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Based on the generalized frequency selective surface (FSS) theory, we prove that the dual-layer dual-polarization transmission FSS can achieve 360° phase coverage at a limited loss. As a verification, a dual-layer dual-polarization full-phase unit cell with vias is proposed, which can achieve a phase range of more than 360° under 2 dB transmission loss. In addition, we innovatively apply the proposed dual-layer full-phase FSS to the design of a continuous 2-D beam scanning antenna based on the Risley prism (RP). This scheme effectively reduces the number of dielectric substrate layers required by the phase shifting surface (PSS), reduces the rotating scanning inertia, and effectively improves the aperture efficiency. The measured results show that the maximum scanning range of the 2-D beam scanning antenna can reach ±46° in the elevation plane and 360° in the azimuth plane. When operating at the center operating frequency of 21 GHz, the maximum gain of the antenna is 35.75 dBi with an aperture efficiency of 44.1%. [ABSTRACT FROM AUTHOR]

In this article, a fast high-order volume surface integral equation (HOVSIE) formulas solver will be presented to fast calculate the wideband electromagnetic (EM) scattering of anisotropic medium-metallic composite objects. First, in the HOVSIE, the equivalence volume and surface current vectors are discretized by the high-order hierarchical vector basis functions (HVBFs), which can reduce unknowns and facilitate the calculation of the broadband EM scattering. Second, a fast wideband algorithm, i.e., the hybrid multilevel accelerated Cartesian expansion–multilevel fast multipole algorithm (MLACE-MLFMA), is integrated to accelerate the matrix-vector multiplication in the iterative solution. Finally, in order to improve the iterative convergence, a simple overlapping domain decomposition method (ODDM)-based preconditioner is also employed in the proposed HOVSIE enhanced by the MLACE-MLFMA. Summarily, three advantages can be found here: 1) more flexible calculation of the wideband EM scattering; 2) less memory occupation; and 3) better iterative convergence. The accuracy, efficiency, and flexibility will be demonstrated in the numerical examples. [ABSTRACT FROM AUTHOR]

The miniaturization design of the beamforming network (BFN) is the key to improving the application value of the multibeam array antenna. The traditional miniaturization method of the BFN mostly solves the miniaturization of the transverse width, while the miniaturization of the longitudinal length is rarely involved. In this article, a coexistence-mode (Co-mode) composite right-/left-handed (CRLH) substrate-integrated waveguide (SIW) transmission line technology is proposed, and this technology aims to solve the problem of miniaturization in the longitudinal length of the Butler matrix (BM). Its core is to introduce a longitudinally extended interdigital slot (IDS), force the SIW to incorporate an interdigital capacitor, and realize the phase constants of the TE10 mode and the TE20 mode reverse change. Then, the coupling region length of the couplers based on the Co-mode CRLH SIW transmission line can be reduced, and the longitudinal miniaturized directional coupler and the longitudinal miniaturized cross coupler are obtained. Finally, three types of $4\times 4$ longitudinal miniaturized BMs based on the Co-mode CRLH SIW transmission line are designed, whose longitudinal lengths are reduced by 32%, 22.1%, and 30.7% compared with those of their SIW counterparts. In addition, a miniaturized multibeam array antenna based on the Co-mode CRLH $4\times 4$ H-plane SIW BM is fabricated and measured, which verifies the applicability of Co-mode CRLH SIW transmission line technology. [ABSTRACT FROM AUTHOR]

A novel method is presented to efficiently synthesize linearly polarized shaped patterns for antenna arrays mounted on complex platforms surrounded with many scatters. The vectorial active element patterns (Vec. AEPs) are adopted to include the mutual coupling and complex platform effect. The vectorial least-square (LS) active element pattern expansion (Vec. LSAEPE) method is developed to approximate each Vec. AEP as the radiation from a virtual subarray with identical element patterns, so that the fast Fourier transform (FFT) can be utilized to efficiently perform the forward and backward transformations between the excitation distribution and the vectorial array pattern including mutual coupling. An energy-based weighted averaging method is introduced to merge the excitation vectors obtained from copolarization (CoP) and cross-polarization (XP) pattern synthesis in each iteration and consequently the obtained final excitation vector can simultaneously meet both the CoP and XP pattern requirements. The method is called the iterative Vec. LSAEPE-FFT significantly extends the FFT-based synthesis technique to be capable of controlling the CoP main lobe shape, sidelobe distribution, and the XP level. Three examples for synthesizing different shaped patterns for different antenna arrays on complex platforms are conducted to validate the effectiveness of the proposed method. A comparison with some other representative methods is also provided to verify the advantages of the proposed method in both accuracy and efficiency. [ABSTRACT FROM AUTHOR]

In this article, we present a low-cost microstrip phased-array antenna, which is composed of electronically reconfigurable elements. The p-i-n diodes’ integrated elements have various functions, such as tunable polarization characteristics and adjustable radiation phases. The high sidelobe level (SLL) due to the 2-bit phase shifter can be reduced by a randomly rotated (RR) array element. It is shown that the array can realize electronic beam-steering capabilities and keep −10 to −14 dB sidelobes without tapering. To verify the above theory, an eight-element linear array prototype working at 3 GHz was designed, fabricated, and tested. Numerical simulations and experimental results show that, by controlling the “ON” and “OFF” states of p-i-n diodes, the radiation beam can be controlled to steer in a circular polarization (CP) mode, wherein the scanning angle is up to ±45°. Furthermore, the principle of suppressing the vector scattering field by the opposite phasing cancellation method can achieve in-band radar cross section (RCS) reduction. Simulation results show that approximately 15 dB in-band RCS reduction can be realized for both bistatic and monostatic RCS reduction with an 8 × 8 array. [ABSTRACT FROM AUTHOR]

