Ultra-wideband Radar Cross Section Research Articles

A segmented conformal surface for ultrawideband monostatic and bistatic RCS reductions

In this paper, a segmented cylindrical metal surface based on an optimal arrangement is proposed to achieve ultrawideband and wide-angle radar cross section (RCS) reduction. Firstly, a multi-stage semi-cylindrical surface that uses the difference in radius between each cylinder to achieve phase cancellation is designed. The PSO algorithm is used to obtain the best length of each cylinder. Then, each semi-cylinder is equally divided into a certain number of sub-surfaces. Subsequently, in the axial direction, the sequence of these sub-surfaces with different radii is disrupted according to the optimal arrangement to form discontinuous surface reflection phases. A 10-dB RCS reduction under normal incidence is achieved from 4.36 to 20.6 GHz, and the bandwidth ratio reaches 4.72:1. The theoretical analysis and simulated results are in good agreement with the measured results, and the design has an important reference value for ultrawideband monostatic and bistatic RCS reductions for cylinder-like targets.

An absorptive coding metasurface for ultra-wideband radar cross-section reduction

In this paper, an absorptive coding metasurface (ACM) is proposed for ultra-wideband radar cross section (RCS) reduction, the design process is presented in detail, in which a lossy polarization conversion metasurface (PCM) is proposed at first. The lossy PCM is an anisotropic resistive structure with both polarization conversion and absorption performances, so that its co-polarization reflection coefficients under u- and v-polarized incidences can be kept at less than − 10 dB in magnitude in the frequency range from 7.5 to 45.2 GHz. Though the magnitude of the cross-polarization reflection coefficient cannot be very small only due to the absorption, its phase will be changed by nearly 180° when the unit-cell structure of the lossy PCM is rotated by 90°. Thus, the lossy PCM can be used as one of the two types of lossy coding elements for an ACM when its unit-cell structure is rotated by 90° or not. Based on the lossy PCM, an ACM is proposed. The simulation and experimental results show that the ACM has an excellent RCS reduction performance under arbitrary polarized incidence, it can achieve effective RCS reduction under normal incidence in the ultra-wide frequency band from 7.4 to 45.5 GHz with a ratio bandwidth (fH/fL) of 6.15:1; moreover, an ultra-wideband RCS reduction can still be achieved when the incident angle is increased to 45°, which indicates that the ACM has good stealth performance under the detection of various radars working in X, Ku, K and Ka bands, it is very practical.

Ultra-wideband radar cross section reduction achieved by an absorptive coding metasurface

An absorptive coding metasurface (ACM) is proposed to achieve radar cross section (RCS) reduction in this paper. In the design progress of the ACM, two different lossy coding elements are proposed at first, which can both be regarded as a composite composed of a two-layer resistive frequency selective surface (RFSS) and a polarization conversion metasurface (PCM). The two-layer RFSS has a certain wave-absorbing property due to ohmic loss. In addition, the PCM can achieve ultra-wideband linear polarization conversion, and the polarization-converted reflected waves in the two coding elements under the same incidence will differ by nearly 180° in phase because the sub-unit-cell structures in them are perpendicular to each other. Thus, based on the two lossy coding elements, the ACM is proposed, which can achieve ultra-wideband RCS reduction due to absorption and phase cancelation. Numerical simulations demonstrate that the RCS of the ACM under normal incidence can be reduced more than 10 dB in the ultra-wide frequency band from 6.9 to 41.2 GHz with a relative bandwidth of 142.6%. Moreover, it has the advantages of polarization-insensitivity and wide incident angle. Finally, one effective experimental verification is carried out, and a reasonable agreement is observed between the simulation and experimental results.

Ultra-wideband and wide-angle RCS reduction of a concave structure based on a chessboard polarization conversion metasurfaces

In this paper, ultra-wideband and wide-angle radar cross section (RCS) reduction of a concave structure is designed and realized based on a chessboard polarization conversion metasurface (CPCM), employing an ultra-wideband polarization conversion metasurface (PCM) composed of a single layer of square split-ring resonators. The concave structure, which is equivalent to an octagonal-like prism, is divided into eight regions. To achieve perfect phase cancellation in the non-central region, it can be equivalent to oblique incidence when the central region is under normal incidence, and phase compensation of the unit cell of metasurfaces in the non-central region is considered. The simulated results demonstrate that the RCS reduction of the proposed concave structure is less than −10 dB in the frequency ranges of 8.8 GHz to 35.75 GHz with fractional bandwidths of 120.99% and exceeds −30 dB at numerous resonant frequencies such as 9.52 GHz, 13.89 GHz, 23.45 GHz, and 35.2 GHz under normal incidence. The experimental results are in good agreement with the simulations. Furthermore, the RCS reduction characteristics of the proposed concave structure at different azimuth angles are also evaluated. Numerical calculations and experiments show that the wide-angle RCS reduction from 0° to 34° is achieved. To the best of the information we have, this is the first time that the chessboard metasurfaces, which consist of several polarizing reflectors, have been employed to obtain broadband and wide-angle RCS reduction for the concave structure. This technique validates the novelty and effectiveness of wide-angle and ultra-wideband RCS reduction of the concave structure.

