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Metasurface provides an unprecedented means to manipulate electromagnetic waves within a two-dimensional planar structure. Traditionally, the design of meta-atom follows the pattern-to-phase paradigm, which requires a time-consuming brute-forcing process. In this work, we present a fast inverse meta-atom design method for the phase-to-pattern mapping by combining the deep neural network (DNN) and genetic algorithm (GA). The trained classification DNN with an accuracy of 92% controls the population generated by the GA within an arbitrary preset small phase range, which could greatly enhance the optimization efficiency with less iterations and a higher accuracy. As proof-of-concept demonstrations, two reflective functional metasurfaces including an orbital angular momentum generator and a metalens have been numerically investigated. The simulated results agree very well with the design goals. In addition, the metalens is also experimentally validated. The proposed method could pave a new avenue for the fast design of the meta-atoms and functional meta-devices.

Surface plasmon polaritons (SPPs) and their counterparts at low frequency (i.e., spoof SPPs) have been attracting a lot of attention recently due to their potential application for routing information with high speeds and bandwidth. To further develop integrated plasmonics, a high-efficiency surface plasmon coupler is required for full elimination of the intrinsic scattering and reflection when exciting the highly confined plasmonic modes, but a solution to this challenge has remained elusive so far. To take on this challenge, here we propose a feasible spoof SPP coupler based on a transparent Huygens’ metasurface, which is able to realize more than 90% efficiency in near- and far-field experiments. To be specific, electrical and magnetic resonators are designed separately on both sides of the metasurface to satisfy the impedance-matching condition everywhere, leading to full conversion of plane wave propagation into surface wave propagation. Moreover, a well-optimized plasmonic metal which is able to support an eigen SPP is designed. This proposed high-efficiency spoof SPP coupler based on a Huygens’ metasurface may pave the way for the development of high-performance plasmonic devices.

Metasurfaces offer an unprecedented opportunity for flexible manipulation of electromagnetic wave. The azimuth-rotation-independent (ARI) polarization conversion metasurface (PCM) is an ultrathin device, which could convert an arbitrary linearly-polarized incident wave to its cross-polarized state. However, the bandwidth of an ARI PCM with a high cross-polarized transmission is usually limited. Here, a topology optimization method of multi-feature points based on the differential evolution (DE) algorithm is adopted to enhance the bandwidth of the traditional ARI PCM while maintaining a high transmission and polarization conversion ratio. The simulated results of the optimized structure indicate a 2.08 times bandwidth expansion in the cross-polarization conversion compared with the original structure. In addition, the measured results are consistent with the simulated ones and the ARI characteristic is validated. The proposed method provides a promising route for efficient high-performance metasurface designs.

In this paper, a novel broadband circularly polarized transmitarray antenna (CPTA) enabled by axial-ratio-improved receiver-transmitter metasurface loaded with parasitic patches is proposed. Split-ring-shaped parasitic patch is utilized to generate an additional resonant mode and significantly broaden the 3-dB axial ratio (AR) bandwidth of proposed receiver/transmitter patches from 6.64% to 15.61%. By cascading the receiver and transmitter with the same polarization and then rotating the cell, Pancharatnam-Berry phase can be exploited for providing a 2π phase shift. As verification, a CPTA prototype integrated with a self-made circularly polarized patch antenna is designed, fabricated, and measured. Experimental results show that the proposed CPTA obtains a 3-dB AR bandwidth of 27.1% from 12.1 to 15.9 GHz and an impedance bandwidth of 20.6% from 12.5 to 15.2 GHz. Additionally, it has a flat gain with a 3-dB gain bandwidth of 18.8% from 12.5 to 15.1 GHz, and a maximum gain of 25.6 dBi at 13.1 GHz is achieved. With the advantages of simple design, wide AR bandwidth, and flat gain performance, the proposed CPTA presents great potential applications in wireless systems.

Vortex beam generators are increasingly in demand for their enormous potential in improving communication capability. Along with the continuous integration of electronic product, devices with single function cannotsatisfy the requirements of the people. Here, by employing an anisotropic metasurface (MS), we propose a transparent multi-functional vortex beam generator to obtain vortex beams with reconfigurable polarization status. An anisotropic element is firstly optimized to control x- and y-polarized wave independently, and then is applied to assemble a vortex beam generator that is not only able to convert spherical wavefront into a vortex one but also able to transform linearly polarized mode into the circular polarized counterpart. Interestingly, the polarized status of the generated vortex beam changes from x-polarization to left hand circularly polarization (LHCP) to y-polarization and finally to right hand circularly polarization (RHCP) when the spot source is rotated with different angles. For verification, the prototype of the practical configuration is fabricated and measured. Coinciding well with the simulated results, the measured ones show that linearly polarized spherical wave has been converted into LHCP or RHCP vortex beams with operating efficiency of 85.8% or 83.3% respectively.