A volume equivalent shooting and bouncing ray (VESBR) method is proposed to analyze the electromagnetic scattering of dielectric and composite objects with thick dielectric medium. Different from traditional high-frequency methods which utilize surface sources, this VESBR considers the propagation of electromagnetic waves inside the dielectric media and introduces volume equivalent sources to calculate the scattering fields. Compared with traditional methods, two different problems need to be solved in this method, i.e., the ray tracing on dielectric boundary and the volume integral in ray tube. For ray tracing process, a refined formula is proposed to acquire the information of reflection waves and transmission waves on dielectric boundary. For volume integral in ray tube, the integral is transformed to five surface integrals based on Gauss’s law. The simulations of four cases show that the results of VESBR agree well with those of surface integral equation (SIE), while the computation time and the required memory of VESBR are much less than those of SIE. [ABSTRACT FROM AUTHOR]

An efficient thin dielectric sheet (TDS) model is presented to compute the radome targets made from high contrast sandwich structure material. By applying the dimensional analysis, this communication has first ever identified the intrinsic stratified distribution of the diagonal entries in the TDS model. Two scaling schemes are accordingly proposed to recover the well-conditioning of the system matrix. The proposed method can improve the computational efficiency of the radome targets considerably, benefiting the fast simulation in practical engineering. [ABSTRACT FROM AUTHOR]

We propose a novel scheme to accelerate the computation of the finite-element method-boundary element method (FEM-BEM) for 3-D electromagnetic scattering. It builds on the FEM-domain decomposition method (FEM-DDM) and the degenerated boundary element method (BEM) developed for the body of revolution (BoR), which is, thus, referred to as BEM-BoR. When coupled with FEM in the framework of domain decomposition, the infinite computational domain is truncated by a closed rotationally symmetric surface enclosing the 3-D scatterer, and BEM-BoR is then applied on this surface as a radiation boundary condition (RBC). The finite-domain interior to this surface is further decomposed into several subdomains, which are connected by the second-order transmission conditions (SOTCs) imposed on nonconformal meshes. We refer to the resultant solver as a hybrid FEM-DDM and BEM-BoR (FEM-BEM-BoR). Since BEM-BoR can be divided into several 2-D problems instead of the original 3-D one, the proposed FEM-BEM-BoR is more efficient than the original FEM-BEM. Numerical examples are presented, and the comparisons of the simulation results with FEM-BEM confirm the accuracy and efficiency improvement of FEM-BEM-BoR. In addition, its practical applicability is demonstrated by modeling large-scale objects. [ABSTRACT FROM AUTHOR]

A nonconformal and nonoverlapping domain decomposition method (DDM) based on hybrid volume and surface integral equation (VSIE) is presented for modeling complex thin dielectric/perfect electric conductor (PEC) composite targets. To reduce the unknown amount of the conventional volume integral equation (VIE) for thin dielectric bulks, the improved simplified prism vector (ISPV) basis function is developed. By using the basis function, the volume integrals can be simplified into surface integrals or line integrals, which significantly reduce the simulation time. Prism grids can also avoid the overmeshing problem for thin dielectrics. Moreover, they can be perfectly matched to the triangular meshes widely used in surface integral equation (SIE) hence assures a simple and robust VSIE implementation. Next, in order to increase the flexibility of geometrical modeling and accelerate the convergence of the presented VSIE system for electrically large and multiscale composite targets, a DDM is further developed. In this DDM scheme, discontinuous Galerkin approaches are, respectively, employed for VIE and SIE, accounting for conformal/nonconformal volume grids and surface grids between adjacent subdomains. In addition, an interior penalty term is introduced to stabilize the DDM solution. Finally, some numerical results are considered and analyzed to show the validity, efficiency, and applicability of the presented scheme. [ABSTRACT FROM AUTHOR]

A millimeter-wave (mm-wave) multibeam array antenna based on folded C-type substrate integrated waveguide (FCSIW) is presented for the first time. The design steps for its two main elements are described, namely an FCSIW Butler matrix (BM) and an FCSIW single-branch slot array antenna. Both of them exhibit a significant miniaturization in comparison with their substrate integrated waveguide (SIW) counterparts, leading to 40% and 33.2% reduction in occupied surface for the BM and the whole multibeam array antenna while maintaining similar performances, respectively. In addition, an optimized transition connection structure from ground coplanar waveguide (GCPW) to FCSIW is designed to facilitate the measurement of the multibeam array antenna. Finally, the FCSIW multibeam array antenna is optimized, manufactured, and measured, which can help verify the feasibility of FCSIW for the miniaturized multibeam array antenna. [ABSTRACT FROM AUTHOR]

A fast direct surface integral equation (SIE) solver based on a novel skeletonization factorization scheme is proposed for electromagnetic scattering from electrically large and complex conducting objects. A novel skeletonization strategy is utilized to accelerate the skeletonization with the Huygens’ principle and proxy surface. Different from the auxiliary Rao–Wilton–Glisson (RWG) bases used in conventional methods, the constant basis functions are employed to discretize Huygens’ surface in the novel skeletonization strategy. By doing these, the number of basis functions on the surface can be greatly reduced. Moreover, the skeleton basis functions in selected neighboring groups are used to account the neighboring interactions. With these ideas, the dimensions of proxy matrix constructed for selecting skeleton can be greatly reduced. Next, a recursive skeletonization factorization (RSF) is proposed to further enhance the computational efficiency. The inverse of system matrix can be expressed as the multiplication factorization form with RSF rather than conventional recursively additive low-rank update. The computational time would be significantly saved with the application of RSF. A series of the numerical results are presented to show both the accuracy and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, surface integral equation domain decomposition method (SIE-DDM) based on a hybrid direct–iterative approach is proposed for multiscale electromagnetic simulation. The solution of SIE-DDM matrix system is typically built on the strategy of inner-outer loop. Therefore, the direct approach is preferred to the subsolver in each decomposed domain. Here, a fast direct approach based on an enhanced hierarchically off-diagonal low-rank (HODLR) format involving extended admissibility condition (EAC) is present as an alternative subsolver, in which a reconstructing and recompression technique (RRT) is proposed. The efficiency and accuracy can be further improved by using this technology. The inverse of each subdomain is obtained by Sherman–Morrison–Woodbury algorithm (SMWA), while the global system is still solved by the iterative method. This hybrid framework makes full use of strengths of terative and direct approaches. On the other hand, the fast direct solver provides a robust preconditioner for the matrix system, especially for ill-conditioned cases. Several numerical examples will demonstrate the proposed method. [ABSTRACT FROM AUTHOR]

