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Infinite periodic arrays of antennas that can be individually described by means of spherical modes are analyzed starting from the generalized scattering matrix (GSM) of an isolated element. After computing the GSM of an isolated element with the finite-element method (FEM), a fast postprocessing can be carried out to calculate the response of the element in an infinite array environment by using addition theorems for spherical modes. For this purpose, an efficient computation of lattice sums of spherical harmonics is used. The main advantage of this method is that the antenna is analyzed only once whatever the array lattice or scan angle. In addition, fast frequency analysis can be performed since the starting point is the computation of the isolated antenna with the FEM, which is suitable for fast frequency sweep. The active reflection coefficient and the embedded radiation pattern of the infinite periodic array are calculated for several examples to show the capabilities of the proposed method. [ABSTRACT FROM AUTHOR]

Due to that the polarization scattering matrices (PSM) of single reflection (SR), double reflection (DR), and single diffraction (SD) at different angles are ignored, the PSM of trihedral corner reflector (TCR) is usually assumed to be [1 0; 0 1], which results in inaccuracy by utilizing its polarization to antijamming. Therefore, this article comprehensively analyzes the PSM of TCR based on high-frequency approximation. First, we separately analyze various reflection components based on the physical optics (PO)-shooting bouncing ray (SBR) model, so as to cure the deficiency that the classification discussion methods are susceptible to changes in target size and shape. Then, the PSMs of SR, DR, triple reflection, and SD are rigorously deduced and demonstrated by combining amplitude/phase information. In this process, we successfully integrate the six kinds of DR by the transforming of polarization base. Subsequently, the PSMs in the 2-D space are extended into the 3-D space, which are more suitable for the polarization characteristics of TCR. Finally, we compare the model in this article with the method of moment (MoM) of Feko software and obviously accelerate the model in this article through compute unified device architecture (CUDA). The conclusion of this article is significant for the polarization analysis of TCR to antijamming. [ABSTRACT FROM AUTHOR]

Arrays fed by substrate-integrated waveguides (SIWs) are a current topic of interest. However, most designers have to rely on general-purpose commercial software, usually inefficient for multiple full-wave simulations in a design process. This work proposes a new fast full-wave strategy, with very low iteration times, based on the simultaneous use of addition theorems for spherical and cylindrical modes. After a domain decomposition of the array into fixed or modifiable (to be optimized) sections, each section is analyzed using a finite-element/modal analysis to obtain its general scattering matrix. Fixed sections are only once coupled at the beginning, while each optimization iteration is calculated with full-wave precision by adding the interactions with the modifiable sections. A complete design process of a novel 16-slot progressive-wave SIW-fed array is performed to validate the strategy usefulness. 112800 iterations, with 47 optimization variables, are calculated in under 4 h (speed-up factor of over 2000 compared to general-purpose commercial software). The designed device is manufactured and experimentally characterized, measuring a 1.05 GHz $\vert S_{11} \vert $ bandwidth under −10 dB and a maximum gain of 15.6 dBi at $\theta =-11^\circ $ in the array plane. [ABSTRACT FROM AUTHOR]

This communication presents a novel technique for obtaining bistatic radar cross sections (RCSs) extracted from a monostatic scattering field dataset using a discrete scattering center model and basis pursuit denoising (BPDN) algorithm, which is compressive sensing (CS) technique. With the high-frequency assumption, a complex vector of independent point sources is formulated in a monostatic configuration for a geometrical relationship among the transmitter, receiver, and equivalent scatterers. A matrix equation for the scattering problem of an underdetermined form is effectively calculated by an iterative BPDN solver. Then, compensating the phase difference in the bistatic condition can derive the bistatic RCS at specific frequency points and observation angles. The accuracy of the proposed method for extracting bistatic results is verified using two numerical examples, and the performance of the method in terms of measurement efficiency and data resolution in frequency and angle domains is compared with that of conventional method. [ABSTRACT FROM AUTHOR]

A novel approach based on the use of a resistor-loaded meta-surface (RL-MS) with optimized resistor values is proposed for scattering control in wideband conformal phased arrays. Specifically, the resistance of the loaded resistor in each RL-MS element is varied. As a result, the proposed RL-MS structure not only absorbs incident EM waves but also scatters the remainders away from threatening directions. To accelerate the design process, the scattering matrix approach is used to calculate the scattering patterns efficiently. Proper resistor element distribution can be achieved by optimizing the scattering characteristics. The RL-MS structure is used as the cover layer of a wideband conformal array. By loading the optimized resistors, scattering in the proposed array is reduced to a relatively low level with little degradation of radiation performances. The final designed array achieves 3:1 impedance bandwidth with scanning up to $\pm 60^{\circ }/\pm 45^{\circ }$ in the E-/H-plane. Remarkably, a monostatic scattering reduction of approximately 30 dB is observed throughout the X-band in the simulated results of the optimized array. To demonstrate the effectiveness of this design, prototype arrays are fabricated and measured. The measured results are in reasonable agreement with the simulated results. [ABSTRACT FROM AUTHOR]