Low-profile shared-aperture metasurface array antenna with ultra-wideband radar cross section reduction and circularly polarization

This paper proposes a circularly-polarized (CP) metasurface antenna with ultra-wideband radar cross section (RCS) reduction. Initially, the relationship between RCS reduction and phase difference with different reflection amplitudes is analyzed theoretically. Inspired by the shared-aperture principle, a high-frequency resistive layer is introduced into the antenna element to further fulfill ultra-wideband RCS reduction and low-profile requirements. Numerical simulations demonstrate that the inserted layer has no effect on the radiation performance of the antenna array. Then, the proposed element and its orthogonal unit are arranged in a checkerboard pattern for good CP radiation. In this configuration, the proposed metasurface array antenna has a maximum gain of 16.7 dBi with 72.1% aperture efficiency. The bandwidth of 5 dB RCS reduction with x- and y-polarized incidences is 7.10–17.95 GHz and 7.34–17.85 GHz, respectively. The proposed design is verified by the fabrication of prototype antennas and measurements.

Ultra-wideband radar cross-section reduction based on phase cancellation

ABSTRACT In this study, a 2-bit coding metasurface is proposed, which can achieve ultra-wideband radar cross section (RCS) reduction under arbitrary polarized incidences due to phase cancellation. In the design process of the 2-dit coding metasurface, a novel polarization conversion metasurface (PCM) is proposed at first, which can realize ultra-wideband circular-polarization (CP) maintaining reflection; moreover, when its unit cell structure is rotated by an angle ψ, ±2ψ Pancharatnam-Berry (PB) phase will be generated in its co-polarized reflection coefficients under CP incidence. Thus, based on the PCM, an ultra-wideband 2-dit coding metasurface is conveniently proposed. Numerical simulations demonstrate that the coding metasurface has excellent RCS reduction performance. Compared with a pure metallic plate with the same size, its RCS can be reduced more than 10 dB under normal incidences with arbitrary polarizations in the ultra-wide frequency band of 6.9–33.1 GHz with a relative bandwidth of 131%. Moreover, when the incident angle is increased to 45°, the RCS reduction performance can be kept well. Finally, one laboratory sample of the coding metasurface is fabricated and measured, a reasonable agreement is observed between the measured and simulated results.

Ultrawideband and Omnidirectional RCS Reduction by Using Symmetrical Coded Structures

In this letter, a planar structure for ultrawideband and omnidirectional radar cross section (RCS) reduction is designed. The means of omnidirectional is the capability of RCS reduction in all of φ in certain θ . To achieve this, the theory of diffraction in periodic structures as well as symmetrical pixelated geometry of unit cell are employed. According to this theory, the dimension of unit cell is larger than one wavelength, which induces multiple Floquet harmonics each in certain direction and causes diffusion in scattering. Addition of symmetry to the geometry of unit cell causes the omnidirectional RCS reduction; besides, pixelating of geometry is optimized with the goal of wideband RCS reduction. Finally, a 2 × 2 array of this unit cell is simulated and fabricated.

Ultra Wideband Radar Cross Section Reduction by using non-Resonant Unit Cells

A general approach is proposed to design ultra-wideband radar cross section reduction (RCSR) metasurface by using non-resonant unit cells in chessboard arrangement. The proposed miniaturized artificial magnetic conductor unit cell is composed of two stacked non-resonant patches separated from one another by thin dielectric substrates. The genetic optimization algorithm is used to optimize the unit cell design parameters and obtain wide 10-dB RCSR bandwidth. The proposed approach is performed to design three different RCSR metasurfaces, ideal, ROGERS and low cost. The low cost RCSR metasurface composed of low cost commercially available FR-4 substrate is fabricated and tested which reduces RCS more than 10-dB from 5.22 GHz to 30.85 GHz, 142% fractional bandwidth. This metasurface has significantly wider RCSR bandwidth rather than the state of the art references as well as low cost, simple and light weight structure which facilities its practical applications.

