Low Radar Cross Section Research Articles

Receiving Paths Improvement of Digital Phased Array Antennas Using Adaptive Dynamic Range

In contemporary radar technology, the observation and detection of objects with low radar cross-sections remains a significant challenge. A multi-functional radar model employing a digital phased array antenna system offers notable advantages over traditional radar in addressing this issue. Nonetheless, to fully capitalize on these benefits, improving the structure of the receiving path in digital transceiver modules is crucial. A method for improving the digital receiving path model by implementing a matched filter approach is introduced. Given that the return signals from objects are often lower than the internal noise, the analog part of the digital transceiver modules must ensure that its dynamic range aligns with the level of this noise and the weak signal. The output signal level of the analog part must correspond to the allowable input range of the analog-to-digital converter. Improvements in the receiving path to achieve a fully matched model can reduce errors in the phase parameters and amplitudes of the useful signal at the output. The simulation results presented in this paper demonstrate a reduction in amplitude error by approximately 1 dB and a phase error exceeding 1.5 degrees for the desired signal at the output of each receiving path. Consequently, these improvements are expected to enhance the overall quality and efficiency of the spatial and temporal accumulation processes in the digital phased array antenna system. Furthermore, to maintain the matched filter model, we also propose incorporating an adaptive “pseudo-expansion” of the linear gain range. This involves adding a feedback stage with an automatic and adaptive bias voltage adjustment for the intermediate-frequency preamplifier in the analog part of the receiving path. Simulations to qualitatively verify the validity of this proposal are conducted using data from practical operational radar system models.

Wide-angle low-scattering transmitarray antenna based on transmit-reflect selective metasurface

Abstract A high-gain transmitarray antenna with low radar cross section (RCS) properties is presented in this paper. Compared with conventional high-profile multilayer designs, we introduce a transmit-reflect selective metasurface integrated with high-gain transmission and random scattering functions, achieving a reduced thickness of 0.13 λ 0 (where λ 0 is the wavelength at the center frequency). For the meta-atom design, we combine geometric rotation and dimension optimization to realize 1-bit independent transmit and reflection phase modulation, respectively. Moreover, in metasurface coding strategy, we employ an initial phase optimization method and a simulated annealing algorithm to determine the optimal coding matrices. The experimental results demonstrate high-performance radiation characterized by the peak gain of 23.6 dB, maximum aperture efficiency of 28.5%, and 3 dB gain bandwidth of 18.4%. For x-polarization, measured 10 dB RCS reduction bandwidth under transverse magnetic (TM) 0°-45° and transverse electric (TE) 0°-20° incidence are 9.02–11.36 GHz. For y-polarization, 10 dB RCS reduction bandwidth under TM 0–60° and TE 0–30° incidence is 8.82–10.96 GHz.

Broadband low radar cross section frequency selective surface radome based on phase cancellation and spatial filtering

AbstractThis letter introduces a novel design approach for broadband radar cross section (RCS) reduction of frequency selective surface (FSS) radomes. The approach integrates the principles of phase cancellation and spatial filtering together through a hybrid design method. The phase cancellation is obtained through the checkerboard arrangement of units, and the spatial filtering characteristics is achieved by the slot etched on the ground plane. Experimental and simulation results demonstrate that etching slots on the ground plane maintains broadband in‐phase reflection and bandpass characteristics, thereby extending the bandwidth of RCS reduction through a combination of two operation bands. Theoretical analysis of the working mechanism is also provided using equivalent circuit models. In comparison to the conventional radomes, the proposed FSS radome achieves significant bandwidth improvement for RCS reduction, indicating that it has promising prospects in future low‐RCS radome applications.

A switchable PCM-based integrated structure with alternative radiation and stealth functions

In this work, based on the switchable polarization conversion metasurface (SPCM), the dual functions of high gain right-handed circularly polarized (RHCP) radiation and wideband 10 dB radar cross section (RCS) reduction stealth are achieved in one structure. As the key component to achieve good radiation and low RCS, the proposed SPCM unit consists of the asymmetrical Jerusalem Cross top layer and switchable metal plate bottom layer separated by an air space. Then the SPCMs are arranged in a chessboard configuration and placed above a patch array antenna with the sequentially rotated feeding network. When p-i-n diodes are on, low RCS is implemented by 180° (±37°) reflection phase differences between two neighboring SPCM cells. When p-i-ns are off, the chessboard SPCM provides a transmission window for highly directional RHCP wave radiation.

