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Copyright of Telecommunication Engineering is the property of Telecommunication Engineering 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.)

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering 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.)

This paper proposes an extremely thin, conformal ultra-wideband polarization-independent metasurface absorber. The proposed unit cell is backed with copper on an FR4 substrate. To increase the absorption bandwidth, four lumped resistors are linked to four identical circular metallic sectors in the structure's uppermost layer, and an air spacer is used in between the substrate and ground layer. The near-unity absorption and greater than 20 dB RCS reduction, as well as more than 40 dB shielding effectiveness in the frequency range of 4.3 to 10.5 GHz, are unique features of this design. The simulation includes a surface current density analysis, normalized impedance, field distributions, conformality analysis, and a parametric examination. The numerical results are validated analytically using an equivalent circuit model. This structure is analyzed in depth for RCS reduction and EMI shielding applications. The fabricated model undergoes experimental characterization and validation, displaying remarkable alignment with the simulated outcomes. [ABSTRACT FROM AUTHOR]

This 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. [ABSTRACT FROM AUTHOR]

This article presents an ultrathin chiral metasurface which can exhibit multiband asymmetric absorption as well as symmetric transmission in a specific frequency band outside the absorption regions. Unlike most electromagnetic metasurface absorbers, the proposed structure does not have a continuous conducting sheet at the bottom which also allows it to act as a bandpass spatial filter. The metasurface has a substrate thickness of only λhigh/62.5 and λlow/34 at the highest and lowest operational free‐space wavelengths, respectively. The transmission band is centered at 5.5 GHz, and the asymmetric absorption bands are centered at 3, 3.33, and 4.5 GHz, respectively. The operational bands can be tuned as per user requirements. The metasurface has an angular stability of 45° for both TE and TM incidence. It can be used for radar cross‐section (RCS) reduction, electromagnetic shielding, and as a spatial bandpass filter. [ABSTRACT FROM AUTHOR]

Metasurface absorbers (MSAs) are of significant importance in a wide range of applications, such as in the field of stealth technology. Nevertheless, conventional designs demonstrate limited flexible characteristics and a lack of transparency, hence constraining their suitability for certain radar stealth applications. This study introduces a novel MSA operating in the broad microwave range, which exhibits both optical transparency and flexibility. The structure consists of a flexible substrate made of polyvinyl chloride (PVC), along with a resistive film composed of indium tin oxide (ITO). The proposed structure exhibits the ability to effectively absorb over 90% of the energy carried by incident electromagnetic (EM) waves across the frequency range of 9.85–41.76 GHz within an angular range of 0° to 60°. In addition, to assess the efficacy of the absorption performance, an examination of the radar cross-section (RCS) characteristics is conducted. The results indicate a reduction of over 10 dB across the aforementioned broad frequency spectrum, regardless of the central angle. [ABSTRACT FROM AUTHOR]

This review is based on the radar cross-section (RCS) reduction techniques, with the prominence of the metasurface and its design. The thorough detail starts with introducing the concepts of the RCS and its reduction techniques. Then, traditional and recent techniques are provided to reduce RCS, emphasizing the scattering and absorption methods. An in-depth analysis of shaping processes and Radar Absorbing Materials (RAM) is provided, which are two standard RCS reduction techniques. It also thoroughly analyses the metamaterial-based RCS reduction, considering both active and passive configurations. The primary aspects covered regarding the utilization of metasurfaces for reducing RCS include profile, conformality, polarization sensitivity, and design complexity. To provide comparison and evaluation, the review includes tabulated information on performance parameters such as the method used, frequency range, size, optimization method, and planar or conformal design of RCS reduction. Additionally, the paper identifies areas within the field that require further in-depth research and investigation.

Based on the far field function of electric field, a new glass carbon fiber gradient-stitched structure is proposed and designed in the paper. In the frequency range of 8–28 GHz, the electric field distribution of transverse electric and magnetic field (TEM) waves incident obliquely on the surface of the structure by optimizing the glass fiber fabric units. It is confirmed that the surface has the function of suppressing electromagnetic wave reflection. The electrical performance simulation and testing results of the structure show that the radar cross section (RCS) is reduced by 90% in the frequency range of 12.3–26.5 GHz. In addition, a multi-scale analysis model is established to quickly predict the tensile modulus and strength of the composite material. The strength and modulus reached 26.9 GPa and 403 MPa, respectively. The simulating and testing results of mechanical properties are in good agreement. [ABSTRACT FROM AUTHOR]

This letter presents the theoretical investigation by a transmission line model and the physical implementation of a novel frequency reconfigurable microstrip antenna with switchable states. More specifically, by using voltage‐controlled PIN diodes, the antenna can be switched between a radiation state and a low‐scattering state. In the radiation state, the operation frequency of the antenna can be electrically modified between 1.5 and 2.3 GHz by acting on the voltage applied to the varactors. In the low‐scattering state, the antenna achieves a significant in‐band radar cross section reduction, with a maximum value of 26.7 dB. The proposed antenna is fabricated and measured. The validity of the proposed strategy is verified by the good agreement between simulated and measurement results. The antenna designed by the proposed approach has great advantages in the radiation performance, aperture size, profile height and design freedom. This work indicates the feasibility of employing the reconfiguration technique to mnipulate the scattering features of an antenna without deteriorating its radiation characteristics. [ABSTRACT FROM AUTHOR]

