prediction of the reduction frequency band and reduction value is derived by transmission line theory, which serves as guidance to design the EM surface for the required operating band. Using this technique, an EM surface is designed for 10 dB RCS reduction over multiple frequency bands, and the first two reduction bands are 5.98–16.23 GHz and 26.69–37.1 GHz with fractional bandwidths of 92.3% and 32.6%, respectively. The non-reduction frequency band between the first two reduction bands is almost at the K-band (18–27 GHz), which is unusable for long-range transmission because of its high atmospheric loss. Moreover, the bandwidth of RCS reduction bands is stable for oblique incident angles up to 40° for both TE and TM polarizations. Based on theoretical study and simulation results, a prototype of this EM surface is fabricated and experimentally characterized. The theoretical analysis, simulation and experiment results are in good agreement. The proposed method comprehensively solves the problems of narrow bandwidth, time-consuming optimization of the unit cell, high bistatic RCS value, and sensitivity to polarization and incident angles found in recent RCS reduction research.

Chipless RFID Tag With Enhanced RCS Used as a Phthalocyanine-Based Solvent Vapors Sensor

A novel uniplanar chipless RFID solvent vapors/gas sensor is proposed in this letter. The sensor etched on an extremely thin capton substrate is composed of the folded dipole resonator loaded by the interdigital capacitor located inside the planar rectangular metallic loop that improves the radar cross section (RCS) response. When illuminated by a plane wave, the folded dipole causes a notch in the RCS response of the loop located near its resonant frequency. The high RCS level (-18 dBsm), together with the notch depth (16 dB) assure a reliable detection of its position within the frequency dependence of RCS curve. In order to enhance the structure sensitivity to the presence of acetone vapors, the tetrasulfonated copper phthalocyanine thin film was applied as a sensitive layer during the process of folded dipole metallization. The experimental verification confirmed the viability of sensor proof-of-concept for the detection of chemical vapors.

Frequency-Coded mm-Wave Tags for Self-Localization System Using Dielectric Resonators

The paper describes the development of passive, chipless tags for a novel indoor self-localization system operating at high mm-wave frequencies. One tag concept is based on the low-Q fundamental mode of dielectric resonators (DR) which exhibits peak scattering at its resonance frequency. As the radar cross-section (RCS) of DRs at mm-wave frequencies is far too low for the intended application, arrays of DRs and combinations with dielectric lens and corner reflectors are investigated to boost the RCS while keeping the scattering retro-directive over wide-angle incidence. Satisfactory results are demonstrated experimentally in W-band with metal corner reflectors combined with planar arrays of DRs; the tags produce a high RCS level over a moderately broad angular range and a wide frequency range where they exhibit a notch at the resonance frequency of the dielectric resonators. These designs suffer from low coding range of 3 to 6 bit, degradations of RCS in angular range, and a difficult separation of the tag response from strong clutter. Both the suppression of large clutter interference by using time gating of the tag response and a larger coding range are promised by a chipless tag concept based on multiple high-Q resonators in photonic crystal (PhC) technology. Experimental samples are characterized as transmission resonators and as retro-directive tags at the 230 GHz band. As a concept to boost the retro-directive RCS with a truly wide-angle response, the integration of PhC resonators with a Luneburg lens is discussed.

Frequency Selective Surface Coded Retroreflectors for Chipless Indoor Localization Tag Landmarks

This letter presents the integration of frequency selective surfaces (FSSs) with retroreflectors for the realization of chipless wireless indoor localization tag landmarks. As an example, the high radar cross section (RCS) of a trihedral corner reflector is signed with an FSS-based stopband filter, so that the backscattered power from several corner reflectors can be distinguished by a mobile reader according to the frequency response of the FSS. Measurement results with a 3 × 3 × 3 cm3 trihedral corner reflector and a stopband FSS in a Rogers RT/Duroid 5880 high-frequency laminate at 90 GHz shows an RCS above $-$ 25 dBsqm for 90° coverage in the TM plane. Due to the high RCS, measurements at distances up to 4 m with a standard 25 dBi gain horn antenna and a vector network analyzer as a reader are shown. These preliminary results show the potential of the concept for applications such as indoor localization with sub-mm accuracy, where high bandwidths, but only a low number of bits, are needed for the identification of the tag landmarks.

Gradient-Index-Based Frequency-Coded Retroreflective Lenses for mm-Wave Indoor Localization

This article introduces retroreflective lenses for millimeter-wave radio-frequency indoor localization. A three-dimensional (3D) gradient-index Luneburg lens is employed to increase radar cross section (RCS) of photonic-crystal high-Q resonators and its performance is compared to conventional radar retroreflectors. A classic Luneburg lens with and without a reflective layer is realized with 25 mm diameter ( $6.7~\lambda _{0}$ ), showing a realized gain of 24.6 dBi and a maximum RCS of −9.22 dBm2 at 80 GHz. The proposed Luneburg lens with embedded high-Q resonators as frequency-coded particles in a photonic crystal structure, operating as a reflective layer, achieved a maximum RCS of −15.84 dBm2 at the resonant frequency of 76.5 GHz and showed a repeatable response each 18° over ±36° in two perpendicular planes. With this high RCS of the Luneburg lens, a maximum readout range of 1.3 m could be achieved compared to 0.15 m without the lens at 76.5 GHz for the same transmit power, receiver sensitivity, and gain of the reader antenna.