High-gain H-plane SIW horn antenna loaded with dielectric slab for ku band low RCS applications

This article presents the design, simulation and experimental measurements of an H-Plane substrate-integrated waveguide (SIW) Horn Antenna Loaded with FR-4 Slab for Low RCS (radar cross section) applications like defence sector at Ku band (12-16 GHz). The design facilitates high gain and good impedance bandwidth (IBW). Also, the proposed structure has simple feed, planar structure with low-cost FR-4 substrate as dielectric material and decomposed into two parts. The former part of the antenna is the feeding part, which consists of two metallic plates filled with air substrate and a 90-degree corner reflector designed by shortening the metallic plates. The later part of the antenna is loaded with the FR-4 substrate that enhance the peak gain of the structure significantly. A simple coaxial probe is employed for the excitation of the corner reflector antenna. After the design is conferred by simulations, the same is fabricated and the performance measured experimentally. The experimental results are in close agreement with the simulated results. The design has yielded a 10 dB bandwidth of 30% (11.6–16 GHz), and a stable endfire radiation pattern over the entire bandwidth with a peak gain of 18.5 dBi at 14 GHz. Also, the design has F/B ratio > 20 dB over entire 10 dB bandwidth. Moreover, the antenna produced low RCS < 20 dB(m2) from −30° to +180° of elevation angle. Therefore antenna can’t easily detected from the radar system and suitable for defence applications.

Design and Application of High-Density Cold Plasma Devices Based on High Curvature Spiked Tungsten Structured Electrodes

Advances in radar technology have driven efforts to develop effective countermeasures. Plasma is recognized as a highly effective medium for absorbing electromagnetic waves. Recent research has focused on enhancing plasma element performance. This paper achieved ultra-high-density, low-pressure cold plasma with a density of 1.15 × 1012 cm−3, surpassing similar studies by more than an order of magnitude. Tungsten electrodes with high-curvature spiked structures were invented to replace traditional iron–nickel alloy electrodes, increasing plasma density by 88.2% under the same conditions. Lightweight and cost-effective tubular and annular ultra-high-density, low-pressure cold plasma devices were developed, demonstrating exceptional performance in electromagnetic wave absorption, plasma transient antennas, and radar stealth technology. The influence of plasma on electromagnetic waves and its numerical relationship were analyzed. By measuring the radar cross-section (RCS), the reduction in radar detection rates was quantified. The results show that the ultra-high-density cold plasma devices exhibit very low intrinsic RCS values, suitable for plasma antenna applications. The array of plasma elements generates a large-area high-density low-pressure cold plasma. This plasma effectively reduces the radar cross-section (RCS) of metallic equipment in the S and C bands and shows attenuation in the X band. These effects highlight the superior characteristics of plasma technology in electronic warfare. This exploratory research lays the groundwork for further defense applications.

RCS reduction of wide-band, high-gain antenna array based on asymmetric transmission metasurfaces

In this paper, an ultra-wideband stealth antenna with high gain on the basis of asymmetric transmission metasurface (ATMS) is proposed. ATMS can convert an incident y-polarised sphere wave into an x-polarised plane wave at the front side and controls the scattering of the incident y-polarised wave to the back side. Excitation of ATMS via a horn antenna, a low radar cross-section (RCS) and wideband antenna system is designed. Furthermore, through design of the meta-atoms and optimization of the macrosequencing, broadband RCS reduction is achieved. The experimental data indicated the reduction of the RCS of the antenna system by up to 10 dB and more than 20 dB in the frequency range of 10.1 GHz to 18 GHz (relative bandwidth is 56.2%) and 13.9 GHz to 18 GHz (relative bandwidth is 25.7%), respectively. In addition, a 3 dB gain relative bandwidth of 57.4% is achieved between 10 and 18 GHz, with a peak gain of 28.2 dB. It is noteworthy that the high gain and low scattering performance of the antenna are achieved in the same spectral range (10–18 GHz), and there is no interference between the scattering performance and radiation performance of the antenna, which could be controlled separately.

