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This article presents a fast direct solver based on surface integral equation (SIE) to solve electromagnetic (EM) scattering from homogeneous penetrable objects. The proposed method relies on a strong admissibility skeletonization factorization (SASF) algorithm and Poggio–Miller–Chang–Harrington–Wu–Tsai (PMCHWT) formulation. In the SASF scheme, only well-separated groups that satisfy the strong admissibility condition are considered to be compressed and thus relatively fewer skeleton basis functions are selected. It is an effective way to compress the matrix with small ranks. An independent compression technique is developed for dielectric problems involving electric and magnetic currents, in which skeleton basis functions representing electric and magnetic currents are obtained separately. Moreover, a novel strategy based on matrix normalization is proposed to treat the arising “fill-in” blocks when far-field interactions are compressed. Ultimately, the impedance matrix can be cast into products of a series of block unit triangular matrices and a block diagonal matrix. Several numerical results show that the proposed approach is effective and stable as well as provides an accurate solution for scattering problems of homogeneous penetrable objects. [ABSTRACT FROM AUTHOR]

A recent analysis has investigated a possible new type of magnetic antenna that is characterized by an electric current that flows azimuthally on the surface of a sphere with a density magnitude that scales as the sine function applied to the spherical polar angle. This analytic theory has yielded an exact solution of the Maxwell equations for the electromagnetic (EM) fields of the resulting radiation for all spatial regions, including that both interior and exterior to the spherical current shell. In the present investigation, the EM fields are expressed in terms of an alternative, and perhaps more intuitive, form such that the radial dependence varies as a product of polynomial and exponential functions. In addition, the subject spherical current density is shown to produce exactly the same purely dipole radiation fields exterior to the spherical current shell as that of an infinitely small magnetic dipole moment antenna. Furthermore, the present analysis calculates various radiation properties corresponding to the subject spherical current antenna concept, including the Poynting vector, radiation impedance, quality factor, and maximum effective area. Finally, the present investigation reveals that the subject spherical electric current density achieves the minimum quality factor that can be attained for all antennas. [ABSTRACT FROM AUTHOR]

This article focuses on further improving the characteristic mode theory (CMT) for metal-material composite scattering objects. The improved CMT is alternatively established in a novel work-energy principle (WEP) framework. Under the WEP framework, a novel driving power operator (DPO) is introduced as the generating operator for characteristic modes (CMs). Then, a novel diagonalizing DPO method is proposed to construct the CMs. In addition, a novel solution domain compression (SDC) scheme is developed to suppress spurious modes. Compared with the conventional integral equation (IE) framework, the novel WEP framework more clearly reveals the core physical feature of CMs, and then easily derives the famous Parseval’s identity. Compared with the conventional impedance matrix operator (IMO), the novel DPO is more advantageous in the aspect of distinguishing independent variables from dependent variables, and has a smaller computational burden, and has a more acceptable numerical performance in the aspect of calculating CMs. Compared with the conventional dependent variable elimination (DVE) scheme, the novel SDC scheme is equally effective in the aspect of suppressing spurious mode, and reconfirms the same conclusion that the spurious modes result from ignoring the dependence relationships among the currents contained in DPO. [ABSTRACT FROM AUTHOR]

A novel low-profile circularly polarized (CP) diversity patch antenna with extremely small edge-to-edge distance, reduced size, and low mutual coupling is proposed under dual modes. Initially, the single microstrip patch antenna (MPA) is theoretically investigated by using characteristic mode analysis. It demonstrates that a large number of radiative modes, i.e., CM1 to CM7, are excited for the traditional MPA. By selecting its quarter patch configuration with shorting pins, only a few modes, i.e., CM2 and CM7, could be resonated for the quarter patch antenna (QPA). Meanwhile, their nonbroadside radiated fields could be transformed into the broadside radiation. Particularly, the polarizations of CM2 and CM7 are maintained orthogonally with each other. Next, a linear slot is etched on the patch to reduce the magnitude ratio between $\vert E_{\mathrm {\theta }}\vert $ and $\vert E_{\varphi }\vert $ components. After that, the resonant frequency of CM7 is moved closely to that of CM2 for nearby 90° phase difference. With these arrangements, the compact CP performance is acquired by combining its CM2 and CM7. Furthermore, a pair of QPAs with CP diversity is deeply studied. The results prove that the antenna has successfully acquired both of left-handed CP (LHCP) and right-handed CP (RHCP) performances at dual ports. Moreover, the low mutual coupling between them is generated under extremely small spacing. In final, the proposed antenna is fabricated and tested. Both of LHCP and RHCP patterns are formed of around 4.785 GHz. Besides, the proposed antenna occupies the small overall volume $0.023\lambda _{\mathrm {g}}^{3}$ ($\lambda _{\mathrm {g}}$ is the guided wavelength), that is only half of the traditional patch ($0.045\lambda _{\mathrm {g}}^{3}$), and maintains the isolation as high as about 24 dB under extremely small distance (0.3 mm). [ABSTRACT FROM AUTHOR]

We present a study on beam coupling in radiating structures that support multiple simultaneous beams. The formation of multiple beams is relevant in modern wireless communication applications when diverse data streams can be sent from a single transmitter to users located in different directions. General expressions are provided that relate the coupling between radiated beams to the associated current distributions on the radiating aperture. When expanding the currents in terms of basis functions, the beam coupling can be also written in terms of coupling contributions due to each pair of basis functions. The analysis is applied to antenna arrays with different levels of mutual coupling between the array elements. More specifically, arrays of resonant elements, characterized by very low mutual coupling, are compared with arrays of connected elements, which are strongly coupled. We show that, even for a very high level of mutual coupling between individual array elements, it is possible to obtain orthogonal beams if the total current distributions associated with the beams are uncoupled. [ABSTRACT FROM AUTHOR]

