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In this article, we propose an equivalent circuit theory-assisted deep learning approach to accelerate the design of metasurfaces. By combining the filter equivalent circuit theory and a sophisticated deep learning model, designers can achieve efficient metasurface designs. Compared with most existing metasurface generative design methods that rely on arbitrarily generated training dataset (TDS), the proposed method can adaptively produce highly relevant and low-noise training samples under the guidance of filter equivalent circuit theory, resulting in a significantly narrowed target solution space and improved model training efficiency. Furthermore, we select the variational autoencoder (VAE) as a generative model, which can compress the raw training samples into a lower-dimensional latent space where optimization methods, such as genetic algorithm, can be more efficiently executed to find the optimal design than a brute-force search. To verify the effectiveness of the proposed method, we apply it in the creation of three examples of frequency selective surfaces (FSSs), presenting wide-band, dual-band, and band-stop responses. Experimental results show that the proposed method can realize much faster and more stable convergence than deep learning design methods without domain knowledge. [ABSTRACT FROM AUTHOR]

In this communication, a novel message passing interface (MPI) parallel algorithm for nodal discontinuous Galerkin time-domain (NDGTD) method has been developed. A unified MPI + MPI technique has been introduced for extreme parallelism on a large-scale computer cluster. Through the data transmission between CPU nodes using MPI persistent nonblocking two-side communication and the direct data connection between processors in the same node via MPI shared memory windows, a two-layered parallel architecture is implemented to minimize the communication. To further accelerate the solution of the multiscale problems, the local time stepping (LTS) technique has been employed in the NDGTD method. A fast time step estimation method has been presented in this communication. With high overlap between the information transmission and the data calculation, the proposed MPI + MPI scheme overcomes the degradation of the parallel efficiency of the pure MPI technique in the scenario of the LTS technique and the large-scale CPU cores. Up to 94% parallel efficiency in 6400 CPU cores is achieved for the average single-core loading about 1700 finite elements, and 18 times acceleration for time step estimation can be obtained with the fourth-order basis function. Three practical complex examples are given to demonstrate a good performance of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, penalty factor threshold and time step bound in discontinuous Galerkin time method based on vector wave equation (DGTD-WE) method are well estimated. Based on the semidiscrete form of the DGTD-WE method, properties of the system matrices are studied and the stability condition related to the penalty factor is derived. By decomposing the global system matrices of the DGTD-WE method into the local ones and developing an efficient iteration procedure, the lower bound threshold of the penalty factor is well estimated to guarantee the positive semidefinite property of the global system matrices. With the calculated penalty factor, the maximum time step is analytically determined by approximating spectral radius of the local system matrix. Both the penalty factor bound and the maximal time step are computed element-wise instead of a global system matrix operation, and thus, the proposed method can be efficiently applied into the large-scale meshes with different types of the basis functions and boundary conditions. Numerical examples are presented to demonstrate the validity and good performance of the proposed methods. [ABSTRACT FROM AUTHOR]

This article presents a polarization-reconfigurable wideband high-gain antenna based on liquid metal tuning. The antenna consists of a center-feed circular patch antenna with a C-shaped slot as the driven element. To broaden the bandwidth and improve the realized gain, a parasitic circular disc and 13 circular directors are employed. The direction of polarization can be tuned by changing the location of the liquid metal alloy contained in the tube. The relationship between the dimensions and the maximally achievable gain has been analyzed. The antenna has exhibited a −10 dB impedance bandwidth from 4.3 to 5.3 GHz (a fractional bandwidth of 21.2%). A 14.4 dBi gain is achieved at 5.3 GHz. The simulation and measurement results show good agreement with each other. [ABSTRACT FROM AUTHOR]