The presented method describes reflection and transmission of electromagnetic waves at multiple closely stacked metal grids using multimodal S-parameter propagation. For that, the periodic surface admittance curve of every metal layer was determined through a novel semianalytic approach that uses simple Fourier transformations instead of solving an integral equation. The modal components of this surface admittance were used to express the generalized scattering matrices of the individual grids. By applying multimodal propagation techniques to the resulting scattering parameters, it was possible to model the electromagnetic interactions within a multilayer stack of periodic impedance sheets. Resulting reflection and transmission parameters perfectly matched the corresponding full-wave simulations even above the grating lobe regime. In the end, the universal mode propagation method enabled modeling of a layer stack, connected to lumped components. [ABSTRACT FROM AUTHOR]

The concept of digital twins (DTs) for reflectarray (RA) unit cells (UCs) is discussed and implemented by exploiting electromagnetic-driven machine learning (ML) techniques. Toward this end, several open challenges are addressed, such as the reliability and the effectiveness of using surrogates for modeling different, in terms of descriptors and complexity, UCs, the accuracy in predicting the scattering matrix entries of both single- and dual-polarization elements, the implementation of effective and efficient strategies for the setup of the training set, and the definition of generalized and robust guidelines for the use of popular ML techniques to the problem at hand. Representative results of an extensive numerical validation are presented to assess the performance and the potentialities of DTs when dealing with different RA modeling problems and training sets. [ABSTRACT FROM AUTHOR]

This article presents a novel method to design the decoupling and matching network (DMN) for dual-band multi-input–multioutput (MIMO) antennas. The DMN consists of a grid of metallic microstrip stubs, some of which are connected while others are not. The connecting condition in the DMN is the only unknown variable for realizing high antenna isolation. It is determined by rigorous design formulas upon scattering matrix and optimized by the binary optimization algorithm, e.g., genetic algorithm (GA). Thus, high isolation among antennas can be achieved without requiring the optimization process in the electromagnetic simulation tool. Three decoupling examples of two two-element symmetric and asymmetric arrays and a four-element array are presented to elaborate the design procedure and verify the advance of the proposed decoupling method. Results show that the adoption of DMN offers enhancement in impedance matching, isolation, and efficiency, as well as the reduction of envelop correlation coefficient within two desired frequency bands for all cases, validating the proposed decoupling method. [ABSTRACT FROM AUTHOR]

The concept and development of a highly efficient pyramidal horn is described. The radiating element comprises a rectangular radiating aperture fed by two smaller flared square waveguide sections via a bifurcated H-plane surface discontinuity. For the simultaneous feeding of the two-port radiating element, the total antenna includes a compact H-plane power divider. Properly weighted TE $_{n0}$ modes ($n\in N^{\ast }$) are excited at the output of the two flared waveguide sections. The bifurcation is responsible for the recombination of the incoming fields. The low-dispersive modal coupling coefficients (or transmission coefficients of the bifurcation’s generalized scattering matrix) between the excitation and the aperture modes enable the broadband realization of the targeted aperture modal content. The common waveguide section is responsible for the phase alignment of the aperture modes. The design method targets a preoptimized model, which approximates the amplitude of the aperture modes TE $_{m0}$ ($m = 1, 3, 5, \ldots $) in the order of 1/ $m$ and minimizes their relative phase difference. Finally, maximum aperture efficiency can be achieved by fine tuning and with low computational complexity. Design principles are given and illustrated by means of an example involving an antenna with aperture size of about $2.8\lambda _{0} \times 1.4\lambda _{0}$ ($\lambda _{0}$ is the free-space wavelength at the central frequency of operation). The antenna exhibits aperture efficiency levels above 95% over the entire Ku-Tx-band (10.7–12.75 GHz), as well as a compact profile ($4.1\lambda _{0}$). The measured results of a prototype manufactured through milling verify experimentally the numerically predicted performance. [ABSTRACT FROM AUTHOR]

