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Copyright of Dokuz Eylul University Muhendislik Faculty of Engineering Journal of Science & Engineering / Dokuz Eylül Üniversitesi Mühendislik Fakültesi Fen ve Mühendislik Dergisi is the property of Dokuz Eylul Universitesi Muhendislik Fakultesi Fen ve Muhendislik Dergisi and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Frequency encoding chipless Radio Frequency Identification (RFID) tags have been frequently using the radar cross section (RCS) parameter to determine the resonant frequencies corresponding to the encoded information. Recent advancements in chipless RFID design have focused on the generation of multiple frequencies without considering the frequency position and signal amplitude. This article proposes a novel method for chipless RFID tag design, in which the RCS response can be located at an exact position, corresponding to the desired encoding signal spectrum. To achieve this, the empirical Taguchi method (TM), in combination with particle swarm optimization (PSO), is used to automatically search for optimal design parameters for chipless RFID tags with a fast response time, to comply with the frequency encoding requirements in the presence of the mutual coupling effect. The proposed design method is validated using I-slotted chipless tag structures that are fabricated and measured with different sets of resonant frequencies. [ABSTRACT FROM AUTHOR]

Aiming at the problem that the radar signal of ballistic target is easily affected by the environment and the target recognition accuracy is low, a radar cross section (RCS) recognition method of ballistic target based on dual-tree complex wavelet transform (DTCWT) and variational autoencoder (VAE) is proposed. Firstly, the dynamic datas of ballistic target RCS are preprocessed by DTCWT. Then, the hidden variable features of target are extracted by VAE. Finally, the support vector machine (SVM) classifier is used to identify the data. Experimental results show that compared with the existing methods, the proposed method has higher recognition probability and better robustness. [ABSTRACT FROM AUTHOR]

In this work, an ultra-wideband absorptive coding metasurface (ACM) is proposed for radar cross-section (RCS) reduction. The ACM is composed of two types of lossy coding elements arranged in an appropriate manner, the two types of lossy coding elements both have a certain wave-absorbing performance due to ohmic loss, and the main reflection phases will differ by almost 180° under same incidence in an ultra-wide frequency arrange. Therefore, the ACM can achieve ultra-wideband RCS reduction by means of diffusion and absorption. The simulation results demonstrate that the RCS of the ACM under normal incidence with arbitrary polarization can be effectively reduced in the ultra-wide frequency band of 7.5–43.0 GHz with a relative bandwidth of 140.6%; moreover, when the incident angle is increased to 45°, an ultra-wideband RCS reduction can still be achieved. Finally, an experimental prototype is fabricated and measured, and the performance of the ACM is experimentally validated. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this letter, a tunable hybrid metasurface (THMS) with electromagnetic switching characteristics based on the field‐programmable logic gate array (FPGA) is developed, which combines the mechanisms of both phase cancellation and absorption. Compared to other hybrid metasurface, the proposed design possesses two major functions of electromagnetic switching and dynamic tuning. By adjusting the bias voltage of the active components controlled by FPGA module, the in‐band tuning and active switching at different frequency bands of 3.63–5.57, 4.86–10.47, and 9.40–12.36 GHz can be obtained. A physical prototype with the size of 350 mm × 370 mm is fabricated and measured for verification, and the measurement shows that the monostatic radar cross section achieves varying degrees of reduction from 1.66 to 12.04 GHz. [ABSTRACT FROM AUTHOR]

In this work, an ultra-wideband reflective polarization conversion metasurface (PCM) is proposed at first. Because the PCM is an anisotropic structure that is symmetric with respect to both x- and y-axes, and the reflection phase difference under x- and y-polarized incidences is close to 180° in an ultra-wide frequency range, the PCM can achieve both linear polarization conversion and circular-polarization (CP) maintaining reflection in the ultra-wide frequency band from 8.3 to 41.3 GHz except for near the frequency point of 38.8 GHz. Moreover, when its unit cell structure is rotated by 90°, its cross-polarized reflection coefficient under LP incidence, together with the co-polarized reflection coefficient under CP incidence, will be changed by almost 180° in phase. Thus, based on the PCM, an ultra-wideband coding diffusion metasurface (CDM) is further proposed for radar cross section (RCS) reduction. The simulation and experiment results indicate that the CDM can achieve effective RCS reduction in the ultra-wide frequency band of 8.2–41.7 GHz under normal incidence with arbitrary polarization; in addition, an ultra-wideband RCS reduction can still be realized under oblique incidence with an incident angle less than 45°, which shows that the CDM is of good application value in radar stealth technology. [ABSTRACT FROM AUTHOR]