This review is based on the radar cross-section (RCS) reduction techniques, with the prominence of the metasurface and its design. The thorough detail starts with introducing the concepts of the RCS and its reduction techniques. Then, traditional and recent techniques are provided to reduce RCS, emphasizing the scattering and absorption methods. An in-depth analysis of shaping processes and Radar Absorbing Materials (RAM) is provided, which are two standard RCS reduction techniques. It also thoroughly analyses the metamaterial-based RCS reduction, considering both active and passive configurations. The primary aspects covered regarding the utilization of metasurfaces for reducing RCS include profile, conformality, polarization sensitivity, and design complexity. To provide comparison and evaluation, the review includes tabulated information on performance parameters such as the method used, frequency range, size, optimization method, and planar or conformal design of RCS reduction. Additionally, the paper identifies areas within the field that require further in-depth research and investigation. [ABSTRACT FROM AUTHOR]

In this paper, an ultra-thin tri-functional coding metasurface based on frequency and polarization selection is proposed to achieve different functions at different polarizations and frequencies. The proposed metasurface uses a cross shape as a polarization-sensitive phase response structure in the Ku-band and a deformed H shape as a polarization-insensitive phase response structure in the Ka-band. As a proof of concept, beam splitting, radar cross section (RCS) reduction, and vortex beam generator can be realized by changing the polarization state of the incident wave at different frequencies. These three functions can be operated independently, and the theoretical calculation results, simulation results, and measurement results are in good agreement. This tri-functional coding metasurface can provide a flexible and reliable method to manipulate EM waves with different polarizations and frequencies, as well as to integrate different functions into a single planar device, providing an efficient way to realize multifunctional devices. [ABSTRACT FROM AUTHOR]

Recently, modern technology has towards stealth technology, especially in military applications so, this paper presents a terahertz radar cross-section (RCS) reduction utilizing reconfigurable graphene-based artificial magnetic conductor (AMC) arrays. The AMC unit cell has a Vivaldi shape with circular slots etched in the radiator to reduce the RCS from metallic surfaces at THz bands. The AMC cells affect the surface impedance of the metallic objects which reduces the reflected EM waves from them. The RCS reduction bandwidth is achieved and controlled by varying the voltage applied to graphene cells which varies its chemical potential (µc). The effect of changing the graphene conductivity on the RCS reduction is investigated. Different arrangements to obtain maximum RCS reduction are presented. A 12 × 12 hybrid arrangement of the graphene-based AMC structures achieved maximum RCS reduction from 1.5 to 4 THz with 22 dB greater than the unloaded metallic surface. The CST simulator is employed in the simulation. [ABSTRACT FROM AUTHOR]

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

Electromagnetic (EM) absorbers are specially designed structures that dissipate the absorbed EM energy into heat by minimizing the reflection as well as transmission. The absorbers operating in microwave and millimetre wave regimes have been found essential in applications such as radar, communication systems, EM interference prevention, and stealth technologies. Design concepts such as Salisbury, Jaunman screens, and impedance-matching layers are discussed. As a game-changing innovation in wave attribute manipulation, metamaterial behaviour provides an unprecedented command over how waves interact with matter. This review examines the significant hurdles and restrictions metamaterial absorbers must overcome, like fabrication, the tradeoff between absorption bandwidth and thickness, and material losses. Broadband absorption, tunability, and feasibility of producing thin, lightweight absorbers all contribute to their desirability for various applications. Different losses responsible for the absorption phenomena are detailed for both narrowband and broadband cases. This critical analysis highlights the enormous promise of metamaterial absorbers while emphasizing the ongoing research efforts needed to overcome the associated obstacles. Its goal is to advance state-of-the-art designs by critically assessing the existing status of the field, thereby guiding future research, development, making it easier to implement microwave and millimetre wave absorbers in a wide range of real-time applications. [ABSTRACT FROM AUTHOR]

With the rapid development of terahertz radar technology, the electromagnetic device for terahertz radar cross-section (RCS) reduction is worth investigating. However, the existing research concentrates on the RCS reduction metasurface with fixed performance working in the microwave band. This paper proposes a terahertz dynamic coding metasurface integrated with vanadium dioxide (VO2) for dual-polarized, dual-band, and wide-angle RCS reduction. The simulation result indicates that by switching the state of the VO2 between insulator and metal, the metasurface can realize the effective RCS reduction at 0.18 THz to 0.24 THz and 0.21 THz to 0.39 THz under the left-handed and right-handed circularly polarized incident waves. When the polar and azimuth angles of the incident wave vary from 0° to 40° and 0° to 360° respectively, this metasurface can maintain a 10 dB RCS reduction. This work has potential value in the terahertz stealth field. [ABSTRACT FROM AUTHOR]