A new model-based parameter estimation (MBPE) method for multilayer periodic EM surfaces is discussed in this article. By applying the proposed method to predict the generalized scattering matrix (GSM) of each unit layer section, the response of a composite structure can be determined by cascading GSMs while allowing the salient behavior of each section to be accurately captured. Based on the spectral properties of Green’s functions with high-order wavenumbers and chosen basis functions, an advanced interpolation model is developed to estimate the broadband response of periodic structures in a robust and efficient manner. It needs fewer samples in the interpolation compared to the state of the art, and no restriction for the sample selection is required. Numerical analysis has been carried out for two types of multilayer structures, and a good agreement between the conventional periodic method of moments (PMM) and the proposed method has been obtained. [ABSTRACT FROM AUTHOR]

Greedy pursuit algorithms (GPAs) are widely used to reconstruct sparse signals. Even though many electromagnetic (EM) inverse scattering problems are solved on sparse investigation domains, GPAs have rarely been used for this purpose. This is because 1) they require a priori knowledge of the sparsity level in the investigation domain, which is often not available in EM imaging applications and 2) the EM scattering matrix does not satisfy the restricted isometric property. In this work, these challenges are, respectively, addressed by 1) using an artificial neural network (ANN) to estimate the sparsity level and 2) adding a Tikhonov regularization term to the diagonal elements of the scattering matrix. These enhancements permit the compressive sampling matching pursuit (CoSaMP) algorithm to be efficiently used to solve the 2-D EM inverse scattering problem, which is linearized using the Born approximation, on spatially sparse investigation domains. Numerical results, which demonstrate the efficiency and applicability of the proposed ANN-enhanced CoSaMP algorithm, are provided. [ABSTRACT FROM AUTHOR]

An accurate equivalent circuit model (ECM) for general multiwire multiorder printed circuit board (PCB) metagratings (MGs) is developed. The effective impedances of the grating wires are modeled as lumped loads in the ECM. The numerous propagating Floquet harmonics supported by the grating are modeled as circuit ports. Based on the desired field transformation for the MG, a set of required scattering parameters for its ECM is derived. The equivalent lumped loads are subsequently optimized to realize these parameters, which is analogous to shaping the diffraction pattern of the MG to match the desired functionality. Within this framework, it is possible to encode multiple functions into a single device by simultaneously optimizing all relevant entries of the ECM scattering matrix. Using the proposed technique, an angle-multiplexed multifunctional MG is designed and investigated. [ABSTRACT FROM AUTHOR]

Polarimetric multiple input and multiple output (MIMO) radar is capable of acquiring target’s high-resolution images and polarization scattering matrix (PSM). In this article, calibration of a polarimetric MIMO array of an instrumentation radar for near-field measurement is achieved at ${X}$ -band by using a rotatable double-antenna polarimetric active radar calibrator (RODAPARC) and a metal cylinder quickly and accurately. The theoretical PSM of the RODAPARC with different antenna rotation angles is derived from Huygens’ radiation electric field which is applicable to different bistatic angles. A polarimetric signal model is adopted to reduce the impact of the RODAPARC on calibration. Experimental studies are conducted on a polarimetric MIMO array which is measured and divided into quasi-monostatic and bistatic transceiver channels for assessment on the calibration performance. Promising calibration results are obtained with a polarization isolation improvement of about 16 dB and great reduction of the polarization channel gain error less than ±0.5 dB in amplitude and ±3° in phase. The calibrated polarization signatures for classic objects are consistent with the theoretical results. [ABSTRACT FROM AUTHOR]

A thin laminated composite is proposed in this article for highly efficient microwave absorption at both high frequency and low frequency. It is composed of two layers of carbon-fiber-reinforced planar structure. In each layer, periodically arranged fiber array with the axes of the fibers parallel to each other is embedded into a ceramic matrix which is used to bind the fibers together and to provide necessary mechanical or chemical properties. Stacking up two layers of the planar structure with the fibers in different layers orientated into different directions produces a lamina which can be further parallely stacked up to provide the whole laminated material. The influence of the structural and electromagnetic parameters on the microwave absorption efficiency is first studied in detail with scattering matrix and boundary-mode matching method. Then the genetic algorithm and the sequential quadratic programming methods are used to form a two-step strategy based on the mode-matching method to optimize the structural and electromagnetic parameters for a highly efficient microwave absorption in both high-frequency and low-frequency bands. Numerical examples are also given to demonstrate the high absorption efficiency of the designed laminated material. [ABSTRACT FROM AUTHOR]