In this study, a coding diffusion metasurface (CDMS) based on a circular-polarization (CP)-maintaining metasurface is proposed for radar cross-section (RCS) reduction. The CP-maintaining metasurface can achieve ultra-wideband CP-maintaining reflection, and its main reflection phase under CP incidence can be adjusted at will by the Pancharatnam-Berry phase generated by the rotation of its unit cell, so it can be used to design CDMS. Thus, based on the CP-maintaining metasurface, the 2-bit CDMS is proposed. The simulated and measured results demonstrate that the CDMS can achieve highly effective and ultra-wideband RCS reduction under arbitrarily polarized incidences, compared with a pure metallic plate of the same size, its RCS can be reduced by more than 10 dB under normal incidence in the ultra-wide frequency band of 7.1-33.6 GHz with a relative bandwidth of 130.2%; moreover, when the incident angle is increased to 40°, an ultra-wideband RCS reduction can still be achieved. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In response to the broadband stealth challenges faced by armed helicopters, this paper proposes a method that utilizes ray-tracing and inverse synthetic aperture radar (ISAR) imaging to pinpoint the locations of strong scattering sources of the helicopter. The paper introduces a conceptual design that integrates electromagnetic metamaterials and magnetic materials into the strong scattering source regions of the helicopter. The stealth effects are calculated and analyzed after incorporating two types of stealth materials onto the helicopter. The paper firstly analyzes the principles of equivalent medium theory, ray-tracing and ISAR imaging. Subsequently, through the calculations of ray-tracing and ISAR imaging, the locations of strong scattering source can be captured accurately and intuitively. Finally, the reflection coefficients of the two types of stealth materials are presented and mono-station radar cross section (RCS) changes are analyzed after materials are loaded on the helicopter. The calculation results show that the two different types of stealth materials can achieve the RCS reduction in the special angular domain after covering part of the helicopter’s strong scattering source, providing a reference for the integration design of stealth materials, helicopter skins and main-rotors. [ABSTRACT FROM AUTHOR]

This paper equates chaff clouds to dipole clusters and studies the electromagnetic scattering problem of dipole clusters based on the linear method of moment (LMM) that solve the electric field Integral equation with the pulse basis function. Firstly, the radar cross section (RCS) of three dipole elements is calculated. The dipole element is divided into 11 segment line units using pulse basis functions. The actual chaff clouds are modeled as two nearest dipole cluster models, which are cubic dipole cluster with uniform distribution formed and spherical dipole cluster with Gaussian distribution formed. The total RCS and total E‐Field magnitude of two dipole cluster models were calculated. Finally, two physical models are constructed based on the simulation models and an experiment is designed. The electromagnetic scattering characteristics of the two models are measured, which verifies the accuracy of the simulation results and the operability of the experiment. [ABSTRACT FROM AUTHOR]

This paper develops a novel stochastic geometry model to investigate design tradeoffs in a large-scale radar-aided millimeter-wave cellular network to eliminate the beam training overhead. In the proposed system, each base station comprises two sub-systems: the sensing sub-system, where radar localizes users, and the communication sub-system, where directional antennas serve the detected users. Both sub-systems operate simultaneously to eliminate the beam training overhead and reduce misalignment errors. The system is modeled under realistic fading conditions with scatterers and interferers in the environment. System parameters, such as the density of mobile users and undesired clutter, radar cross-section fluctuations, radar search duration, antenna directivity, and bandwidth are considered in the analytical model. Two scenarios are studied; the first considers antenna misalignment for the communication sub-system, where error magnitude depends on the radar sub-system accuracy. The other scenario considers perfect alignment for benchmarking. It is demonstrated that the radar search duration, which controls the radar antenna beamwidth, is a crucial parameter for optimizing the system throughput. Moreover, the beamwidth of the communication antenna exhibits a tradeoff in which a narrow beam yields higher gain and reduces interference but increases the misalignment error impact. The results demonstrate that if the beamwidths of both sub-systems are carefully chosen, the proposed system can eradicate the beam training overhead without compromising the system’s performance, in addition to significantly enhancing the average total system throughput.

Incoherent backscattering of mm-waves from natural rough surfaces is considered. A novel method is proposed to determine the statistical properties of surface scattering from range profile measurements. The method is based on modeling the road surface as a grid of uncorrelated scattering elements, described by normalized scattering matrices. Using this model, expressions are derived to estimate the mean value and covariance matrix of surface scattering from measurement data. This procedure is then applied to measurement data of four road surface types, namely: 1) dry asphalt, 2) wet asphalt, 3) asphalt covered by basalt gravel, and 4) old asphalt. Using the derived statistical normalized radar cross-section models, two novel applications are proposed. First, a procedure for synthesizing/simulating surface clutter is proposed. This procedure is subsequently used to simulate received power from surfaces comprising patches of one or multiple road surface conditions. Excellent agreement between simulation and measurement results is demonstrated. Second, a method for determining the optimal polarization of the electromagnetic sensing waves used in a single-polarized radar system is proposed. This method is based on factorizing the antenna polarization vector into two bounded parameters, allowing for numerical evaluation of the minima and maxima for targets with a specified scattering matrix. This method is further extended to work with statistical descriptions of scattering matrices by means of Monte Carlo simulations.

In this article, a new type of EBG structure known as frequency selective surface (FSS) with reconfigurable capability is investigated. The proposed design introduces a new adjustable band stop filter equipped with PIN diodes. Operating frequency of the FSS structure is in the C-band and in the frequency range of 4GHz to 8GHz, which at the central frequency of 4.75GHz, provides a bandwidth of about 1 GHz, when the state of the diode being on. The center frequency of this filter is shifted to 5.23 GHz when the diode is off. In fact, this structure is supposed to be used as a type of electromagnetic coating filter for space payload in the next generation satellites. After the design and simulation of the final cell, an equivalent circuit model is also presented to confirm the design and simulation. These structures protect electronic modules of satellite payload against electromagnetic radiation, electronic warfare. The RCS reduction is the other application of the FSS structure.