A frequency-tunable patch antenna with reduced radar cross section (RCS) based on absorbing metamaterial is proposed. By controlling the external voltage of the varactor diodes, the working frequency of the patch can be adjusted. Through an investigation of the composite structure of the patch and absorbing metamaterial, RCS reduction is achieved over the entire wide tunable frequency range of the antenna. Measured results illustrate that the proposed patch antenna can dynamically operate in the range from 2.28 to 3.6 GHz with a gain variation of 7.1–8.7 dBi. Meanwhile, the RCS can be reduced by at least 7 dB and up to 20 dB in a fractional bandwidth of 44.9% of the antenna under a normal incidence. In comparison to conventional RCS-reduced antennas, the proposed one features a broader frequency tuning range and has potential value in wideband radar systems under complex electromagnetic interference environments. [ABSTRACT FROM AUTHOR]

Modern stealth application systems require integrated meta-devices to operate effectively and have gained significant attention recently. This research paper proposes a 1-bit coding metasurface (CM) design. The fundamental component of the proposed CM is integrated to convert linearly polarized incoming electromagnetic waves into their orthogonal counterpart within frequency bands of 12.37–13.03 GHz and 18.96–32.37 GHz, achieving a polarization conversion ratio exceeding 99%. Furthermore, it enables linear-to-circular polarization conversion from 11.80 to 12.29, 13.17 to 18.44, and 33.33 to 40.35 GHz. A second element is produced by rotating a fundamental component by 90°, introducing a phase difference of π (pi) between them. Both elements are arranged in an array using a random aperiodic coding sequence to create a 1-bit CM for reducing the radar cross-section (RCS). The planar structure achieved over 10 dB RCS reduction for polarized waves in the frequency bands of 13.1–13.8 GHz and 20.4–30.9 GHz. A prototype was fabricated and tested, with the experimental results showing a good agreement with the simulated outcomes. The proposed design holds potential applications in radar systems, reflector antennas, stealth technologies, and satellite communication. [ABSTRACT FROM AUTHOR]

In this paper, a broadband reconfigurable active frequency selective rasorber is proposed, which can be used as a radome for antenna radar cross section (RCS) reduction. By tuning the active components, the radome can achieve in‐band RCS reduction and reconfigurable absorptive/transmissive states. In the absorptive state, the max bandwidth with an absorption rate greater than 90% spanning from 1.62 to 5.37 GHz; in the absorptive/transmissive state, 2.2 GHz is the transmissive frequency with the insertion loss of 93% while absorbing in 0.94–2.06 GHz and 2.63–6.5 GHz, which demonstrate impressive characteristics of broadband and a high absorption rate. Additionally, the radome can maintain performance at ±35° angular incidence and is insensitive to incident wave polarization. Furthermore, it features a lightweight and low‐profile design, with a cell electrical size of just 0.078λ × 0.078λ × 0.066λ. The prototype test shows a noteworthy correlation with simulation. This study has wider applications in the electromagnetic stealth of communication antennas and aircraft, as well as in the control of electromagnetic pollution signals in space. [ABSTRACT FROM AUTHOR]

In this study, we introduce a strategy for constructing an absorptive metasurface, which integrates the absorption and phase cancellation mechanisms. Through topological optimization and the synthesis of a checkerboard metasurface array, we achieve a significant reduction in ultra-wideband RCS. A prototype of the suggested design is produced and tested to confirm the effectiveness of the absorptive coding metasurface. When compared to a metallic plate of the same dimensions, a notable decrease in reflection is observed within the 4.0–12.0 GHz range. The RCS reduction exceeds 15 dB within the same frequency range (the fractional bandwidth is 100%). The proposed methods of phase and amplitude control, along with topological optimization, prove to be efficient strategies for wideband RCS reduction applications. [ABSTRACT FROM AUTHOR]

This work focuses on 1- and 2-bit coding metamaterials by designing unit cell structures, also known as binary elements, that possess 0-, 90-, 180-, and 270-degree phase responses. Several parametric studies are mainly investigated, for instance, various coding sequence patterns and a few numbers of lattices likely 4, 8, and 12 in each bit. The RCS reduction analysis revealed a promising outcome where the distinct coding sequences exhibited way better reduction behaviour than others. For instance, coding sequences likely CS3, CS4, and CS5 exhibit excellent reduction behaviour when the lattices increase from 4 to 12. However, the 2-bit coding metamaterial exhibits superior reduction behaviours in RCS values, where the maximum points reached when adopting the CS5 design ranged from −75.2 to −55.6 dBm2.Concisely, the proposed coding metamaterial satisfied the target of this investigation to gain optimal RCS reduction by adopting both 1- and 2-bit design structures for terahertz frequency.

In this work, a metasurface-based radome composite (MRC) with customized electromagnetic (EM) functions is proposed. By employing a beam-scattering mechanism, high transmission at 2–4 GHz and significant radar cross-section (RCS) reduction at 8–18 GHz are achieved. The MRC prototype features a sandwiched construction and is fabricated using quartz fiber-reinforced composite (QFRC) skins, polymethacrylimide (PMI) foam cores, and silver-based frequency selective surface (FSS) screens. The calculation, simulation, and measured results demonstrated that the transmission of the planar specimen is larger than −1 dB at 2–4 GHz and the RCS reduction is less than −10 dB at 8–18 GHz. The measured results also verified that in the HH and VV polarizations, the mono-static RCS of a square pyramid (SP) specimen at specific directions from 8 GHz to 12 GHz is significantly reduced. It is believed that our finding has great application potential in stealth radome technology.