In this article, a novel dual-band dual-mode (DBDM) patch antenna is proposed with flexible radiation coverage and a simple structure. Distinct radiation properties with high-gain in the lower band and wide-beam in the upper band could be attained under a small frequency ratio and a single element. The working principle of the wide-beam radiation is, for the first time, proposed and theoretically analyzed based on the electric current calculation, providing a good insightful understanding of the radiation of the inverse currents. The high-gain radiation in the lower band is realized by introducing the shunt inductive effect while maintaining a negligible influence on the upper band. In terms of realization, a pair of stubs and shorting pins are properly loaded on a square patch to achieve the conditions required in the theoretical analysis. It indicates that the proposed method could be easily achieved with the simple structure of a single layer and a single element. Additionally, further discussion on the size reduction of the patch is provided with good cross-polarization. Two prototypes are finally designed, fabricated, and tested. The simulated and measured results exhibit good agreement with each other, certifying the validity of the proposed method. All these attractive merits, such as flexible coverage with high-gain and wide-beam radiations, simple structure with a single element, small achievable frequency ratio, and low profile, demonstrate that the proposed antenna could be a good potential candidate in the modern wireless systems. [ABSTRACT FROM AUTHOR]

In this article, a nonconformal domain decomposition method (DDM) based on the hybrid finite element method (FEM) and boundary element method (BEM) is proposed to solve arbitrary 3-D anisotropic (including bianisotropic and single anisotropic) multiscale composite objects. The object is divided into interior and exterior regions. The interior region is solved by the bianisotropic finite element domain decomposition method (FEM-DDM), and the exterior region is solved by the discontinuous Galerkin (DG) method based on the combined field integral equation (CFIE). In order to decouple the electric and magnetic fields of the bianisotropic object, a new finite element–boundary element–domain decomposition method (FEM-BEM-DDM) formulation is derived. To ensure the continuity of electric current and electric field between anisotropic FEM subdomains, a new auxiliary current is introduced into the interface of different subdomains of FEM and the interface of FEM subdomains with BEM subdomains. The former uses second-order transmission conditions (SOTCs) to ensure continuity, whereas the latter uses Robin transmission conditions (RTCs) to ensure continuity. The BEM dense matrix–vector multiplication is accelerated by a multilevel fast multipole algorithm (MLFMA). The proposed FEM-BEM-DDM allows for nonconformal discretization between any touching subdomains and provides an effective preconditioner. In numerical examples, the accuracy and effectiveness of the method are verified. [ABSTRACT FROM AUTHOR]

The finite-difference time-domain (FDTD) method has been widely used for the electromagnetic analysis of complex dispersive media. The shift-operator (SO)-FDTD or auxiliary differential equation (ADE)-FDTD formulation has been mainly employed for dusty plasma. Each FDTD formulation has its pros and cons. SO-FDTD is accurate but not computationally efficient. ADE-FDTD needs fewer computational resources, but its accuracy is poor. Here, we propose an accurate and efficient FDTD formulation for dusty plasma, based on the bilinear transform (BT). We perform a comprehensive study on the numerical permittivity and the computational efficiency for three FDTD formulations. Numerical examples are employed to illustrate that the proposed BT-FDTD outperforms the previously reported FDTD formulations for dusty plasma. In addition, based on the proposed BT-FDTD simulations, the effect of dust particles on EM wave propagation is investigated in the GHz band and the THz band. [ABSTRACT FROM AUTHOR]

The mechanism for the radiation efficiency local minimum in antennas, especially for open-slot antennas and T-shaped antennas, has been investigated. It is found that the local minimum in those antennas always corresponds to an ideal differential mode. Furthermore, the frequency position of the ideal differential mode is decided by the parasitic parts of the antennas. Simple methods for estimating the local minimum position are proposed based on the mechanism we have found. In addition, the duality relation between those two types of antennas is also discussed. Our findings provide a guideline for designing mobile phone antennas with improved efficiency. [ABSTRACT FROM AUTHOR]

A complementary source array with enhanced beamwidth is presented based on the substrate-integrated waveguide (SIW) in this communication. The orthogonal complementary source consists of a SIW slot and a vertical monopole, of which the radiation pattern is heart-shaped, pointing to the direction perpendicular to both slot and monopole. To achieve an enhanced beamwidth from the heart-shaped pattern, the complementary sources are cascaded to form an array. In particular, the slots are etched alternately on both sides of the central axis to achieve an in-phase excitation, while the monopoles are uniformly loaded with an alternate antiphase excitation. This arrangement makes the heart-shaped pattern of each complementary source element alternately point to either side of the array axis, so that the synthesized radiation beamwidth is enhanced in the E-plane. Based on the proposed idea, a nine-element line array is designed, fabricated, and tested. Compared with the same-sized referenced SIW slot array with an E-plane half-power beamwidth (HPBW) of only 80°, the proposed complementary source array extends the HPBW to 180°. [ABSTRACT FROM AUTHOR]

