Design Methods for Dual Polarized Metasurface Antennas: Three Simple Approaches

Tunable surface waves supported by graphene-covered left-handed material structures

A metasurface (MS) antenna that allows polarization reconfigurability is proposed. The MS antenna is formed by a MS and source antenna, separated by a small air gap. The MS consists of 16 identical unit cells on a substrate, where each unit cell used is a corner truncated square patch. A microstrip fed slot antenna (MFSA) is used as the source antenna. The MS converts the linearly polarized (LP) signal generated by the MFSA into a circularly polarized (CP) signal with wider return loss bandwidth(RLBW). By rotating the MS relative to the MFSA, different polarizations could be achieved. For verification of simulation results, the MS antennas are fabricated and measured. Simulated and measured results show good agreements. The MS antenna has an operating frequency of 2.4 GHz, suitable for WLAN applications.

On wave diffraction of two-dimensional moonpools in a two-layer fluid with finite depth

This study examines the analytical and numerical solution of electromagnetic surface waves supported by a resistive metasurface-covered grounded metamaterial structure. To simulate the metamaterial, the Kramers–Kronig relation based on the causality principle is used, while the modeling of the resistive metasurface has been done by implementing the impedance boundary conditions. The analytical expressions for the field phasors of surface waves are developed for the transverse magnetic (TM) polarized mode and transverse electric (TE) polarized mode. The characteristic equations are computed for both modes, and the unknown propagation constant is evaluated numerically in the kernel. After computation, the dispersion curves, electric field profiles, effective mode index (N_{eff}), and phase speeds (v_{p}) are presented for both the TM and TE polarized modes. To study the tunability of surface waves, the influence of the thickness of the metamaterial slab (d), effective permittivity of the metamaterial (varepsilon_{1}), thickness of the resistive metasurface (t), and effective permittivity of the metasurface (varepsilon_{r}) on all the numerical results has been studied. However, the geometrical parameters are found to be more sensitive to the effective mode index (N_{eff}) and phase speed (v_{p}) of the surface waves. The results are consistent with the published results, which reflects the accuracy of the work. It is concluded that the appropriate choice of parameters can be used to achieve surface waves with the desired characteristics in the GHz range. The present work may have potential applications in surface waveguide design, surface wave speed controllers, surface communication devices, and light trapping configurations.

This paper presents new designs, implementation and experiments of metasurface (MTS) antennas constituted by subwavelength elements printed on a grounded dielectric slab. These antennas exploit the interaction between a cylindrical surface wave (SW) wavefront and an anisotropic impedance boundary condition (BC) to produce an almost arbitrary aperture field. They are extremely thin and excited by a simple in-plane monopole. By tailoring the BC through the shaping of the printed elements, these antennas can be largely customized in terms of beam shape, bandwidth and polarization. In this paper, we describe new designs and their implementation and measurements. It is experimentally shown for the first time that these antennas can have aperture efficiency up to 70%, a bandwidth up to 30%, they can produce two different direction beams of high-gain and similar beams at two different frequencies, showing performances never reached before.

A new architecture is provided for the efficient generation of shaped beams and multiple shaped beams (in amplitude, phase, and polarization), with leaky-wave (LW) metasurfaces (MTSs). Those antennas are usually fed by a surface-wave (SW) launcher, which evenly illuminates the MTS versus azimuth, through a cylindrical SW. When the interest lies in generating pencil beams or particular types of shaped beams, the required radiating aperture field (linked to the Fourier transform of the desired radiation pattern) on the MTS is almost azimuthally symmetric in amplitude. However, for a wide class of shaped beams, the desired aperture field is far from being azimuthally symmetric. This leads to an MTS design in which some sectors exhibit a very small surface impedance modulation. Those sectors tend to leave the SW intact until it reaches the rim of the surface, where the power is either reflected or diffracted at the slab rim. We solve this efficiency problem by reducing the amount of power fed into some sectors, through the use of an array of feeding monopoles. The azimuthal illumination of the feeder should be designed to match the azimuthal asymmetry of the desired aperture field. The corresponding MTS surface impedance is then determined using a method of moments (MoM)-based synthesis technique. Several examples are provided to illustrate the concept. The improvement in terms of antenna efficiency is numerically demonstrated.