Epsilon near zero metasurface for ultrawideband antenna gain enhancement and radar cross section reduction

A non-resonant metamaterial unit cell is proposed to design a metasurface for ultrawideband (UWB) gain enhancement and radar cross section (RCS) reduction of an UWB antenna. Epsilon near zero (ENZ) property and negative refractive index of metamaterial is achieved to ensure low loss and amplification of electromagnetic waves (EM) passing through it. The proposed metamaterial is designed on a 6 mm × 6 mm FR4 substrate with dielectric constant 4.4, height 1.6 mm and loss tangent 0.01. The unit cell is simulated with periodic boundary condition to get the properties of periodically arranged unit cells in one plane called metasurface. A Metasurface is designed by planar arrangement of 5×5 unit cells of proposed metamaterial unit cell and is kept at height of 2 mm above an ultrawideband planar microstrip antenna. Antenna system with metasurface has physical and electrical dimensions of 32 × 32 × 5.2 mm3 and 0.34λ0×0.34λ0×0.05λ0 respectively, where λ0 is the free-space wavelength at 3.2 GHz. The bandwidth of UWB patch antenna (3.1–10.6 GHz) is unaffected by the presence of metasurface. The analysis of radiation mechanism shows the phase difference of EM waves passing through metasurface with and without reflection is 300°–400°. This indicates emergence of coherent waves from metasurface and contributes in gain enhancement. Maximum gain is 5.7 dB at 6.8 GHz with radiation efficiency of 88.5% and maximum gain enhancement is 10.1 dB at 9.8 GHz. The reflection phase analysis of normal incident wave predicts the frequency for maximum RCS reduction as 6.4 GHz. Maximum RCS reduction of antenna with application of metasurface is 21 dB at 6.7 GHz. Significant gain enhancement and reduction of RCS is achieved for ultrawideband. The proposed antenna system metasurface with enhanced gain and reduced RCS is a good candidate for application in stealth and military platforms.

A Multi-Elements Chessboard Random Coded Metasurface Structure for Ultra-Wideband Radar Cross Section Reduction

In this paper, a novel method of realizing the ultra-wideband (UWB) radar cross section (RCS) reduction is proposed. We combine the chessboard structure of multi-elements which are all polarization conversion metasurface (PCM) units with random coding. Four different kinds of PCM units all with UWB and much high polarization conversion rate (PCR) are selected. Morever, their polarization conversion frequency bands are optimized not only in the high frequency segment but also in the low frequency segment. The final designed structure can achieve 10 dB RCS reduction within 6.9 GHz–20.1 GHz in the high frequency segment and 15.5 GHz–51.2 GHz in the low frequency segment, respectively. In addition, the effects of RCS reduction by the square chessboard structure composed of different numbers of these PCM units are compared. The proposed metasurface structure provides an efficient scheme to reduce the scattering of the electromagnetic waves.

Ultra‐wideband Low‐Detectable Coding Metasurface

A coding metasurface is designed based on hybrid Array pattern synthesis (APS) and Particle swarm optimization (PSO) method for ultra-wideband low-detectable application. The metasurface is composed of Electromagnetic band-gap (EBG) structures of two Minkowski fractal elements with reflection phase difference of 180° (±37°) over a wide frequency range. Two different types of EBG unit cell printed on a thin grounded dielectric substrate produce reflection phase difference of about 180 degrees over a wide frequency range. Ultra-wideband Radar cross section (RCS) reduction results from the phase cancellation between two local waves produced by these two unit cells. The diffuse scattering of EM waves is caused by the optimization of phase distribution, leading to a low monostatic and bistatic RCS simultaneously. The proposed metasurface can achieve 10 dB monostatic and bistatic RCS reduction in a wide frequency band from 5.8 to 18.0 GHz with a ratio bandwidth (fH/fL) of 3.10:1 under normal incidence for both polarizations. The theoretical analysis, simulation and experiment results are in good agreement and validate the proposed metasurface can achieve ultra-wideband RCS reduction and diffuse scattering.