Novel characteristic mode (CM) formulations for penetrable objects based on explicit separation of dissipation power from the total active power and use of single surface integral equation (SSIE) are proposed. Due to the separation of the dissipation power, the right-hand side of the generalized eigenvalue equation can be set to be exclusively related to the radiated power, which permits the far-field pattern by different CMs to be orthogonal whether the material is lossless or not. The use of SSIE allows both the equivalent electric and magnetic currents to be expressed by a single effective electric or magnetic current, so that the conventional inverse to express the equivalent electric current by the equivalent magnetic current or vice versa is avoided, which is favorable for frequency sweeping simulations. Numerical examples for verifications are provided by comparing with acknowledged results or measured data. [ABSTRACT FROM AUTHOR]

Problems of radiation pattern synthesis, sidelobe suppression, or back radiation suppression appear when using antennas with reflectors or ground planes. The use of a semitransparent surface allows the required shape of a radiation pattern to be synthesized efficiently through the variation of reflection and transmission coefficients. Effective radiation pattern synthesis is possible when using analytical formulas designed for the radiation patterns of antennas with semitransparent reflectors. In this article, we present a model for the scattering of a toroidal wave of a general form by means of a semitransparent reflector of revolution. The model allowed us to simulate the radiation patterns of various kinds of axisymmetric antennas with semitransparent reflectors and ground planes. Two asymptotic expansions of the radiation pattern of the model were found in the physical optics approximation. The expansions allow the radiation pattern for the entire space to be determined. As an example of its application, we used the model to calculate the radiation patterns of a plane with Archimedean two-wire spiral antenna and a loop antenna above concave and convex reflectors, as well as an Archimedean slot spiral antenna with a ground plane. We synthesized the optimal profiles of perfectly conducting and semitransparent reflectors and ground planes to improve the front-to-back ratio of the antennas. [ABSTRACT FROM AUTHOR]

This article is devoted to the analysis of the electromagnetic scattering from a thin resistive disk. The problem is formulated in terms of a singular integral equation in the vector Hankel transform domain for each cylindrical harmonic of the effective electric current density. Two new unknowns are introduced by means of Helmholtz decomposition: the surface curl-free contribution and the surface divergence-free contribution of the general harmonic of the effective electric current density. Galerkin method with a complete set of orthogonal eigenfunctions of the static part of the integral operator reconstructing the edge behavior and the behavior around the disk center of the unknowns is used to discretize the integral equation. The obtained matrix equation is a Fredholm second-kind equation for which the fast convergence is guaranteed. Moreover, the matrix coefficients are accurately and efficiently evaluated by means of a suitable integration procedure in the complex plane. The numerical results and comparisons with the commercial software CST Microwave Studio are provided in order to show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A reduced-basis approximation to solve for the electromagnetic scattering from nonpenetrable targets in a frequency band of interest is studied in detail. Perfect electric scatterers in homogeneous media are considered. Even though the frequency behavior can be complicated, the electromagnetic scattering does not arbitrarily change in the frequency band of interest. Thus, instead of using computationally inefficient, large-dimension numerical approximation scenarios, such as the method of moments, to solve for integral equations in the band of interest, a low-dimension reduced-basis space is identified to approximate the smooth evolution of the electromagnetic scattering itself as frequency changes. As a result, the frequency-parameter scattering problem is solved within a reduced-order model approach. The electric field integral equation formulation is addressed and properly selected electric currents are considered to span the reduced-basis space in the frequency band of interest. The involved frequency dependence in the integral equation due to the wave propagation phenomena described in the free-space Green’s function has traditionally limited the applicability of reduced-basis approximations for fast frequency sweep in integral equation methods in electromagnetics. In this article, we focus on this difficulty and propose a physics-based approach where the frequency-parameter dependence shows an affine behavior in the integral equation, without relying on rather complicated interpolation schemes. As a result, a fast frequency sweep for integral equation problems in electromagnetics is proposed. Finally, real-life applications will illustrate the capabilities of this methodology. [ABSTRACT FROM AUTHOR]

This article presents a new self-dual integral equation (SDIE) for electromagnetic scattering from arbitrarily impedance boundary condition (IBC) objects including partly coated objects. The proposed SDIE is constructed by using the combined field integral equation (CFIE) and IBC, shorted as C-SDIE. To overcome the difficulty of discontinuous surface impedance from nonuniform IBC/partly coated objects, the discontinuous Galerkin (DG) method is applied to discretize the C-SDIE. Numerical experiments confirm that the DG-C-SDIE has promising numerical performance in terms of accuracy and efficiency. Furthermore, the domain decomposition preconditioning based on DG is employed to further enhance the proposed DG-C-SDIE for large-scale, multi-scale objects. The numerical results demonstrate the capability of the proposed DG-C-SDIE. [ABSTRACT FROM AUTHOR]

An efficient equivalence principle algorithm with spherical equivalent source (SEPA) is proposed to analyze the electromagnetic scattering from a metal–dielectric composite and randomly distributed bodies of revolution (BoRs) cluster, which is called SEPA-CBoR for short. Due to the rotationally symmetrical property, the electromagnetic currents on the BoRs and the equivalence spheres (ESs) are all expanded by the basis functions of BoR. In this way, the self-action and the interaction can be both calculated by using the method of moment for BoR (BoR-MoM). With the repeatability fully used, the self-action for the BoRs with the same size just needs to be calculated once. Moreover, the interaction can also be got once when the size and relative displacement vector of their corresponding ESs are the same. Since these self-action/interaction matrices are constructed in mutually orthogonal Fourier modes, the entire problem is eventually solved by a couple of small matrix equations independently. As a result, the SEPA-CBoR method can greatly save the memory requirement and solution time. Several numerical examples are presented to demonstrate the accuracy and efficiency for the composite BoRs cluster problems. Especially, it is helpful to distinguish the fake targets with the accurate echo signs obtained from the efficient SEPA-CBoR method. [ABSTRACT FROM AUTHOR]