A new broadband circularly polarized (CP) metasurface (MS) antenna based on characteristic mode analysis (CMA) is proposed. The antenna consists of 4×4 truncated Γ-shaped unit cells and is fed by an improved slot coupling structure. The characteristic modes required to achieve CP are analyzed by CMA, and the CP performance is improved by changing the characteristic currents distribution. By introducing a stepped slot structure on the slot floor, the bandwidth of the antenna has been further broadened. By loading the microstrip line to feed the MS, left-handed circular polarization (LHCP) can be realized. In addition, the equivalent circuit method is used to explain how the designed MS antenna achieves CP. The overall size of the designed and fabricated MS antenna is 0.72 λ 0 ×0.72 λ 0 ×0.08 λ 0 at 6.2 GHz. The measured −10 dB impedance bandwidth of the antenna is 25.17% (5.21 GHz-6.71 GHz) and the measured 3 dB axial ratio bandwidth is 17.42% (5.87 GHz-6.99 GHz). Moreover, the highest gain in the working frequency band is 7.52 dBic. The proposed CP MS antenna has good application prospects in C-band satellite communications.

We consider the modes of surface waves with the diffusion mechanism by the band transport model of the photorefractive effect and the nonlinear equation for the first time. We demonstrate the relationship between the modes of surface waves and the angles of incidence. The conditions for the realization of surface modes at the interface between photorefractive crystal and a metal, a linear dielectric with a lower refractive index, or another photorefractive crystal are discussed.

This paper presents an efficient approach for the method of moments (MoM) analysis of metasurface (MTS) antennas. Instead of simulating the actual structure, made of several thousands of subwavelength patches, the presence of the MTS is accounted for using an impedance boundary condition in the integral equation. Then, when the MTS antenna exhibits rotational symmetry, the integral equation can be efficiently solved adopting a formulation for bodies of revolution. On the other hand, a novel type of basis functions can also be applied to the analysis of planar MTSs without any particular symmetry. The advantages of such basis, in both the space and spectral-domain, are outlined. Indeed, their closed-form spectrum allows one to efficiently compute the MoM impedance matrix using the spectral-domain approach. More importantly, these basis functions represent the global evolution of the surface current density in an effective manner. In both approaches, one obtains a drastic reduction in the number of unknowns, with respect to the cases in which the actual structure has been meshed with sub-entire domain basis.

This article presents an exact solution for a perfect conversion of a TM-polarized surface wave (SW) into a TM-polarized leaky wave (LW) using a reciprocal and lossless penetrable metasurface (MTS) characterized by a scalar sheet impedance, located on a grounded slab. On contrary to the known realizations of LW antennas, the optimal surface reactance modulation which is found here ensures the absence of evanescent higher-order modes of the field Floquet-wave expansion near the radiating surface. Thus, all the energy carried by the SW is used for launching the single inhomogeneous plane wave into space without accumulation of reactive energy in the higher-order modes. It is shown that the resulting penetrable MTS exhibits variation from an inductive to a capacitive reactance passing through a resonance. The present formulation complements a previous article of the authors, in which a perfect conversion from TM-polarized SW to TE-polarized LW was found for impenetrable boundary conditions. Here, the solution takes into account the grounded slab dispersion, and it is convenient for practical implementation.