In this article, a graphic processing unit (GPU)-based acceleration implementation of a hybrid discontinuous Galerkin time domain method based on Maxwell’s equations and Helmholtz vector wave equation (HDGTD) has been developed. The computational domain is discretized by tetrahedrons and the resultant meshes are categorized into two regions solved by Maxwell’s equations and Helmholtz vector wave equation, respectively. The hierarchical vector basis functions are used to expand the unknowns in the HDGTD method, and a universal matrix technique is proposed to decompose the geometry-dependent matrices in each tetrahedron into the summation of universal matrices defined in barycentric coordinates, thus giving rise to a great decrease of the memory usage. A local time stepping (LTS) method based on a simple interpolation is introduced in the proposed HDGTD method to achieve highly efficient solution of multiscale problems. Two kinds of compute unified device architecture (CUDA)-based mapping techniques, i.e., 1-D and 2-D blocks, are implemented to achieve a tradeoff between the parallel speedup and the memory usage. With the 1-D block mapping, over 590 times speedup can be achieved, and in the case of the 2-D block mapping, over 150 times acceleration and 13 times memory reduction are obtained. Some practical complex examples are given to demonstrate a good performance of the proposed parallel method. [ABSTRACT FROM AUTHOR]

In this paper, we propose and develop a leaky-wave antenna (LWA) by periodically loading shunt radiation element pairs along a host transmission line (TL). Each pair of radiation unit consists of one capacitive element and one inductive element, which are susceptance-complementary with each other. The complementary radiation element loading leads to an effective open-stopband (OSB) suppression, thereby facilitating a continuous leaky-wave beam scanning from backward, through broadside, to forward. Compared with the previously studied OSB-suppressed LWAs containing only one type of susceptive radiation elements, the proposed LWA features two unique properties: constant radiation efficiency over the operation band, and unit cell period only related to the host TL regardless of parameter values of the radiation elements. The aperture synthesis of the proposed LWA is hence straightforward as the radiation elements can be designed to be equally spaced. Experimental prototypes are designed and fabricated based on microstrip line structure as a proof of concept. Desired measured results agree well with the theoretical predictions. [ABSTRACT FROM AUTHOR]

In this paper, a beam switching antenna (BSA) based on a reconfigurable cascaded feeding network (RCFN) is presented. The RCFN is engineered by cascading several varactor-loaded quasi-lumped couplers (QLCs). As the output port of the RCFN, the coupled port of every QLC is connected to an endfire radiator. BSAs based on two types of RCFN, the open-loop RCFN and closed-loop RCFN, are designed, simulated, and measured. The open-loop design features flexible beam switching strategies with the dynamic control of operation modes allocating the input power to the intended radiator(s), and single-/multibeam switching is achieved. In the case of the closed-loop RCFN, a power-recycling circuit is introduced to improve the efficiency of the single-beam switching mode of the BSA. Measured results show that the BSA operating in single-beam mode is able to radiate six switched beams each with a 3 dB beamwidth of 60°, covering 360° in the azimuth plane. The return losses and gain fluctuation of both prototypes are better than 15 dB and less than 1 dB, respectively. The corresponding experiments agree well with both the theoretical analysis and the simulation results. [ABSTRACT FROM PUBLISHER]

Transient electromagnetic scattering by composite structures is formulated by time-domain combined field integral equations (TDCFIEs). Traditionally, the TDCFIEs are solved by combining the method of moments (MoMs) in space domain and march-on-intime (MoT) scheme in time domain. The space-domain MoM requires two basic functions to represent the electric and magnetic current densities on material interfaces, respectively, and the conventional choice of \hat n\times \mathrm RWG basis function for representing the magnetic current density may not be good in the TDCFIEs. In addition, the MoT scheme has a well-known late-time instability problem, which will aggravate in the surface integral equations with penetrable media. In this communication, the TDCFIEs for composite structures are solved by a different approach in which the Nyström method is used to discretize the space domain, while the Galerkin method with Laguerre basis and testing functions is employed to discretize the time domain. The proposed approach can fully overcome the drawbacks of the traditional approach as demonstrated by numerical examples. [ABSTRACT FROM AUTHOR]

In this paper, we propose an approach to realize substrate integrated waveguide (SIW)-based leaky-wave antennas (LWAs) supporting continuous beam scanning from backward to forward above the cutoff frequency. First, through phase delay analysis, it was found that SIWs with straight transverse slots support backward and forward radiation of the $-1$-order mode with an open-stopband (OSB) in between. Subsequently, by introducing additional longitudinal slots as parallel components, the OSB can be suppressed, leading to continuous beam scanning at least from $-40^\circ$ through broadside to 35°. The proposed method only requires a planar structure and obtains less dispersive beam scanning compared with a composite right/left-handed (CRLH) LWA. Both simulations and measurements verify the intended beam scanning operation while verifying the underlying theory. [ABSTRACT FROM PUBLISHER]