An In-Band Low-Radar Cross Section Microstrip Patch Antenna Based on a Phase Control Metasurface

An in-band low radar cross section (RCS) microstrip patch antenna based on a phase control metasurface is proposed. As the size of the phase control metasurface changes, it will have different phase adjustments to the incident electromagnetic wave. Two kinds of phase control metasurfaces with a 90° reflection phase difference are arranged in a checkerboard configuration and loaded above a microstrip array antenna. The metal of the microstrip array antenna can fully reflect the electromagnetic wave, so the incident wave passes through the metasurface again and forms a reflected wave with a phase difference of 180° ± 37° when passing through the phase control metasurfaces of different sizes. Thus, the microstrip array antenna can achieve in-band RCS reduction. The metamaterial forms a transmission window in the microstrip patch array antenna band to maintain the radiation performance. Finally, a reasonable agreement is obtained between the measured and simulated results.

Conformal frequency selective rasorber in S, C, X-band with low backward-scattering

In this paper, a polarization-insensitive high transmittance bandpass filter with low radar cross section (RCS) in both S- and X-band is proposed. This is the first study to use the partition layout loading approach for conformal structures with transmissive windows, reducing the operating band RCS. Curved structures have stronger radiation at a smaller angle to the incident wave, and that is how their scattering differs from uniform scattering from flat structures. The structure is divided by analyzing the radiative contribution of different regions. The surface was discussed in regions according to surface angles, and a new partition layout loading method was used to suppress the side currents and decreased backward scattering, achieving a backward RCS reduction of more than 10 dB at 4-8 GHz (66.7%). The bandpass layer operating at 6.9 GHz is designed through equivalent circuit theory. In combination with the lossy layer, absorption above 0.8 at 3.7-5.6 GHz and 9.1-12.5 GHz was achieved. Further, the structure was fashioned into a curved surface with varying curvature, demonstrating its effective absorption and transmission properties across different curvatures. A 15 × 15 cell structure was designed and fabricated, and there was good agreement between the test results and simulation results. The proposed structure has important applications in radomes, conformal structures, and electromagnetic shielding.

In-band dual-polarization RCS reduction of waveguide slot array antenna integrated with AMC and PEC chessboard structure

An in-band low radar cross section (RCS) waveguide slot array antenna (WSAA) is proposed by using a chessboard structure composed of artificial magnetic conductor (AMC) and perfect electric conductor (PEC), which serves as the antenna radiator. The method for RCS reduction is the reflection energy cancellation. Standing wave array is used to achieve higher energy efficiency and more compact antenna structure. Experimental results show that the in-band monostatic RCS is sufficiently reduced with the chessboard structure application for both co- and cross-polarized incident waves, where 10-dB RCS compression is realized among the frequency range of 9.7–9.91 GHz for co-polarization and 9.5–9.85 GHz for cross-polarization with maximum RCS reductions of −13.3 dB and −11.9 dB, respectively. Meanwhile, the designed WSAA maintains the high gain characteristics of the original WSAA. The paper provides a simple, practical and effective strategy for stable RCS compression in the operation band of waveguide antenna array, which has potential applications in stealth platforms.

Broadband low-scattering and high-efficiency transmission radome by combining phase gradient metasurface and FSS

In this paper, a novel method to achieve high-efficiency transmission radome with broadband low radar cross section (RCS) is proposed by combining phase gradient metasurfaces (PGMs) and frequency selective surface (FSS). The PGMs-FSS is an ultra-thin single-layered structure composed of a modified Jerusalem resonator backed with an FSS. The FSS works as a high-pass filter for transmitting the in-band signals and reflecting the out-of-band signals, and the PGMs works for reducing the RCS. The insertion loss is less than −1 dB within the passband of 15.95 GHz–17.7 GHz. Moreover, the particle swarm optimization (PSO) algorithm is used to extend the RCS reduction bandwidth as well as in-band high transmission. A prototype with a thickness of 0.08 λl (λl is the wavelength of the low frequency) is designed, fabricated, and measured. The results demonstrate that an over 10 dB RCS reduction is obtained from 7.95 GHz to 18.12 GHz, i.e., the relative bandwidth reaches 78.02%. The proposed method of combining PGM-FSS can be used in designing radomes of stealth platforms for the requirements of broadband RCS reduction as well as high-efficiency signal transmission.