Stealth radome (SR), especially with an ultra-broad and nearly transparent window between two absorption bands, plays a crucial role in stealth techniques, antenna radomes, and so on. However, current devices have the defects of narrow transmission bands, high insertion loss, and wide transition bands between the transmission and absorption bands, which are unfavorable for the stealth of broadband radar and communication systems. In this paper, a novel SR with an ultra-broad and high-efficiency inter-absorption band transparent window is proposed by combining broadband resonance lumped circuits with a multi-layer cascaded frequency-selective surface (FSS). The equivalent circuit model (ECM) and transmission line method (TLM) are provided and analyzed as a guideline for the SR design. The SR consists of a resistive lossy layer loaded with wide passband lumped circuits and two stacked lossless FSS layers to collectively achieve the high selectivity and ultra-broad transmission band. Simulated results indicate that the proposed SR exhibits an ultra-broad passband from 8.2 to 11.2 GHz (31%) with transmission amplitude more than 0.85 and two 90% absorption bands over 6.8-7.8 GHz and 12-13 GHz, and the transition bands at both sides are only 0.4 GHz and 0.8 GHz, respectively. Our findings can stimulate the promising applications of SR in broadband stealth devices with integrated ultra-broad communication capability or in other electromagnetic (EM) compatibility facilities.

In this letter, we present a single-layered circularly polarized reflectarray antenna with a broad operating bandwidth in terms of realized gain, axial ratio (AR), radiation pattern, and aperture efficiency (AE). By employing multiple plasmon resonances, the proposed quasi-I-shaped element achieves a broadband linearly polarized conversion effect, which will contribute to a broadband reflectarray design. Thus, based on the element angular rotation method, a broadband offset-fed reflectarray with size of 215 × 215 mm2 and cells of 43 × 43 is designed, simulated, and then fabricated and measured. Good performances can be observed from both simulated and measured results, which confirm that the reflectarray antenna achieves a 75% 3 dB AR bandwidth (10–22 GHz) and a 49.7% 3 dB gain bandwidth (12.4–20.6 GHz). Furthermore, the measured AE exceeds 50% within a 28.2% bandwidth.

In this paper, we proposed for the first time a novel mechanism to design a tri-band low-scattering metasurface. The radar cross section (RCS) reduction in the three operational bands relies on scattering diffusion, absorption, and scattering cancellation, respectively. The diffusion metasurface was realized by distributing scattering unit cells with different rotation angles. For the absorption, four units operating at different frequencies were combined to achieve a broadband absorption. The scattering cancellation was realized by arranging two out of phase elements in a chessboard configuration. The tri-band metasurface was constructed by directly combining the three metasurfaces in a single assembly. The simulated and measured results have a good agreement. The tri-band RCS reduction is well preserved up to 45° with polarization-independent performance. This paper provides an alternative approach to design the multi-band metasurface for stealth application.

Although nipple-sparing mastectomy (NSM) is being used more frequently, the oncological safety of NSM remains unclear, particularly in young patients (0.05). Following adjustment for clinical stage, the LR and DFS rates between the two groups exhibited no significant differences. Analysis of the prognostic factors demonstrated that clinical stage, lymph node status, estrogen and progesterone receptor status and human epidermal growth factor receptor 2 status were associated with DFS (P

This paper proposes an easy, efficient strategy for designing broadband, wide-angle and polarization-independent diffusion metasurface for radar cross section (RCS) reduction. A dual-resonance unit cell, composed of a cross wire and cross loop (CWCL), is employed to enhance the phase bandwidth covering the 2π range. Both oblique-gradient and horizontal-gradient phase supercells are designed for illustration. The numerical results agree well with the theoretical ones. To significantly reduce backward scattering, the random combinatorial gradient metasurface (RCGM) is subsequently constructed by collecting eight supercells with randomly distributed gradient directions. The proposed metasurface features an enhanced specular RCS reduction performance and less design complexity compared to other candidates. Both simulated and measured results show that the proposed RCGM can significantly suppress RCS and exhibits broadband, wide-angle and polarization independence features.