In this research, a manpack radar is designed using frequency modulated continuous wave (FMCW) technology. The signal is continuously transmitted by separate antennas with microstrip array antenna technology for the transmitter and receiver. The use of new technology allows the manpack radar to detect targets using low transmit power (=10 W) so that it can operate on batteries. With dimensions of 520 mm (W) x 410 mm (H) x 108 mm (D) and weighing only 15.9 kg, this radar can be easily carried by personnel for maneuvering in the field. Although the dimensions of this manpack radar system are small, it has high detection capability, whereby it can detect drones, humans, small vehicles and large vehicles at ranges of up to 2, 3, and 5 km respectively. In addition, this radar system not only detects targets horizontally, but also vertically so that it can calculate the height of the target. It can also track multiple targets simultaneously and display the parameters of each target, such as distance, speed and altitude. With these aspects, this radar system design is effective for use by Indonesian National Armed Forces (TNI) personnel in the field to conduct surveillance for supporting combat operations. [ABSTRACT FROM AUTHOR]

Frequency encoding chipless Radio Frequency Identification (RFID) tags have been frequently using the radar cross section (RCS) parameter to determine the resonant frequencies corresponding to the encoded information. Recent advancements in chipless RFID design have focused on the generation of multiple frequencies without considering the frequency position and signal amplitude. This article proposes a novel method for chipless RFID tag design, in which the RCS response can be located at an exact position, corresponding to the desired encoding signal spectrum. To achieve this, the empirical Taguchi method (TM), in combination with particle swarm optimization (PSO), is used to automatically search for optimal design parameters for chipless RFID tags with a fast response time, to comply with the frequency encoding requirements in the presence of the mutual coupling effect. The proposed design method is validated using I-slotted chipless tag structures that are fabricated and measured with different sets of resonant frequencies.

In this work, an ultra-wideband coding phase gradient metasurface (CPGM) is proposed for radar cross section (RCS) reduction. The design process is presented in detail, in which eight types of coding elements are proposed firstly by using Pancharatnam-Berry (P-B) phase. The eight types of coding elements have different reflection direction or phase response under the same EM-wave incidence for they can introduce a series of phase gradients with different directions or starting- values under both right-handed and left-handed circular-polarized incidences, so the proposed CPGM composed of these coding elements has excellent performance in RCS reduction. The simulated results show that, compared with a pure metallic plate with the same size, the RCS of the CPGM can be reduced more than 10 dB in the ultra-wide frequency band of 9.2-46.2 GHz under normal incidence with arbitrary polarization, the relative bandwidth is up to 133.6%; moreover, the RCS reduction under oblique incidence with arbitrary polarization can still be kept larger than 9.3 dB in the frequency band of 13.1-42.5 GHz when the incident angle is increased to 45°. Finally, one experiment is carried out, a reasonable agreement exists between the simulated and experimental results. [ABSTRACT FROM AUTHOR]

Radar Cross Section (RCS) plays a significant role in detecting and tracking the space-based objects such as launch vehicles, missiles, aircrafts etc. In space applications, Radar systems are used to track and provide real-time trajectory information of the satellite launch vehicles after the lift off from the launch pad for range safety purpose. RCS is a critical key parameter that determines tracking performance of the Radar and it is highly dependent on both Radar operating parameters and the target characteristics. For space-based applications, a good quantity of RCS is required for quick detection by the Radar for continuous tracking. In order to choose the best Radar tracking configuration for real time tracking of the launch vehicle, it is required to model and simulate the launch vehicle’s RCS fluctuations prior to launch in order to predict the real time Signal to Noise Ratio (SNR) for its complete dynamic trajectory. This modeling and simulation methodology will help to choose the optimum Radar configuration for obtaining a good quantity SNR in the real-time launch. This study also provides good guidance to Radar operators for the effective Radar operation during real time space object tracking. This paper demonstrates, the real-time RCS fluctuations of a typical ISRO launch vehicle through simulation for its dynamic trajectory using physical optics based EM software prior to launch. Furthermore, the simulation results are validated with real time monostatic Radar tracking data, which showed good agreement. [ABSTRACT FROM AUTHOR]

Measuring the radar cross-section (RCS) of a far-field (FF) target in engineering can be challenging, especially when remote measurement is difficult. To overcome this challenge, an FF RCS can be predicted by near-field (NF)-extrapolated transformation. However, due to the relative error between the theoretical and measured electric field (E-field) values in a NF, the extrapolation calculation of a FF can be carried out by correcting the NF amplitude. This paper proposes the use of the state space method (SSM) to estimate the amplitude-only of NF E-fields for improving the prediction accuracy of FFs. The simulation results demonstrate that the SSM can estimate NF amplitude, which can be transformed into a FF, and which can lead to improved prediction accuracy when compared to reference-FF-calculated and to circular-NF-to-FF-transform-(CNFFFT)-calculated RCSs. [ABSTRACT FROM AUTHOR]