Metasurface absorbers (MSAs) are of significant importance in a wide range of applications, such as in the field of stealth technology. Nevertheless, conventional designs demonstrate limited flexible characteristics and a lack of transparency, hence constraining their suitability for certain radar stealth applications. This study introduces a novel MSA operating in the broad microwave range, which exhibits both optical transparency and flexibility. The structure consists of a flexible substrate made of polyvinyl chloride (PVC), along with a resistive film composed of indium tin oxide (ITO). The proposed structure exhibits the ability to effectively absorb over 90% of the energy carried by incident electromagnetic (EM) waves across the frequency range of 9.85–41.76 GHz within an angular range of 0° to 60°. In addition, to assess the efficacy of the absorption performance, an examination of the radar cross-section (RCS) characteristics is conducted. The results indicate a reduction of over 10 dB across the aforementioned broad frequency spectrum, regardless of the central angle.

As a representative technique in electronics, the Smith Chart provides a fast, less‐computation, and graphical approach to solve the problems related to impedance matching. In this paper, we transplanted the Smith Chart into the design and analysis of a microwave metamaterial absorber (meta‐absorber) to develop an analytical and graphical approach for impedance matching of electromagnetic wave absorption. Before the structural design, four traces on the Smith Chart plane from the load to arrive at the impedance matching point (the center of the Smith Chart) can be graphically found to obtain perfect absorption. Then, we have designed four impedance matching circuit networks made of resistance, inductance, and capacitive elements and transmission lines to fit the four traces. Then, the matching circuits are mapped into the meta‐absorber structure by using three types of proposed layers. The full simulation method based on the finite element method is used to verify the proposed concept. Furthermore, an external dielectric loading strategy has been developed to achieve good angular stability up to 60° for the radar cross section reduction under transverse electric and transverse mangetic polarization incidence. The proposed method may provide a convenient way for various microwave devices, such as antennas. [ABSTRACT FROM AUTHOR]

As theoretical research further develops, coding metasurfaces have been widely studied and applied due to their uniqueness in digital characterization and sequence arrangement. In this work, based on highly conductive graphene‐assembled film (GAF), an ultralight anisotropic broadband coding metasurface (ABCM) is proposed. The GAF ABCM consists of 16 units with specific phase responses and enables complete metal substitution. By arranging the unit cells in a specific order, the GAF ABCM realizes the functions of anomalous reflection, polarization conversion, and radar cross‐section (RCS) reduction. Results validate that the GAF ABCM has a measured 10 dB normal incidence backward RCS reduction within the working frequency band of 7–18 GHz, which fully covers the X‐band and Ku‐band for radar application. Furthermore, due to the lightweight property of GAF, the density of the GAF ABCM is only 0.06 g/cm3 (surface mass density of 0.038 g/cm2). All results indicate that the lightweight GAF metasurface is promising in radar stealth and communication fields. [ABSTRACT FROM AUTHOR]

In this study, a metasurface-based linear and circular polarization converter operating on the reflection mode is proposed for X- and Ku-band microwave applications. The proposed converter offers an optimum performance with a polarization conversion ratio (PCR) and polarization matching ratio (PMR) greater than 93 % in the 8.32 -- 17.55 GHz bandwidth for a linearly polarized in the y-direction and right-handed circular polarized (RHCP) incident waves. Besides, the design performs over 80 % PCR performance up to 45 ∘ under oblique incidence. Moreover, the proposed converter is capable of left-handed circular polarization conversion between 7.42 and 7.68 GHz for a y-polarized incident wave. The design offers a relative bandwidth (RBW) of 71.36 %. The converter design is constructed with metal termination, an easily accessible FR-4 substrate and a simple design metasurface. Surface currents of the polarization converter at resonance frequencies of 8.77, 12.88 and 16.7 GHz were examined to understand its working mechanism. In addition, when the proposed design is rearranged with the appropriate geometry, the monostatic RCS reduction value in the 8.0–17.7 GHz range is observed to be higher than 10 dB. CST program (a commercial 3D electromagnetic simulator) was used in simulations. The simulated device was fabricated with a traditional board fabrication technique. Simulation results were verified with free space measurements calibrated by the thru-reflect-line calibration procedure. The performance and efficiency of the proposed polarization converter were compared with other converters in the literature. [ABSTRACT FROM AUTHOR]