RCS Reduction Based on Concave/Convex-Chessboard Random Parabolic-Phased Metasurface

A hybrid design method for broadband radar cross section (RCS) reduction based on reflection diffusion is proposed and successfully demonstrated. To this end, we first analyze the scattering behavior of full parabolic-phased metasurface and find out its weaknesses in achieving perfect diffusive patterns. Then, we alleviate the issue of full parabolic-phased method through hybridizing two strategies, i.e., concave/convex chessboard arrangement and random focal lengths. The proposed hybrid design makes the phase profile aperiodic without any mirror symmetry, which is the key for achieving perfect diffusive scattering behavior within a wide operation band. The numerical and experimental results show that our proposed design features broadband, polarization insensitivity, and wide incidence angle and can efficiently decrease the RCS more than 10 dB within 7.8–23.2 GHz. Our approach comprehensively solves the issues of narrow band, high bistatic RCS value, time-consuming optimization process, and sensitivity to different polarization and incident angles, promising great potential in stealth applications.

Electromagnetic Signature of a Quadcopter Drone and Its Relationship With Coupling Mechanisms

This paper presents an investigation of the electromagnetic signature and the coupling mechanism of quadcopter drones with incident electromagnetic (EM) wave and radar cross section (RCS) analysis. Coupling analysis is performed based on the dominant coupling path: when an incident EM wave with a magnitude of 50 kV/m contacts a commercial quadcopter drone, its motor power wires are identified as the dominant coupling path. Higher coupling voltages are obtained for frequencies that have large impedance values at both ends of the load on the motor power wire. This induced voltage can affect the integrated circuit chip on a printed circuit board, as well as parallel plate resonances. Furthermore, the RCS of a quadcopter drone is measured in the frequency range of 0.5-3 GHz. The internal-component vulnerability characteristics of quadcopters can spike at specific frequencies with high RCS values and can be analyzed with or without motor power wires. We verified these hypotheses via 2D inverse synthetic aperture radar images, and we analyzed the results by comparing the empirical and full-wave simulation values.

Accurate Analysis of Target Characteristic in Bistatic SAR Images: A Dihedral Corner Reflectors Case.

The dihedral corner reflectors are the basic geometric structure of many targets and are the main contributions of radar cross section (RCS) in the synthetic aperture radar (SAR) images. In stealth technologies, the elaborate design of the dihedral corners with different opening angles is a useful approach to reduce the high RCS generated by multiple reflections. As bistatic synthetic aperture sensors have flexible geometric configurations and are sensitive to the dihedral corners with different opening angles, they specially fit for the stealth target detections. In this paper, the scattering characteristic of dihedral corner reflectors is accurately analyzed in bistatic synthetic aperture images. The variation of RCS with the changing opening angle is formulated and the method to design a proper bistatic radar for maximizing the detection capability is provided. Both the results of the theoretical analysis and the experiments show the bistatic SAR could detect the dihedral corners, under a certain bistatic angle which is related to the geometry of target structures.

Preliminary Research of Low-RCS Moving Target Detection Based on Ka-Band Video SAR

Conventional synthetic aperture radar (SAR) ground moving target detection is only effective for targets with high radar cross section (RCS), and its performance is degraded by focusing distortion caused by the motion of the target. This letter proposes a new low-RCS moving target detection method which exploits the target’s shadow using high-resolution sequential images captured by a Ka-band video SAR system. First, the characteristics of target shadow are investigated, which are mainly influenced by the size of the target, the incidence of the radar beam, and the target velocity. Then the presented method based on video SAR system is described, and its moving target detection performance is also analyzed. As a preliminary study, a simulated experiment is conducted in which the signal of a low-RCS moving target is simulated and inserted into real airborne Ka-band video SAR images. The results demonstrate the feasibility of the proposed method for low-RCS moving target detection.

A Compact Dual-Polarized Chipless RFID Tag by Using Nested Concentric Square Loops

This letter presents a compact dual-polarized chipless tag. The chipless tag consists of nested concentric coplanar square loops, and adjacent loops are connected by two stub lines at the center of the opposite sides, respectively. There are two critical factors in achieving small size. One is due to the integration of multiple square loops in a nested structure, sharing the same sides. The structure is designed to obtain the following function relationship between the loop number $n$ and resonant mode number $N: N\,= \,2(n- 1)$ . The other critical factor for minimization is that it is the coupling of adjacent loops that responds to resonances. The gap size only influences the coupling strength, and shifts resonance frequency a little, and does not influence the sharp-edged resonance in spite of small gap. This is one highlight. The other highlight is that four variations can be independently adjusted on the basis of the proposed reference tag, and a lot of different encoding identifications can be obtained. In addition, the proposed tag also has the following advantages. The proposed tag is magnetic, and the radar cross section (RCS) magnitude is insensitive to the medium where it is pasted. High RCS magnitude is realized at the condition of minimization. The connected coplanar square loop resonators are reused in both vertical and horizontal polarizations to double the encoding capacity within a fixed bandwidth. The RCS curve keeps unchanged until the orientation angle rotates up to 35°. An 18-bit tag is developed by the proposed nested loops, and ${\text{19bits/cm}}^{2}$ data density is obtained.