A nonconformal twofold domain decomposition method (TDDM) based on the hybrid finite element method-boundary element method (FEM-BEM) is proposed for analyzing 3-D multiscale composite structures. The proposed TDDM starts by partitioning the composite object into a closed exterior boundary domain and an interior volume domain. The interior and exterior boundary value problems are coupled to each other through the Robin transmission conditions (RTCs). Both domains are then independently decomposed into subregions to facilitate computation. Specifically, FEM-DDM with the second order transmission conditions (SOTCs) is employed for the interior domain, and BEM-discontinuous Galerkin (BEM-DG) based on the combined field integral equation (CFIE) is applied for the exterior boundary domain. The proposed TDDM allows for nonconformal discretization between any touching subdomains. Without the introduction of a stabilization term that relies on a line integral over intersection of nonmatching meshes and relevant terms involving surface-line integrals, the proposed TDDM provides an effective domain decomposition (DD) preconditioner for the global system. Numerical examples are presented, and the comparisons of the simulation results with FEM-BEM confirm the validity and accuracy of TDDM. Moreover, its ability to model practical large-scale and multiscale targets is also demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, a fast interpolation algorithm [multilevel accelerated Cartesian expansion (MLACE)-multilevel fast multipole algorithm (MLFMA)-reduced basis method (RBM)] is proposed for the first time by leveraging the benefits of the MLACE, the classical MLFMA, and the RBM; furthermore, a novel nonblind sampling method (NBSM) is proposed to approximate an orthogonal subspace for the MLACE-MLFMA-RBM. By integrating the empirical interpolation method (EIM) and the error-based compensation method (EBCM) into the NBSM, we first efficiently establish a robust and precision-controllable orthogonal subspace. Next, with the accurate orthogonal subspace, the MLACE-MLFMA-RBM can simplify the iterative solution process of the MLACE-MLFMA or the MLFMA into $N_{\text {g}}$ matrix–vector multiplications (MVMs) and the solution of a reduced $N_{\text {g}}$ -dimensional linear equation ($N_{\text {g}}$ is the number of orthonormal vectors). Note that only the MVMs between the far-region impedance matrix and the orthogonal vector bases are calculated. In comparison with the classical MLACE-MLFMA and the MLACE-MLFMA-RBM based on different sampling methods for wideband electromagnetic (EM) responses, our proposed algorithms require less memory and CPU time and integrate higher flexibility. The numerical results are provided to demonstrate the accuracy, efficiency, and flexibility. [ABSTRACT FROM AUTHOR]

A useful method to transform the smartphone metal cover into an antenna booster for near-field communication (NFC) antenna installed in a full metal cover (FMC) smartphone is proposed. In this proposed work, by properly embedding a series capacitor into a meticulously selected location within the metal cover, strong coupling between the NFC antenna coil and the metal cover will be generated, which mitigates the reverse eddy current induced on the metal cover. Because of that, the performance of the NFC antenna (located below a narrow horizontal slot-loaded metal cover) is substantially improved, as compared to a reference stand-alone NFC antenna in free-space conditions. To verify this proposed methodology, an ordinary single-turn coil reference NFC antenna 1 (ref 1) and a 3-turn coil reference NFC antenna 2 (ref 2) are initially designed via simulation, followed by the conducting of several typical experiments on these two reference antennas. Finally, the two reference prototype NFC antennas that have utilized this method for a single horizontal slot-loaded FMC are also certified by the Europay, MasterCard, and Visa (EMV) test. [ABSTRACT FROM AUTHOR]

A low-profile stacked patch antenna is proposed for pattern-reconfigurable (PR) applications. A referential circular radiation patch with desired conical beams and broadside beams operation is analyzed. However, due to bad port isolation, slant radiation patterns with high cross-polarization levels occur. Suspended pin loading and gap-coupled feeding techniques are introduced to achieve better port isolation, which leads to stable radiation patterns and low cross-polarization levels. Meanwhile, in order to broaden the operation bandwidth, two stacked square patches integrated with a T-shaped feeding branch are utilized and analyzed for exciting low-frequency resonances at the broadside mode. By controlling the p-i-n diodes implanted in the feeding network, reconfigurable conical and broadside beams are obtained. The measured results show that the proposed antenna yields a 10 dB operation impedance bandwidth of 11%, ranging from 2.41 to 2.69 GHz. The peak gains operating at the conical state and broadside state are 4.5 and 7.7 dBi, respectively. The overall profile of the proposed antenna is only $0.07\lambda _{0}$ , where $\lambda _{0}$ is the free space wavelength at 2.55 GHz. [ABSTRACT FROM AUTHOR]

The adaptive cross approximation (ACA) algorithm is adopted to efficiently compute the discretized forward integral equation operator in the near-field (NF)–far-field transformation process by utilizing the rank-deficient nature of the well-separated interactions between the equivalent sources and the measurement probes. The threshold of the ACA compression is carefully investigated to achieve results that are more accurate. Besides, an octree-based geometrical-adaptive grouping scheme is proposed where two different grouping strategies are designed for planar and spherical measurements, respectively. To further increase the accuracy and efficiency of the computation, the leaf-level cube size for the sources and probes are also flexibly decided, since the corresponding two spatial distribution densities vary significantly. The effectiveness of the proposed method is validated with synthetically generated NF data and with spherical measurements of a double-ridged waveguide antenna. [ABSTRACT FROM AUTHOR]