Structural Engineering of Hierarchical Magnetic/Carbon Nanocomposites via In Situ Growth for High-Efficient Electromagnetic Wave Absorption

HighlightsHierarchical Fe3O4-Fe@CNFs/Al-Fe3O4-Fe nanocomposites were constructed by in situ growth, vacuum-assisted filtration, and self-reduction methods.The carbon framework, with in situ grown magnetic nanoparticles, supports two-dimensional magnetic nanosheets, achieving excellent electromagnetic performance and good impedance matching.Excellent reflection loss value (− 59.3 dB), broadband wave absorption (5.6 GHz at 2.2 mm thickness), and low radar cross-section value were achieved.

Multifunctional Ultrathin Metasurface with a Low Radar Cross Section and Variable Infrared Emissivity.

The development of stealth devices that are compatible with both infrared (IR) and radar systems remains a significant challenge, as the material properties required for effective IR and radar stealth are often contradictory. In this work, based on an IR electrochromic device (IR-ECD), concepts of metamaterial manipulating electromagnetic waves are applied to develop a multifunctional ultrathin metasurface with a low radar cross section (RCS) and variable infrared emissivity. This paper presents a linear-to-linear polarization conversion metasurface (PCM) designed by hollowing the IR-ECD. In this way, the IR-ECD based on polyaniline (PANI) can also modulate the reflection waves in the microwave band without affecting its features in the infrared region. Thus, the proposed metasurface integrates both microwave stealth and variable infrared emissivity through a single layer. The measured results show that a 10 dB RCS reduction is achieved in the band of 8.46-9.5 GHz, and the infrared emissivity can be adjusted from 0.870 to 0.513 in the infrared stealth band of 8-14 μm. Due to the ultrathin thickness (only 0.081λ0 at 9 GHz), low RCS in the X-band, and variable infrared emissivity, the designed multifunctional stealth metasurface has promising applications on military platforms with various surrounding environments.

Mesh-based antenna with broadband transparency for dual-band shared-aperture array

Mesh-based antenna with broadband transparency for a dual-band shared-aperture array is proposed in this design. The low-radar cross section (RCS) frequency selective surface (FSS) cell is obtained firstly by combining the capacitive and inductive strips. It can be found that the electromagnetic (EM) transparent bandwidth across the high band (HB: n77) of the FSS can be enhanced by increasing in the number of strips. Then the low band (LB) antenna composed of low-RCS mesh-based elements is constructed. Remarkably, the EM transparent characteristic and the LB working performance can be individually controlled, avoiding time-consuming optimization. Subsequently, the LB transparent antenna is introduced into the array to eliminate the blockage effect on the HB antenna. The radiation patterns of the HB antenna are recovered well across the entire HB. Finally, the array prototype is fabricated and measured results show that the array covers a dual band of 1.7–2.7 GHz (45%) and 3.3–4.2 GHz (24%), showing stable radiation patterns in both LB and HB antennas. The average gains of the LB and HB antennas are 8.64 dBi and 8.58 dBi, respectively. The results verify that the proposed broadband transparent mesh-based antenna is attractive in the shared-aperture array.

Reducing radar cross section through absorption metamaterial antenna for concealment and detection applications

In this work, the technology of metamaterials (MM) is utilized to build a low radar cross-section (RCS) antenna through absorption MM array for concealment and detection applications. A novel MM unit cell is proposed and designed, and then an array of the proposed MM unit cell is constructed. A patch antenna is designed and implemented with the MM array to construct the whole absorption metamaterial RCS antenna. The designed RCS antenna is tested in two modes, in the transmitting mode, it operates at a specified frequency of 5.8 GHz with high impedance matching, high gain, and high efficiency. In the receiving mode, the antenna can scatter the electromagnetic waves transmitted by other devices at the specified frequency by absorbing them. The proposed antenna is designed, simulated, fabricated, and then tested. The measured results demonstrate that the proposed antenna has an absorption factor of 99 %, efficiency of exceeds 90 %, reflection coefficient of −36.8 dB and high gain of 6.7 dBi at the designated frequency, which much agrees with the simulation data.

