Low Radar Cross Section Research Articles

A low radar cross section antenna array based on a liquid metal metasurface

AbstractA low RCS (radar cross section) slot array antenna based on a liquid metal metasurface is proposed. The metasurface consists of 6 × 6 nested ring‐shaped element. The inner ring with a checkerboard distribution can realise 180° ± 37° phase difference, which can effectively reduce the scattering performances for the slot array. The outer and inner ring together can excite more energy from the slot array, thus resulting in increased radiation gains. Therefore, by changing the layout of liquid metal on the metasurface, scattering and radiation enhancement modes can be switched. The measured results show that in the scattering mode, the RCS can be reduced from 8.1 to 17 GHz. While in the radiation enhancement mode, the proposed array with the metasurface can achieve a −10‐dB impedance bandwidth of 9.4–11.2 GHz (17.4%) with a maximum gain of 8.12 dBi. Compared with the slot array without the metasurface, the realised gain is enhanced by 1.2 dBi from 6.9 dBi. The measured results correspond well with the simulated ones.

MOF Derivatives with Gradient Structure Anchored on Carbon Foam for High-Performance Electromagnetic Wave Absorption.

The impedance matching and high loss capabilities of composites with homogeneous distribution are limited owing to high addition and lack of structural design. Developing composites with heterogeneous distribution can achieve strong and wide electromagnetic (EM) wave absorption. However, challenges such as complex design and unclear absorption mechanisms still exist. Herein, a novel composite with a heterogeneous distribution gradient is successfully constructed via MOF derivatives Co@ nitrogen-doped carbon (Co@NC) anchored on carbon foam (CF) matrix (MDCF). Notably, the concentration of MOF can easily control the gradient structure. In particular, the morphologies of MOF derivatives on the surface of CF undergo a transition from the collapse of the inner layer to the integrity of the outer layer, accompanied by a continuous reduction in the size of Co nanoparticles. Correspondingly, enhanced interface polarization from the core-shell of Co@NC and good impedance matching of MDCF can be obtained. The optimized MDCF exhibits the minimum reflection loss of -68.18dB at 2.01mm and effective absorption bandwidth covering the entire X-band. Moreover, MDCF exhibits lightweight characteristics, excellent compressive strength, and low radar cross-section reduction. This work highlights the immense potential of composites with heterogeneous distribution for achieving high-performance EM wave absorption.

Deep learning for airfoil aerodynamic-electromagnetic coupling optimization with random forest

Reducing the design variable space is crucial in multi-objective airfoil profile optimization to improve optimization efficiency and reduce computational costs. Based on random forest and deep neural networks (DNNs), this work performs range reduction on ten design variables obtained through a fourth-order class shape transformation parameterization method for subsonic airfoil profiles. Three aerodynamic performance objectives (lift coefficient, drag coefficient, and lift-to-drag ratio) are evaluated using the Reynolds-averaged Navier–Stokes equations, and two radar stealth performance objectives (horizontal and vertical polarization radar cross sections) are assessed through the method of moments. By combining a DNN architecture with an improved regression prediction capability, predictive models are trained for mapping design variables to design objectives. The prediction errors are below 3% for the aerodynamic performance design objectives and below 1% for the stealth performance design objectives. The particle swarm optimization algorithm provides optimized airfoil profiles for three scenarios. First is a higher lift coefficient with a lower radar cross section. Second is a lower radar cross section. Third is a higher lift coefficient. Increasing the airfoil curvature and reducing the maximum thickness improves the lift coefficient by 386 counts and reduces the drag coefficient by 17 counts. By curving the airfoil leading edge, the radar cross section for the transverse electric and transverse magnetic polarizations decreased by 2.78 and 2.09 dBsm, respectively.