In order to increase radiation modes for slot antennas, a new method of loading a parasitic loop pair is proposed. By adding switches to control the open- or closed-state of each loop, the loop pair works at four states, generating multiple radiation modes. Consequently, besides the original bidirectional broadside mode, two additional directional radiation modes are generated, radiating to endfire. As a result, a simple slot antenna could work in multiple radiation modes with the proposed method; meanwhile, no much-increased size or complicated structure is needed. Thus, a single slot antenna can be employed to meet the requirement for multifunction and multienvironment applications. To demonstrate this design concept of using the parasitic loop pair, an antenna structure is designed and fabricated. One parasitic loop is formed by connecting two printed metallic strips with copper shorting pins; p-i-n diode switches and bias circuits are inserted to control the state of the two loops with dc signals. Both measured and simulated results indicate that the proposed parasitic loop pair is effective in providing multiple radiation modes for slot antennas. [ABSTRACT FROM AUTHOR]

A compact ultra-wideband (UWB) slot antenna using narrow slots is proposed. Different from the traditional wideband slot antennas with multiple resonant modes, the proposed design of this paper utilizes the traveling-wave mode. By using a slotline–CPW transition as the convertor, which connects a slotline and four open slots, the forward wave in the slot has small reflection. The working mode keeps stable at different frequencies, i.e., operating in the traveling-wave mode. As a result, both wide bandwidth and stable radiation patterns are achieved with inherent characteristic of traveling-wave mode. The proposed antenna occupies a small area and the slot width is narrow, which make it suitable to be mounted on the edge of metallic surface for wireless devices. Given an instance for validation, a prototype is fabricated, with a slit width of 0.2 mm and a total size of $25\times 30\times 0.762 $ mm3 ($0.24\times 0.29\times 0.007 \lambda _{L0}^{3} $ , $\lambda _{L0} $ is the wavelength in free space at the lowest operating frequency). Measured results show that a relative bandwidth (VSWR < 2) of about 121% is achieved, covering the entire UWB. Besides, stable gains and radiation patterns are obtained in the operating band. The time-domain characteristic is also investigated, and a small-signal distortion is achieved. [ABSTRACT FROM AUTHOR]

In this communication, a novel compact and unidirectional circularly polarized antenna based on the crossed printed tapered slot radiation elements is proposed with the ultra-wideband operation. The antenna consists of two crossed tapered slot radiation elements, a compact dual-feed network, and a dial-shaped parasitic metallic strip. The tapered slot element is applied and investigated for wideband coverage within a compact size. By using the proposed parasitic patches, an additional resonant point is formed to improve the operation bandwidth for the low band. To enhance the directivity in the low band, a dial-shaped parasitic metallic strip is loaded on the top substrate. With the proposed structure, a compact volume of $0.33\lambda \times 0.33\lambda \times 0.3\lambda $ is obtained, where $\lambda $ is the free-space wavelength at the lowest frequency of 1.85 GHz. A prototype is fabricated and measured for validation. The overlapping bandwidth of the 10 dB impedance bandwidth and the 3 dB axial ratio bandwidth is 105.8% (1.85–6 GHz). [ABSTRACT FROM AUTHOR]

A flexible surface integral equation domain decomposition method (SIE-DDM) with reverse operation self-consistent evaluation (ROSE) is proposed to analyze the electromagnetic (EM) scattering by electrically large, multiscale, perfect electrically conducting objects. ROSE is developed for the robust implementation of the Robin transmission condition between adjacent subdomains in SIE-DDM. By interpolating a set of plane waves on the touching faces, small linear systems are constructed, and the entries of the transmission matrix can be solved algebraically. In doing this, direct numerical integration involving complicated geometrical operations over a nonconformal mesh can be avoided. Several numerical results will be presented to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

An \mathcal H -matrices compressed multiplicative Schwarz (MS) preconditioner for the nonconformal finite-element method (FEM)–boundary element method (BEM)–Domain decomposition method (DDM) is proposed to analyze the electromagnetic radiation and scattering from periodic structures such as frequency-selective surfaces (FSSs) or antenna arrays. To improve the overall convergence, an MS preconditioner is proposed for the DDM matrix. The hierarchical matrix ( \mathcal H -matrices) technique is introduced into the preconditioned system to compress the dense matrices to further improve the efficiency. Moreover, a finite-element tearing and interconnecting like algorithm is adopted to eliminate the interior volumetric FEM unknowns and the multilevel fast multipole algorithm is integrated to reduce the computational complexity of BEM. Numerical examples are presented to validate the proposed method. It is observed that this method exhibits superior performance and consumes far less memory and CPU time than the traditional implementation. [ABSTRACT FROM PUBLISHER]

Scattering from composite planar thin dielectric-conductor objects is calculated by the hybrid volume-surface integral equation (VSIE) approach. To highly efficient model such objects, the prism elements are used for volume regions instead of general tetrahedral elements, and the simplified prism vector basis functions are proposed so that the volume integral can be simplified into either surface integral or line integral. As a pair, the RWG basis is used for arbitrarily shaped conductor surface. This proposed method has several advantages for objects comprising planar thin dielectric materials. First of all, the use of prism elements can significantly reduce the number of unknowns compared with the general tetrahedral mesh scheme so that the CPU time consumption and memory occupation are reduced. In addition, the prism elements also result in a more convenient meshing procedure. Finally, the simplification of volume integral further reduces the CPU time consumption, while maintaining comparable accuracy. Since the proposed scheme can be easily accelerated by fast algorithms, our VSIE method combined with the multilevel fast multipole algorithm is employed for the scattering analysis from the electrically large objects. Several numerical results are reported to show the good accuracy and efficiency of the proposed method. [ABSTRACT FROM PUBLISHER]

A novel method for wireless power transfer (WPT) in complex multipath propagation environments of human body, based on the reversal pretest and the principle of reciprocity, has been proposed in this paper to adaptively enhance the intensity of the field on the surface of implanted antenna. As a model-independent scheme, this method makes all the field components focus adaptively on a given position in unknown inhomogeneous media which can be very complicated, random, and even time varying. The principle and the steps of the adaptive focus (AF) WPT are described first. The design of the implanted antenna conformal with a capsule inside the tissue and the multiple antennas out of the body is then given to build a principled prototype for the AF-WPT. Both the numerical simulation and the experimental measurement for the AF-WPT model with the operation frequency in Industrial Scientific Medical Band have been given to show the validation of this method. It has been shown from the simulation and experimental results that in comparison with the other methods, the field focusing scheme increases 6 dB higher intensity of the field at the position of the capsule antenna while keeping the level of the received power more stable with the continuous shifting of the implanted antenna. [ABSTRACT FROM PUBLISHER]