Different types of stealth films and their electromagnetic (EM) behavioral characteristics have been studied to fulfil the stealth requirements of today's electronic warfare (EW) for military mission success. The EM performance of stealth films has been measured using two different measurement methods: wave guide measurement (WGM) and open area test site (OATS). Polyethylene terephthalate (PET) (sample B1) has been used as the base material to design and fabricate composite stealth films, films N (PET + conductive paint), S (PET + conductive paint + fumed silica), Q (PET + conductive paint + aluminum), and P (PET + conductive paint + aluminum + fumed silica). The conductive paint and fumed silica are used to design and fabricate small unmanned aerial vehicle (sUAV) model stealth frames. The detailed parametric studies of these films and frames have been analyzed in terms of EM wave parameters, S11 (reflection coefficient), S21 (transmission coefficient), I1 (input power at port 1), O1 (output power at port 1), O2 (output power at port 2), Pin (input power incident on sample specimen), Prefle (reflected power at a point close to the transmitter), Ptrans (power transmitted through the sample), SErefle (shielding effectiveness of reflection loss), SEabs (shielding effectiveness of absorption loss), SEtot (total shielding effectiveness), and RCS (σ) (radar cross-section). These parameters have been verified in the X-band frequency operation in the 8- to 12-GHz frequency range. Using these stealth films and frames, the minimum values of S11, S21, and SEtot of − 40 dB, − 0.6 dB, and 0.7 dB, respectively, in WGM and − 75 dB, − 76 dB, and − 75 dB, respectively, in OATS, were achieved. Further, the achieved RCS reduction level falls in the range of 0.09–1.5 m2 over the 8–10.1 GHz frequency range, and in the range 1.6–4 m2 above 10.1 GHz and up to 12 GHz, as presented in this paper. The experimental results give a good agreement between the design material and their EM behaviors, so their suitability for stealth applications is justified. [ABSTRACT FROM AUTHOR]

Coding metasurfaces, characterized by processing the electromagnetic waves for specified functions through predesigned coding sequences either in space or time, can manipulate the electromagnetic waves in both space frequencies and time frequencies. They have been emerging as the revolutionary platforms for metasurface technologies in recent years. In this paper, we first introduce the general concept and operating principle of the coding metasurfaces. Then, two design strategies for realizing the coding metasurface particles, altering resonant states and switching current phase, are provided, respectively. Next, two recent reported applications that are based on space-coding metasurface for RCS reduction and time-coding metasurface for spread-spectrum wireless communication are presented, respectively. Finally, existing challenges and potential future research directions in coding metasurfaces are discussed. [ABSTRACT FROM AUTHOR]

With the rapid development of terahertz radar technology, the electromagnetic device for terahertz radar cross-section (RCS) reduction is worth investigating. However, the existing research concentrates on the RCS reduction metasurface with fixed performance working in the microwave band. This paper proposes a terahertz dynamic coding metasurface integrated with vanadium dioxide (VO2) for dual-polarized, dual-band, and wide-angle RCS reduction. The simulation result indicates that by switching the state of the VO2 between insulator and metal, the metasurface can realize the effective RCS reduction at 0.18 THz to 0.24 THz and 0.21 THz to 0.39 THz under the left-handed and right-handed circularly polarized incident waves. When the polar and azimuth angles of the incident wave vary from 0° to 40° and 0° to 360° respectively, this metasurface can maintain a 10 dB RCS reduction. This work has potential value in the terahertz stealth field.

Modern stealth application systems require integrated meta-devices to operate effectively and have gained significant attention recently. This research paper proposes a 1-bit coding metasurface (CM) design. The fundamental component of the proposed CM is integrated to convert linearly polarized incoming electromagnetic waves into their orthogonal counterpart within frequency bands of 12.37–13.03 GHz and 18.96–32.37 GHz, achieving a polarization conversion ratio exceeding 99%. Furthermore, it enables linear-to-circular polarization conversion from 11.80 to 12.29, 13.17 to 18.44, and 33.33 to 40.35 GHz. A second element is produced by rotating a fundamental component by 90°, introducing a phase difference of π (pi) between them. Both elements are arranged in an array using a random aperiodic coding sequence to create a 1-bit CM for reducing the radar cross-section (RCS). The planar structure achieved over 10 dB RCS reduction for polarized waves in the frequency bands of 13.1–13.8 GHz and 20.4–30.9 GHz. A prototype was fabricated and tested, with the experimental results showing a good agreement with the simulated outcomes. The proposed design holds potential applications in radar systems, reflector antennas, stealth technologies, and satellite communication.

In this paper, to achieve ultra-wideband radar cross section (RCS) reduction, a coding phase gradient metasurface (CPGM) is proposed by using Pancharatnam-Berry (P-B) phase. The CPGM is composed of eight types of CPGM elements, and a series of phase gradients with different directions or starting-values will be introduced in these types of CPGM elements under the same EM-wave incidence, so it can not only achieve anomalous reflection to reduce its specular RCS but also reduce the maximum bi-static RCS due to phase cancelation. The simulation results demonstrate that the CPGM has an excellent performance in RCS reduction, compared with a pure metallic plate with the same size, its specular RCS under normal incidence with arbitrary polarization can be reduced more than 10 dB in the ultra-wide frequency band of 8.8–34.8 GHz with a relative bandwidth of 119.3%, and its maximum bi-static RCS can also be reduced effectively in the ultra-wide frequency band; moreover, when the incident angle is increased to 45°, the RCS reduction can still be achieved in an ultra-wide frequency band. Finally, an effective experimental verification is carried out. [ABSTRACT FROM AUTHOR]