In order to solve the problem of electromagnetic wave scattering on non-convex objects, a combined method based on the method of physical optics with corrections for multiple reflections was discussed. The calculation of these corrections was carried out by the ray method. The article considered the effect of taking into account the curvature of the surface on the calculation error. The results of the calculations of the test example were compared with the calculations by the rigorous method of moments. [ABSTRACT FROM AUTHOR]

ObjectivesChanges in attitude caused by sailing motion will lead to changes in the probability density of the radar cross section (RCS) of a ship. As such, it is necessary to master the influence degree of various motion conditions on the probability density of the RCS of a ship under grazing incidence. MethodUsing the quasi-static method, a hydrodynamic and electromagnetic scattering characteristic co-simulation model and calculation process are constructed. A 10 GHz continuous wave at grazing incidence is selected as the radar detection wave threat, and the RCS probability distributions of the ship's body under different statistical times, sea states, speeds, headings and other parameters are compared and analyzed.ResultA lognormal distribution model is used to simulate the distribution characteristics of the static RCS of the ship model. The probability distribution of the dynamic RCS is basically stable when the statistical time is longer than 250 seconds. There exists a "burr" phenomenon in the dynamic RCS probability distribution curve under low sea states, following waves or beam sea drifting conditions.ConclusionThe effects of the ship's speed on its RCS probability density distribution can be ignored. The influence of the sea wave direction angle on the RCS probability density distribution is obvious only in high sea states. The increase of the sea state makes the RCS distribution probability curve increasingly smooth. Statistical time has a great influence on the RCS probability density distribution, so it is necessary to accumulate sufficient data to carry out a test or simulation that can provide an accurate grasp of a ship's RCS probability distribution characteristics.

ObjectiveIn order to clarify the interference of ship movement on the radar cross section (RCS) measurement statistics of a real ship, the statistical characteristics of ship body X-band RCS under various motion states are analyzed.MethodsA dynamic RCS simulation method of a ship body under low sea state motion is established, and a unified model of hydrodynamic simulation and electromagnetic scattering is created on the basis of the DTMB 5415 benchmark surface ship model. The dynamic RCS data of ships detected by X-band radar at a horizontal incident angle are obtained, and the influence boundaries and rules of statistical time, sea state, speed and sea wave direction on the statistical features of RCS are analyzed. Results The results show that the statistical characteristics of the dynamic RCS of a ship body are different from those in a static state. The influence range of the general values of RCS under low sea state, speed and wave angle is within 0.9 dB. The RCS of a ship's characteristic direction is sensitive to changes in the sea wave direction angle, and decreases gradually with the increase of the sea state.ConclusionsThe results of this study can provide references for better understanding the interference of ship motion on the statistical characteristics of RCS measurement, and support the selection of real ship RCS measurement conditions.

Radar cross section (RCS) is a scattering measure of an object that scatters to the radar. However, existing methods for near-field (NF) measurement and data processing rarely extract amplitude characteristics, and there is a lack of effective verification of far-field (FF) data in the process of NF to FF transformation, which leads to inaccuracies in FF prediction accuracy. In this paper, we propose a method to establish the relationship between the NF and FF RCS using the state space method (SSM), which is based on accurate estimation of the NF amplitude in NF measurement, and then deriving the FF RCS from the NF scattering signal convolved with a near-to-far kernel. The proposed solution to address the uncertainty issue in reference FF data involves using the geometric theory of diffraction (GTD) scattering center model as the reference FF data and establishing a linear equation with the derived FF model. The negative gradient search (NGS) system identification concept is used to optimize the FF model in order to reduce the discrepancy between the reference and derived values. Finally, the corrected RCS error is provided as additional proof of the effectiveness of these techniques in enhancing near-to-far transformation accuracy by examining the outcomes of three experiments. [ABSTRACT FROM AUTHOR]

A new idea is proposed for a radar cross section (RCS) reduction metasurface, which consists of three types of artificial magnetic conductor (AMC) units. Using resonance circuit and transmission line theory, the reactance expression of an ideal AMC unit with a destructive phase difference is derived. First, the parallel LC resonant circuit that conforms to the reactance expression is designed. Taking the resonant circuit as the equivalent circuit of the unit, the AMC unit corresponding to the circuit model is obtained. Then there is a destructive phase difference (180° ± 37°) between the designed AMC units. Secondly, the phase difference frequency band is expanded from 11.5–17.25 GHz to 7.25–17.25 GHz by adding the AMC3 unit. Finally, three AMC3 cells are arranged into metasurfaces in a new triangular arrangement, and the metasurface achieves RCS reduction at 6.5–16.7 GHz. [ABSTRACT FROM AUTHOR]

This paper proposed a plasmonic absorbing structure suitable for super high frequency. The plasmon absorbing structure is a periodic square cavity structure; the bottom of the cavity is a metal plate, the wall of the cavity is a polyester plate, and metal frames loaded with lumped resistors are printed on both sides of the polyester plate. The transmission characteristics of the absorbing structure are studied using the finite difference time domain method. The results show that the plasmon resonance characteristics can be effectively improved by loading the lumped resistance reasonably. The absorption rate of the absorbing structure is over 80% in the 4.3–21.5 GHz frequency band, and in the 4.3–7.7 GHz and 14.2–21.5 GHz frequency bands, the absorption rate is around 90%. Under different polarization modes, it is less sensitive to the incident angle. The transmission response of the absorbing structure is measured in a microwave anechoic chamber, and the measurement results agree well with the simulation results. After replacing the metal bottom plate of the absorber with a metal cavity, the radar cross-section of the cavity is reduced by 99.45% at 10 GHz. It proves that the designed and fabricated absorbing structure has the broadband absorbing ability, high angular stability, and broad application prospects. [ABSTRACT FROM AUTHOR]