Previous studies on tightly coupled dipole arrays (TCDAs) are mainly focused on 2-D phased arrays, where very wide bandwidth can be achieved as compared to 1-D TCDAs. Moreover, for the dual-polarized case, the interelement coupling is not sufficient in the polarization along the transverse direction of linear array, which leads to a much narrower bandwidth. In this communication, a wideband dual-polarized tightly coupled dipole linear array (TCDLA) is proposed. A novel vertical parasitic superstrate layer is employed in the dual-polarized linear array to compensate the impedance variation in beam scanning cases. As compared to traditional wide-angle impedance matching layer composed of layered dielectric sheets, the vertical parasitic superstrate layer greatly reduces the weight of the array. Simulation results show that the TCDLA achieves 5:1 bandwidth and 4:1 bandwidth in the vertical polarization and horizontal polarization, respectively, for VSWR < 3.0:1, while scanning up to ±60°. Prototype for a $1 \times 26$ linear array is fabricated and measured. Good agreement is achieved between measured and simulation results. [ABSTRACT FROM AUTHOR]

A compact multimode monopole antenna for hepta-band metal-rimmed smartphones is proposed. The metal bezel is kept unbroken and no lumped element is needed. To cover the low band, the bezel mode is excited by a capacitive coupling vertical plate, and a bandwidth enhancement technique is introduced for this mode. For the high band, printed multiple branches on both sides of substrate are well designed to obtain multiple modes to cover a wide band. With the proposed structure, the frequency bands can be widened by tuning and optimization. The new-type monopole occupies an area of 60 \times 5 \times 5 mm ^{3} on a 120 \times 60 mm ^2 system board, which has a narrow ground clearance and a low profile. A prototype is fabricated and measured to validate the proposed design. Measured results show that the proposed antenna has two impedance bands with S11 less than −6 dB, i.e., 23% for the low band (0.76–0.96 GHz) and 57% for the high band (1.51–2.72 GHz). The proposed monopole antenna is capable of covering the GSM/DCS/PCS/UMTS and LTE2300/2500 bands for modern metal-rimmed mobile phone applications. [ABSTRACT FROM PUBLISHER]

A low-profile dual-polarized wideband omnidirectional antenna with artificial magnetic conductor (AMC) reflector is proposed. The proposed antenna is operated in the long term evolution band (1.7–2.7 GHz), and has a compact size of 200 mm $\times200$ mm $\times $ 30.6 mm (about $0.25\lambda $ height at 2.7 GHz). The antenna structure consists of a horizontally polarized circular loop antenna, a vertically polarized low-profile monopole antenna, and an AMC reflector. By carefully designing the reflection characteristics of the AMC reflector, the profile height of the proposed antenna is significantly reduced as compared with those of antennas backed by conventional perfect electric conductor (PEC) ground planes. Simulated and measured results show that the proposed antenna is able to achieve over 45% impedance bandwidth (VSWR <1.8) with stable radiation patterns in the band of 1.7–2.7 GHz. Owing to the attractive wide bandwidth, low-profile configuration, and ease of fabrication, the proposed antenna is suitable for microbase station systems, especially for indoor ceiling antenna networking applications. [ABSTRACT FROM AUTHOR]

A Gaussian point-adaptive grouping scheme for the multilevel fast multipole algorithm (MLFMA) has been proposed in this communication to significantly reduce the heavy memory cost resulted from using the basis functions defined on large patches without sacrificing the accuracy of the numerical solutions. The grouping process in the MLFMA has been considered as a single-objective optimization problem and is solved by using the clustering algorithm for Gaussian quadrature points on each patch. Meanwhile, the constraint of the addition theorem for MLFMA is still satisfied. As a result, the presented scheme is able to acquire an optimal number of multipoles for each basis function. Compared to the conventional octree grouping scheme or other grouping schemes used in the past, the method in this communication is advantageous in terms of the memory efficiency and the solution accuracy. Numerical examples have been given to demonstrate the validity and effectiveness of the proposed scheme. [ABSTRACT FROM PUBLISHER]

This communication presents a design of a new compact circularly polarized (CP) slot antenna fed by a microstrip feedline. The 3-dB axial ratio band can be achieved by simply protruding a horizontal stub from the ground plane toward the center of the wide slot (WS) and then feeding the WS with a microstrip feedline positioned to the side of the WS, underneath the protruded stub. The feedline and metallic stub are perpendicular to each other, and they resemble a T shape when viewed from the top. The proposed antenna is fabricated with an area of 25 \times 25\;mm^2. Measurement results show that the antenna attains an S11\le-10\;dB impedance matching bandwidth of 90.2%, from 3.5 to 9.25 GHz, and a broadband 3 dB-AR bandwidth of 40%, ranging from 4.6 to 6.9 GHz. A peak gain of 0.8–4.5 dBi is achieved within the AR band. The proposed antenna is suitable for circular polarization applications in C band. [ABSTRACT FROM AUTHOR]

A dual-polarized magnetically coupled patch antenna array with high isolation is presented in this paper. The proposed ${{1}} \times {{2}}$ antenna array is composed of two square patches printed on the horizontal substrate, two pairs of feeding structures printed on the two vertical substrates, a pair of metal cavities and a novel artificial periodic structures (APS) composed of metal strips etched vertically on the ground plane. Each feeding structure is orthogonally mounted and excites the square patch magnetically. The feeding structure comprises a metal loop or quasi-loop printed on one side of the vertical substrate and an open-ended transmission line printed on the other side. The metal cavities and APS can further improve the port isolation between array elements. The simulation and measurement results of single antenna element demonstrate its extremely high port isolation (better than 45 dB over 20% impendence bandwidth for {\text{VSWR}} < \,1.5). For the array, numerical and experimental results show that the port isolation with same polarization can be improved to over 45 dB across the frequency band of 2.5–2.7 GHz. The proposed antenna array achieves wide bandwidth with very high isolation, high gain, and high radiation efficiency. [ABSTRACT FROM AUTHOR]