Pancharatnam—Berry (PB) phase metasurface, as a special class of gradient metasurfaces, has been paid much attention owing to the robust performance for phase control of circularly polarized waves. Herein, we present an element-based polarizer for the first step, which enables the incident electromagnetic waves into the cross-polarized waves with the relative bandwidth of 71%, and the polarization conversion ratio exceeds 90% at 6.9–14.5 GHz. Then an eight-elements coding polarizer based on the PB phase is presented for the applications on beam control and radar cross section reduction. The simulated values indicate that the reduction of radar cross section is more than 10 dB at 6–16 GHz. Our work reveals the availability of manipulating the waves, beamforming in communication systems and electromagnetic stealth, and so on. [ABSTRACT FROM AUTHOR]

This article presents a linear microstrip patch antenna array at the X-band that incorporates an aperiodic artificial magnetic conductor (AMC) metasurface which utilizes phase cancellation techniques for reducing both the in-band and out-of-band Radar Cross Section (RCS). The structure consists of two substrates with three layers, the top layer consists of 8 antenna elements along with AMCs which are aperiodically oriented for wideband RCS reduction, and the middle layer (in between the two substrates) consists of a corporate feed network for the antenna array, followed by the ground plane in the bottom layer. Few AMC blocks have been used to achieve a wideband RCS reduction in the frequency range of 6 GHz to 16 GHz with more than 85% reduction in both X- and Y-polarizations utilizing a low profile, compact design. Along with the monostatic RCS reduction, a bistatic RCS reduction up to 40° has also been observed in simulations. The proposed structure has been fabricated and measurements of the reflection coefficient, gain, patterns, and monostatic RCS plots have been carried out. Measured results indicate good agreement with the results of the simulations after considering all measurement errors.

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica 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.)

Traditional stealth technologies all have their problems such as high cost and large thickness. To solve the problems, we used novelty checkerboard metasurface in stealth technology. Checkerboard metasurface does not have as high conversion efficiency as radiation converters, but it has many advantages such as small thickness and low cost. So it is expected to overcome the problems of traditional stealth technologies. Unlike other checkerboard metasurfaces, we improved it further by using two types of polarization converter units to be arranged in turn to form a hybrid checkerboard metasurface. Because the checkerboard metasurface composed of one type of polarization converter units can have a relatively wide radar cross-section (RCS) reduction in bandwidth when two types of polarization converter units are arranged in turn to form a hybrid checkerboard metasurface and mutual compensation of the two polarization converter units can broaden RCS reduction band further. Therefore, by designing the metasurface to be independent from the polarization, the effect of RCS reduction can be insensitive to the polarization of the incoming EM waves. The experiment and simulation results showed the value of this proposed hybrid checkerboard metasurface for RCS reduction. Mutual compensation of the units is a new attempt in the field of checkerboard metasurfaces for stealth technology and proved to be effective. [ABSTRACT FROM AUTHOR]

In this work, a circularly polarised (CP) slot antenna based on linear polarisation conversion metasurface (PCM) is proposed for broadband radar cross-section (RCS) reduction and gain improvement. The proposed metasurface is designed using the chequerboard alignment of PCM unit cells and its mirrored ones to meet the phase cancellation principle required for RCS reduction. An improved loading technique of the PCM consisting of rearrangement of the PCM unit cells across the radiating slot is employed to enhance the gain of the proposed antenna. The measured results show that the operating bandwidth of the proposed antenna is in the range of 9.8–10.8 GHz. The maximum gain achieved is 2.4 dB more than the reference antenna while the 3-dB axial ratio bandwidth (ARBW) obtained is 9.8–10.6 GHz. The proposed antenna achieves an average RCS reduction of 11 dB in the frequency region of 6–18 GHz in comparison to the reference antenna. [ABSTRACT FROM AUTHOR]

In this paper, reconfigurable chessboard coding plasma-based dielectric resonator structure for radar cross section reduction is investigated. The radar cross section (RCS) reduction is essential in military applications. The metallic conductor surface is covered with plasma-based dielectric resonator (DRA) unit-cells arranged in chessboard configuration. The plasma DRA unit-cell consists of concentric cylindrical ring filled with ionized plasma placed over FR4 dielectric substrate. The plasma ionization voltage values are tuned to reflect the electromagnetic wave with phase shift of 180° and equal amplitudes. The phase 0° state represents the logic "0" while the phase 180° state represents the logic "1". The chessboard arrangement consists of super-cells with 0/1 logic states. Different sizes of uniform super-cells 3 × 3, 4 × 4, 6 × 6, and 12 × 12 unit-cells are investigated for maximum RCS reduction. The scattered beams are directed to (± 30°, 180° ± 30°), (± 25°, 180° ± 25°), (± 20°, 180° ± 20°), (± 15°, 180° ± 15°) and (± 10°, 180° ± 10°) for 3 × 3, 4 × 4, 6 × 6, 8 × 8, and 12 × 12 uniform super-cells, respectively. The RCS is reduced over a wide angle range reduction with − 18 dBm2 at the broadside direction and below − 32 dBm2 over the angular range from − 90° to 90° according to the super-cell size. The non-uniform allocation of unit-cells in the super-cell chessboard arrangement is investigated. The RCS reduction bandwidth extended from 8.5 to 9.65 GHz. The scattered beam produces null in the broadside direction with wideband RCS reduction. The proposed structures are simulated using CST-MWS electromagnetic simulator. [ABSTRACT FROM AUTHOR]