In this paper, a unique structural design methodology for chipless radio-frequency identification (RFID) tags in frequency domain is presented. The tag geometry is developed by loading an open-loop resonator with micro-metallic-cells (MMC). The realization give rise to a checkerboard resonator type with electromagnetic signatures in its radar cross section that are extremely efficient to manipulate. The resonators layout is distributed on either side of a Rogers substrate to double its coding density. The proposed chipless RFID tag has a memory of 8-bits in total. The operating band of the tag is 6.5-10.5 GHz. The tag has a high bit coding density of 10.94 bits/cm2 and spectral efficiency of 2 bits/GHz. The tag has a very compact size of 17.4 × 4.2 mm2. The simple structuring methodology and efficient resonators layout will give RFID system designers the flexibility to apply the proposed tag in a wide range of modern applications.

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. [ABSTRACT FROM AUTHOR]

In the process of using the Distributed Radar Network Localization System (DRNLS) further to improve the survivability of a carrier platform, the random characteristics of the system's Aperture Resource Allocation (ARA) and Radar Cross Section (RCS) are often not fully considered. However, the random characteristics of the system's ARA and RCS will affect the power resource allocation of the DRNLS to a certain extent, and the allocation result is an essential factor determining the performance of the DRNLS's Low Probability of Intercept (LPI). Therefore, a DRNLS still has some limitations in practical application. In order to solve this problem, a joint allocation scheme of aperture and power for the DRNLS based on LPI optimization (JA scheme) is proposed. In the JA scheme, the fuzzy random Chance Constrained Programmin model for radar antenna aperture resource management (RAARM-FRCCP model) can minimize the number of elements under the given pattern parameters. The random Chance Constrained Programmin model for minimizing Schleher Intercept Factor (MSIF-RCCP model) built on this basis can be used to achieve DRNLS optimal control of LPI performance on the premise of ensuring system tracking performance requirements. The results show that when RCS has some randomness, its corresponding uniform power distribution result is not necessarily the optimal scheme. Under the condition of meeting the same tracking performance, the required number of elements and power will be reduced to a certain extent compared with the number of elements in the whole array and the power corresponding to the uniform distribution. The lower the confidence level is, the more times the threshold is allowed to pass, and the lower the power is, so that the DRNLS can have better LPI performance. [ABSTRACT FROM AUTHOR]

The traditional power allocation method for multi-target localization adopts the Robust Chance Constrained Power Allocation Scheme (RCC-PA), which does not consider the strong clutter characteristics in the current radar detection environment. However, how to reasonably allocate the power required for the radar to locate the target in the strong clutter is a fundamental challenge for improving the combat capability of the radar. Since Simultaneous Multi-beam Digital Array Radar (SM-DAR) can provide high-resolution information on targets in strong clutter, this paper extends the RCC-PA scheme to strong clutter and introduce an extended target model suitable for high-resolution SM-DAR. At the same time, the Gamma distribution is used to reflect the statistical characteristics of the Radar Cross Section (RCS) so that the extended RCC-PA scheme (ERCC-PA) can be suitable for all the scatterers whose RCS belong to Gamma distribution families. In the ERCC-PA scheme, the Strong Clutter Information Reduction Factor (SCIRF) of the extended target is first derived. Then, a Gamma Chance-constraint Programming Model (Γ -CCP model) is constructed to optimize the power allocation for locating multiple extended targets in strong clutter. The extended dichotomy method for power allocation is also given. Theoretical analysis shows that the power of multi-target localization in strong clutter can still be reasonably allocated under the target with multi-measurement characteristics. In addition, the power distribution of multi-target localization in the strong clutter is negatively correlated with the shape parameter of the Gamma distribution. Specifically, the larger the shape parameter characterizes the larger individual strong scatterer, resulting in the SM-DAR requiring less positioning power. The experimental results verify the theoretical analysis and show that the ERCC-PA scheme can improve the utilization of power compared with the benchmark and has the advantage of robustness to the fluctuation of the target RCS. [ABSTRACT FROM AUTHOR]