In this letter, a low-scattering metasurface with dual-band, wide-angle, and polarization-insensitive features is proposed and validated by measurement. The metasurface converts incident electromagnetic wave into heat at S-band frequency, and disperses it into various reflected directions across X- and Ku-band frequencies. Furthermore, each operational mode works independently. The agreement between simulated and measured results demonstrates that more than 8 dB radar cross-section reduction can be realized over 3.9–4 and 7.7–19 GHz under different polarized wave incidences. The dual-band and wideband characteristics are also well maintained within 0°–45° oblique incidence.

A high-gain lens antenna employing single-layer focusing metasurface (MS) is proposed in this article. The single-layer element achieves a 360° transmission phase range with a transmission magnitude better than 0.9. And the focusing MS consists of 169 elements was designed by utilizing the technique of varying rotation angle to compensate the phase delay. Thus, a lens antenna is constructed by placing a circularly polarized (CP) patch antenna at the focal point of the MS. The fabricated lens antenna demonstrates a good performance of 4.6 % 3-dB axial ratio bandwidth and 6 % 1-dB gain bandwidth, respectively. Moreover, the maximum gain is 18.3 dBic at 15 GHz, which is enhanced by 11.4 dBic compared with the patch antenna. Due to the single-layer structure, this design has a low profile and easy fabrication process compared with the conventional designs, making it an attractive alternative to compact high-gain antenna.

By adding a PIN diode in the single right/left-handed transmission line unit, a zeroth-order resonance antenna with frequency reconfigurability is designed and presented in this paper. The proposed antenna is feed by coplanar waveguide and seized of compact structure of $32\mathrm{mm}\times 22\mathrm{mm}$ . Simulated and measured results display good agreements and demonstrate that the proposed could shift its operation frequency between 2.45GHz and 3.0GHz by switching the state of PIN diode, achieving frequency reconfigurable characteristic. At both operation states, the antenna feature good omnidirectional radiation characteristic and efficiencies. Besides, the proposed frequency reconfigurable antenna is capable of integrating in modern application and devices with PCB process conveniently and very suitable for advanced multi-standard wireless communication systems.

Multifunctional metasurface integrating different functions can significantly save the occupied space, although most of bifunctional metasurfaces reported to date only control the wave in either reflection or transmission regime. In this paper, we propose a scheme that allows one to independently control the reflection and transmission wavefront under orthogonal polarizations. For demonstration, we design a bifunctional metasurface that simultaneously realizes a diffusion reflection and a focusing transmission. The diffusion reflection is realized using a random phase distribution, which was implemented by randomly arranging two basic coding unit cells with the aid of an ergodic algorithm. Meanwhile, the hyperbolic phase distribution was designed to realize the focusing functionality in the transmission regime. To further show the potential applications, a high-gain lens antenna was designed by assembling the proposed metasurface with a proper feed. Both simulation and measurement results have been carried out, and the agreement between the two results demonstrates the validity of the performance as expected. The backward scattering can be reduced more than 5 dB within 6.4-10 GHz compared with the metallic plate. Moreover, the lens antenna has a gain of 20 dB (with around 13 dB enhancement in comparison with the bare feeding antenna) and an efficiency of 32.5%.

Goubau line is a single-conductor transmission line, featuring easy integration and low-loss transmission properties. Here, we propose a periodic leaky-wave antenna (LWA) based on planar Goubau transmission line on a thin dielectric substrate. The leaky-wave radiations are generated by introducing periodic modulations along the Goubau line. In this way, the surface wave, which is slow-wave mode supported by the Goubau line, achieves an additional momentum and hence enters the fast-wave region for radiations. By employing the periodic modulations, the proposed Goubau line LWAs are able to continuously steer the main beam from backward to forward within the operational frequency range. However, the LWAs usually suffer from a low radiation efficiency at the broadside direction. To overcome this drawback, we explore both transversally and longitudinally asymmetrical modulations to the Goubau line. Theoretical analysis, numerical simulations and experimental results are given in comparison with the symmetrical LWAs. It is demonstrated that the asymmetrical modulations significantly improve the radiation efficiency of LWAs at the broadside. Furthermore, the measurement results agree well with the numerical ones, which experimentally validates the proposed LWA structures. These novel Goubau line LWAs, experimentally demonstrated and validated at microwave frequencies, show also great potential for millimeter-wave and terahertz systems.