To overcome the narrow axial ratio (AR) bandwidth inherent in conventional linearly to circularly polarised converters, this research proposes a metasurface (MS) with a diamond‐shaped configuration that can mitigate the effect of surface wave (SW) along the MS edge and achieve a wider 3 dB AR bandwidth. The diamond‐shaped MS structure is realised by slanting a square MS by 45°, and it consists of constituent unit cells of rectangular and arbitrary shapes. The rectangular unit cells are positioned 45° to the square dielectric substrate, and the unit cells along the MS edge are partially cut into arbitrary shape to be perfectly aligned along the edge. The 3 dB AR bandwidths and degradation of the MS are characterised by SW and magnetic current distribution. Simulations are carried out and an MS prototype is fabricated to verify the results. The effects of partially cut unit cells (PCUCs) along the MS edge on the SW are characterised. The simulation and measured 3 dB AR bandwidths of the diamond‐shaped MS are 37.6 and 28.8%, respectively. The novelty of the proposed diamond‐shaped MS polarisation converter lies in the implementation of arbitrary‐shaped PCUCs and the use of the diamond‐shaped configuration in place of conventional square geometry to realise wider AR bandwidth.

Based on classic electromagnetic Huygens' Principle and the concept of modern metamaterials, metamaterial Huygens surface, namely, metasurface (MTS) is presented to be the two-dimensional analogues of metamaterials. With the dense arrays of electrically small unit cells, the MTS can control electromagnetic waves and fields in either usual or unusual ways. Such unique electromagnetic properties greatly offer additional opportunities to innovate new antennas. This paper updates the latest progress in the MTS based antenna at microwave bands. First, the concept of the MTS is briefly introduced with a summary of applications of the MTS in microwave antenna design. After that, three of selected MTS based antenna techniques are elaborated with design examples. Finally, the promising applications of the MTS in antenna engineering are commented.

This paper presents a dual-band holographic meta-surface antenna capable of generating steered beams with both right-hand (RH) and left-hand (LH) circular polarization (CP). The proposed unit cell consists of three stacked layers above a ground plane. The first layer features a mode-selective electro-magnetic bandgap structure that effectively isolates transverse magnetic (TM) and transverse electric (TE) surface-wave modes. Such isolation allows independent operation at distinct frequencies for various beam directions, while maintaining radiation efficiency comparable to single-mode designs. The second layer employs split-ring elements designed for the TE mode, and the third layer utilizes split-patch patterns for the TM mode. The dual-port configuration provides distinct polarization control: the TM mode at 11 GHz, excited by a vertical monopole, achieves RHCP, while the TE mode at 14 GHz, excited by a horizontal dipole, produces LHCP. Each port supports directional beam radiation at 30° and 20°, respectively, with measured gains of 17.47 dBi and 18.01 dBi, and corresponding axial ratios of 0.53 dB and 0.43 dB.

This paper presents the characteristics of guided (surface) waves and leaky waves on multilayer structures with planar implanted periodic dielectric blocks. A three-dimensional (3-D) integral-equation formulation in conjunction with the method of moments (MoM's) is used to find the propagation constants of the surface-wave and leaky-wave modes. The analysis deals with layered structures with irregular implants. Photonic band-gaps of both guided waves and leaky waves for rectangular air-implants are identified. Anisotropic properties of the surface waves and leaky waves are investigated. The design of leaky-wave antennas with the information of mode characteristics is discussed. The analysis is validated through the comparison with a low-frequency effective-medium approach and results for linear gratings.

A compact polarization demultiplexer (P-DeMux) is proposed and characterized to enable wavelength-divisionmultiplexing and mode-division-multiplexing simultaneously. The proposed structure is composed of a microring resonator in ultrathin waveguide and two bus channels in the novel silicon nitride silica silicon horizontal slot waveguides. In the slot waveguide, the transverse electric (TE) mode propagates through the silicon layer, while the transverse magnetic (TM) mode is confined in the slot region. In the designed ultra-thin waveguide, the TM mode is cutoff. The effective index of the TE modes for ultrathin and slot waveguides have comparable values. Thanks for these distinguishing features, the input TE mode can be efficiently filtered through the ultra-thin microring at the resonant wavelength, while the TM mode can directly output from the through port. Simulation Results show that the extinction ratio of the proposed P-DEMUX for TE and TM modes are ∼36.5 and 31.27 dB, and the insertion losses are ∼0.22 and 0.249 dB respectively.