Ultra-wideband RCS reduction based on reflection cancellation and tunable absorption

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.

In this communication, wide-angle monostatic radar cross section (RCS) reduction of a metal plate is reported. The whole angular range (0°–90°) is divided into three parts according to the different dominant scattering mechanisms. Each dominant scattering mechanism is accurately identified and suppressed effectively. Frequency selective surface (FSS) absorber is employed to reduce the specular echo intensity within the first angular part. The tapered resistive sheets (TRSs) are loading as an edge termination to the metal layer and FSS layer, respectively, providing a slowly varying surface current to taper the transition between the free space and the targets. Significant RCS reduction in the rest two angular parts is achieved. Simulation results clearly show that more than 10 dB monostatic RCS reduction is realized within a wide angular range (0°–10° and 30°–85°) for the frequency band ranging from 1.3 to 2 GHz. Samples have been fabricated and measured in the anechoic chamber, and a remarkable agreement between the simulation and measurement is obtained. The effectiveness of the design is fully verified.

This paper explores the mechanism of radar cross section (RCS) reduction under plasma. The Runge–Kutta exponential time differencing–finite difference time domain method is used to compute the radar cross section of a target covered by plasma. Then, a method for analyzing the electromagnetic coupling effect between electromagnetic waves and plasma-covering targets based on field intensity visualization images and a probe is proposed. This method can elucidate the interaction process between electromagnetic waves and plasma-covering targets, ultimately revealing the key finding that the complex multiple reflections between the air–plasma interface and the plasma–metal interface are the fundamental mechanism of radar cross section reduction. Furthermore, the influence of the electron density, collision frequency, plasma thickness, electromagnetic wave frequency, and non-uniform distribution characteristics on the radar cross section reduction is discussed. A radar cross section reduction ridge is discovered in a two-dimensional diagram of radar cross section variation with electron density and electromagnetic wave frequency. It can be observed that the places where radar cross section reduction is more significant all satisfy the condition that the frequency of the electromagnetic wave is slightly higher than the cutoff frequency of the plasma, which provides guidance for the design of plasma stealth parameters.

A new design method for ultrabroadband radar cross section (RCS) reduction by exploiting characteristic complementary polarization conversion metasurfaces (PCMs) is proposed and validated. The proposed method lifts the conventional bandwidth limitation enforced by the performance of a single PCM and expands the RCS reduction bandwidth. A systematic strategy for ultrabroadband RCS reduction design is developed and an effective reflection coefficient amplitude of the composite surface ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Gamma _{ {eff}}$ </tex-math></inline-formula> ) is derived as a new RCS reduction indicator. Based on this indicator, complete polarization conversion (CPC) frequency points of PCM are identified as important characteristics, and PCM pairs with interleaved CPC points, termed as initial PCM (I-PCM) and complementary PCM (C-PCM), are designed to compensate each other for ultrabroadband RCS reduction. A scaling-and-tuning two-step method for designing the C-PCM of a specific I-PCM is developed and validated. To further improve RCS reduction performance, taking the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Gamma _{ {eff}}}$ </tex-math></inline-formula> as an indicator, the particle swarm optimization (PSO) algorithm is used to select the optimal I-PCMs, C-PCMs, and their area ratios. Finally, an ultrabroadband RCS reduction surface is designed, fabricated, measured, and validated. It realizes 10-dB monostatic RCS reduction ranging from 7.6 to 26.2 GHz (110.7% relative bandwidth) which exceeds the polarization conversion bandwidth of each individual PCM. Besides, good polarization insensitivity and bistatic RCS reduction performance are also obtained. The proposed method provides a new route for designing broadband RCS reduction surface based on PCMs with unsatisfactory characteristics and greatly alleviates the performance requirement for PCMs.

This article presents an efficient and effective design approach of the phase distribution calculation across metasurface for significant radar cross section (RCS) reduction of a circular polarization (CP) and liner polarization (LP) radar waves. The RCS reduction using the proposed design approach is achieved by imposing a novel cusp phase mask (which is usually used to generate 3D self-accelerating and self-healing cusp beams) at each geometric phased anisotropic unit cell composing the proposed cusp phased metasurface. By solving the cusp phase formula using MATLAB, it is found that the cusp phase mask required to achieve more than 10 dB of RCS reduction over a wide frequency band can be calculated without the need of significant lengthy optimizations or huge computer resources. The ability of such cusp phase mask metasurfaces to achieve significant backward scattering and RCS reduction has been rigorously investigated by means of simulations and measurements. When illuminated by a far-field radar CP or LP plane wave, the proposed cusp phased metasurface realizes more than 10 dB of RCS reduction from 10.9 to 26 GHz, corresponding to a fractional bandwidth of FBW = 81.8%. The 10 dB RCS reduction bandwidth of the cusp metasurface is maintained under both normal and wide angular incidence up to 75∘. The proposed cusp metasurfaces have potential applications to make objects stealthy where the incidence radar signal has an unknown frequency, polarization, or angle of incidence.