This paper presents a new metasurface inspired by Tai-Chi shape, which is applicable to dual-band radar cross section (RCS) reduction. The Tai-Chi-shape unit cell features a rotational self-complementary property. The metasurface, composed of such cells with different rotations, exhibits randomly distributed phase shift covering 2π range, giving rise to a diffusion of backscattering. Therefore, the RCS of the metasurface is substantially reduced compared to one of the equal-sized metallic plates. The full-wave simulation results show that the proposed metasurface can obtain nearly 8dB RCS reduction from 14.7GHz to 20.6 GHz and from 22.7GHz to 23.7GHz with polarization-independent performance.

The Radar Cross Section (RCS) of moving targets varies dramatically with aspect or time. The accuracy of simulated dynamic RCS is very important for radar system simulation. A novel approach to simulate the dynamic RCS of aircraft is proposed in this paper. Firstly, the electromagnetic (EM) model of aircraft is built and the all-space monostatic RCS database calculated. Secondly, the aspect angles (azimuth and elevation) in target coordinate system are calculated from ∞ight path by coordinate transformation. Then dynamic RCS is obtained based on database and aspect angles by linear interpolation method. Account for the in∞uence results from aircraft vibration in target motion, we use a white Gaussian distributed random series to modify the simulated results. The statistical characteristics of three kinds of dynamic RCS values are investigated, and the desirable agreement of results between modiflcation and measurement shows the applicability of this simulation approach.

A novel feed network based on the microstrip/slotline transition is proposed in this paper. This feed network not only has ultra-wide impedance bandwidth but also can improve space utilization and make the design of antenna array easier. Then an ultra-wideband (UWB) antenna array with four elements fed by the network is designed. The antenna array is simulated, manufactured and measured. The results show that the impedance bandwidth with return loss under i10dB is 88.76%, from 2.35GHz to 6.1GHz. Within the impedance bandwidth, the radiation performance is satisfactory, and the gain of the array is 2.1{7.1dB, higher than that of the element. The cross-polarization level of the array is lower than i20dB, just as the element. A reasonable agreement of results is achieved between simulation and measurement.

Planar focusing metasurface is capable of converting spherical waves into plane waves, while gradient phase distribution on metasurface contributes to anomalous reflection. By combining the double cases, we propose a new route of both gain enhancement and anomalous reflection. By using a compact ultra-thin anisotropic element, we design a polarization beam splitter under spherical waves’ illumination. With different phase gradients for x/y-polarized waves, the anisotropic metasurface has function of gain enhancement of 12.4 dB on average and reflecting x/y-polarized waves in −x/+y direction with the same reflected angel of 33° at the operating frequency of 15 GHz. For verification of simulation results, the metasurface sample with size of 102 × 102 mm2 and cells of 17 × 17 is fabricated and measured. Experimental results are in excellent agreement with the simulated ones, in which the high isolation of 30 dB at 15 GHz between x- and y-polarized waves is obtained. Due to the great performance in beam steering and thickness reduction, our design provides a promising approach of beam splitting, steering and gain enhancement in microwave region.

Pancharatnam-Berry (PB) metasurfaces have intrigued a great deal of interest in recent years for anomalous reflection/refraction, vortex plate, orbital angular momentum, flat lens, photonic spin hall effect (PSHE), holograms and reflect/transmit arrays. However, almost all designs are restricted to fixed electrical performance/functionality once the design is finished. Here, we report for the first time a strategy for PB metasurface with agile working frequency by involving each meta-atom with tunable PIN diodes. For verification, a tunable PB metasurface with frequency reconfigurability is designed and numerically characterized across C and X band. By controlling the external voltages imposed on the diodes, numerical results show that the operation band with 180° phase difference between orthogonal reflection coefficients can be dynamically controlled. As such, the resulting PB metasurface composed of these orderly rotated meta-atoms exhibits a broadband PSHE with nearly 100% conversion efficiency in the "On" state while switches to dual well-separated bands in the "Off" state. Our proposal, not confined to PHSE, set a solid platform for PB phase control and can be populated to any dual-functional and/or multifunctional devices with high integrity, stability and low cost.

A novel transmissive phase gradient metasurface (GPGM) is proposed to obtain high efficiency anomalous refraction. The super-cell of GPGM is constructed from six rotated unit cells having high transmission efficiency. The GPGM can provide the desired adverse phase gradients for left- and right-handed circularly polarized (LCP and RCP, respectively) waves at 15GHz. Therefore, the transmitted waves under normal incident linearly polarized wave are separated into two counter-directionally propagating circularly polarized waves. The simulated refractive power density spectrum is well consistent with the theoretically designed anomalous refraction direction.