Broadband Metamaterial Surface for Antenna RCS Reduction and Gain Enhancement

This paper presents a broadband metamaterial surface with low radar cross section (RCS) and introduces its application on antenna. The metamaterial surface is composed of polarization-dependent artificial magnetic conductors (PDAMCs), which are orthogonal arranged in chessboard-like configuration for backscatter cancellation. By optimizing the PDAMC cell, effective phase difference is obtained in wideband and the surface achieves 10dB RCS reduction over the bandwidth of 32%. As a potential application, the metamaterial surface is employed to replace the metallic ground of a slot antenna. Illustrated by detecting wave, the novel antenna shows low RCS at boresight. While the antenna operates, the gain gets enhanced as a result of parasitic radiation of the surface. Full wave simulations and measurements validate that the novel antenna achieves both broadband low RCS and high gain compared with the slot antenna installed on a same-size metallic plate.

Fabrication of flower-like CoFe/C composites derived from ferrocene-based metal-organic frameworks: an in situ growth strategy toward high-efficiency electromagnetic wave absorption.

Magnetic/dielectric composites can achieve high-efficiency electromagnetic wave (EMW) absorption performance by integrating multiple mechanisms such as dielectric loss and magnetic loss. The bimetallic metal-organic frameworks (MOFs) assembled from ferrocene (Fc) derivative-based bridging ligands are considered ideal precursors for the preparation of magnetic/dielectric composites due to tailored alloy components with magnetic losses. Herein, a novel CoFe/C composite with nanoflower structures is successfully obtained via an in situ growth strategy to decompose an Fc-based bimetallic MOF assembled from 1,1'-ferrocene dicarboxylic acid as bridging ligands and Co2+ ions. Notably, the nanoflower structures of the obtained composites provide an effective path for the scattering and reflection of the EMW, thereby improving the impedance matching by combining dielectric and magnetic loss. The CoFe/C composite exhibits excellent EMW absorption performance and has a minimum reflection loss of -61.6 dB at 3.7 mm and an effective absorption bandwidth of 6.24 GHz at a corresponding thickness of 2.2 mm. Moreover, the obtained composite exhibits lightweight characteristics and a low radar cross-section. This work presents a novel method through Fc-based bimetallic MOF derivatives to design and develop novel magnetic/dielectric composites with efficient EMW absorption properties for comprehensive applications.

A Wideband Circularly Polarized Metantenna with Low Radar Cross-Section

A Wideband Circularly Polarized Metantenna with Low Radar Cross-Section

Broadband low radar cross section antennas based on H‐shaped metasurface

AbstractThis paper presents a novel metasurface antenna element and a novel metasurface antenna array, both of which have broadband low radar cross section (RCS) performance. The antenna element is constructed by two kinds of H‐shaped metasurface unit cells. One kind of H‐shaped metasurface unit cells is properly fed to radiate, and the other unit cells are used to cancel the scattering field from the former. Thus, an integration of metasurface and antenna is performed and broadband low RCS is obtained. Furthermore, a H‐shaped metasurface antenna array is also proposed by deliberately introducing metallic vias for isolation. Both the proposed antenna element and the array have almost the same radiation performance with conventional patch antennas. Numerical calculations and experimental measurements are conducted. The results verify the effectiveness of the proposed novel antennas.

A Low RCS Waveguide Slot Antenna array with Metamaterial Absorber

We propose a novel design to reduce the radar cross section (RCS) of ridged waveguide slot antenna array with metamaterial absorber (MMA). The MMA consists of metallic pattern and solid metal on sides of a dielectric slab, of which the absorbing characteristics and mechanism are analyzed. The PEC ground plane of a ridged waveguide slot antenna array is covered by MMA. Both the simulated and measured results show that compared with the waveguide slot antenna array with a PEC ground plane, the RCS of proposed antenna array are reduced dramatically without degradation of antenna performance. Combining with the bandpass frequency selective surfaces technology, the guideline illustrated by the proposed examples will serve as a good candidate for the future design of low RCS antenna.