This paper proposes a fast far-field estimation method of electrically long antenna in compact measurement space. The presented method estimates a far-field pattern on an orthogonal cut plane from the linear equivalent electric current and circular current distribution. The equivalent electric current data is measured in a reactive near-field region using a small loop probe. In the proposed method, the linear equivalent current distribution is extended by a simple numerical extrapolation formula for improving the accuracy of the estimated far field in the broadside direction. In the horizontal plane, the far-field pattern is calculated from both the circular equivalent electric and the magnetic distribution approximating equivalent magnetic current with equivalent electric current. We confirmed the validity of the proposed method from the numerical simulation and measurements results. The method allows accurate directivity measurement in a small space in about a few minutes. [ABSTRACT FROM AUTHOR]

Tightly coupled arrays (TCAs) have received considerable interests recently. Although various TCAs have been reported, they are generally limited to single or dual linear polarizations. Considering the importance of circularly polarization in various wireless systems, it is meaningful to design a circularly polarized (CP) TCA with a simple configuration. This communication presents a CP tightly coupled crossed dipole array (CP-TCCDA) with intrinsic CP feeding structure, which achieves wide overlapped impedance bandwidth and axial ratio (AR) bandwidth. An analysis is given to explain the principles of AR bandwidth improvement and is validated by the comparison of radiated E-fields between a CP-TCCDA and a conventional CP crossed dipole array. To verify the design concept, a $4 \times 4$ CP-TCCDA with elaborate feeding network is fabricated and measured. The measured results confirm that the proposed array achieves VSWR < 3 bandwidth from 2.06 to 6.46 GHz (3.14:1) and 3 dB AR bandwidth from 2.35 to 5.6 GHz (2.38:1), which are much wider than the bandwidth of an isolated element and a conventional array using the same element. [ABSTRACT FROM AUTHOR]

Full-wave electromagnetic simulations of electrically large arrays of complex antennas and scatterers are challenging, as they consume a large amount of memory and require long CPU times. This paper presents a new reduced-order modeling technique to compute scattering and radiation from large arrays of complex scatterers and antennas. In the proposed technique, each element of the array is replaced by an equivalent electric current distribution on a fictitious closed surface enclosing the element. This equivalent electric current density is derived using the equivalence theorem, and it is related to the surface currents on the scatterer by the Stratton–Chu formulation. With the proposed approach, instead of directly solving for the unknown surface current density on the scatterers, we only need to solve for the unknowns on the equivalent surface. This approach leads to a reduction in the number of unknowns and better conditioning when it is applied to problems involving complex scatterers with multiscale features. Furthermore, the proposed approach is accelerated with the adaptive integral equation method to solve large problems. As illustrated in several practical examples, the proposed method yields the speedup of up to 20 times and consumes up to 12 times less memory than the standard method of moments accelerated with the adaptive integral method. [ABSTRACT FROM AUTHOR]

This paper presents a novel method of decoupling inverted-F antennas (IFAs) with high-order modes of a ground plane in 5G mobile multiple-input multiple-output (MIMO) platform. The proposed method is illustrated in a dual-antenna 5G mobile platform operating at 3.5 GHz. An IFA excites a high-order mode of the field distribution in the ground plane at 3.5 GHz. The electric field of the excited high-order mode forms several stable null-amplitude field points located on the edge of the ground plane. The other IFA is then placed in one of the stable null points. By doing this, the two IFAs are decoupled with high isolation. The simulated results show that isolation improvements of 20–40 dB can be achieved when the positions and orientations of the two IFAs are optimized. The measured results confirm that the fabricated antennas have peak isolations of 45–56 dB. Finally, the proposed method is applied to design a three-IFA-based MIMO platform which verifies that the suggested concept can effectively simplify the decoupling mechanism and works well in a multiantenna-based mobile MIMO terminal. [ABSTRACT FROM AUTHOR]

A new efficient aggregate basis function method is proposed for the electromagnetic scattering from composite structures consisting of finite periodic array and other object. The aggregate basis functions composed of Rao–Wilton–Glisson basis functions are defined, which leads to a good decrease in the number of unknowns, but with the enough accuracy. To obtain the aggregate basis functions, the approximate solution is implemented. By taking advantage of the nature of periodic array, the filling number of the impedance matrix blocks is substantially decreased, and the procedure of getting the approximate solutions is accelerated. The accuracy and efficiency of the proposed method are demonstrated in a typical scattering example. [ABSTRACT FROM AUTHOR]

