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In this work, we show how we can improve the image resolution capabilities of a Phase Conjugating (PC) lens as well as the angular resolution of Luneburg lens antennas by employing signal processing techniques such as the Correlation Method (CM), the Minimum Residual Power Search Method (MRPSM), the sparse reconstruction method, and the Singular-Value-Decomposition (SVD)based basis matrix method. In the first part, we apply these techniques for sub-wavelength imaging in the microwave regime by combining them with the well-known phase conjugation principle. We begin by considering a one-dimensional microwave sub-wavelength imaging problem handled by using three signal processing methods, and then we move on to two- or three-dimensional problems by using the SVD-based basis matrix method. Numerical simulation results show that we can enhance the resolution significantly by using these methods, even if the measurement plane is not located in the very nearfield region of the source. We describe these proposed algorithms in detail and study their abilities to resolve at the sub-wavelength level. Next, we investigate the sparse reconstruction method for a normal Luneburg lens antenna and the Correlation Method and the SVD-based basis matrix method for a flat-base Luneburg lens antenna to estimate the Direction-of-Arrival (DOA). Numerical simulation results show that the signal processing techniques are capable of enhancing the angular resolution of the Luneburg lens antenna enabling the lens to locate multiple targets with different scattering cross-sections and achieving higher angular resolution.

In this letter, we show how we can improve the resolution capability of a phase-conjugating lens by employing a signal processing algorithm, namely the Minimum Residual Power Search Method (MRPSM), and we apply it for subwavelength imaging in the microwave regime by combining it with the well-known phase conjugation (PC) technique, which has been extensively used in the electromagnetics area for imaging purposes. We show that by using such a combination, we can achieve subwavelength resolution on the order of λ/10, even if the phase-conjugating lens or the measurement plane is located in the far-field region of the source. We describe the proposed algorithm in detail and study its ability to resolve at the subwavelength level, as well as its computational efficiency in a comparative manner.

In this paper we present two simulation techniques for modeling periodic structures with three-dimensional elements in general. The flrst of these is based on the Method of Moments (MoM) and is suitable for thin-wire structures, which could be either PEC or plasmonic, e.g., nanowires at optical wavelengths. The second is a Finite Difierence Time Domain (FDTD)-based approach, which is well suited for handling arbitrary, inhomogeneous, three-dimensional periodic structures. Neither of the two approaches make use of the traditional Periodic Boundary Conditions (PBCs), and are free from the di-culties encountered in the application of the PBC, as for instance slowness in convergence (MoM) and instabilities (FDTD).

In this letter, we present a characteristic basis function method (CBFM) algorithm for an efficient “full-wave” analysis of printed microwave circuits and antennas etched on layered media. The main contribution of the proposed approach is a technique for the generation of the primary characteristic basis functions (PCBFs) in conjunction with the employment of high-order characteristic basis functions (CBFs), which enables us to implement a totally general decomposition scheme of the circuit under analysis. Numerical examples are presented to demonstrate the efficiency and the accuracy of the proposed approach.

In this letter, we present an improvement over the conventional thin dielectric sheet (TDS) formulation for the analysis of thin dielectric sheets. Our focus is to address the problem of scattering from thin penetrable scatterers by developing a volumetric formulation based on the use of macro-basis functions. The electric fields produced by the source basis functions are derived directly, bypassing the summation of scalar and vector potentials. The latter results in a considerable time advantage in comparison to the conventional method of moments (MoM) solution of the volume electric field integral equation (V-EFIE), while the accuracy remains comparable. In contrast to the TDS formulation, both tangential and normal currents are employed so that problems with high and low permittivity, as well as those involving grazing incident angles, can be accurately analyzed. Several examples are reported that show excellent agreement with conventional techniques and demonstrate the effectiveness of the new approach.

An efficient characteristic basis function (CBF)-based method is proposed to analyze conformal frequency selective surfaces (FSS) that are not amenable to analysis by using conventional numerical methods typically used to model infinite, planar, and doubly periodic FSSs. The technique begins by employing the CBFs to describe the currents induced on the elements. The reaction integrals needed to derive the reduced matrix elements are computed either in the spatial domain, or spectral domain, depending on the separation distance between the blocks, so as to make the process numerically efficient. The spectral domain integrals are evaluated by making use of the spectral rotation (SR) on the spectra of the CBFs to alleviate the computational burden to be associated with full three-dimensional (3-D) Fourier transform, which is required in the conventional spectral domain approach applied to nonplanar geometries. Numerical results from the new method have good agreement with the fully spatial characteristic basis function method (CBFM) and the conventional method of moments (MoM). However, the required central processing unit (CPU) time is greatly reduced.

Plane wave scattering by a perfectly conducting strip grating is considered. A methodology for the computation of the induced currents is proposed, which utilizes the knowledge of the current induced in the center region of a truncated finite grating with only a moderate number of strips.