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.

To achieve radar stealth and address the issue of narrow bandwidth in radar cross section (RCS) reduction, this paper proposes a chessboard metasurface structure with broadband RCS reduction performance. The designed cell exhibits effective polarization conversion performance in the frequency band from 7.5 GHz to 14.1 GHz. These unit cells, along with their mirror counterparts, are arranged in a classic checkerboard array to form a metasurface, achieving RCS reduction over a broad bandwidth. The simulation results obtained by CST show that under the condition of vertical incidence of plane waves, the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10 \times 10 metasurface array achieves more than 10 dB$</tex> reduction in RCS within the frequency band of 7.5 GHz to 13.6 GHz, with a reduction of more than 30 dB at 7.9 GHz. Based on this metasurface, an antenna design is proposed, where the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\left\vert\mathbf{S}_{\mathbf{11}}\right\vert&lt;-10 \text{dB}$</tex> bandwidth spans two intervals: 8.95 GHz to 9.5 GHz and 9.57 GHz to 11.3 GHz. This design achieves RCS reduction both within and outside the operational band.

In this paper, an all-metal magneto-electric dipole (ME-dipole) antenna array working in the S-band is proposed, featuring radar cross section (RCS) reduction in the X-band achieved through phase cancellation. To realize stealth performance in the X-band, a kind of RCS reduction units with a chessboard configuration is designed. For verification, a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2 \times 2$</tex> antenna array operating in the S-band (2.36–2.92 GHz) with RCS reduction capability in the X-band (8.0-12.0 GHz) is constructed. Simulation results demonstrate that the monostatic RCS of the proposed antenna array is reduced by more than 10 dB across the entire X-band under normal plane wave incidence. Furthermore, the integration of the X-band RCS reduction units preserves the original array footprint without any dimensional expansion.

In this paper, we present a design of the linear polarization conversion metasurface (MS) for the broadband radar cross section (RCS) reduction based on split-ring resonator (SRR) structure in microwave region. The corresponding phase gradient can be obtained through the stable phase difference of basic units of polarization conversion MS. The designed polarization conversion MS is applied in coded electromagnetic (EM) matrix by defining two basic units “0” and “1”, respectively. Based on the principle of planar array theory, a new random coding method named by matrix-type coding is proposed. Correlative RCS reduction mechanism is discussed and verified, which can be used to explore the RCS reduction characteristic. The simulated linear polarization conversion rate of the designed structure is up to 90% in the frequency range of 6–15 GHz, and the RCS reduction results verify the theoretical assumptions. Two kinds of matrix-type coding MS samples are prepared and measured. The experimental results indicate that the reflectance of MS is less than –10 dB on average under normal incidence in frequency range of 5.8–15.5 GHz. The average RCS reduction is essentially more than 10 dB in frequency range of 5.5–15 GHz and the corresponding relative bandwidth is 92.7%, which reasonably agrees with simulation. In addition, excellent RCS reduction characteristic of the designed MS can also be achieved over a wide incident angle.

Metasurface has attracted much attentions due to its ability of flexible manipulation of electromagnetic wave. However, the metasurface is limited to the single operating band and poor design generality when it is used for radar cross section (RCS) reduction. In this paper, a stacked metasurface design method has been developed to flexibly achieve dual wide band RCS reduction. Two subarrays with polarization conversion characteristic are firstly designed to operate in two wide bands, respectively. Then a low-pass frequency selective surface (FSS) is developed and sandwiched between two metasurface subarrays to achieve a subarray with the dual-band polarization conversion performance. With the arrangement of the dual-band subarray into a 2×2 array in a rotation way according to the polarization cancellation, the resultant metasurface structure has two −10 dB RCS reduction bands covering 6.6-12.7 GHz and 27.8-38.1 GHz. The designed prototype is fabricated and measured. The simulation and measurement results are given to demonstrate the good dual-band RCS reduction performance.

