Radar Cross Section Levels Research Articles

Facilitating learning adaptive V-tail of a supersonic missile for radar cross-section reduction during interval flight

To study the V-tail inclination of a supersonic missile that meet the requirements of low electromagnetic scattering characteristics in interval flight, an automatic tilt scheme is presented. The improved annealing algorithm is used to determine the optimal solution of the V-tail tilt angle, where multiple scattering of the physical optics plus physical theory of diffraction is used to calculate the radar cross section (RCS) of the target. The results show that the optimal solutions of V-tail inclination are different in various flight intervals of the horizontal observation field. In the forward side flight interval, changing the initial azimuth has less influence on the optimal solution of V-tail tilt angle, while more influence on the missile RCS indicator. In the side tail flight interval, the RCS level of the missile is low, and there is an optimal solution and a few feasible solutions for the V-tail inclination. The feasible solution of V-tail tilt angle in the lateral flight interval is obviously increased. The presented automatic tilt scheme is effective for studying the low scattering performance of the supersonic missile V-tail.

A varactor-based 1024-element RIS design for mm-waves

This paper reports a reconfigurable intelligent surface (RIS) for beamforming and beam steering applications operating in the millimeter wave (mm-waves) frequency band. The proposed 2-bit RIS design is implemented using a radar cross-section (RCS) approach in ANSYS HFSS for performance evaluation and system-level analysis. It is based on split-ring resonator (SRR) unit cells, tuned by varactor diodes, comprising 1,024 elements arranged in a 32 × 32 matrix with linear gradient phase configuration operating at 24.5 GHz over the fifth generation of mobile communications New Radio (5G NR) frequency range 2 (FR2). A beam steering from −60° to 60° in the azimuth plane is demonstrated for mm-waves coverage extension. Numerical simulations of RCS patterns from −10° to −60° and from 10° to 60° with approximately 3 dB scan loss manifest the applicability of the proposed RIS towards the sixth generation of mobile communications (6G). Furthermore, simulated results of angular reciprocity prove the RIS response up to 110° under an oblique incident wave at 60°. To the best of our knowledge, this is the highest RIS angular reciprocity reported in the literature, validating its application to coverage extension from −60° to 60°. In addition, the RCS level and reflected angle relationship are modeled for system-level analysis purposes.

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.

RCS Measurement and Characteristic Analysis of a Sea Surface Small Target with a Shore-Based UHF-Band Radar

Effectiveness verification of weapon equipment and the selection of stealth material are inseparable from target radar cross-section (RCS) measurement. For RCS characteristic analysis of sea surface small targets, a fishing vessel was measured using a shore-based ultra-high-frequency (UHF) band radar. In this article, a full program of RCS measurement and characteristic analysis is presented, and three strategies are adopted to guarantee its high precision. For this, a scheme was designed for RCS dynamic measurement, along with the construction of a two-stage median filter to improve target positioning precision, and an RCS estimation procedure with sea clutter removal is elaborated upon, which increases RCS accuracy. Note that the test range satisfies the far-field criterion, and the multipath effect is modified by external calibration in our data. The measurement results reveal that the RCS level of the sea surface small target is sensitive to the aspect angle and wave height at a low grazing angle, but the RCS fluctuation characteristic is not. Therefore, the aspect angle and wave condition must be considered for sea surface small target detection, classification, or identification.

Study of the Radar Cross-Section of Turbofan Engine with Biaxial Multirotor Based on Dynamic Scattering Method

With the continuous advancement of rotor dynamic electromagnetic scattering research, the radar cross-section (RCS) of turbofan engines has attracted more and more attention. In order to solve the electromagnetic scattering characteristics of a biaxial multirotor turbofan engine, a dynamic scattering method (DSM) based on dynamic simulation and grid transformation is presented, where the static RCS of the engine and its components is calculated by physical optics and physical theory of diffraction. The results show that the electromagnetic scattering of the engine is periodic when the engine is working stably, while the rotors such as fans and turbines are the main factors affecting the dynamic electromagnetic scattering and the ducts greatly increase the overall RCS level of the engine. The proposed DSM is effective and efficient for studying the dynamic electromagnetic scattering characteristic of the turbofan engine.