A Shape-Changeable Antenna Constructed by Distilled Water for Low-Profile and Low-Radar-Cross-Section Applications

A Shape-Changeable Antenna Constructed by Distilled Water for Low-Profile and Low-Radar-Cross-Section Applications

A broadband AMC metasurface for radar cross section reduction and application in microstrip antenna

ABSTRACTA broadband checkerboard artificial magnetic conductor (AMC) metasurface with a 61% bandwidth is proposed. Two different AMC unit cells with 180° (±37°) effective reflection phase difference over a wide frequency range from 7.3–14 GHz are designed. A checkerboard metasurface is structured with two AMC unit cells and is applied in a microstip antenna for radar cross section (RCS) reduction. The simulated results show that the antenna can achieve more than 10 dB RCS reduction from 7.2–13.1 GHz. The maximum RCS reduction is 36 dB. Meanwhile, the radiation performance of the antenna has been well kept. Finally, the low RCS antenna is manufactured and measured. The measured results are in agreement with the simulations.

Radial Line Slot Array of Low Radar Cross Section for Target Detection and Radar Stealth in Missile-Borne Sensing Systems

Radial Line Slot Array of Low Radar Cross Section for Target Detection and Radar Stealth in Missile-Borne Sensing Systems

Low-RCS low-profile MIMO antenna and array antenna using a polarization conversion metasurface.

A specially designed dumbbell type polarization conversion metasurface (PCM) is proposed. The designed PCM achieves line-to-line polarization conversion in ultra-wideband (UWB) from 7.63 GHz to 18.80 GHz. A low-profile metasurface antenna composed of PCM and slot feed is proposed based on characteristic mode analysis (CMA), which realizes the integrated design of radiation and scattering. Because of the checkerboard scattering properties, low-radar cross section (RCS) low-profile multiple-input-multiple-output (MIMO) antenna and array antenna are designed with PCM. The low-RCS high-isolation low-profile MIMO antenna with size of 1.27×1.27×0.07λ 0 3 (λ0: the free-space wavelength corresponding to the center frequency point) operating at 5.8 GHz consists of four orthogonal arranged metasurface antennas. The isolation is greater than 26 dB with impedance bandwidth from 5.51 GHz to 6.06 GHz. In addition, the low-RCS high-gain low-profile array antenna with size of 2.55×2.55×0.07λ 0 3 is also designed. The operating band covers from 5.63 GHz to 6.12 GHz with the gain of 12-15.6 dBi. The RCS reduction of the two antennas for normal incidence is between 6 dB and 23 dB in both X- and Ku-bands. The measured results of the antennas agree with the simulated results, which shows that they have potential application value in 5.8 GHz WLAN wireless communication.

Coherent Accumulation for Measuring Maneuvering Weak Targets Based on Stepped Dechirp Generalized Radon–Fourier Transform

The problem of accurately measuring the motion parameters of low radar cross-section (RCS) maneuvering targets has long been a hurdle in the radar technology landscape. Small targets, due to their elusive characteristics, are particularly difficult to detect with conventional radar systems. In this paper, we investigate the capabilities of dechirp-receiving stepped-frequency radar, a modern system using a linear frequency modulation signal for downconversion. This permits the radar to function at reduced sampling rates while maintaining the transmission of large-bandwidth signals and achieving synthetic imaging. Our primary contribution is introducing the stepped dechirp generalized Radon–Fourier transform (stepped DGRFT) algorithm. This novel approach allows the radar system to perform coherent accumulation, enhancing the accuracy of motion parameter estimates for low-RCS maneuvering targets. Results from our simulations and measured data analysis validate the effectiveness of our proposed algorithm, demonstrating its superiority over other methods.

Wideband Multifunctional Polarization Converter: Application to Low Radar Cross-Section Radiating System