Detection of Drones using SDR as a RADAR

With the evolution of technology, the application of drones in Fourth Generation Warfare has increased manifolds. Drones offer many advantages as they are inexpensive to operate, can fly for longer periods, and are less vulnerable to enemy fire. This makes them an ideal, inconspicuous, and low-cost weapon for both conventional and non-state actors to carry out targeted attacks on valuable targets. Detection of drones is a major challenge as they offer minimum Radio signature and low Radar cross-section. A credible method to detect incoming drones is by employing Software Defined Radio as a RADAR

Broadband Dual-frequency High Isolation Base Station Antenna with Low RCS Structure Loaded

A novel dual-band dual-polarization shared aperture antenna is proposed, which covers frequencies 1.7–2.6 GHz and 3.3–3.8 GHz. The structure, with low radar cross section (RCS), is designed to reduce the radiation interference on the high band (HB) antenna. Additionally, by introducing U-shaped slots on the arms of the low band (LB) antenna, polarization isolation between the HB elements is significantly enhanced, which can reach up to 25 dB across the whole band. Moreover, to restore the radiation pattern of the LB antenna, the dielectric substrate is employed beneath the HB antenna as a substitute for the ground plane. The antenna proposed in this paper possesses attributes of broadband, compact size, and simplified structure.

Antenna array-based metasurface for multi-scenario wide-angle polarization-insensitive radar cross section reduction

In this paper a novel antenna array-based metasurface design method for wide-angle and polarization-insensitive radar cross section (RCS) reduction has been proposed, which can be applied to a variety of RCS reduction scenarios. The proposed metasurface subarray design employs a dual-element antenna array in which the two ports of each element are connected through a Wilkinson power divider, and meanwhile, two power dividers are connected through a microstrip line with a lumped resistor. The use of dual-polarized wide-beam antennas enables the metasurface array to respond to arbitrarily polarized as well as wide-angle obliquely incident electromagnetic waves. A portion of the electromagnetic waves received will be absorbed by the lumped resistor and converted into heat, while the remaining portion will be canceled in the space, achieving the low RCS characteristic. The proof-of-concept experiments have been conducted in several application scenarios for RCS reduction, including a metasurface array integrated with a microstrip antenna, a densely distributed dual-element metasurface array, and a randomly distributed dual-element metasurface array. Simulated and measured results confirm that the proposed method opens up a new avenue for more flexible and versatile RCS reduction devices and systems.

Comprehensive Review: Effectiveness of MIMO and Beamforming Technologies in Detecting Low RCS UAVs

Unmanned aerial vehicles (UAVs) are increasing in popularity in various sectors, simultaneously rasing the challenge of detecting those with low radar cross sections (RCS). This review paper aims to assess the current state-of-the-art in radar technology, focusing on multiple-input multiple-output (MIMO) and beamforming techniques, to address this growing concern. It explores the challenges associated with detecting UAVs in urban settings and adverse weather conditions, where traditional radar systems often do not succeed. This paper examines the existing literature and technological advancements to understand how these methodologies can significantly boost detection capabilities under the constraints of low RCS. In particular, MIMO technology, renowned for its spatial multiplexing, and beamforming, with its directional signal enhancement, are evaluated for their efficacy in the context of UAV surveillance and defense strategies. Ultimately, a comprehensive comparison is presented, drawing on a variety of studies to illustrate the combined potential of integrating these technologies, providing the way for future developments in radar system design and UAV detection.

Broadband RCS reduction metasurface based on vortex singularities generated by Spin-to-Orbital angular momentum conversion

A broadband radar cross-section (RCS) reduction employed by the vortex metasurface is proposed. The underlying physics is associated with the Pancharatnam-Berry geometrical phases involved in spin-to-orbital angular momentum conversion. The proposed metasurface generates spin-controlled vortex waves with different topological charges. The vortex singularity implements specular extremely low RCS reduction. The prototypes are fabricated and measured to verify the wideband performance of the RCS reduction. The simulated results illustrate that −10 dB broadband RCS reduction from 9 GHz to 22.5 GHz and the RCS reduction has peak values −37.2 dB, −40.8 dB, and −42.5 dB at 9.8 GHz, 13.1 GHz, and 20.8 GHz, respectively. The measurement results illustrate that −10 dB RCS reduction over 9.1–18 GHz is realized, and the RCS reduction peak −53 dB at 10.1 GHz. The measured electric field intensities and phase distribution of the vortex metasurface also be displayed. Due to the limitation of experimental conditions, no test was done in the range greater than 18 GHz. Far-field results achieve good agreement between simulations and experiments, and the near-field measurements are a subtle difference in the experimental results. This work reveals the potential advantages of vortex waves in the fields of multifunctional electromagnetic stealth, beamforming for communication systems, etc.