We demonstrate an efficient back-fire to forward wide-angle beam steering leaky-wave antenna (LWA) based on a large dispersion gradient planar spoof surface plasmon polariton (SSPP) transmission line (TL) with split-ring units. To convert the highly confined SSPP waveguiding mode to a radiation mode, two arrays of metallic patches are periodically arranged on both sides of the SSPP TL. The patches are designed as two combined half-elliptical shapes to mitigate the open stopband effect and enhance the radiation performance. We propose a theoretical method to interpret the mechanism and predict the directional pattern of the LWA. To verify the proposed method, the SSPP TL and LWA prototypes are fabricated and measured. The calculation, simulation, and experimental results match well and show that the main beam of the LWA can steer a wide range of 112° from back-fire (−90°) to the forward quadrant of 22° passing through the broadside in 6.3–11 GHz, demonstrating a large scanning rate of 2.07°/%. Furthermore, the LWA also possesses the advantages of low profile, high average gain (12 dBi), high average efficiency (95%), and low sidelobe level (<−13 dB). This work provides an alternative route to achieving wide-angle LWAs for promising microwave radar and wireless communication applications.

Efficient generation of orbital angular momentum (OAM) modes is a key foundation for electromagnetic vortex wave communications or radar applications. The usual OAM generation methods based on phase-shifted circular ring arrays require complex feed network. In this paper, a ring array with low-order OAM single antennas as the array elements of in-phase feed is proposed to simplify the array structure and increase the practicality. The theoretical analysis shows that the phase singularity of the radiation fields appears in the array boresight direction. The region just close to the array axis radiates only the 1st order OAM mode, independent of the antenna element OAM order. Outer these regions, however, 1 - N order vortex waves determined only by the array element number N can be realized. The hexagonal array of the 5th order OAM has experimentally confirmed these conclusions. Clearly, for this kind of array, higher order OAM modes are easily achieved and the order can be controlled by regulating the number of array elements. Since it is fed in phase, this construction method for OAM antenna array is very practical.

Three-dimensional (3-D) electromagnetic (EM) scattering and inverse scattering of magnetodielectric objects with arbitrary anisotropy embedded in layered uniaxial media are studied. The stabilized biconjugate gradient fast Fourier transform (BCGS-FFT) method is employed to solve the forward scattering problem formulated by the combined field volume integral equation (CFVIE). In the inversion, we use the variational Born iterative method (VBIM) enhanced by the structural consistency constraint (SCC) to reconstruct eighteen unknown dielectric parameters of the scatterers simultaneously. In order to further improve the accuracy of the reconstructed permittivity, permeability, and conductivity of the scatterers, we propose the structural continuity scanning (SCS) technique. Comparisons between the BCGS-FFT solution and simulated results from finite element method (FEM) are performed to verify the reliability and accuracy of the forward solver. Meanwhile, we reconstruct the multiple anisotropic parameters of several typical structures embedded in layered uniaxial media to show the feasibility and anti-noise ability of the inversion algorithm.

This paper presents the three-dimensional (3-D) inversion of biaxial anisotropic objects embedded in layered uniaxial media by the variational Born iterative method (VBIM). While previously only the isotropic complex permittivity profile was reconstructed, here we retrieve all the six diagonal anisotropic permittivity and conductivity parameters simultaneously. In the forward model, the stabilized biconjugate gradient fast Fourier transform (BCGS-FFT) method is used to solve the volume electric field integral equation (EFIE). In the inversion model, VBIM is employed to minimize the cost function. In order to improve the inversion results, we propose a novel structural consistency constraint (SCC) applied to VBIM. The SCC is based on the Monte Carlo method and reduces the computational domain in the Born iteration. The major new contribution of this work is to combine the deterministic inversion algorithm VBIM with the stochastic Monte Carlo method to reconstruct all the diagonal anisotropic parameters of the scatterers. Several typical numerical models are simulated, and the results validate the efficiency, anti-noise ability as well as accuracy of VBIM-SCC for reconstructing 3-D biaxial anisotropic objects embedded in multilayered uniaxial media.

In electromagnetic (EM) well logging for petroleum exploration, off-centered tools within a noncircular borehole and invasion zones in multilayered media represent a challenging 3-D problem for traditional numerical methods. The 3-D finite-element numerical mode-matching (FNMM) method and the spectral numerical mode-matching (SNMM) method are developed to address this problem in this work. The numerical mode-matching (NMM) methods reduce the original 3-D well logging problem into a series of 2-D open waveguide eigenvalue problems plus a 1-D layered medium problem, which can be analytically solved by a recursion procedure. These waveguide eigenvalue problems with anisotropic inhomogeneous media in the horizontal directions are solved numerically by the mixed finite-element method (MFEM) with the flexibility for the complex geometry and the mixed spectral element method (MSEM) with the exponential convergence. A general operator form of Maxwell’s equations is also derived to obtain the source excitation vector independent of the $z$ -axis. Therefore, the NMM solvers can effectively and accurately simulate the response of off-centered EM well logging tools in an irregular borehole in complex formations. The NMM methods are applied to simulate three formations including a five-layer isotropic homogeneous formation, an off-centered logging tool in a noncircular borehole with anisotropic invasion zones in a five-layer anisotropic formation, and the Oklahoma formation. Numerical experiments indicate that the NMM methods are highly efficient and accurate for the EM well logging models.

In this paper, a systematic design strategy of polarization-insensitive, broadband, and high-efficiency metasurface is reported, and the proposed metasurface has excellent performance in holographic imaging. First, we utilize a multi-objective differential evolution algorithm to rapidly design a high-performance meta-atom group, capable of achieving a reflected amplitude (efficiency) exceeding 0.91 (83%) within the bandwidth of 8.21-17.50 GHz. Subsequently, a wideband phase distribution method is proposed for calculating the imaging phase map. Guided by the phase map, the meta-array is designed for the generation of letter-shaped images under distinct polarization excitation across the entire bandwidth. Finally, calculations, simulations, and experiments collectively verify the effectiveness of the systematic design strategy utilized in holographic imaging. The metasurface sample has the capability to generate letter-shaped images at varying heights with an imaging efficiency over 62.8%. The proposed method can be employed to achieve the unrestricted distribution of electromagnetic wave energy in three-dimensional space, encompassing applications such as wireless charging, data storage, and microwave imaging.