In this paper, we present a novel procedure for an efficient and accurate electromagnetic simulation of microstrip circuits and printed antennas etched in layered media. The proposed approach, based on a new algorithm referred to herein as the equivalent medium approach (EMA), is applied for a rapid design of the preliminary desired circuit prototype. The illustrated technique yields reliable results and reduces the computational time in comparison with the conventional method of moments (MoM). Some examples that demonstrate the accuracy and the efficiency of the described procedure are included.

The article presents a numerically efficient and accurate technique for the analysis of doubly-infinite periodic arrays, which find applications as frequency selective surfaces, electronic bandgap structures and metamaterials that often utilize periodic elements with fine features. The method derives its efficiency by projecting the solution to the infinite array problem from that of a corresponding truncated array of relatively small size, typically comprising of only four to six rings. Furthermore, it reduces the matrix size needed to solve for the induced current to only two or three. Another feature of the method is that it involves reciprocity principle to compute the reflection and transmission coefficients of the array, using a technique that avoids the need to integrate the currents induced on the unit cell via the periodic Green's function, as well as the evaluation of the latter integral in the far-field. The results derived are compared with commercial software tools to assess the validity of the approach and to demonstrate the time advantage of the present scheme over the existing techniques. V C 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1108-1116, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/ mop.26730

Numerical simulation of electromagnetic models with multiscale features is highly challenging due to the fact that electrically large as well as small features are simultaneously present in the model, which in turn requires that the computational domain be discretized such that the number of degrees of freedom (DOF) is very large and hence, levies a heavy burden on computational resources.

In this work, we describe a hexa-band mobile phone antenna with a metallic backing, designed for SAR reduction. The proposed antenna has a simple structure comprising of two radiating strips and a coupling strip which serves to enhance the bandwidth at high frequency. The antenna has been designed to cover multiple bands, namely LTE Band 13 (747–787 MHz); DCS 1800 (1710–1880MHz); PCS 1900 (1850–1990MHz); WCDMA (1920–2170MHz); LTE Band 40 (2300–2400 MHz); and Band 41 (2496–2690MHz). The designed antenna only occupies a small area of 15×29.5 mm2 on the system circuit board. By adjusting the shape, location and size of the backing, the SAR is effectively reduced over all of the bands, while the efficiency of the antenna is preserved. Thus, the antenna is an excellent candidate for incorporation into smart phones for next generation wireless systems.

This paper describes the performance of a multi-band antenna with a Partially Reflective Surface (PRS) printed underneath the substrate to reduce the level of Specific Absorption Rate (SAR). The frequency band considered ranges from 850 MHz to 977 MHz and from 1.7 GHz to 2.1 GHz. The multi-band antenna placed above an FR4 substrate with the PRS printed below was found to reduce the 1-g average SAR in a specific anthropomorphic mannequin (SAM) model by 16.7–28.9 % as compared to the average SAR level of the no-PRS case, without unduly sacrificing antenna gain and radiation efficiency.

Summary form only given. Despite the availability of modern supercomputers, direct solution of multiscale problems by means of conventional CEM methods-be it FEM, FDTD or MoM-is highly challenging. This is because modeling of structures with fine features, which might share the computational domain with other large objects, often requires dealing with a large number of degrees of freedom. Dealing with such multiscale problems often forces us to compromise the accuracy of the numerical discretization process when faced with the problem of capturing the small-scale features, in order to cope with the limited available resources in terms of CPU memory and time.Many fine-featured structures that are integral parts of sensors and other complex systems have dimensions that are often only a small fraction of the wavelength in the medium and require a very fine mesh to capture the nuances of their geometry. In the past, it has been demonstrated that the electromagnetic properties of small objects can be accurately and conveniently characterized by a Dipole Moment (DM) representation, which is valid both in the nearand far-field regions of the scatterer. Based on this, a hybrid FDTD method has been proposed, which models the fine features by using a DM located at the center of the FDTD cell. Since the DM is always located in close vicinity of the grid lines of the cell containing the DM, the 1/r3 term dominates within the cell, rendering the fields “time independent” and identical to those from a static charge. These fields are then passed on to the FDTD, which automatically performs the analytic continuation of the quasi-static solution into the region external to the cell containing the small object, as a consequence of the dynamic nature of Maxwell's equations. However, when modeling straight wires passing through multiple FDTD cells, the above hybrid method fails since the quasi-static approximation of the DM is no longer valid over the entire wire. To address this problem, we propose to model the wire by using basis functions which can be conveniently expressed in closed forms, not only in the frequency domain, but in the time domain as well. The scheme is simpler and also computationally more efficient than the conventional Time Domain Integral Equation (TDIE) algorithms, especially when a large number of unknowns is involved. However, we have found that the proposed algorithm becomes unstable when we generalize the field expressions in order to model bent wire geometries, for which a time domain basis function which is convenient, causal and stable cannot be found. In this work we propose a novel DM-FDTD hybrid technique when dealing with an arbitrarily shaped wire, which may span several cells. The key is to use a modified DM approach, in which all the three terms of the fields generated by the DM, corresponding to both the near and far-field regions, are expressed in the time domain in convenient closed forms. Thus, the field contributions can be calculated at any arbitrary distancefrom the DM source and can be coupled with the FDTD. The proposed method is universal and can be used for scatterers traversing through multiple cells. Also, since the fields produced from an arbitrary scatterer can always be represented as a superposition of electric and/or magnetic DMs, the method can be employed to model an arbitrarily shaped thin scatterer without altering the FDTD updating scheme or the size of the FDTD discretization, which can be the nominal λ/20, even when dealing with objects with fine features that are small fractions of the wavelength.