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.

Planar microwave retroreflector based on transmissive gradient index metasurface

In this paper, a novel planar microwave retroreflector based on a transmissive gradient metasurface combined with a curved metal mirror is proposed and demonstrated. The transmissive metasurface can efficiently converge a wide-angle incident wave to a pre-designed curved metal mirror behind it with a proper distance, which acts as an effective reflective surface that can greatly enhance the backscattering of the incident wave with a wide-angle view. According to the full-wave simulations, the proposed metasurface retroreflector can perform an excellent retroreflective effect for incident microwaves of angle view between −30° and 30° range. A prototype was fabricated and the experimental results verify that the metasurface retroreflector can realize the monostatic radar cross section (RCS) enhancement with a continuous wide incident angle view from −30° to 30° at 10 GHz within a stable 3 dB RCS level. It is further demonstrated that the excellent wide-angle backscattering performance (absolute RCS enhancement value, operational bandwidth and/or incident angle view) of the proposed microwave metasurface retroreflector is competitive against the traditional trihedral corner reflector with comparable dimensions, thus opening up new possibilities to substitute the traditional bulky radar retroreflector by using a planar compact metasurface structure for microwave engineering. The presented microwave metasurface retroreflector is promising to develop into a low-profile, light weight and planar radar retroreflector which possesses tremendous RCS backscattering enhancement and wide-angle view operation range.

Nickel-coated glass/epoxy honeycomb sandwich composite for broadband RCS reduction

In this paper, a new proposed radar-absorbing honeycomb sandwich composite with nickel-coated glass fabric, implemented via electroless plating, was applied to the leading edge of a NACA 0012 wing airfoil model to reduce the echo radar cross-section (RCS) level. The composite was designed and fabricated without dispersing conductive nanoparticles or metal magnetic micropowders in polymer materials. The proposed composite exhibited −10 dB microwave absorption in the frequency range of 5.8–16.3 GHz, with a resonance peak of −38.1 dB at 8.2 GHz under TM mode, and an RCS reduction of 10 dB for VV polarization and 8 dB for HH polarization in the frequency range of 6.0–17.8 GHz. When the proposed absorber was applied to the leading edge of NACA 0012, the simulated echo RCS level was reduced by 10 dB from C-band to Ku-band under both horizontal and vertical polarizations. A flatwise compressive test was conducted to evaluate mechanical performance of the composite. The proposed composite can be potentially applied to the radar-absorbing structure of stealth aircrafts.

Dual-Polarization and Low-Sidelobe Corrugated Rectangular Horn Antennas for Outdoor RCS Measurement

AbstractOutdoor radar cross section (RCS) measurement suffers background clutter. Such clutter needs to be minimized, especially when measuring low RCS level objects. To do this, a pair of corrugated horn antennas with a rectangular aperture has been designed, fabricated, and measured to improve the performance of outdoor RCS measurement. This antenna consists of a coaxial-waveguide adaptor, a square-rectangular waveguide transition, a corrugated rectangular horn, and chokes. A comparison of the performances of several corrugation profiles is provided. The tangential profile surpasses others because it provides the necessary low sidelobe level and narrow elevation beamwidth. The proposed antenna achieves −30 dB sidelobe level, fan-shaped beam pattern, and dual-polarization with −26 dB cross-polarization level over the band from 8.5 GHz to 12.5 GHz. The effectiveness of the antenna has been verified experimentally on a roof with two corner reflectors that were deployed intentionally to enlarge the effects of background clutter.

Dielectric Resonator-Based Passive Chipless Tag With Angle-of-Arrival Sensing

Passive chipless tags based on dielectric resonators (DRs) have been proposed for a novel millimeter-wave indoor self-localization system to mark fixed reference nodes. The tags employed in the system provide a unique spectral signature (resonance peaks) with much-increased radar cross section (RCS) by placing several identical DRs at the focal line of a spherical dielectric lens. Resonators of optimized geometry allow a modification of this original DR-lens tag by combining the lens with different size DRs which exhibit resonant frequencies separated by large frequency gaps. For easier manufacturing and testing, a demonstrator tag was designed for a “scaled” frequency range of 5–6 GHz with this configuration and is shown to produce spectral signatures of the monostatic RCS which are uniquely related to the angle of arrival (AoA) of the incident wave from a reader. Simulated signatures of a lens of 120-mm diameter with seven spherical DRs are presented and results are supported by experiment. Correlation processing of the signatures can give a resolution of few degrees in AoA while the bistatic RCS half-power beamwidth is on the order of 20°, and RCS levels of resonant peaks are produced between 0 and −6 dBm2.