This paper introduces a fast full-wave methodology for the analysis of antenna arrays placed on the top plate of substrate integrated waveguides (SIWs). The methodology is based on the generalized scattering matrix (GSM) of each array element in terms of spherical and cylindrical modes and plane-port feeding modes, and the simultaneous use of addition theorems for spherical and cylindrical waves. Addition theorems allow the analytical translation of spherical and cylindrical modes, so that the GSMs can be simultaneously connected in the SIW layer and in the radiation region, to obtain the full-wave response of the array. The proposed methodology is validated by means of full-wave simulations with commercial and in-house softwares. [ABSTRACT FROM AUTHOR]

Array antennas are increasingly used for transmission and reception in applications such as telecommunication, medical imaging, radar, or radio astronomy. Low-loss matching networks are inserted in each channel between the antenna and amplifiers in order to optimize power transfer in transmission and/or signal-to-noise ratio (SNR) in reception. The adjustment of these matching components becomes challenging if residual coupling between antenna elements significantly influences the results. The most general, so-called, array noise matching then leads to the optimum SNR taking into account the noise-coupling effects also. This paper describes that concept completely in the scattering matrix domain using waves for signal and noise rather than voltages and currents. [ABSTRACT FROM AUTHOR]

A rigorous and efficient approach for the design of radomes that are closely spaced to the radiating aperture of a phased array is proposed. The method relies on a generalized scattering matrix (GSM) description of both source and radome based on a Floquet modal expansion. The GSM of the unit cell of the radiating array is calculated only once. The radome, which is also frequently addressed as wide-angle impedance matching, is optimized simply by iterating with a fast solver based on the periodic method of moments. The effect of the antenna is taken into account through the connection of the GSM matrices. The proposed approach is sufficiently fast, versatile, and highly rigorous as neither homogenization procedures nor equivalent circuits are exploited. In order to verify the validity of the proposed approach, numerous examples are provided. In addition, an analysis of the accuracy of the method determined by the number of the adopted modes is also presented. [ABSTRACT FROM AUTHOR]

A hybrid algorithm that combines the finite-element time-domain (FETD) method and generalized scattering matrix (GSM) technique is proposed to efficiently compute the broadband monostatic radar cross section (RCS) of a large and deep open cavity. The formulation and implementation for the numerical modal analysis of arbitrary cross sections and the FETD method equipped with complex frequency-shifted perfectly matched layers for transient simulations are presented. The broadband monostatic RCS is evaluated using a broadband GSM obtained by the FETD solutions. Several examples are presented to demonstrate the accuracy and efficiency of the proposed hybrid FETD-GSM algorithm for broadband monostatic RCS computation and inverse synthetic aperture radar imagery of large and deep open cavities. [ABSTRACT FROM AUTHOR]

A new modeling approach for the design of planar multilayered meander-line polarizers is presented. For the first time a multielement equivalent circuit is adopted to characterize the meander-line unit cell. This equivalent circuit significantly improves the bandwidth performance with respect to the state-of-the-art. In addition to this, a polynomial interpolation matrix approach is employed to take into account the dependence on the meander-line geometrical parameters. This leads to an accuracy comparable to that of a full-wave analysis. At the same time, the computational cost is minimized so as to make this model suitable for real-time tuning and fast optimizations. A four-layer polarizer is designed to validate the presented modeling procedure. Comparison with full-wave simulations confirms its high accuracy over a wide frequency range. [ABSTRACT FROM AUTHOR]

We present a novel beam summation (BS) formulation for tracking wavefields in fluctuating media. This formulation utilizes the ultrawideband phase-space BS method, which is structured upon a windowed Fourier transform (WFT) frame expansion of the sources and expresses the field as a discrete phase-space sum of beam propagators. This paper extends the frame concept, proving that this beam set constitutes a frame not only in the source domain, where it reduces to the conventional WFT, but everywhere in the propagation domain. This “beam frame” provides a self-consistent framework for tracking wavefields through scattering media in which the local interaction of the incident beams with the medium is expanded using the same set of beams. The resulting beam-to-beam (B2B) scattering coefficients depend on the local spectral properties of the medium. The overall B2B scattering matrix is therefore compact, coupling only beams that are adjacent in phase space, given the fluctuation properties. The new formulation expresses the entire scattering problem in terms of coefficients dynamics in the phase space. As demonstrated, the formulation is computationally efficient and captures all the relevant phenomenology. Part II extends this formulation for stochastic fields in random fluctuating medium characterized by the medium statistics. [ABSTRACT FROM PUBLISHER]