A novel circularly polarized (CP) complementary source antenna with endfire radiation is proposed in Ka-band. With the existence of two antipodal notches etched at the edges of the two broad walls of an open-ended substrate-integrated waveguide, two orthogonal electric field components radiated from the equivalent magnetic current, and the electric currents separately can be excited simultaneously. The magnitude and phase differences between the two filed components can be controlled effectively by properly tuning the dimensions of the notches. The operating mechanism and the design procedure of the antenna are analyzed in detail. Wide −10 dB impedance and 3 dB axial ratio bandwidths of 64% and 51%, a gain varying from 3.1 to 6.4 dBic, and the symmetrical radiation pattern are obtained. In order to further increase the gain and front-to-back ratio (FTBR) of the antenna, a dielectric rod structure is then integrated with the antenna. An overlapped operating bandwidth of 41%, an improved gain up to 12 dBic and the stable radiation pattern with an FTBR close to 20 dB are verified by a fabricated prototype. The antenna presented in this paper provides a new mean to design the wideband endfire CP antenna with a simple configuration, which would be attractive for future millimeter-wave wireless systems. [ABSTRACT FROM AUTHOR]

A new approach to generate beam steering for the circularly polarized (CP) antenna array without phase shift circuits is proposed. The proposed approach is a low cost one compared with those with phase shifters. It is found that in spherical coordinate system ( $r$ , \theta $ , and \varphi $ ), for any constant r$ and \theta $ , as \varphi $ varies from 0 to 2\pi $ , the phase of the CP antenna’s copolarized far field will progress linearly by 2\pi $ , and the magnitude is constant. If a CP antenna is rotated around its own phase center by certain degrees, there is a phase difference between the copolarized electric far fields generated by the antenna before and after rotation. An N \times N , 45°, and 90°, the mainlobe can be scanned from −25° to +24°, −36° to +35°, and −24° to +25°, respectively. [ABSTRACT FROM PUBLISHER]

A new augmented electric field integral equation (A-EFIE) formulation is discussed in the low frequency. In the new formulation, both the electric current and charge are considered as unknowns. Different from the conventional A-EFIE, a constraint on the normal component of the magnetic field is added to modifying the formulation of A-EFIE for improving the accuracy and a kind of constant nodal functions is introduced for expanding the electric charge. With the proposed method, besides avoiding the low-frequency breakdown, the storage of impedance matrix is reduced over 35% compared with the conventional A-EFIE, which is owing to the application of constant nodal functions associated with vertices. Numerical examples illuminate the validity and performance of the new A-EFIE with constant nodal functions. [ABSTRACT FROM PUBLISHER]

We previously proposed an approximate relation between admittance Ymn and Y^\prime mn , where Ymn is the admittance of a set of dipoles whose ports are located at their centers and Y^\prime mn is the admittance of the same set of dipoles with one is removed. Based on the relation, approximate expressions of Ymn were derived for the case that dipoles are symmetrically arranged. Their validity is examined by simulations and experiments in this communication. [ABSTRACT FROM PUBLISHER]

In this paper, a novel marching-on-in-degree-based time-domain electric field integral equation (TD-EFIE) is proposed for the analysis of conductors coated with thin dispersive dielectric. The algorithm begins with representing the polarization electric current/charge of the dielectric part in terms of the surface electric current of the conductor. Then, the TD-EFIE can only be formulated with the surface electric current by using the thin dielectric sheet approach. Since the spatial unknowns are only assigned to the surface of the conductor, the computational resources can be saved significantly. Besides, the analytical solution can be obtained for the convolution of the medium susceptibility and the divergence of surface electric current. Moreover, the time variables can be eliminated by using the Galerkin testing with the weighted Laguerre polynomials. As a result, the late time stability can be guaranteed. Numerical examples of Debye, Lorentz, and Drude media are given to demonstrate the validity of the proposed algorithm. [ABSTRACT FROM AUTHOR]

A nonconformal discretization of the electric current volume integral equation (JVIE) is presented for the electromagnetic scattering analysis of inhomogeneous dielectric objects. This JVIE is based on higher order geometrical and current modeling, where curved tetrahedral elements and higher order hierarchical vector (HOHV) basis functions are adopted. In order to implement the nonconformal discretization, the half face-based HOHV basis function is introduced to address the nonconformal volumetric elements. Compared to the conventional low-order conformal/nonconformal VIE, our nonconformal HOHV-based JVIE has the advantage of improving the computational efficiency and accuracy. Compared to the previous VIE discretized by other higher order functions, our nonconformal JVIE is based on the higher order geometric modeling and the HOHV bases. In order to improve the efficiency, the basis expansion and recombination technique is introduced to significantly accelerate the matrix filling. Moreover, the flexibility of basis order selection is further enhanced by the mixed order schemes. Numerical results are given to demonstrate its accuracy, efficiency, and flexibility. [ABSTRACT FROM AUTHOR]

An iterative-based hybrid method, which combines the volume-surface integral equation (VSIE) and the modified surface integration (MSI) method, is presented to analyze the radome-enclosed antennas in receiving mode. Compared with the previously published hybrid approaches, this method improves computational accuracy by including the effects of shaded wall of the radome and the mutual interactions between antennas and radome during the numerical solution of the VSIE in an iterative manner. By embedding different parts of the antenna-radome structure (ARS) into three distinct oct-trees, the multilevel fast multipole algorithm (MLFMA) is used to accelerate both the VSIE solution and the surface/volume integrations in the MSI stage. The new method obtains more accurate results than its original version within less CPU time, and keeps good accuracy with much less memory usage and computational time when compared with the MLFMA-accelerated full-wave VSIE solution for the entire ARS. [ABSTRACT FROM PUBLISHER]