Ultra-wideband RCS reduction and gain enhancement of patterned-surface-based aperture coupling patch antenna with optimized arrangement method

A patterned-surface-based aperture coupling patch antenna (ACPA) with ultra-wideband radar cross section reduction (RCSR) and gain enhancement is presented in this paper. Due to the air-filled gap structure of the ACPA, an air spacer is introduced to design double-layer patterned surface (PS), which broadens the RCSR bandwidth of ACPA. Moreover, to obtain better gain of antenna, the arrangement of PS is optimized based on its current distributions. Experimental results show that impedance matching of PS-based ACPA is preserved well and operation band is broadened slightly from 8.0 to 11.3 GHz. The boresight gain is enhanced from 7.5 to 11.5 GHz, with a peak gain enhancement of 4.1 dB at 9.7 GHz. Meanwhile, the PS-based ACPA possesses the ability of specular RCSR over the band 3.0-20.0 GHz for both polarizations. The 10-dB RCS reduction of the antenna is achieved almost from 5.5 to 17.0 GHz for normal incidence.

Ultra Wideband Radar Cross Section Reduction by Using Polarization Conversion Metasurfaces

In this paper, a polarization conversion metasurface (PCM) is designed for ultra wideband radar cross section (RCS) reduction. The proposed polarization conversion metasurface consists of double-heads arrow unit cell with its 90°, 180° and 270° rotated ones to create the destructive interferences cancellation and radar cross section (RCS) reduction, consequently. The proposed metasurface demonstrates ultra-wide band 10-dB RCS reduction from 9 to 40 GHz (126.5%) for normally TM- and TE- polarized incident waves. The good agreement between the simulation and measurement results at 0°, 20° and 40° incident angles prove the idea, also. The ultra wideband RCS reduction of the proposed metasurface as well as its low profile, light weight and low cost prove its high capability compared with the state of the art references.

Lightweight ultra-wideband radar cross section reduction structure using double-layer metasurfaces

In this paper, we propose the design of a lightweight RCS reduction structure using double-layer metasurfaces. The structure is composed of two layers of metasurfaces spaced by PMI foams. To extend the bandwidth, two unit structures are firstly designed to operating in two respective bands for circularly polarized (CP) waves, which are then combined to act as the unit structure of the double-layer metasurface. The metasurface is expected to operate in two continuous bands. Nevertheless, due to the couplings between the two unit structures, there is Fano resonance that prohibits merging of the two bands. To solve this problem, we tune the resonant frequency of the bottom unit structure to suppress the Fano resonance and obtain a merged band. The combined unit structure is employed as the element of chessboard configuration, which can reduce RCS by more than 10 dB in an ultra-wide band (4.5–16.5 GHz). We designed, fabricated and measured a lightweight prototype (the aerial density is 726 g m−2). Both the simulation and experiment result verify the design. This work provides an effective method of extending the operation band of RCS reduction without sacrificing the efficiency.

Ultra-wideband low radar cross-section metasurface and its application on waveguide slot antenna array** Project supported by the National Natural Science Foundation of China (Grant Nos. 61671464, 61701523, and 61471389).

A novel approach devoted to achieving ultra-wideband radar cross section reduction (RCSR) of a waveguide slot antenna array (WGSAA) while maintaining its radiation performance is proposed. Three kinds of artificial magnetic conductors (AMCs) tiles consisting of three types of basic units resonant at different frequencies are designed and arranged in a novel quadruple-triangle-type configuration to create a composite planar metasurface. The proposed metasurface is characterized by low radar feature over an ultra-wideband based on the principle of phase cancellation. Both simulated and measured results demonstrate that after the composite metasurface is used to cover part of the antenna array, an ultra-wideband RCSR involving in-band and out-of-band is achieved for co- and cross-polarized incident waves based on energy cancellation, while the radiation performance is well retained. The proposed method is simple, low-cost, and easy-to-fabricate, providing a new method for ultra-wideband RCSR of an antenna array. Moreover, the method proposed in this paper can easily be applied to other antenna architectures.

Uneven-Layered Coding Metamaterial Tile for Ultra-wideband RCS Reduction and Diffuse Scattering

In this paper, a novel uneven-layered coding metamaterial tile is proposed for ultra-wideband radar cross section (RCS) reduction and diffuse scattering. The metamaterial tile is composed of two kinds of square ring unit cells with different layer thickness. The reflection phase difference of 180° (±37°) between two unit cells covers an ultra-wide frequency range. Due to the phase cancellation between two unit cells, the metamaterial tile has the scattering pattern of four strong lobes deviating from normal direction. The metamaterial tile and its 90-degree rotation can be encoded as the ‘0’ and ‘1’ elements to cover an object, and diffuse scattering pattern can be realized by optimizing phase distribution, leading to reductions of the monostatic and bi-static RCSs simultaneously. The metamaterial tile can achieve −10 dB RCS reduction from 6.2 GHz to 25.7 GHz with the ratio bandwidth of 4.15:1 at normal incidence. The measured and simulated results are in good agreement and validate the proposed uneven-layered coding metamaterial tile can greatly expanding the bandwidth for RCS reduction and diffuse scattering.