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An ultra wideband (UWB) radar cross-section (RCS) reduction metasurface has received attention in recent years. However, the majority of the research has concentrated on the physics and design of planar surfaces, which do not meet the standards of modern aerodynamics and aesthetics. In this paper, we offer a sophisticated strategy for designing a metasurface that can conform to the shape of any object, even those of moderate curvature, and can also achieve UWB RCS reduction by combining absorption, polarization conversion, and diffusion mechanisms. Firstly, an absorbing-polarization converter is designed, composed of a square patch with a truncated diagonal strip and ring. A thin Rogers RT/Duroid 5880 dielectric substrate layer is used in the structure, which is also appropriate for conformal conditions. The substrate layer and the ground plane are separated by an air gap to enhance the polarization conversion bandwidth (PCBW). For normal incident electromagnetic (EM) waves, the PCBW ranges from 10.8 to 31.3 GHz with polarization conversion ratio (PCR) values greater than 0.9 dB. Up to a 45 ∘ oblique incidence angle over the aforementioned band, the PCR efficiency is well maintained. Then, the optimized coding metasurface is formed by the Pancharatnam–Berry (PB) phase, consisting of meta-atoms "0" and "1" of the same size but different orientations, to realize the concept of cross-polarization diffusion. A theoretical investigation has been performed to analyze the RCS reduction performance of planar as well as conformal cylindrical surfaces. The results show that more than 10 dB of RCS reduction is experienced over UWB (10.8–31.3 GHz) for planar metasurfaces under linearly and circularly polarized incidence waves. Furthermore, the RCS reduction for cylindrical surfaces can be achieved in a similar frequency band above 10 dB up to an angle of 90 ∘ . It can be deduced that our proposed flexible metasurface can be used as an absorber or a polarization converter and provide broadband RCS reduction, which is essential for multi-function and conformal stealth applications. [ABSTRACT FROM AUTHOR]

In the past few decades, metamaterial absorbers (MA) have become an important area of research due to their potential application as ultrathin perfect absorbers. There are various approaches proposed in the literature to obtain multiband and broadband absorption characteristics. This paper presents all the different approaches followed by different authors along with their respective drawbacks and advantages. Metamaterial absorbers have numerous applications in today's technological advancement. This paper presents the review of literature on previously proposed MA applied for radar cross‐section reduction and used as sensors in several applications. The aim is to help the user choose a suitable approach for particular specifications and also develop new devices in the future. [ABSTRACT FROM AUTHOR]

This paper investigates the low-RCS Ka-band receiving and transmitting satellite communication antennas co-designed with the high-performance absorbent frequency-selective radomes (AFSR). Consisting of the metamaterial absorber (MA) upper layer and bandpass FSS lower layer, two AFSRs operating at 19 and 29 GHz (receiving and transmitting central frequency) with low-frequency wideband absorbing and high-frequency low-insertion-loss transmission performances are proposed. To meet the needs of Ka-band satellite communication, two 4 × 4 microstrip array antennas working at the same central frequencies are co-designed with the AFSRs. We demonstrate the effectiveness of the proposed AFSRs and co-designed antenna through simulations and measurements. The results show that the gain degradations are only 0.44 dB and 0.58 dB at two central frequencies after loading the AFSRs separately, and 10-dB RCS reduction bandwidths are ranging from 6.1–16.3 GHz (relative bandwidth 91.1%) and 10.2–24.8 GHz (relative bandwidth 83.4%) individually. [ABSTRACT FROM AUTHOR]

A circularly polarized (CP) Fabry–Perot (FP) resonator antenna with well radar cross section (RCS) reduction property is presented in this article. Wideband and well in‐band RCS reduction for both x‐ and y‐polarized waves are obtained by the proposed antenna. A polarization conversion metasurface (PCM) is designed to make the antenna realize circularly polarized radiation and RCS reduction simultaneously. The PCM consists of two unit cells which show same polarization conversion capability but 180° reflection phases difference when the wave incident from the top side. The polarization conversion capability can make the antenna realize circularly polarized radiation, while the chessboard arrangement of two unit cells can reduce the RCS of the antenna. Besides, the high reflectivity of the PCM also make the antenna obtain high gain and well in‐band RCS reduction property. The radiation and scattering performance of the antenna is verified by the measured results of the fabricated antenna. The antenna obtains maximum gain of 13.9 dBic at 10 GHz and average RCS reduction of 10 dB in the band of 6–16 GHz. Besides, the RCS reduction of the antenna at 10 GHz for both polarizations are all large than 14 dB. [ABSTRACT FROM AUTHOR]