In this paper, characteristic mode (CM) formulations are developed from surface integral equation (SIE) for the modal analysis of dielectric coated conducting bodies. The electric field integral equation-Poggio, Miller, Chang, Harrington, Wu, and Tsai SIE is used for modeling the dielectric coated conducting bodies. By ensuring the field continuity on the interface boundary, two types of generalized eigenvalues equations are formulated to determine the resonant behavior of the dielectric coated conducting bodies. Following Poynting’s theorem, the resultant eigenvalues indicate the ratio of the imaginary and real part of the complex power for each CM. Zero eigenvalues indicate the resonance in dielectric coated conducting bodies. The corresponding modal fields provide with clear physical insights into the radiation/scattering mechanisms. Numerical results are presented to demonstrate the accuracy of the proposed CM formulations. [ABSTRACT FROM AUTHOR]

A marching-on-in-degree (MOD)-based time-domain domain decomposition method is proposed to efficiently analyze the transient electromagnetic scattering from electrically large multiscale targets. The algorithm starts with an octree that divides the whole scattering target into several subdomains. Then using the equivalence principle algorithm, each subdomain is enclosed by an equivalence sphere (ES), where both the RWG and BoR spatial basis functions are employed to expand the unknown currents. The interactions of the near-field subdomains are directly calculated by the method of moments, while the far-field interactions can be converted into the interactions of corresponding ESs. This scheme implicitly satisfies the current continuity condition, and the convergence can be accelerated as well. By harnessing the rotational symmetry of the ESs, the computational resources are reduced significantly compared with the traditional MOD method. Several numerical examples are presented to demonstrate the accuracy and efficiency of the proposed algorithm. [ABSTRACT FROM AUTHOR]

A new planar quasi-magnetic–electric circularly polarized (CP) antenna is proposed. The antenna has a simple planar structure with a small size and a single feed, and produces an omnidirectional CP radiation pattern. It is based on a quarter-wave shorted patch connected with two printed strips. The tangential electric field at the main open aperture of the shorted patch can be considered as an equivalent magnetic current, while the two strips contribute two electric currents. With a single feed, the proposed antenna exhibits an inherent phase difference of about 90° for the two kinds of currents, and therefore, a CP radiation is obtained. The antenna is designed and fabricated. Measured results show that the antenna has an impedance bandwidth of 4.3%. In the band of interest, the antenna generates a circular polarization and an omnidirectional pattern in the plane perpendicular to the magnetic and electric currents, with an average axial ratio below 1.5 dB and a gain between 2.4 and 3.3 dBi. [ABSTRACT FROM PUBLISHER]

An antenna reciprocity relation that relates the far-field transmitted and scattered wave amplitudes with the relevant Kirchhoff-network quantities is derived via the reciprocity theorem of the time-correlation type. The obtained relation can be envisaged as the complement of the well-known time-convolution antenna relation from which the antenna equivalent circuits can be rigorously constructed. A corollary of the result is the equivalent (“far-field”) matching condition whose validity is verified on electric and magnetic dipole antennas. [ABSTRACT FROM PUBLISHER]

In this communication, we report a theoretical and experimental research work related to the interaction between microwaves and finite length Co-based ferromagnetic microwires exhibiting giant magnetoimpedance effect. The electric current induced along the microwire by the electromagnetic wave determines the scattering properties of the magnetic microwires. The electric current depends on the microwire impedance Zi as well as on the relationship between its length and the wavelength of the microwave. Numerical results describe the dependence of the induced current on the microwire magnetic permeability that determines Zi. Furthermore, it is shown how Zi can be effectively tuned through the application of a bias magnetic field. Suitable combination of magnetoimpedance effect and shape resonances opens the perspective to use this system as a wireless field microsensor element as well as a sensing element for constructing codified tags. [ABSTRACT FROM PUBLISHER]

The problem of the lower bound on the radiation $Q$ for an arbitrarily shaped finite size antenna of nonzero volume is formulated in terms of equivalent electric and magnetic currents densities distributed on a closed surface coinciding with antenna exterior surface. When these equivalent currents radiate in free space, the magnetic current augments the electric current, so that the fields interior to the surface vanish. In contrast to approaches based solely on electric currents, the proposed technique ensures no stored energy interior to the antenna exterior surface, and thus, allows the fundamental lower bound on $Q$ to be determined. To facilitate the computation of the bound, new expressions for the stored energy, radiated power, and $Q$ of coupled electric and magnetic source currents in free space are derived. [ABSTRACT FROM AUTHOR]

Real-valued partial differential equations (PDEs) are obtained by substituting the rectangular form of the complex envelope (CE) field and source quantities into the CE versions of Faraday’s and Ampere’s laws, and then separating each resulting complex PDE into real and imaginary parts. These real-valued PDEs result in a CE FDTD scheme that uses only real numbers and operations. As presented here, this CE FDTD scheme alternates at intervals of half a time step between solving for the real and imaginary portions of the CE fields, exactly as the Yee grid alternates spatial components of the fields at half spatial steps. The scheme is demonstrated here for the two-dimensional (2-D) transverse-magnetic case. A split-step method is used in the implicit formation such that only tridiagonal matrices have to be solved. FDTD results are presented for a 2-D cavity with an electric current source. [ABSTRACT FROM PUBLISHER]