This paper presents a study on linear frequency modulation (LFM) pulsed signal transmission by four-dimensional (4-D) antenna arrays. LFM pulse is used as the input of 4-D antenna arrays and the influence brought by the periodic time modulation is analyzed. The relationship among pulse duration, chirp rate, sample frequency, time-modulation frequency, and propagation direction is analyzed and the restrictions to these parameters are highlighted. The transmitting and receiving structures are introduced and relevant signal processing steps are described. Numerical examples with several different time schemes, including the pulse shifting (PS) scheme and binary phase center motion (BPCM) scheme, are presented to demonstrate the effectiveness of the LFM signal transmission by 4-D arrays. Simulation results validate that original chirp signal can be correctly recovered and low sidelobe power patterns can be simultaneously achieved by 4-D antenna arrays, as long as the proposed limitations are satisfied. [ABSTRACT FROM PUBLISHER]

It is shown in this communication that the problem of synthesizing a frequency-invariant (FI) beam pattern with as few elements as possible can be transformed into a sequence of weighted $\ell_1$ optimizations under multiple convex constraints. The objective of the weighted $\ell_1$ optimization is to minimize the number of radiating elements. For the filter-and-sum beamforming structure, this is equivalent to minimizing the number of filters, each with a set of optimized coefficients. The multiple constraints are adopted to individually control the mainlobe and sidelobe pattern characteristics, so as to preserve the FI property in the mainlobe region while satisfying a given upper bound in the sidelobe region. The WNG constraint can also be incorporated into the proposed method to enhance the synthesis robustness. This method can be easily implemented by iterative second-order cone programming (SOCP), and only few iterations are required to reach the convergence. A set of examples for the synthesis of FI patterns with uniform sidelobe level (SLL) or multiple nulls, scannable FI patterns, and the synthesis of FI pattern for an arc array with directive elements, is presented to validate the effectiveness and advantages of the proposed method. The element saving is about 23.3%–50% for the test cases. [ABSTRACT FROM PUBLISHER]

Due to simplicity, hybridization of geometrical optics (GO) and physical optics (PO) based on ray tracing has been widely used for fast scattering analyses. However, when targets of curved concavities are discretized by flat facets, the loss of divergence factor (DF) will degrade the simulation accuracy. To remedy this loss, a simple and efficient factor, entitled virtual divergence factor (VDF), is proposed to play the role of DF. To prove the validity of VDF and simulate the scattering of concave complex targets, a hybrid method of GO/PO and physical theory of diffraction (PTD) is elucidated. With VDF correction, several typical targets, including a S-shape cavity, are simulated by this hybrid method. In comparison to multilevel fast multipole algorithm (MLFMA) or measurements, the validaty of VDF is fully demonstrated by good agreements and the excellent performance relative to DF on canonical surfaces, where the great efficiency and flexibility of this hybrid method are also shown. Moreover, one interesting and important issue, the dependance of field convergence on the maximum number of ray reflections, is also investigated for the first time. [ABSTRACT FROM PUBLISHER]

In this communication, a printed unidirectional antenna with improved upper band-edge selectivity is proposed to realize bandpass filtering gain performance. This antenna consists of a printed rectangular loop with two gaps: 1) a parasitic strip and 2) a parasitic loop. The rectangular loop provides good lower band-edge selectivity and the parasitic strip decides the location of upper band-edge selectivity. The parasitic loop, which acts as a director, is used to improve the capacity of upper band-edge selectivity. In addition, the passband bandwidth controllability of the antenna has also been explored. To demonstrate the effectiveness of this design, an antenna prototype is fabricated and tested. Experimental results verified the effectiveness of the proposed design. Measured results show that the fabricated antenna provides a 56.6% passband bandwidth, ranging from 2.18 to 3.9 GHz. Good bandpass filtering gain performance with a flat passband gain better than 4.4 dBi is achieved. Stable unidirectional radiation patterns with nearly identical $E$- and $H$-plane patterns in the operating bandwidth are also achieved. The measured front-to-back ratio is better than 10 dB. [ABSTRACT FROM PUBLISHER]

Simulation of electromagnetic scattering by complex multiscale objects in a half space is addressed in this communication. The objects under investigation can be situated above, embedded in, or even penetrating the interface of the half space. In this analysis, the electric field integral equation is formulated with the kernel of a half-space Green's function. The Calderón preconditioner is employed to improve the convergence of the Krylov-subspace iterative solvers. A new preconditioning operator is proposed to substantially reduce the construction cost, yet maintain the effectiveness. Moreover, a novel multilevel implementation of the adaptive cross approximation (ACA) algorithm is further adopted to make the method capable for problems with moderate size. The proposed scheme is examined by several multiscale problems, which constitute the most common scenarios in the near-surface applications. [ABSTRACT FROM PUBLISHER]

A compact dual-polarized printed dipole antenna for wideband base station applications is presented in this communication. The proposed dipole antenna is etched on three assembled substrates. Four horizontal triangular patches are introduced to form two dipoles in two orthogonal polarizations. Two integrated baluns connected with 50 \Omega SMA launchers are used to excite the dipole antenna. The proposed dipole antenna achieves a more compact size than many reported wideband printed dipole and magneto-electric dipole antennas. Both simulated and measured results show that the proposed antenna has a port isolation higher than 35 dB over 52% impendence bandwidth (VSWR< 1.5). Moreover, stable radiation pattern with a peak gain of 7 dBi – 8.6 dBi is obtained within the operating band. The proposed dipole antenna is suitable as an array element and can be used for wideband base station antennas in the next generation IMT-advanced communications. [ABSTRACT FROM PUBLISHER]