This paper proposes the synthesis of aperiodic arrays of realistic antennas excited with uniform amplitude, where the mutual coupling between elements is rigorously taken into account. A cost function that involves the expression of the radiated field of the coupled array is obtained and its gradient is evaluated in order to move the elements in the corresponding direction at each iteration. The synthesis method involves the calculation of the gradient of the field radiated by the coupled array, which is obtained analytically by using a full-wave method based on the generalized scattering matrix, spherical mode expansions and rotation, and translation properties of spherical waves. [ABSTRACT FROM PUBLISHER]

The problem of generalized scattering matrix (GSM) transformation during an angular or linear displacement of the antenna is considered. To work out the problem, it is suggested that the entries of the antenna GSM are presented as two different sets of matrices. One set is used for GSM transformation in case of antenna rotation, whereas the other in case of antenna linear displacement. Expressions have been derived that allow GSM calculation for the antenna’s new position in space from its initial, i.e., predisplacement or prerotation GSM. The derived computation formulas comprise universal and independent of a particular moving antenna transformation matrices, the sizes of which are smaller than the dimension of the overall transformation matrix usually required to perform GSM calculations. Results of a practical computation verifying the derived equations are presented. [ABSTRACT FROM PUBLISHER]

A general method to obtain a matrix which allows the compensation of mutual coupling effects in transmitting arrays for the total field in all directions is introduced. This method is independent of the numerical method used in the analysis and it can include the effect of the antenna platform. The starting point can be the active element patterns or the spherical mode expansion from spherical near-field antenna measurements. Additionally, the spherical mode expansion is also used to find a matrix which allows the compensation of mutual coupling effects in receiving arrays. Through this theory, a simple relation between the compensation matrices of the transmitting and the receiving arrays is found. As a consequence, the scattering matrix of a circuit that allows the simultaneous compensation of mutual coupling effects for the transmission and the reception problem can be easily defined. Finally, it will be shown how the capabilities of the compensation in all directions depend strongly on the array element. [ABSTRACT FROM PUBLISHER]

A closed-form spatial Green's function for a truncated dielectric slab is derived by using a combination of the characteristic Green's function (CGF) and perfectly matched layer (PML) method. The original structure is terminated by PML that is backed by perfect electric conductor (PEC) in semi-infinite layer at the top and/or bottom. The eigenmodes of the closed structure by PML construct the continuous spectrum contribution of the original structure efficiently. Derived Green's function is exact for separable finite structure while it is approximate for nonseparable one especially in the corners. Generalized scattering matrix (GSM) of truncating surface which contains possible conversions between all modes is computed with mode-matching method. It is demonstrated that by importing GSM in CGF formulation, more exact results for nonseparable structures can be obtained. The source and observation points dependence is analytically available in derived expression and allows very efficient computation and storage of the spatial Green's function. Very close to the source, where the large number of modes must be considered, Shank's transform is used to preserve the efficiency of the method. The main advantage of the method lies in its accuracy and low dependency of the result to the PML parameters. Excellent agreements with the rigorous method of moments (MoM) are shown in several examples. [ABSTRACT FROM PUBLISHER]

A method is presented to analyze the maximum power transfer efficiency of a wireless power transfer system and its electromagnetic fields via spherical modes. The Z-parameter and Y-parameter for two coupled antennas are derived using the antenna scattering matrix and an addition theorem. In addition, formulas for calculating the maximum power transfer efficiency and optimum load impedance are presented. A formula is derived to calculate the electromagnetic field generated by a wireless power transfer system from the antenna scattering matrix. [ABSTRACT FROM PUBLISHER]

This paper proposes a circular polarization selective surface (CPSS) design consisting of two meander-line circular polarizers and a linear polarizer. No vias are required. These polarizers are individually designed with ANSYS-HFSS (High Frequency Structure Simulator) software whereas the response of the overall cascade CPSS is computed with the GSM approach. A cascade CPSS which includes three-layer meander-line polarizers is designed and fabricated. Good agreement is shown between experimental and simulated results, with only the TE00 and TM00 modes in the GSM analysis. Finally, analysis of the circular polarizers based on simple filter theory is done to better understand how the performance of the whole structure can be improved. [ABSTRACT FROM PUBLISHER]