In this communication, a compact frequency reconfigurable antenna for LTE/WWAN mobile handset applications is proposed. The proposed antenna mainly consists of radiating elements and two PIN diodes. In addition, the antenna has a simple structure with a compact size of 36.5 \times 10\;\textmm^2. This antenna operates in six modes, and each mode is given a different resonant pathway by adjusting the bias states of two PIN diodes. When PIN diodes #1 and #2 are in the on and off states, respectively, the proposed antenna can cover the LTE700 (698–787 MHz) band by operating in mode 1. Moreover, the wide bandwidth in a higher band formed by combining modes 2 and 3 can cover the LTE2300 (2305–2400 MHz) and LTE2500 (2500–2690 MHz) bands. When PIN diodes #1 and #2 are in the off and on states, respectively, a resonant frequency in the lower band is formed by integrating modes 4 and 5. This can cover the GSM850 (824–894 MHz) and GSM900 (880–960 MHz) bands. When the two PIN diodes are in the on state, the proposed antenna can cover the GSM1800 (1710–1880 MHz), GSM1900 (1850–1990 MHz), and UMTS (1920–2170 MHz) bands in operating mode 6. [ABSTRACT FROM PUBLISHER]

A marching-on-in-time (MOT) solution of the time-domain integral equation (TDIE) using the higher order Nyström scheme is developed to analyze the transient electromagnetic scattering from arbitrarily shaped perfect electrically conducting (PEC) objects. In this scheme, the curvilinear triangular patches are utilized to discretize the PEC objects for their great ability to model geometric configuration. Moreover, we use the Lagrange interpolation polynomials to stand for the spatial basis functions, and the triangle functions to represent the temporal basis functions. Furthermore, the spatial and temporal point-matching is applied. Numerical examples demonstrate that the proposed scheme is stable, accurate, and efficient. [ABSTRACT FROM PUBLISHER]

Plane wave scattering by an infinite, three-dimensional wedge whose faces are characterized by periodic anisotropic impedances is investigated. An improved hybrid of the moment method (MM) and the physical optics (PO) is proposed to calculate the equivalent electric current on the wedge surface. As for the infinite periodic wedge surface, a periodic representation of the scattering surface is used to prevent nonphysical edge effects in the scattering evaluation. The surface of the wedge is split into an MM region and a PO region. In the implementation of MM, the evaluation of the interaction matrix elements in the MM region is simplified by deriving six universal series. Moreover, the PO-current is modified by a diffracted current to improve its accuracy. The accuracy and effectiveness of the proposed approach is validated and demonstrated by using series solution, the method in [T. B. A. Senior, “Solution of a class of impedance wedge problem for skew incident,” Radio Sci., vol. 21, no. 2, pp. 185–191, 1986], and the two-dimensional improved MM-PO approach under several canonical two-dimensional wedge cases. At last, the proposed approach is applied to analyze the scattering from the wedges with periodic anisotropic impedance faces, and the numerical results are presented. [ABSTRACT FROM PUBLISHER]

In this communication, a novel domain decomposition method (DDM) based on integral equation is developed for solving scattering problems of very thin, conducting cavity. By imposing equivalent electric and magnetic currents on the aperture, the original problem is transformed into interior and exterior problems. Different from traditional method based on interior-exterior equivalence principle, this work couples the exterior and interior problems only through the transmission condition on the aperture. Based on this DDM, a well-posed combined field integral equation (CFIE) is successfully developed to realize fast solution of electromagnetic scattering from open-ended cavity with extremely thin or zero thickness. Compared to the electric field integral equation, the proposed CFIE significantly improves the convergence rate of iterative solvers. Numerical results are given to demonstrate the validity and advantages of the present method. [ABSTRACT FROM PUBLISHER]

A methodology is presented for analytically modeling the reflection and transmission of line-source excited pulsed electromagnetic fields at a thin, planar layer with high-contrast dielectric and conductive properties. Closed-form analytic time-domain expressions are derived for the field components in a 2-D setting via an extension of the Cagniard–DeHoop method. The response to the power exponential source and the power exponential monocycle pulse were studied using the newly proposed method. [ABSTRACT FROM PUBLISHER]

Round semitransparent ground plane was studied for the purpose of optimizing radiation pattern and down-up (DU) ratio of a patch antenna. This paper describes a three-dimensional diffraction of an extraneous source as a ring of magnetic current with a standing wave relative to the azimuthal coordinate on a semitransparent disk. An algorithm is given to determine the unknown electric current of the ground plane by solving the integral equation. Construction of experimental layout and method of definition of average impedance for this construction are presented. The calculated and measured radiation patterns and the DU ratio of the patch antenna with a semitransparent ground plane are compared with the conductive ground plane of the same size. The impact of the phase distribution of impedance on the DU ratio is investigated. [ABSTRACT FROM PUBLISHER]

The exact analytical solution of the electromagnetic field distribution produced by uniform electric currents excited on Cartesian half-planes and quadrants is presented. The total field is expressed in terms of geometrical optics (GO) and diffracted field contributions that remain valid for arbitrary observation points and frequency. The jump discontinuity of the GO field is exactly compensated by the diffracted field whose spatial distribution is described in terms of the incomplete Hankel functions and by means of a novel special function. The expression of the diffracted field includes contributions arising from the edges and the vertex of the considered Cartesian domain, illustrating the analytical behavior of the near-field singularities and providing insight into the physical mechanisms governing the field diffractive processes. The proposed solution yields a method to determine the physical optics (PO) response of flat metallic screens excited by uniform plane waves, as well as the fields produced by pulse-shaped basis functions used in the method-of-moments (MoM) solution of electromagnetic problems, showing the relevance of the exact analytical expressions of the GO and diffracted fields arising from edges and vertices of each rectangular pulse domain. Numerical examples validate the accuracy of the proposed field representation. [ABSTRACT FROM AUTHOR]