Laguerre–Gaussian (LG) beam scattering by a perfect electromagnetic conductor (PEMC) cylinder coated with a metamaterial is analyzed. In order to obtain the LG beam scattering from PEMC cylinder, the beam expressions are modified by considering the LG potential and plane wave scattering. The influence of beam parameters such as; the radial mode (p) , azimuthal mode (l) , and beam waist radius (w 0) is studied. The normalized bistatic radar cross section can be amplified or repressed using these parameters. A comparison of our results for p = 0 and l = 0 (fundamental Gaussian beam) by a PEMC coated cylinder is carried out and indicates good agreement for plane wave scattering. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, a novel broadband and low profile magnetoelectric dipole (MED) antenna with a low radar cross section (RCS) is proposed. The 10 dB RCS reduction is achieved by shifting the reflected energy to six directions, which is an efficient optimization method based on convolutional operations. Specifically, the polarization conversion metasurface (PCM) unit with high polarization conversion rate is constructed and employed in the MED antenna for RCS reduction. The proposed antenna is fabricated and measured. Measured results depict that the low RCS antenna offers good impedance matching in 12–15.6 GHz (relative bandwidth 26%). Compared with the reference antenna, the RCS of the proposed antenna is reduced by more than 10 dB from 9.9 to 16 GHz. It is proved that the proposed antenna has broadband and stable radiation performance and outstanding specular reflecting suppression capabilities. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surfaces (RIS) have been considered as a promising solution to enhance the spectrum and energy efficiency of the 5G+ and future 6G wireless communication systems. The performance of RIS will become the key metric of these communication systems. In this paper, we proposed a wideband Lorenz resonance-based metasurface reconfigurable reflectarray (MSRRA) realization scheme with low energy consumption targeted at the center frequency of 28 GHz. A compact voltage bias network for the varactor diodes is carefully designed to reduce losses in RF current and the influence of the bias circuit on the radiating element effectively. An equivalent circuit model for the MSRRA unit cell is also introduced to predict the properties of the MSRRA system, which can be used to optimize the MSRRA design efficiently. In the experimental tests, the proposed MSRRA system can be optimized to cover a dynamic reflection phase range of over 300° with a bandwidth of 3.83 GHz, which is consistent with the simulation results. The measured single-scattering beam bandwidth is 1.85 GHz at the center frequency of 28 GHz, which can fully cover the whole n257 channel of 5G NR. The proposed continuous tunable MSRRA can support 5G+ and 6G indoor, short-range links, and outdoor point-to-point communications. [ABSTRACT FROM AUTHOR]

An anisotropic complementary metantenna (ACMA) is proposed for the integration of low sidelobe radiation and low in-band co-polarized (IBCP) scattering with the aid of characteristic mode analysis (CMA). With the guidance of CMA, the proposed ACMA evolving from a conventional metantenna (MTA) not only generates a coding phase distribution for low scattering but also restores broadside radiation modes like a uniform MTA. With the IBCP conditions set to $x$ -polarization and the band around 9 GHz, the ACMA is constructed by mixing two types of double-layer anisotropic complementary metasurface (MTS) unit cells. Two desired characteristic modes of ACMA are simultaneously excited by a substrate integrated waveguide (SIW) cavity through dual bow-tie slots. Both the simulation and experiments demonstrate that the proposed ACMA achieves both the $x$ -polarized broadside radiation with sidelobe level below −18.9 dB and IBCP scattering levels below −17.8 dB over the frequency range from 8.87 to 9.78 GHz. [ABSTRACT FROM AUTHOR]

There is currently a growing interest in the development of communication systems that consume as little energy as possible, with the idea of eliminating the presence of batteries, which are a very polluting component. This is why the principles of communication based on backscatter modulation, or even more simply on backscattering by a device that takes the form of a label, like a barcode, are being studied more and more. In the latter case, the idea is to use the radar signature of this totally passive label, the geometry of the elements printed on it having been specially designed to perform the desired functions. These new systems cannot claim to do the same things as those working with a power supply or a chip, but they may be of interest for certain applications where the reading distances do not exceed one metre. Compared to barcodes, the main advantages are related to the use of RF waves to communicate, which makes it possible to read through certain objects that are opaque to light, or to significantly reduce the acquisition time of identifiers by being able to scan larger reading areas more easily.

Innovating passive and chipless coded landmarks have recently emerged for high accuracy self-localization systems. Existing landmarks make use of the combination of retro-directive devices, corner reflectors and lenses, with a coding particle in order to give a high RCS response over a wide angle. In this paper, with a consideration of important practical parameters unappreciated in existing designs, we propose a wide-angle retro-directive frequency-coded lens based on a curved one-dimensional Photonic Crystal (PhC) resonator. The proposed frequency-coded lens is made of two parts: a homogenous lens and a curved PhC resonator where the resonator is located along the lens focal line. A frequency coding is used, where the presence or absence of a notch frequency in a specified information channel encodes an information bit. A PhC resonator provides unique advantages over existing coding particles due to its continuity along the lens focal line which creates a stable ID appearance over wide-angle. In addition, the potential of coding in its volume, rather than on the surface, allows for a high coding capacity. Two frequency-coded lenses with single and dual defect resonators are EM simulated, fabricated, and experimentally validated in the W-band (75 GHz-110 GHz). Simulated results show that a wide detection angle of 170° can be achieved where the tag ID is maintained over all angles. A wide retro-directivity of 80° and 60° is experimentally demonstrated for frequency-coded lenses by a single defect (single notch) and a dual defect (double notch) PhC resonator, respectively.