The problem of long distance wave propagation in a sparse random medium is considered in this paper. A mathematical technique for modeling the behavior of electromagnetic wave propagation as a function of distance in a 2-D sparse random media at millimeter wave (MMW) regime is presented. The proposed model is a field method based on Maxwell's equation and, thus, the phase and magnitude of the field in the random medium can be tracked accurately. The random media is characterized by low volume fraction but electrically large scatterers having relatively high dielectric constant. The technique relies on discretizing the random media into thin slabs and relating the forward and backward scattered plane wave spectra from the individual slabs by an equivalent spectral bistatic scattering matrix. By cascading the scattering matrices of the individual slabs, the statistics of the overall scattered wave in both forward and backward directions are obtained. This technique will be referred to as statistical S-matrix approach in spectral domain, or SSWaP-SD. Using this method, it is shown that after propagation to a critical range inside the random media, the incoherent component of the forward propagating wave overcomes the mean-field component resulting in a dual-slope attenuation curve as a function of distance. The accuracy of the model is examined against a full wave Monte Carlo simulation and a very good agreement is observed. Finally, based on the proposed model, analytical expressions for predicting the forward path-loss as well as the back scattered power from a sparse, translational invariant discrete random media are derived. The analytical expressions are tested against Monte Carlo simulation for a very long random medium and very good agreements are demonstrated. [ABSTRACT FROM PUBLISHER]

The two-dimensional scattering of a plane wave from an arbitrary arrangement of infinite cylinders in two dielectric half-spaces is considered. The electromagnetic fields are decomposed into cylindrical waves so that the boundary conditions for the cylinders can be satisfied directly. The boundary conditions for the planar interface separating the two dielectric half-spaces are addressed by decomposing the cylindrical waves into plane waves and applying the planar reflection/transmission coefficients. This decomposition produces integrals that can be evaluated numerically. When the cylinders are significantly separated from the planar interface, the method of stationary phase can be used to approximate the integrals. [ABSTRACT FROM PUBLISHER]

The compactness of antenna arrays is highly restricted due to the mutual coupling between the radiation elements, which degrades the performance of impedance matching, radiation efficiency and antenna diversity. For this reason, networks based on eigenmode theory or conjugate matching methods have been introduced in a number of previous works to overcome these effects. With this objective, a matching and decoupling network is required between the input ports and the antenna array, whose function is to improve power matching and ports decoupling. In this paper, three designs with one-layer microstrip line structure of matching and decoupling networks based on a balun technique and neutralization lines are discussed. Two two-element monopole antenna arrays with 0.1 \lambda separation and a four-element monopole array with 0.07 \lambda separation operating around 2.5 GHz are fabricated and measured. The theoretical analysis is based on the scattering matrix. A comparison of the two approaches is illustrated in the paper. Good matching and decoupling behavior of the antenna arrays is found. Overall, it is found that arrays with only 0.1 \lambda element separation or even less can provide reasonable antenna performance. [ABSTRACT FROM PUBLISHER]

A full-wave antenna modeling method by means of elementary sources described in terms of colocalized infinitesimal dipoles is presented in this paper. The procedure provides a generalized scattering matrix (GSM) in terms of equivalent infinitesimal dipoles from the GSM of the antenna by using rotation and translation of spherical modes. The number of equivalent infinitesimal dipoles and their positions are optimized by using a genetic algorithm. The application to the full-wave analysis of arrays is also presented, providing very accurate results even when the minimum spheres of the antennas in the array environment overlap considerably, which cannot be solved by the direct coupling of generalized scattering matrices in terms of spherical waves. Some examples of antenna modeling and their application to the analysis of arrays of antennas on a metallic plane will be shown. [ABSTRACT FROM PUBLISHER]

Antenna polarization states always vary with scan direction. Here this phenomenon is called spatial polarization characteristic (SPC) of antenna. Based on the single polarized radar antenna, by sufficiently utilizing of the inherent polarization property of antenna (i.e. the property that polarization state is not a constant but a function of antenna's spatial scanning direction), a novel polarization scattering matrix (PSM) measurement method is established. This method has the following advantages: (i) It does not need dual orthogonal polarization channels; (ii) the PSM of target can be obtained just by using the prior knowledge of SPC and by improving the signal processing mode of received radar signal. The modern radar systems can make use of this property in its measurement of target polarization scattering property in the searching or angle tracking stage. [ABSTRACT FROM PUBLISHER]

A non-reciprocal antenna radome based on the Faraday rotation effect in a ferrite slab is proposed and analyzed. This radome allows transmission in one direction and attenuates the signal in the opposite direction. It includes two layers of strip gratings on each side of the ferrite slab, consisting of highly conductive strips for proper reflection, and thin highly lossy strips for reflection/dissipation, and three dielectric layers for matching. The radome is analyzed rigorously by the generalized scattering matrix (GSM) method and its performance experimentally demonstrated between two broadband antennas. The measured results show 21 dB and 0.85 dB loss in the isolation and transmission directions, respectively. [ABSTRACT FROM AUTHOR]