The scattering of an electromagnetic wave by a perfectly conducting sheet of arbitrary shape can be solved with the Method of Moments (MoM), but the solution obtained with the electric field integral equation (EFIE) yields the sum of the electric current densities on every opposite faces of the sheet, while the magnetic field integral equation (MFIE) cannot be used. In this paper, we first explain in detail the singularities of the MoM impedance matrices formed with the EFIE and MFIE applied to any arbitrarily shaped perfectly conducting sheet. This study suggests a new formulation, the E-MFIE, which is developed first in the most general way, and then in a more efficient form, to obtain the complete solution for the electric current densities on each face individually as well as around all sheet borders. [ABSTRACT FROM PUBLISHER]

The problem of electromagnetic transmission through an arbitrarily shaped aperture in an arbitrarily shaped 3-D conducting surface enclosing homogeneous chiral material is investigated. To solve the problem numerically, the surface equivalence principle and the method of moments are used. The validity of the procedure has been checked by comparing the numerical results to other available solutions whenever possible. Numerical results for the physical electric current on the surface of the obstacle, the internal field, and the bistatic radar cross section are presented for the examples of a sphere and a finite cylinder with circular apertures. These results are computed for various electrical sizes, permittivity values, chirality values, and aperture sizes. [ABSTRACT FROM PUBLISHER]

In this study, equivalent electric current distribution along the semi-transparent ground plane excited by magnetic line current is evaluated analytically and numerically for arbitrary complex layer impedance of a semi-transparent sheet. Relevance to practical cases of thin dense sheet and periodic structure made of narrow strips interconnected by lumped components is demonstrated. Directivity patterns and ground-plane performance characteristics are analyzed. It is shown that ground planes with inductive layer impedance, in some cases, provide advantages for applications. In addition, a practical antenna design example that proves the considerations is also demonstrated. [ABSTRACT FROM PUBLISHER]

A comprehensive analysis is presented for the rectangular waveguide edge slot array with finite wall thickness. To analyze the waveguide structure accurately and efficiently, the magnetic currents are introduced on both the inner and outer surfaces of the slot apertures, and the electric currents are employed on the boundary surfaces of both slot apertures and waveguide exterior area. Moreover, the new coupled integral equations are established according to the boundary conditions, and the method of moments (MoM) with the higher-order basis functions is employed to solve for the equivalent electric and magnetic currents. The proposed method results in less number of unknowns without loss of accuracy compared to the direct methods with the rigorous modeling of waveguide edge slots. Numerical results including the radiation patterns as well as the reflection and transmission coefficients are presented. [ABSTRACT FROM AUTHOR]

Connected arrays constitute the only family of antenna arrays for which the spectral Green's Functions have been derived analytically. This formalism is extended here to the receiving case. When the arrays are assumed to be infinitely extended and periodically excited, rigorous equivalent networks can be derived to represent the electromagnetic field distribution in transmission and/or reception. These equivalent networks are based on Green's functions, thus each components can be associated with a specific physical wave mechanism. Moreover, all components are evaluated analytically. The total power transmitted, received and/or scattered by a connected array with and without backing reflector is discussed. The full efficiency of an array with backing reflector is demonstrated and explained. Finally, measurements from a dual-band connected array prototype validate the equivalent circuit representation. [ABSTRACT FROM AUTHOR]

A Calderon preconditioned (CP) surface integral equation method is developed for the analysis of scattering by piecewise homogeneous dielectric and composite metallic and dielectric objects. The method is based on the electric current formulation (ECF), which only uses the electric surface currents as unknowns. In the ECF the ill-conditioned electric field integral operator and the well-conditioned magnetic field integral operator appear on separate equations, making the application of the CP much easier than e.g., in the PMCHWT formulation where these operators are mixed. In particular, using ECF, Calderon multiplicative preconditioner (CMP) can be straightforwardly extended for composite objects with junctions. Numerical examples demonstrate that the developed formulation, CMP-ECF, is well-conditioned on a very broad frequency range. [ABSTRACT FROM AUTHOR]

We study the effect of surrounding electrically small, top-loaded, electric-dipole antennas with a thin shell of high-permeability magnetic material. The magnetic polarization currents induced in the thin shell of magnetic material reduce the internal stored energy, resulting in a lower Q as compared to conventional designs. The simulated Q's of thin-magnetic-shell cylindrical and spherical antennas are compared to recently derived lower bounds on Q. The high permeability shells reduce the Q of these antennas to values below the lower bounds for purely global electric current sources. In the case of the spherical electric-dipole antenna, a sufficiently large value of permeability enables the Q to be reduced to a value that is only 1.11 times the Chu lower bound. [ABSTRACT FROM AUTHOR]

We examine that an inductively loaded dipole becomes electrical invisible showing that the influence on a nearby antenna's input impedance and on its radiation pattern (scattering) are minimized. We also verify that the direction of the current. reverses on the electrically invisible dipole so that the integral of the dipole current becomes zero. By making an inductive load with a distributed constant line, we fabricate an electrically invisible dipole without using chip devices and evaluate its performance. Furthermore, we propose electrically invisible conductor lines formed by connecting these electrically invisible dipoles in series using open stubs as connectors, and analytically examine their invisible state. [ABSTRACT FROM AUTHOR]