Accurate electromagnetic (EM) analysis for conductive media requires to consider the finite conductivity of the media. Although the problems can be formulated by surface integral equations (SIEs) with an approximate surface impedance, we treat the conductive media as penetrable objects and use volume integral equations (VIEs) to exactly describe their EM features. The VIEs are solved by a point-matching scheme which does not rely on any basis and testing functions and allows the use of nonconforming meshes. Since the VIEs are well-conditioned in general and the integral kernels are free of material parameters, the scheme is flexible to accommodate a wide range of skin depth. Moreover, when the skin depth is small, we can only discretize the skin domain with a current distribution to reduce the cost. For large conductive media, we also incorporate the scheme with the multilevel fast multipole algorithm (MLFMA) to accelerate the solution. Typical numerical examples are presented to illustrate the scheme and its effectiveness has been validated. [ABSTRACT FROM PUBLISHER]

This communication proposed an ultra-high frequency (UHF) stacked Hilbert antenna array to broaden bandwidth and increase gain of Hilbert fractal antenna. Two parasitic curves were added to improve the third order Hilbert curve and stacked structure was applied to the new antenna element. The UHF stacked Hilbert antenna was designed as antenna array that involved 2 \times 2 elements and fed by the Wilkinson's four-way power divider. Measurement results show that the UHF stacked Hilbert antenna array achieves a maximum gain of -1 dBi and exhibits a wide impedance bandwidth. Actual partial discharge (PD) experiments were carried out for typical artificial insulation defect models, while the proposed antenna array and an existing Hilbert fractal antenna were both used for PD measurements. The proposed antenna array was superior in this respect and effective for UHF online monitoring of PDs in electrical apparatus. [ABSTRACT FROM PUBLISHER]

A novel broadband planar antenna is developed for mobile communication base stations. The antenna is composed of a pair of folded dipoles which are coupling fed by an L-shaped microstrip line. Both the dipoles and the coupling microstrip line are etched on the same substrate. The planar antenna achieves a bandwidth of 53% for return\ loss > 15 dB, covering the frequency range 1.65–2.85 GHz for 2G/3G/LTE applications. The antenna gain of the broadband antenna element is about 9 dBi. A \pm45^\circ dual-polarized planar antenna consisting of two broadband antenna elements is proposed, which achieves a bandwidth of about 50% and an isolation of 30 dB. Two 8-element antenna arrays are developed respectively for the broadband antenna and for the \pm45^\circ dual-polarized antenna. Both antenna arrays achieve a bandwidth of more than 58% (1.6–2.9 GHz). The antenna gains achieved for the both antenna arrays are higher than 15.5 dBi. The half-power beam widths in the horizontal plane for the antenna arrays are approximately 65\pm 10^\circ, suitable for base station applications. [ABSTRACT FROM PUBLISHER]

A novel dual-broadband planar antenna is proposed for 2G/3G/LTE (4G) mobile communications. The proposed dual-broadband antenna consists of one element for the lower band and two elements for the upper band, making it possible to be arrayed without appearance of grating lobes in the upper band. The lower-band element comprises a pair of printed dipoles with a pair of parasitic elements for bandwidth enhancement. Two upper-band elements composed of two pairs of folded dipoles are nested inside the lower-band element, forming a compact arrayable antenna unit. The dual-broadband antenna achieves a bandwidth of 20% (800–980 MHz) for the lower band and a bandwidth of 60% (1540–2860 MHz) for the upper band. A dual-broadband antenna array that consists of 4 elements for the lower band and 8 elements for the upper band is developed for base station applications. The dual-broadband array achieves a bandwidth of 22% (780–980 MHz) for the lower band and a bandwidth of 68% (1470–3000 MHz) for the upper band, covering all the frequency bands for 2G/3G/LTE (4G) systems. Measured antenna gains for the array are \sim 12 dBi for the lower band and \sim 13.5 dBi for the upper band, suitable for potential applications in mobile communication base stations. [ABSTRACT FROM PUBLISHER]