A Novel Reflectarray Antenna with Reduced RCS

A novel frequency selective surface (FSS) configuration in the reflectarray antenna is proposed for reduction of radar cross section (RCS) level in this work. Double-layer FSS structure is located behind the reflectarray antenna as a ground. A 9 9 elements FSS with variable size patches has same geometry with the reflectarray antenna. The RCS reduction performance of reflectarray antenna both ground plane backed and FSS backed is compared. The results of simulation are obtained by using CST Microwave Studio. The simulation results show that RCS level of FSS backed reflectarray antenna is reduced both in-band (8-12 GHz) and out-of-band (2-7 GHz and 13-18 GHz). In the literature, RCS reduction of reflectarray antenna with FSS structure has only been achieved out-of-band. Furthermore, the gain and radiation performance of the ground plane backed reflectarray antenna and FSS backed reflectarray antenna are compatible with each other.

Radar-absorbing structure with nickel-coated glass fabric and its application to a wing airfoil model

In this study, a thin lightweight single- and double-slab with a nickel-coated glass-fabric design manufactured via the mass production electroless plating method is proposed for an enhanced echo radar cross section (RCS) for curved surfaces. The main objective of this research is to reduce the echo RCS from the C- band to the Ku-band (in GHz) for a wing airfoil model (NACA0012) radar-absorbing structure. For conventional microwave absorption performance, a high weight percentage of nano-conductive particles within a polymer matrix is crucial. However, certain difficulties are encountered in terms of high viscosity and thickness control in the polymer matrix for its application to the curved surface of the wing airfoil model. The proposed RCS absorber models reduce these difficulties associated with conventional RCS models. When the proposed absorbers are applied to the wing structures to cover the entire surface, the simulated results of the echo RCS level capacity demonstrate a 10-dB reduction from the C-Band to Ku-band for a wide-angle oblique incidence in both the horizontal and vertical polarizations. From a practical standpoint, these results show that nickel-coated-glass-fabric/epoxy composites have a tremendous potential for application to the wing airfoil model in a stealth aircraft.

Influence of aircraft surface distribution on electromagnetic scattering characteristics

In this paper, two typical stealth aircraft concepts (wing fuselage blended and flying-wing) were designed. Then three gradually changed surface distribution models with the same planform for each concept were created. Based on the multilevel fast multipole algorithm (MLFMA), the vertical polarization transmitting/vertical polarization receiving (VV) and horizontal polarization transmitting/horizontal polarization receiving (HH) radar cross section (RCS) characteristics were simulated with five frequencies between 0.1 and 1.0GHz. The influences and mechanisms of aircraft surface distribution on electromagnetic scattering characteristics were investigated. The results show that for the wing fuselage blended concept, the VV RCS of this frequency range is higher than the HH RCS in most cases, while it is just the opposite for the flying-wing concept. As for the two aircraft concepts, the RCS levels of HH and VV both decrease with the frequency increasing, but the HH RCS has a faster downward trend. The surface distribution has little influence on HH RCS characteristics. On the contrary, it has a significant impact on VV RCS characteristics, and the amplitude of the VV RCS increases with the surface thickness.

Active calibration target for bistatic radar cross‐section measurements

AbstractEither passive calibration targets are expensive and complex to manufacture or their bistatic radar cross section (RCS) levels are significantly lower than the monostatic RCS levels of targets such as spheres, dihedral, and trihedral corner reflectors. In this paper the performance of an active calibration target with relative high bistatic RCS values is illustrated as a reference target for bistatic RCS measurements. The reference target is simple to manufacture, operates over a wide frequency range, and can be configured to calibrate all four polarizations (VV, HH, HV, and VH). Bistatic RCS measurements of canonical targets, performed in a controlled environment, are calibrated with the reference target and the results are compared to simulated results using FEKO.