Although conventional Yagi antenna has the advantage of unidirectional radiation patterns, it is not suitable for wideband applications due to its drawback of narrow bandwidth. In this communication, a compact wideband planar printed quasi-Yagi antenna is presented. The proposed quasi-Yagi antenna consists of a microstrip line to slotline transition structure, a driver dipole, and a parasitic strip element. The driver dipole is connected to the slotline through a coplanar stripline (CPS). The proposed antenna uses a stepped connection structure between the CPS and the slotline to improve the impedance matching. Two apertures are symmetrically etched in the ground plane to improve the unidirectional radiation characteristics. Simulation and experimental results show that the unidirectional radiation patterns of the proposed antenna are good. A 92.2% measured bandwidth with S 11 < -10~dB from 3.8 to 10.3 GHz is achieved. A moderate gain, which is better than 4 dBi, is also obtained. [ABSTRACT FROM PUBLISHER]

Double-dipole antennas driven by anti-phase signals (W8JK array) are often used to achieve broadband and good unidirectional radiation patterns. The two dipole elements need a pair of anti-phase signals equal in magnitude. However, realization of anti-phase signals with equal magnitude for the W8JK array is difficult in a planar structure. In this communication, an equivalent feed mechanism of W8JK array is presented. An in-phase power divider is used to realize an anti-phase feeding network for feeding the W8JK array. In order to demonstrate the effectiveness of the designed anti-phase feeding network, an antenna prototype has been designed, fabricated and tested. Experimental results show that the designed anti-phase feeding structure for the W8JK array is effective. The designed antenna provides a 64% measured bandwidth ranging from 6.9 to 13.4 GHz. An excellent endfire radiation characteristic with an F/B ratio better than 17 dB is achieved. The measured gain is better than 4 dBi. [ABSTRACT FROM PUBLISHER]

In this paper, a novel idea is proposed to construct low-cost phased arrays by using the multi-port property of array elements. The operating principles are illustrated and explained in detail. A three-element patch subarray with a periodic lattice is conceived according to the proposed idea. In the subarray, one patch antenna with multiple ports is designed as an active element which is directly fed through the excitation port by a feeding network. The other two parasitic patches are fed by the coupling ports of the active element. Good agreements between simulations and measurements of a two-subarray phased array prototype successfully verify the proposed idea. Then, comparisons to a conventional phased array are performed to highlight its advantages, e.g., high aperture efficiency and low cost. Finally, a second design example is given for more references. [ABSTRACT FROM PUBLISHER]

Previously, the matrix pencil method (MPM) and the forward-backward MPM (FBMPM) were used to effectively reduce the number of antenna elements in the single-pattern linear arrays. This work extends the MPM and FBMPM-based synthesis methods to the synthesis of multiple-pattern linear arrays with a smaller number of elements. The extended MPM (resp., the extended FBMPM) method organizes all the multiple pattern data into a composite Hankel (resp., composite Hankel-Toeplitz) matrix from which the minimum number of elements and the common poles corresponding to element positions can be obtained with similar processing used in the original MPM or FBMPM synthesis method. In particular, the extended FBMPM inherits the advantage of the original FBMPM that a useful restriction is put on the distribution of poles, which makes the element positions obtained much more accurate and robust. Numerical experiments are conducted to validate the effectiveness and robustness of the proposed methods. For the tested cases, the element saving is about 20% ~ 25% for reconfigurable shaped patterns, and can be even more for electrically large linear arrays with scanned pencil-beams. [ABSTRACT FROM PUBLISHER]

The analysis of scattering from multiple bodies of revolution (BoRs) has important applications in microwave remote sensing, radar imaging and other areas. For single BoR, three dimensional problem can be degenerated into 2.5 dimensional problem based on the modal Green functions (MGFs), reducing the solving time and storage remarkably. However, it is difficult to extend the MGF to multiple arbitrarily orientated BoRs. This paper presents a modal characteristic basis function method for solving the scattering from multiple BoRs. It combines the MGF of BoR with the characteristic basis function method, named as the BoR-CBF method. Here, the MGF of BoR is first applied to efficiently solve the current distribution on the surface of each BoR. The singular value decomposition is then used to construct the global modal characteristic basis functions (MCBFs) for each BoR. Finally, the MCBFs are transformed into the RWG basis functions using a basis function mapping technique so that the filling of the interaction matrix can be accelerated by the multilevel fast multipole algorithm. By using the BoR-CBF method, the scattering of multiple arbitrarily orientated BoRs can be solved efficiently. Numerical results are presented to demonstrate the accuracy and efficiency of the BoR-CBF method. [ABSTRACT FROM PUBLISHER]

Four-dimensional (4-D) antenna arrays are formed by introducing a fourth dimension, time, into traditional antenna arrays. In this paper, a time-modulated 4-D array with constant instantaneous directivity is proposed for directional modulation. The main idea is that the 4-D array transmits correct signal without time modulation in the desired direction, while transmitting time-modulated signals in other directions. As longs as the time modulation frequency is less than the bandwidth of the transmitted signal, the time-modulated signals cannot be demodulated correctly due to the aliasing effect, implying that time-modulated signals go distorted. Thus, the 4-D array can be used to transmit direction-dependent signals in secure wireless communications. The proposed idea is verified by experiments based on AM signal transmission through the 4-D array. Moreover, BPSK signal transmission through the 4-D array is studied and the bit error rate (BER) performance is investigated. Simulation results show that the BERs of time-modulated BPSK (TM-BPSK) signals transmitted through the sidelobes of the 4-D array are much higher than those of BPSK signals and almost keep unchanged even under higher SNR. Finally, two enhanced methods are presented to improve the feasibility of directional modulation by using random time sequences and random time modulation frequency. [ABSTRACT FROM PUBLISHER]

A novel broadband dual-polarization antenna utilizing strong mutual coupling with high isolation is presented in this communication. The antenna is composed of two orthogonally situated dipoles which have square-loop shape arms (SLSAs). And to shape the radiation pattern of the antenna, a metal reflector is placed under the antenna. By elaborately utilizing the strong mutual coupling between the two dipoles, very good impedance match and sufficiently high isolation can be achieved simultaneously, the reasons for which are analyzed in this communication. Both the simulated and the measured results show that a more than 57.5% impedance bandwidth with SWR< 1.5 and port-to-port isolation> 31 dB can be achieved for the proposed antenna. As an important advantage, the input impedance of the antenna can be controlled within certain limits by adjusting the configurations, thus the antenna can be fed directly by coaxial cables without using impedance transformers. Besides, the antenna structure is compact and simple. [ABSTRACT FROM AUTHOR]