In this article, a wideband linear-to-linear and linear-to-circular reflective polarization converter is discussed. The proposed polarization converter can efficiently convert an incoming wave with a linear polarization into a reflected wave with orthogonal polarization in the frequency ranges: 7.63–12.21 GHz and 19.34–21.2 GHz. Moreover, a circularly polarized reflected wave in the frequency band of 13.85–18.50 GHz is also obtained. The proposed polarization converter constitutes a split-ring and a metallic strip cut in the middle designed on an ultrathin single substrate layer (thickness of 0.079λ o, where λ o corresponds to wavelength at center frequency of lowest operational bandwidth). The study related to angular dependence of the proposed polarization converter is also carried out and a stability upto 15° is achieved at the lower and upper-frequency bands of operation, respectively. A prototype of the proposed polarization with 25 × 25 cells of the converter is fabricated and measured. Measurement results are in consensus with their simulated counterparts. Furthermore, a 12 × 12 array of the proposed polarization converter is used to study the radar cross-section (RCS) reduction ability of a microstrip patch antenna operating in X-band. The average RCS reduction of about 11 dBsm is obtained at normal incidence. The proposed polarization converter can be utilized in X/Ku/K frequency band applications.

Enhancement of Electromagnetic Scattering Computation Acceleration Using LSTM Neural Networks

This paper presents the electromagnetic long short-term memory neural network (EM-LSTMNN) approach to accelerate radar cross-section (RCS) calculations in optimizing low RCS for electrically large targets. The proposed method converts the conventional electromagnetic numerical calculation into an efficient numerical calculation using the LSTM neural network, resulting in a significant improvement in RCS computation speed. To assess the effectiveness of this approach, a downscaled model of a large-sized ship is employed as the target for low RCS optimization. Each modification made to the target’s mesh data during the optimization process is stored in the dataset as a new element. As the ship scaling model undergoes modifications during the optimization process, the new mesh data are recorded, thus adding a new element to the dataset at each time step. This forms a time series representation of the mesh model. By utilizing the dataset collected throughout the optimization process, the proposed EM-LSTMNN model is trained using data-driven approaches, with a training time of approximately 106 s. It is worth noting that this training time is significantly smaller compared to existing methods that employ fully connected neural networks. The performance of the proposed approach is demonstrated by comparing the RCS calculation results obtained through this method with those obtained through traditional electromagnetic simulations.

Micro-Doppler Signature Detection and Recognition of UAVs Based on OMP Algorithm.

With the proliferation of unmanned aerial vehicles (UAVs) in both commercial and military use, the public is paying increasing attention to UAV identification and regulation. The micro-Doppler characteristics of a UAV can reflect its structure and motion information, which provides an important reference for UAV recognition. The low flight altitude and small radar cross-section (RCS) of UAVs make the cancellation of strong ground clutter become a key problem in extracting the weak micro-Doppler signals. In this paper, a clutter suppression method based on an orthogonal matching pursuit (OMP) algorithm is proposed, which is used to process echo signals obtained by a linear frequency modulated continuous wave (LFMCW) radar. The focus of this method is on the idea of sparse representation, which establishes a complete set of environmental clutter dictionaries to effectively suppress clutter in the received echo signals of a hovering UAV. The processed signals are analyzed in the time-frequency domain. According to the flicker phenomenon of UAV rotor blades and related micro-Doppler characteristics, the feature parameters of unknown UAVs can be estimated. Compared with traditional signal processing methods, the method based on OMP algorithm shows advantages in having a low signal-to-noise ratio (-10 dB). Field experiments indicate that this approach can effectively reduce clutter power (-15 dB) and successfully extract micro-Doppler signals for identifying different UAVs.

Design of a slot array antenna with ultra-wideband low-scattering characteristic

This paper presents a 4 × 4 slot array antenna with ultra-wideband low-scattering characteristic, which integrates a metasurface based on the multielement phase cancellation (MEPC) method. Limited by the characteristics of the slot antenna array, the contradiction between the ideal radiation performance and the requirement of low radar cross section (RCS) has not been well resolved. Therefore, in this paper, a MEPC-based metasurface is designed as the cover-layer of the proposed antenna, which can disperse the reflected energy to more directions without degrading the radiation performance. The proposed antenna operates in a bandwidth of 3.89–4.00 GHz with a maximum gain of 14.3 dBi. Additionally, the 7 dB RCS reduction bandwidth for TE/TM polarization at normal incidence is 5.5–40 GHz (f h / f l = 7.27:1), achieving ultra-wideband out-of-band RCS reduction. Furthermore, low-scattering performance can remain stable at large-angle oblique incidence. To verify the feasibility of the proposed design, a prototype is fabricated and measured for demonstration. The simulated and measured results are in good agreement.