In this paper, a single layer polarization converting metasurface (PCMS) is designed and analyzed for wideband and high efficient cross polarization conversion (CPC) and radar cross section reduction (RCSR). In reflection mode, the PCMS efficiently converts a linearly-polarized (LP) incident electromagnetic (EM) waves to cross-polarized (CP) EM waves from 8.5 to 25.5 GHz with a fractional bandwidth (FBW) of 100%. The polarization conversion ratio (PCR) is more than 90% in the operating band which covers X , Ku , and a portion of K band. There are three resonance frequencies of 9.3, 16.8, and 24.5 GHz over which 100% PCR has been achieved. The unit cell dimensions are 0. 2 λ o × 0. 2 λ o (6.8 mm × 6.8 mm) and the height of the substrate is 0. 085 λ o (3 mm), where λ o is free space maximum wavelength at the minimum frequency of the operating band. The designed metasurface also performs RCS reduction in chessboard-like array arrangement based on the polarization conversion capability of the proposed PCMS. This method lifts the limitations with conventional techniques such as narrow bandwidth, larger size, and complex to design. The designed array produce a phase difference of (180±37°) between the scattered EM waves which fulfills the criteria for RCS reduction. The different orientations of the same unit cell in the chessboard shaped array result in a different reflection phases. The phase difference between reflected EM waves result in scatter wave cancellation (destructive interference) in the source direction and hence RCS reduction. The PCMS achieves RCSR of less than 10 dB from 6.9 to 25 GHz with a FBW of 114%. The array surface is tested experimentally. Simulated and experimental results are quite similar. The designed PCMS has a great potential in the fields of low RCS and wireless communication. • Highly efficient ultra-wideband polarization converter for RCS reduction is designed. • The PCR exceeds 90% in the frequency range of 8.5–25.5 GHz with a FBW of 100%.. • RCS reduction of −10 dB is achieved in the frequency range of 6.9–25 GHz with a FBW of 114%. • The PCMS offers high efficiency, ultra-wide bandwidth, simple structure having a minimal thickness. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the compact 1-bit coding metamaterial design with various conventional and cuboid shapes by analysing the bistatic scattering patterns as well as the monostatic radar cross-section for microwave applications. The construction of this metamaterial design depends on binary elements. For example, 1-bit coding metamaterial comprises two kinds of unit cell to mimic both coding particles such as '0' and '1' with 0° and 180° phase responses. This study adopted a 1 mm × 1 mm of epoxy resin fibre (FR-4) substrate material, which possesses a dielectric constant of 4.3 and tangent loss of 0.025, to construct both elements for the 1-bit coding metamaterial. All simulations were performed using the well-known Computer Simulation Technology (CST) software. The elements were selected via a trial-and-error method based on the phase response properties of the designs. On the other hand, the phase response properties from CST software were validated through the comparison of the phase response properties of both elements with the analytical data from HFSS software. Clear closure was obtained from these findings, and it was concluded that the proposed conventional coding metamaterial manifested the lowest RCS values with an increasing number of lattices. However, the cuboid-shaped design with 20 lattices demonstrated an optimised bistatic scattering pattern of −8.49 dBm2. Additionally, the monostatic RCS values were successfully reduced within the 12 to 18 GHz frequency range with −30 to −10 dBm2 values. In short, the introduced designs were suitable for the proposed application field, and this unique phenomenon is described as the novelty of this study. [ABSTRACT FROM AUTHOR]

In this survey paper, a complete analysis of the theory and applications of metamaterial (MM) has been delivered. It is proclaimed that MM possesses exceptional properties, due to negative permeability and negative permittivity that are not present in nature. Therefore, they are known as artificial materials. The physical significance is also explained in this paper in the terms of an equivalent circuit model to understand the concept of the MM. This paper also deals with an overview of distinct MM shapes and structures for different applications at different frequencies. Furthermore, the different types of MM-based electromagnetic structures are also incorporated. An overview of the traditional metasurface, single-layered metasurface, and multilayered metasurface structures is also explained with their drawbacks and advantages. In addition, a brief review of 3D, conformal, active, and graphene MM is also included. The different designs are also compared in active, conformal, multilayered structures on the basis of bandwidth, absorptivity, thickness, and other important characteristics. The MM-based survey presented in this paper could be productive for the scientific community, who are having an interest in this domain. [ABSTRACT FROM AUTHOR]

Multiple functionalities on a shared aperture are crucial for metasurfaces (MSs) in many applications. In this paper, we propose a coding-feeding metasurface (CFMS) with the multiple functions of high-gain radiation, orbital angular momentum (OAM) generation, and radar cross-section (RCS) reduction based on phase manipulation. The unit cell of the CFMS is composed of a rectangular emission patch and two quasi-Minkowski patches for reflective phase manipulation, which are on a shared aperture. The high-gain radiation and multiple modes of ±1, ±2, and ±3 OAM generation were realized by rationally setting the elements and the phase of their excitation. The CFMS presents a broadband RCS reduction of 8 dB from 3.18 GHz to 7.56 GHz for y-polarization and dual-band RCS reduction for x-polarization based on phase interference. To validate the concept of the CFMS, a prototype was fabricated and measured. The results of the measurement agree well with the simulation. A CFMS with the advantages of light weight and low profile has potential application in detection and wireless communication systems for stealth aircraft. [ABSTRACT FROM AUTHOR]