A compact planar printed quasi-Yagi antenna is presented. The proposed antenna consists of a microstrip line to slotline transition structure, a driver dipole and two parasitic strips. The driver dipole is connected to the slotline through coplanar stripline (CPS). The ground plane is modified by symmetrically adding two extended stubs to reduce the lateral size. Experimental and simulated results show that the proposed quasi-Yagi antenna has a wide bandwidth and good unidirectional radiation characteristics. Compared with conventional printed quasi-Yagi antennas, the width of the proposed quasi-Yagi antenna is reduced by approximately 16.7%. The proposed antenna presents an excellent end-fire radiation with a front-to-back ratio greater than 10 dB. Its measured bandwidth is from 3.6–11.6 GHz with a ratio of about 3.22: 1. A moderate gain, which is better than 4 dBi, is obtained. [ABSTRACT FROM AUTHOR]

A compact dual-polarized double E-shaped patch antenna with high isolation for pico base station applications is presented in this communication. The proposed antenna employs a stacked configuration composed of two layers of substrate. Two modified E-shaped patches are printed orthogonally on both sides of the upper substrate. Two probes are used to excite the E-shaped patches, and each probe is connected to one patch separately. A circular patch is printed on the lower substrate to broaden the impedance bandwidth. Both simulated and measured results show that the proposed antenna has a port isolation higher than 30 dB over the frequency band of 2.5 GHz – 2.7 GHz, while the return loss is less than - 15~dB within the band. Moreover, stable radiation pattern with a peak gain of 6.8 dBi – 7.4 dBi is obtained within the band. [ABSTRACT FROM PUBLISHER]

Time-modulated arrays (TMAs) are studied in the time domain and frequency domain in this paper. The studies are based on the “instantaneous” array factor as a function of time and “average” array factor as a function of frequency, respectively. The two analysis approaches are shown to be unified and complementary through the Fourier transform. Antenna parameters including pattern, directivity, and gain are all addressed. Moreover, an experimental setup for the study of signal transmission is built and measured. Experimental results are in good agreement with the theoretical study. Finally, the bandwidth of TMAs is taken into account, and amplitude modulation (AM) signal transmission through the TMA is studied experimentally. The results presented in this paper can be used to explain the fundamental working principle of TMAs in a clear and comprehensive way. [ABSTRACT FROM PUBLISHER]

In this paper, a novel idea to reduce the number of active elements in a large periodic array is presented and demonstrated firstly by an E-plane microstrip array. High aperture efficiency can be achieved by making use of mutual coupling between array elements, and then the total production cost of the array is greatly decreased by reducing the number of active array elements and associated components. A simple way to control the mutual coupling of the microstrip array is given as an example in this paper. Simulations and measurements show that when the active element spacing is as large as 1.6\lambda0 (\lambda0 is the free-space wavelength at the operating frequency), a - 18.3 dB side lobe level (SLL) and an approximately equal aperture efficiency can be achieved. No obvious performance degradations are found compared to a conventional array with half the element spacing (0.8\lambda0) and an identical total size. Then, simulations and measurements of an H-plane sparse array are given based on the same idea, followed by the simulated results of a planar two-dimensional (2-D) one. [ABSTRACT FROM AUTHOR]

In computational electromagnetics, second-kind integral equations are usually considered less accurate than their first-kind counterparts. The loss of the numerical accuracy is mainly due to the discretization error of the identity operators involved in second-kind IEs. In the previous studies, it was shown that by using the Buffa–Christiansen (BC) functions as testing functions, such a discretization error can be suppressed significantly, and the numerical accuracy of the second-kind IEs in the far-field calculation for spherical objects can be improved dramatically. In this paper, this technique is generalized for generally shaped objects in both perfect electric conductor and dielectric cases by using the BC functions as the testing functions, and by handling the near-singularities in the evaluation of the system matrix elements carefully. The extinction theorem is applied for accurate evaluation of the numerical errors in the calculation of scattering problems for generally shaped objects. Several examples are given to demonstrate the performance of this technique, and several important conclusive remarks are drawn. [ABSTRACT FROM PUBLISHER]

In order to achieve broadband and unidirectional radiation, a planar printed antenna based on closely spaced loading method is proposed and fabricated. This antenna consists of a printed rectangular loop with two gaps and a metallic strip. The rectangular loop has a good direction but has a drawback of narrow band. According to the closely spaced loading theory, the impedance at the upper frequency will decrease when a metallic strip is placed at the maximum radiation direction of the rectangular loop. This improves the impedance matching. A new resonant frequency point is induced. Meanwhile, the resonant frequency point can be changed by modifying the length of the metallic strip. The impedance matching between the two resonant peaks (One peak is determined by the rectangular loop, the other is determined by the metallic strip) is improved by changing the length and the position of the metallic strip. Thus the impedance bandwidth is greatly expanded. Experimental results show good performance of the proposed antenna. It has a 40.7% measured bandwidth, ranging from 2.29 to 3.46 GHz. The measured front-to-back (F/B) ratio of the proposed antenna is larger than 10 dB in the whole frequency band. [ABSTRACT FROM PUBLISHER]

To realize efficient analysis of large scale planar periodic arrays, a two-level characteristic basis functions method accelerated with fast multipole method-fast Fourier transform (FMM-FFT) is developed in this paper. The characteristic basis functions (CBFs) for each element are constructed in a two-level framework, in which the CBFs construction based on plane wave derivation for single element at child level and the CBFs construction based on local interaction between array elements at father level are combined. The number of unknowns is reduced significantly by the two-level CBFs. Further, FMM-FFT is applied to expedite the computation of interaction between elements. Numerical results of large scale planar periodic arrays are given to demonstrate the validity and efficiency of the present method. [ABSTRACT FROM PUBLISHER]