Low cost and thin metasurface for ultra wide band and wide angle polarization insensitive radar cross section reduction

A planar low cost and thin metasurface is proposed to achieve ultra-wideband radar cross section (RCS) reduction with stable performance with respect to polarization and incident angles. This metasurface is composed of two different artificial magnetic conductor unit cells arranged in a chessboard like configuration. These unit cells have a Jerusalem cross pattern with different thicknesses, which results in wideband out-phase reflection and RCS reduction, consequently. The designed metasurface reduces RCS more than 10-dB from 13.6 GHz to 45.5 GHz (108% bandwidth) and more than 20-dB RCS from 15.2 GHz to 43.6 GHz (96.6%). Moreover, the 10-dB RCS reduction bandwidth is very stable (more than 107%) for both TE and TM polarizations. The good agreement between simulations and measurement results proves the design, properly. The ultra-wide bandwidth, low cost, low profile, and stable performance of this metasurface prove its high capability compared with the state-of-the-art references.

Metasurface base on uneven layered fractal elements for ultra-wideband RCS reduction

A novel metasurface based on uneven layered fractal elements is designed and fabricated for ultra-wideband radar cross section (RCS) reduction in this paper. The proposed metasurface consists of two fractal subwavelength elements with different layer thickness. The reflection phase difference of 180° (±37°) between two unit cells covers an ultra-wide frequency range. Ultra-wideband RCS reduction results from the phase cancellation between two local waves produced by these two unit cells. The diffuse scattering of electromagnetic (EM) waves is caused by the randomized phase distribution, leading to a low monostatic and bistatic RCS simultaneously. This metasurface can achieve -10dB RCS reduction in an ultra-wide frequency range from 6.6 to 23.9 GHz with a ratio bandwidth (fH/fL) of 3.62:1 under normal incidences for both x- and y-polarized waves. Both the simulation and the measurement results are consistent to verify this excellent RCS reduction performance of the proposed metasurface.

Ultra-Wideband Low-RCS Circularly-Polarized Metasurface-Based Array Antenna Using Tightly-Coupled Anisotropic Element

A novel broadband circular-polarized array antenna with ultra-wideband low radar cross section (RCS) is proposed. The array is made up of $2\times2$ identically circular-polarized sub-arrays in a chessboard configuration. Furthermore, each sub-array consists of $2\times2$ tightly coupled metasurface-based elements with linear polarization. For radiation, each element is excited and fed with 90° phase shift between adjacent ones to perform broadband circular-polarized operation. For scattering, destructive phase difference is created in an ultra-wide band for orthogonally polarized incidence due to the anisotropic structure. Thus, a considerable ultra-wideband RCS reduction involving in-band and out-of-band is achieved based on energy cancellation. By this means, broadband circular-polarized radiation and ultra-wideband low RCS performance can be achieved in a synthesized design process. The prototype is fabricated and measured. A good agreement between measured and simulated results verifies the validity of our design method.

Pixelated Checkerboard Metasurface for Ultra-Wideband Radar Cross Section Reduction

In this paper we designed and fabricated a metasurface working as a radar cross section (RCS) reducer over an ultra wide band of frequency from 3.8 to 10.7 GHz. The designed metasurface is a chessboard-like surface made of alternating tiles, with each tile composed of identical unit cells. We develop a novel, simple, highly robust and fully automated approach for designing the unit cells. First, a topology optimization algorithm is used to engineer the shape of the two unit cells. The area of each unit cell is pixelated. A particle swarm optimization algorithm is applied wherein each pixel corresponds to a bit having a binary value of 1 or 0 indicating metallization or no metallization. With the objective of reducing the RCS over a specified frequency range, the optimization algorithm is then linked to a full wave three-dimensional electromagnetic simulator. To validate the design procedure, a surface was designed, fabricated and experimentally tested showing significantly enhanced performance than previous works. Additionally, angular analysis is also presented showing good stability and wide-angle behavior of the designed RCS reducer. The automated design procedure has a wide range of applications and can be easily extended to design surfaces for antennas, energy harvesters, noise mitigation in electronic circuit boards amongst others.