Roughly Impedance-Matched Scatterers Constructed With Magnetodielectric Cells

The monostatic theorem of Weston states that a null radar cross section (RCS) will be observed for objects with rotational symmetry that are impedance matched to their host medium, i.e., that have their material parameters $\varepsilon_r = \mu_r$ . A study of the generalization of this result applied to heterogeneous magnetodielectric (MD) scatterers is presented. The entire object of interest is divided into a set of small cubical unit cells in a three-dimensional checkerboard format, i.e., two different materials are distributed alternately in lego-like designs. Numerical computations are presented to compare the RCS levels of perfectly impedance-matched scatterers and their lego-based equivalents. The degree of homogenization that can be attributed to these heterogeneous scatterers for a variety of double positive material choices, including extreme values, is addressed specifically in relation to their satisfaction of Weston’s theorem.

Complex Spiral Antenna with Low Radar Cross Section Level

An ultra-wideband (UWB) circularly polarized complex spiral antenna with low radar cross section (RCS) is proposed in this paper. By replacing the metal reflect board of the antenna with a novel UWB frequency selective surface (FSS), the RCS of the spiral antenna is significantly reduced in a wide frequency range, while the radiation performances of the spiral antenna are maintained. The proposed antenna operates over the frequency band between 2GHz to 6.5GHz under the condition of axial ratio<3dB and |S11| < - 10dB. Simulation and measurement results demonstrate the validation of broadband spiral antenna RCS reduction by using the novel UWB FSS.

Design of Circuit-Analog (CA) Absorber and Application to the Leading Edge of a Wing-Shaped Structure

In this study, first, a circuit analog (CA) absorber consisting of a periodic pattern resistive sheet, glass-fiber/epoxy composite as a spacer, and carbon fabric composite was applied to the leading edge of a wing-shaped structure to reduce the echo radar cross section (RCS). This CA absorber was designed in a flat-plate shape through a parametric study that was performed to optimize the device in the X-band (8.2–12.4 GHz). The reflection loss of the fabricated flat-plate CA absorber was measured with an X-band free-space measurement system. The measured reflection loss was –49.5 dB at 10.15 GHz and the –10 dB bandwidth was about 4.2 GHz. When the CA absorber was applied to the leading edge, the measured echo RCS level showed a 15 dB reduction near 10 GHz and a 10 dB reduction in most of the X-band in both polarizations. Surface discontinuity due to gaps between the leading edge and the wing-box was discussed. From the analysis results, it can be seen that the permittivity of the glass-fiber/epoxy composite material used in the CA absorber was in the proper range for application to a wing-shaped structure.

Design of thin circuit‐analogue multilayer absorber and application to leading edge of wing structure

A new thin multilayer circuit-analogue (CA) absorber design consisting of a patterned resistive sheet, glass/epoxy, and glass/MWCNT-epoxy for X-band radar is presented. The proposed thin multilayer CA-absorber (a total thickness of 2.23 mm) has smaller thickness by 0.71 mm than a single-layer CA-absorber (a total thickness of 2.93 mm). Although the absorption bandwidth of the multilayer CA-absorber in the X-band was slightly narrower than the single-layer CA-absorber, the absorption performance of the multilayer CA-absorber was comparable to that of the single layer. Also, when the CA-absorber was applied to the leading edge of a wing-shaped structure, the radar cross-section level was comparable with the single-layer CA-absorber even though the thickness of the multilayer CA-absorber was less than that of the single-layer CA-absorber.

Research on the L-band circularly polarized antenna with low RCS level

A novel L-band circularly polarized (CP) microstrip antenna for low radar cross-section (RCS) application is proposed in this paper. A corner-cut squarer radiator is used to implement the CP radiation. The antenna RCS is effectively reduced by the special quasi-fractal structure on the ground plane. Its radiation and scattering performances are simulated and experimentally verified by being compared with those of a commonly used CP microstrip antenna which is chosen as a reference antenna. The results show that the proposed antenna has good radiation performances and lower RCS than the reference antenna. The proposed antenna serves as a good candidate in the design of CP antenna with the requirement of low RCS.