Integrated metasurface for efficient polarization conversion and high-gain, low-RCS EM radiation.

This paper presents an innovative design that combines the functionalities of a polarization convertor and an electromagnetic (EM) radiator into a single integrated metasurface. The metasurface consists of two identical metallic split-rings, a circular-shaped patch structure, a dielectric layer, and a reflective metallic ground. The polarization convertor component efficiently converts waves polarized in the x- or y-direction into cross-polarized waves within a frequency range of 8-13 GHz. It exhibits wideband resonances and achieves a high conversion efficiency. In the context of low-observable platforms, traditional high-gain antennas often suffer from a large radar cross section (RCS). To overcome this challenge, the same metasurface is utilized for EM radiation, enabling a high gain of 16.5 dBi while maintaining a low RCS. This is accomplished by strategically rotating the double-slotted metallic split-rings at 90 ∘, 180 ∘, and 270 ∘ in four distinct regions. Through this rotation, destructive interference cancellation occurs, resulting in wideband reduction of the RCS. Experimental results validate the effectiveness of the proposed metasurface in serving both applications, namely polarization conversion and EM radiation.

A Low-RCS Circularly Polarized Reflectarray Antenna With a Linearly Polarized Feed

A low-radar cross section (RCS) circularly polarized (CP) reflectarray antenna with a linearly polarized (LP) feed is designed. The out-of-band RCS of the reflectarray for both the TE and TM polarized incident waves is reduced by replacing its ground with an absorptive frequency selective reflector (AFSR). A systematic methodology based on synthesis of the equivalent circuit model (ECM) is presented to expedite the design of the AFSR. The unit phasing element of the reflectarray is designed in such a way that it exhibits minimum coupling between the two orthogonal reflected LP-field components. Moreover, during the reflectarray construction, a novel phase synthesis is used which takes into account possible lowest of the existing mutual coupling while providing quadrature phase difference between the orthogonal LP components with minimum phase error. The proposed design is fabricated using 14×14 phasing elements to experimentally validate the numerically simulated results. The performance of the reflectarray is compared with a conventional reflectarray without the AFSR. It is observed that when the reflectarray is integrated with the AFSR, its gain is reduced only by 1.16 dB. However, its out-of-band RCS is reduced significantly. The 8-dB RCS reduction bandwidth can be observed from 3.55-7.2 GHz (67.9%) and from 11.85-14.21 GHz (18.11%). Moreover, it provides peak co-pol CP gain of 21.62 dBi, aperture efficiency of 41%, and 1-dB gain-bandwidth from 8.68-8.95 GHz, respectively.

Circularly Polarized Polarization Conversion Metasurface-Inspired Antenna Array With Low RCS Over a Wide Band

A circularly polarized (CP) metasurface-inspired antenna array with low radar cross section (RCS) over a wideband based on polarization conversion metasurface (PCM) is proposed. Without increasing the structural complexity, the PCM units serve directly as antenna radiators, which not only maintains good radiation characteristics but also reduces both the in-band and out-of-band RCS of the antenna. Simulations show that the proposed PCM-inspired antenna array has an impedance bandwidth of 37.6% (8.2 to 12 GHz), a 3 dB axial ratio (AR) bandwidth of 32.5% (8.5 to 11.8 GHz), and a 3 dB gain bandwidth of 23.3% (9.5 to 12 GHz). The RCS of the proposed antenna array is greatly reduced for both polarizations in the frequency range of 7.6 to 16.2 GHz (72.3%) compared to conventional microstrip patch antenna array, with a maximum reduction of 20.6 dB. Moreover, the proposed PCM-inspired antenna array has a smaller element size compared to conventional low-RCS metasurface antennas, making it more conducive to the composition of a phased array. Finally, the proposed array is fabricated and measured, and the results confirm the simulations.