We analyze the scattering by polygonal cross-section lossless dielectric cylinders illuminated by an obliquely incident plane wave. The problem is formulated in terms of a system of surface integral equations opportunely devised so as to be valid for objects with edges and incident angles including the total reflection limit angle. By means of Galerkin's method in the spectral domain with analytically Fourier-transformable expansion functions factorizing the correct edge behaviors and continuity conditions of the unknowns, convergence of exponential type is achieved and the coefficients of the scattering matrix are reduced to single integrals that can be efficiently evaluated. Numerical results for both near field and far field parameters are presented, showing the quick convergence of the method even when applied to composite cylindrical objects. [ABSTRACT FROM AUTHOR]

We present an extension of the linear embedding via Green's operators (LEGO) procedure for efficiently dealing with 3-D electromagnetic composite structures. In LEGO's notion, we enclose the objects forming a structure within arbitrarily shaped domains (bricks), which (by invoking the equivalence principle) we characterize through scattering operators. In the 2-D instance, we then combined the bricks numerically, in a cascade of successive embedding steps, to build increasingly larger domains and obtain the scattering operator of the whole aggregate of objects. In the 3-D case, however, this process becomes quite soon impracticable, in that the resulting scattering matrices are too big to be stored and handled on most computers. To circumvent this hurdle, we propose a novel formulation of the electromagnetic problem based on an integral equation involving the total inverse scattering operator of the structure, which can be written analytically in terms of scattering operators of the bricks and transfer operators among them.We then solve this equation by the method of moments combined with the eigencurrent expansion method, which allows for a considerable reduction in size of the system matrix and thereby enables us to study very large structures. [ABSTRACT FROM AUTHOR]

In this paper, we introduce an approach to analyze the interaction between antennas and the propagation channel. We study both the antennas and the propagation channel by means of the spherical vector wave mode expansion of the electromagnetic field. Then we use the expansion coefficients to study some properties of general antennas in those fields by means of the antenna scattering matrix. The focus is on the spatio-polar characterization of antennas, channels and their interactions. We provide closed form expressions for the covariance of the field multimodes as function of the power angle spectrum (PAS) and the channel cross-polarization ratio (XPR). A new interpretation of the mean effective gains (MEG) of antennas is also provided. The maximum MEG is obtained by conjugate mode matching between the antennas and the channel; we also prove the (intuitive) results that the optimum decorrelation of the antenna signals is obtained by the excitation of orthogonal spherical vector modes. [ABSTRACT FROM AUTHOR]

This paper presents a novel, simple pattern synthesis procedure for linear equispaced arrays which can be characterized by a generalized scattering matrix (GSM) and whose radiated field can be expressed as a weighted sum of shifted spherical waves. It can be viewed as an extension of the classic design techniques of the Fourier series (FS) method or the Woodward-Lawson frequency sampling method, to the case in which the individual antenna elements' patterns and all interelement couplings are taken into account. The design procedure, which yields the excitations needed to achieve the desired pattern, is based on either the FS or the discrete Fourier transform (DFT) of the spherical mode expansion of the array radiated field, as well as on various properties associated to the FS or DFT coefficients. In this work, to compute the GSM of the array and the spherical mode expansion of the field, a validated hybrid full-wave methodology, based on the finite element method and rotation and translation properties of spherical waves, is used. Numerical results of different synthesized array patterns are presented for different arrays made up of dielectric resonator antennas and cavity-backed microstrip circular patches. [ABSTRACT FROM AUTHOR]

A novel method is presented to analyze the electromagnetic characteristics of systems consisting of a large number of scatterers with different shapes and materials. In the method, nearly located scatterers are grouped together, while large bulk materials are divided into subblocks with adequate sizes. A scatterer group or a subblock forms a basic block of the system, and each block is contained with a virtual reference surface. A generalized transition matrix defined on the reference surface is used to characterize the electromagnetic characteristics of the block. The generalized transition matrix relates the rotated tangential components of the scattered fields or the equivalence sources to the rotated tangential components of the incident fields directly. The generalized transition matrix can be calculated for each block in- dependently using proper methods according to its structure and material. Surface integral equations are established on all the virtual reference surfaces, which can be solved by moment method to get the electromagnetic characteristics of the whole system. Characteristic basis functions and synthetic basis functions can be applied to further reduce the unknown number, while fast multipole method can be used to accelerate the evaluation of interactions. Two-dimensional examples are provided to verify the method. [ABSTRACT FROM AUTHOR]