We study the radar cross section (RCS) property of an aircraft considering the electromagnetic (EM) characteristics of a frequency selective surface (FSS) radome, mounted on the aircraft. Instead of full-wave methods, we utilize high-frequency methods, such as the shooting and bouncing rays (SBR), physical theory of diffraction (PTD), and flat model, taking a significant computational efficiency. Based on the developed algorithm, we analyze monostatic and bistatic RCSs of the aircraft equipped with either single- and multi-layer dielectric, FSS, or PEC radomes in terms of frequency and polarization. Our calculations are validated by comparing with those of the commercial EM simulator with significant computational efficiency. The present numerical study indicates that including the radome EM characteristics into the overall aircraft RCS study is crucial for the accurate RCS estimate

This work reports design, development and characterization of both planar and conformal Metasurfaces using resistive Ink based lossy pattern printed on top of FR-4 dielectric substrate for RADAR stealth application. Different geometrical dimensions of the proposed unit cell have been optimized numerically using CST-Microwave Studio, to achieve 20 dB reflection reduction with 60% fractional bandwidth in frequency range 10.5–19.5 GHz under normal incidence with $0.12\lambda _{\mathrm {L}}$ thickness (where $\lambda _{\mathrm {L}}$ corresponds to lower operating frequency) and 10 dB reflection reduction up to 40° oblique angle of incidence in the given frequency spectrum for both TE and TM polarized wave. An equivalent circuit analytical modelling has also been performed to understand and verify the numerical findings which are nearly in agreement. Polarization insensitive characteristics of developed surfaces is achieved using fourfold rotation symmetry of the designed unit cell. The designed absorbers are fabricated in form of planar, cylindrically bent and 90° dihedral Metasurfaces and are characterized using ABmm Vector Network Analyzer (VNA) system and free space measurement method. A thorough different experimental measurements are performed and it is found that measured characteristics are in agreement with numerical-analytical findings.

A metasurface-based polarization converter for ultrawideband radar cross-section (RCS) reduction of planar and conformal surfaces is presented in this paper. Initially, a polarization converter is designed which consists of a modified concentric double (MCD) square ring resonator-based unit cell along with an air gap in between the substrate and the ground plane. This air gap enhances the polarization conversion bandwidth (PCBW) of the converter. An ultrawide PCBW ranging from 6.3 – 20.5 GHz (106%) is obtained with a high polarization conversion ratio (PCR) of 0.9 for normal incident EM waves. The conversion efficiency is also found to be stable for oblique incidences over the aforementioned band with a PCR of above 0.8 upto ±35° angles of incidence. Later on, a checkerboard configuration of the polarization conversion metasurface (PCMS) array and its mirror array is applied on a planar as well as on a cylindrical conformal surface for reducing the radar cross section (RCS). It is observed that a consistent 10 - dB co-polarized monostatic RCS reduction is achieved with the planar PCMS surface over an ultrawideband (5.5 – 20.5 GHz). Even with the cylindrical surface, nearly 10 dB RCS reduction is obtained upto central angles of 60° over a wideband. Both the structures are simulated and measured after fabrication, and a reasonably good agreement is obtained between them.

This communication presents the design of 1 bit coding engineered reflector for wideband monostatic/bistatic radar cross section (RCS) reduction under a wide angle of incidence by redirecting the backscattered electromagnetic (EM) energies into wide and countless angles. The proposed surface can achieve an excellent monostatic/bistatic RCS reduction performance of more than 10 dB over a wide frequency range from 60 to 120 GHz under wide angles of incidence up to 75°. This is achieved by designing a wideband anisotropic polarization rotator unit cell with a relative polarization conversion bandwidth of 66.7% and polarization conversion efficiency of more than 99%. The unit cell and its mirrored version are used to represent the “0” and “1” coding states of an optimized 1 bit coding sequence. The distribution of the “0” and “1” coding states and the dimensions of the anisotropic unit cell are optimized carefully, such that the unit cell will have 180° ± 30° reflection phase difference between the $x$ - and $y$ -axes over the whole three frequency bands (V-, E-, and W-bands) and obtains ultrawideband and wide-angle diffusion scattering patterns under oblique incidence up to 75°. The simulation and experimental results show that the proposed coding engineered reflector has nearly uniform diffusive scattering characteristics under normal and wide-angle off-normal incidences of EM waves up to 75° over the three frequency bands. [ABSTRACT FROM AUTHOR]

Reconfigurable frequency-selective surface (FSS) designs that come with switchable reflection and transmission bands are developed. According to the duality theorem, complementary periodic structures made of similar wire and slot elements shall yield opposite scattering responses. This is facilitated by placing diodes between tips of the proposed #-shaped wire elements. In the reverse-bias state, disconnected elements act as a band-stop-type FSS. By providing a forward bias, connected elements are transformed into a slot array, which generates an inverted passband at the designated resonant frequency. The proposed periodic structure comprises one layer of microstrip line laid on a thin substrate. The #-shaped elements also act as the biasing network for serially connected diodes. Only one bias voltage is needed to control the FSS panel. Range setups and signal processing techniques are devised so that simulated results of infinite FSS can be compared with measured results. By including diode’s equivalent circuits in simulation models, good agreements with prototype measurement results are observed. The complementary reflection and transmission characteristics can be forwarded to advance radome and antenna designs to achieve versatile performance features. [ABSTRACT FROM AUTHOR]