A frequency-reconfigurable antenna with mechanical tuning, providing the frequency tuning from 2.51 to 3.70 GHz, is presented. The design comprises a slot antenna and a novel metasurface (MS) with isosceles triangular-loop unit cells. Through pivoting of the novel MS, this antenna achieved good performance in the frequency reconfiguration. Moreover, the reconfigurable antenna have the advantages of compact structure with a diameter of 50mm and a height of 3mm, and good radiation efficiency of up to 90% across the tuning-range. Measured and simulated results testify the wide frequency tunablity of the reconfigurable antenna, and demonstrate it is suitable for advanced multi-standard wireless communication applications.

In this paper, a novel coding metasurface is proposed to realize polarization-controllable diffusion scattering. The anisotropic Jerusalem-cross unit cell is employed as the basic coding element due to its polarization-dependent phase response. The isotropic random coding sequence is firstly designed to obtain diffusion scattering, and the anisotropic random coding sequence is subsequently realized by adding different periodic coding sequences to the original isotropic one along different directions. For demonstration, we designed and fabricated a flexible polarization-controllable diffusion metasurface (PCDM) with both chessboard diffusion and hedge diffusion under different polarizations. The specular scattering reduction performance of the anisotropic metasurface is better than the isotropic one because the scattered energies are redirected away from the specular reflection direction. For potential applications, the flexible PCDM wrapped around a cylinder structure is investigated and tested for polarization-controllable diffusion scattering. The numerical and experimental results coincide well, indicating anisotropic low scatterings with comparable performances. This paper provides an alternative approach for designing high-performance, flexible, low-scattering platforms.

In this paper, we propose an anisotropic focusing metasurface with function of focusing orthogonally polarized waves in refraction and reflection modes respectively. By employing four layered metallic patches spaced by triple layered dielectric spacers, an anisotropic phase element is designed with capability of transmitting x-polarized waves but reflecting y-polarized beams efficiently. Composed of 21 21 cells and with size of 105 105 mm2, a focusing metasurface operating at 15 GHz is designed with the same focal length of 30 mm for x- and y-polarized waves. By setting a patch antenna at the focal point, the metasurface sample is employed to enhance gain of the radiation source. For verification, the metasurface sample is fabricated and measured. The antenna performance, in terms of realized boresight gain and operating bandwidth under x- and y-polarized waves illumination, is presented. Results show that the 1 dB gain bandwidths are respectively from 14.7 to 15.3 GHz and 14.7 to 15.2 GHz, and the gain are enhanced by 14.1 dB, 15.1 dB in refraction and reflection modes when the metasurface is impinged by x- and y-polarized spherical waves. The proposed anisotropic metasurface may afford an alternative for designing anisotropic planar lens or high-gain antenna.

In this paper, we propose a polarization beam splitter utilizing an ultra-thin anisotropic metasurface. The proposed anisotropic element is composed of triple-layered rectangular patches spaced with double-layered dielectric isolators. By tailoring the metallic patches, the cell is capable of transmitting x-polarized waves efficiently and reflecting y-polarized beams with almost 100% efficiency at 15 GHz. In addition to this, the reflected phases can be modulated by adjusting the size of the element, which contributes to beam steering in reflection mode. By assigning gradient phases on the metasurface, the constructed sample has the ability to refract x-polarized waves normally and reflect y-polarized beams anomalously. For verification, a sample with a size of 240 240 mm2 is fabricated and measured. Consistent numerical and experimental results have both validated the efficiently anomalous reflection for y-polarized waves and normal refraction for x-polarized beams operating from 14.6–15.4 GHz. Furthermore, the proposed sample has a thickness of 0.1λ at 15 GHz, which provides a promising approach for steering and splitting beams in a compact size.

A novel ultra-compact single-negative waveguide metamaterial (WG-MTM) based on a complementary anti-parallel-spiral line (CAPAL) is proposed and investigated by circuit model analysis, electromagnetic simulation and extraction of the effective parameters. The cell is ultra-compact with dimensions of λ0/22.08 × λ0/22.08, which advances a step further toward homogenized concept. Two band-gaps attributing to the negative permeability and negative permittivity appear when the CAPAL-WG-MTM cells response to the time-varying perpendicular E-field and parallel H-field, and thus a high decoupling efficiency is obtained. Mutual coupling reduction of about 8.27 dB is realized by inserting 7 × 1 CAPSL-WG-MTM cells between two closely placed antenna elements with an edge-to-edge separation of only λ0/19.23. Moreover, the radiation characteristics are improved for both the patch element and the antenna array. A higher front-to-back ratio is obtained for the patch element and an increase of 0.64 dB for the gain of the antenna array by using the CAPAL-WG-MTM structure.