An accurate and efficient numerical scheme is presented for incorporating a feed network into the time-domain finite-element modeling of antennas and antenna arrays. The feed network is represented in terms of a rational function form of its scattering matrix in the frequency domain that enables its interfacing with the time-domain finite-element modeling of the array through a fast, recursive time-convolution algorithm. The exchange of information between the antenna elements and the feed network occurs through the incident and reflected modal voltages/currents at properly defined port interfaces. The proposed numerical scheme significantly simplifies the simulation of an antenna system that comprises both antennas and a feed network and allows one to fully utilize the power of an antenna simulation technique to deal with large and complex antennas. Several examples are presented to demonstrate the accuracy and efficiency of the method. [ABSTRACT FROM PUBLISHER]

We describe the factorization (FACTOPO) domain decomposition method based on the boundary element method (BEM) and the finite element method (FEM) applied to the analysis of antenna performance on aircraft. The benefits of the subdomain method are mainly the ability to deal with collaborative studies involving several companies, and the reduction of the computation costs by one or more orders of magnitude, especially in the context of parametric studies. Furthermore, this paper proposes global functions defined on fictitious surfaces surrounding radiating elements, to deal with the computation of antenna far field patterns in a multidomain mode. By masking the complexity of the antenna (wires, thin surfaces, materials, feeding network) the external domain of the aircraft can be closed so that the combined field integral equation can be used, which is better conditioned than the electric field integral equation and converges much faster. The accuracy and efficiency of this technique is assessed by directivity computations of VHF monopole antennas mounted on Fokker 100 and ATR42 scaled mock-up. Domain decomposition results obtained by combining two sets of subdomains are compared with measurements and the FEKO commercial method of moments code. [ABSTRACT FROM AUTHOR]

An efficient fast multipole method (FMM) formalism to model scattering from two-dimensional (2-D) microstrip structures is presented. The technique relies on a mixed potential integral equation (MPIE) formulation and a series expression for the Green functions, based on the use of perfectly matched layers (PML). La this way, a new FMM algorithm is developed to evaluate matrix-vector multiplications arising in the iterative solution of the scattering problem. Novel iteration schemes have been implemented and a computational complexity of order O(N) is achieved. The theory is validated by means of several illustrative, numerical examples. This paper aims at elucidating the PML-FMM-MPIE concept and can be seen as a first step toward a PML based multilevel fast multipole algorithm (MLFMA) for 3-D microstrip structures embedded in layered media. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to beamforming in hybrid antennas. Using a scattering matrix model for the hybrid antenna system, a bidirectional transformation is developed that relates the signals at the hybrid system feed to the signals that would be present in a planar array at the location of the reflector aperture. For example, the received fields at the feed of a hybrid antenna system may be transformed into the fields at the reflector aperture, and these reflector aperture fields may then be processed as if they were received by a planar or linear array. Similarly, the desired field or current distribution across the reflector aperture when transmitting may be transformed into the required field or current distribution at the hybrid system feed. This method allows standard linear or planar array analysis and synthesis techniques to be used with the hybrid system. Examples are provided for transmit and receive weight synthesis. [ABSTRACT FROM AUTHOR]

Presents a scattering-matrix analysis of linear periodic arrays. Linear periodic array of small radiators; Details on the closed-form expression for the propagation constant of the traveling wave antennas; Information on the maximum attainable endfire directivity of a finite array.

Presents information on a study which analyzed the infinite multilayer printed arrays with apertures and patches of irregular shapes using a modular technique based on a generalized scattering matrix (GSM). Computation of the three-port GSM; Analysis of multilayer aperture-coupled arrays; Conclusions.

Shows that banded matrix iterative approach with a canonical grid method (BMIA/CAG) as efficient method for the calculation of scattering for two-dimensional (2-D) geometries such as one-dimensional rough surfaces. Description of the algorithm for the calculations of the contributions of transverse electric (TE) and transverse magnetic (TM) polarization; Relationship between the grid and operator expansion methods.

Studies the utilization of a matrix-pencil superresolution algorithm for the identification of the scattering centers of several canonical targets. Parametrization of frequency-dependent wavefronts; Canonical scattering scenarios; Effects of noise and interscattering-center proximity; Conclusion of the study.