We present an application of adjoint-based adaptive error control and refinement for scattering problems solved using the method of moments (MoM) in the electric field integral equation (EFIE) and the coupled EFIE and magnetic field integral equation (MFIE) formulations. Specifically, we examine the Poggio–Miller–Chang–Harrington–Wu–Tsai (PMCHWT) formulation of the EFIE-MFIE. We first construct the adjoint problems of the EFIE and the EFIE-MFIE for estimating the error of radar cross section (RCS) quantities of interest (QoIs) directly. We then introduce an effective adaptive refinement algorithm based on an error prediction heuristic and a posteriori error estimation, which enables rapid and consistent convergence regardless of a chosen tolerance and the coarseness of the starting discretization. The approach, moreover, inherently promotes equilibration of the QoI error contributions and produces, therefore, consistently balanced meshes. Numerical examples with canonical scattering targets and adaptive $p$ -refinement confirm the strength of the proposed refinement method, demonstrating the ability to generate high-quality discretizations, both in terms of accuracy and efficiency, without expert user intervention. [ABSTRACT FROM AUTHOR]

Asan important means in low-altitude airspace surveillance, passive radar has been widely studied. With the increasing complexity of the low-altitude environment, the urgent need for radar's capability of automatic target recognition (ATR) emerges. In the field of ATR for passive radar, the method based on radar cross section (RCS) is an important direction for the simplicity of feature extraction. In this article, we exploit the compensated quasi-echo-power (CQEP), i.e., quasi-RCS, to realize ATR in passive radar. We propose an ATR method on the basis of the angular diversity. First, we divide the angular space, which consists of four components of the incident angle and scattering angle of electromagnetic wave, into multiple subspaces. Then, we build a subrecognizer in each angular subspace according to the CQEP distribution characteristics. Each receiving station of the multistatic passive radar recognizes targets in an angular subspace corresponding to its observation and outputs a preliminary decision. Based on the preliminary decisions of all receiving stations, a voting strategy is adopted to make the final decision on the unknown target class in the fusion center. Experimental results based on real-life target data show that the proposed method has a significant improvement on the average correct recognition rate with fusion of three receiving stations, which validates the proposed method. [ABSTRACT FROM AUTHOR]

A simple concentric circular ring resonator-based nonreciprocal deca-band absorber is demonstrated in this article. The design primarily consists of two frequency selective surfaces (FSSs) among one is a compliment to the other printed on either side of the 2.4 mm thin FR-4 dielectric substrate. It exhibits near-unity absorption effectively at ten different resonant frequencies over X-Ka bands with an average absorption efficiency of 94.6%. Surface plasmonic resonances are the reason behind the multiband absorption and are illustrated with current profiles at resonant frequencies. The performance is angular stable for both transverse electric and transverse magnetic oblique incidences up to 60o. The design is compact with a structural periodicity of 0.210 ${{\boldsymbol{\lambda }}}_{\boldsymbol{o}}$ and thickness 0.07 ${{\boldsymbol{\lambda }}}_{\boldsymbol{o}}$ , where ${{\boldsymbol{\lambda }}}_{\boldsymbol{o}}$ is the lowest resonant peak's free-space wavelength. The 20×20 array of the design prototype is fabricated, and the measured results agree with the full-wave analysis. Bistatic radar cross section (RCS) analysis of the proposed absorber is evaluated along with a conventional microstrip patch antenna at X-band. Since the absorber design is based on complementary FSSs, it can also be utilized as a reflector for the not absorbing frequencies. The novelty lies in the utilization of the dual-side of the substrate made this design compact with a greater number of absorption peaks and good angular stability, making it potential for real-time RCS, and electromagnetic interference and shielding applications. [ABSTRACT FROM AUTHOR]

In this article, two incomplete partially reflective surface (PRS)-based Fabry–Perot (F-P) antennas each with a high gain, wideband low radar cross section (RCS), and reduced profile are proposed. The reductions of the antenna profiles and RCS are realized based on artificial magnetic conductor (AMC) surfaces and the phase cancellation, respectively. In the first design, two AMC surfaces are placed around the radiation patch and above the PRS. The thickness of the F-P cavity is reduced by half due to the zero-phase reflection of the lower AMC surface around the radiation patch. The income waves are partly reflected by the upper AMC surface above the PRS with zero reflection phase and partly penetrate the PRS and then reflected by the lower AMC surface also with zero reflection phase. The reflected EM waves from the bottom AMC surface travel another distance of quarter wavelength in the upward direction making the total electrical path traveled be half wavelength, thereby causing a phase shift of 180° with the reflected waves from the upper AMC surface, and thus resulting in a wideband RCS reduction. For the second design, another AMC surface is placed below the PRS. On one hand, the middle and lower AMC surfaces have the same reflection phases and then an F-P cavity with a subwavelength thickness is generated. On the other hand, the phase difference between the upper and lower AMC surfaces is also designed as 180°, which is used to suppress the total backward RCS. The two F-P antennas are both fabricated and measured. Measured results validate their reflection, radiation, and scattering performance well. To the best of our knowledge, this work is the first design, which integrates the physical (thin F-P cavity), radiation (gain enhancement), and scattering (broadband RCS reduction) performance of the F-P antenna. [ABSTRACT FROM AUTHOR]