In this paper, a switchable radar cross section (RCS) reduction between the two broadbands' (1-7 GHz and 4-10 GHz) has been achieved by just considering the integration of hybrid frequency selective surface (FSS) based phase cancelation structure (PCS) with a modified ground square patch antenna operating at 2.4 GHz. The full metallic ground plane of the conventional microstrip antenna (MSA) is replaced by a 2 × 2 array of band-stop FSS having the same frequency as that of the MSA. This ground plane modification helps to increase the maximum out-of-band RCS reduction from 16.4 dB to 20 dB. The ground modified MSA without any PCS exhibits both in-band and out-of-band maximum RCS reduction of 20 dB over a wideband (1-7 GHz). A new approach is adopted to form the PCS. It is formed by placing two non-overlapping hybrid FSSs at different heights above the MSA. The MSA with FSS based ground plane along with the hybrid FSS based PCS exhibits good monostatic and bistatic RCS reduction across 4 to 10 GHz without affecting the radiation characteristics of the conventional MSA. The measured results show a close resemblance to the simulated ones.

Radar cross section (RCS) reduction technologies are very important in survivability of the military naval vessels. Ship appearance shaping as an effective countermeasure of RCS reduction redirects the scattered energy from one angular region of interest in space to another region of little interest. To decrease the scattering electromagnetic signals from ship scientifically, optimization methods should be introduced in shaping design. Based on the assumption of the characteristic section design method, mathematical formulations for optimal shaping design were established. Because of the computation-intensive analysis and singularity in shaping optimization, the response surface method (RSM) combined genetic algorithm (GA) was proposed. The polynomial response surface method was adopted in model approximation. Then genetic algorithms were employed to solve the surrogate optimization problem. By comparison RCS of the conventional and the optimal design, the superiority and effectiveness of proposed design methodology were verified.

A broadband polarization rotation reflective surface (PRRS) is designed and applied to wideband radar cross section (RCS) reduction in this paper. The PRRS can convert linearly polarized incident wave to reflective wave with orthogonal polarization, and a high polarization conversion ratio (PCR) can be achieved across a broad band. When the PRRS is arranged with in a chessboard configuration and placed around a microstrip patch, the monostatic RCS of the microstrip patch can be reduced 8dB from 6.9GHz to 14.9GHz. The RCS reduction performance and principle are also analysed.

A novel metasurface (MS)-based method for broadband radar cross section (RCS) reduction of circularly polarized (CP) patch antennas is proposed. The RCS reduction is achieved in a much broader band than the operational band of the antenna. The simple technique is based on MS units on a grounded substrate in a checkerboard-like configuration. The broadband RCS reduction is achieved by combining two different destructive interference principles. In the high-frequency region, for a normal incident wave, the RCS is reduced by the phase cancellation generated by the MSs and the grounded substrate. In the low-frequency region, the RCS is reduced by the polarization conversion property of the MS. In this case, the fields reflected by two MS sections are in counter phase for a normal incident wave. The MS is combined with a CP patch antenna. It concerns a traditional corner-truncated square patch and four sequentially rotated surrounding MS cells. This dedicated MS allows two things: an additional resonant mode is excited resulting in a 3 dB AR bandwidth extension from 4.2% to 15.9% and a broadband RCS reduction of over 6 dB from 4.95 to 15.73 GHz (104.25% bandwidth) for both x- and y-polarized incident waves.

In this paper, we present a metasurface composed of complementary units that can realize orthogonal linear and linear-to-circular polarization conversion in multi-band. Linear polarization conversion has seven high-conversion frequency bands: 9.1–9.7 GHz, 15.6–17.6 GHz, 19.4–19.7 GHz, 21.2–23.1 GHz, 23.5–23.8 GHz, 26.2 GHz, and 27.9 GHz. Linear-to-circular polarization conversion also has seven frequency bands with axial ratios (ARs) less than 3 dB: 8.9–9.0 GHz, 9.9–14.7 GHz, 19.1–19.3 GHz, 23.2–23.35 GHz, 23.4 GHz, 24.1–25.4 GHz, and 27.2–27.8 GHz, with the generation of multiple bands extended by the combination of complementary units. Then, we utilize the combined polarization conversion unit’s mirror placement to form a 4 × 4 array to realize the phase difference cancellation of the reflective field, giving the metasurface the radar cross section (RCS) reduction function and the dual-band 10-dB monostatic RCS reduction bandwidth: 8.9–9.7 GHz and 15.5–26.1 GHz. The measured and simulated results were essentially identical. Because the design uses the complementary units to form an array to expand the polarization conversion frequency bands, it provides a novel idea for future designs and can be applied to multiple microwave frequency bands.