In this paper, signal processing techniques are employed for electromagnetic sub-wavelength imaging. Three signal processing algorithms are investigated, including phase conjugation (PC), correlation method (CM) and maximum search and removal method (MSRM).

Summary form only given. Increasing competition in the communication market has fueled the development of increasingly efficient Computer Aided Design (CAD) tools for simulating the performance of microwave circuits. One approach to accelerating the design process is to use a circuit simulator where the microstrip discontinuities are modeled as lumped elements. However, such a network-theory-type of simulator produces accurate results only at low frequencies, and their accuracy degrades rapidly as the operating frequency is increased to the point where the parasitic coupling effects cannot be neglected. One of the most widely employed full-wave algorithms is the Method of Moments (MoM). Though numerically rigorous and accurate, the MoM requires memory and Central Processing Unit (CPU) resources that are orders of magnitude greater than those associated with conventional circuit simulators. Recently, the Characteristic Basis Function Method (CBFM) has been successfully applied for the analysis of Monolithic Microwave Integrate Circuits (MMICs) and antennas etched on layered media. In the original version of this method, the analyzed geometry is decomposed into smaller regions, called blocks, for which high-level basis functions, the Characteristic Basis Functions (CBFs), are generated. Typically, two types of CBFs are calculated, the Primaries (PCBFs) and the Secondaries (SCBFs). The generation of the PCBFs is started by defining appropriate interfaces, i.e., inner ports, between adjacent blocks and considering each section in isolation. To generate accurate results by using the conventional CBFM, it is important to ensure that the inner ports (see Fig. 1) be defined at locations where the effect of the higher-order modes is negligible and the current distribution can be expressed as a linear combination of a forward and a reflected wave. We have developed a new algorithm for an efficient generation of the Primary CBFs which enables us to generalize the decomposition procedure. The partition scheme is user-independent, and allows the interface locations to be arbitrary (see Fig. 1).

summary form only given. In designing frequency selective surfaces (FSS), one of the desirable design goals is to achieve a wide bandwidth, as well as a sharp transition from pass- to stop-band. There are several techniques used to control the FSS bandwidth, which include: (i) choosing suitable lattice spacing; (ii) using element shapes that provide a sharp frequency transition, e.g., screens with thick apertures; and (iii) cascading multiple layers of FSS screens and dielectrics.

Sub-wavelength imaging, aka Superlensing, is the so-called “holy grail” of imaging, which has been extensively researched by many investigators, who have attempted to achieve it by using Metamaterials—specifically double negative (DNG) materials—Transformation Optics (TO)-based designs, Phase Conjugation(PC), and a number of other techniques. Unfortunately, however, the success to-date in this enterprise has been rather limited, and the search for achieving super-resolution still continues unabated.

In this chapter, we present a numerically efficient and accurate technique for the analysis of doubly-infinite periodic arrays, which find applications as Frequency Selective Surfaces (FSSs), Electronic Bandgap (EBGs) structures, plasmonic sensors at optical wavelength and Metamaterials (MTMs), all of which often utilize periodic elements. The method derives its efficiency by deriving, via extrapolation, the solution to the infinite array problem from that of a corresponding truncated array of relatively small size, typically comprising of only four to six concentric rings surrounding the center element. Furthermore, it reduces the matrix size needed to solve for the induced current to only two or three.

In this chapter, we present a technique for efficient derivation of the Method of Moments (MoM) matrix elements arising in radiation and scattering problems. The proposed method is designed to overcome some of the limits of the conventional MoM formulation, and it aims to provide a robust as well as efficient MoM-based approach. The chapter will begin by introducing a formulation based on the use of Dipole Moment (DM)-type of basis functions, and goes on to present the closed-form expressions for the fields radiated by the employed basis functions.

The paper presents an efficient and accurate technique for the analysis of large, finite and conformal Frequency Selective Surfaces (FSSs) which are not amenable to analysis by using conventional methods. The proposed technique is based on the Characteristic Basis Functions (CBFs) to describe the currents induced on the FSS elements. The reaction integrals needed to derive the reduced matrix elements are either computed in the spatial or spectral domains depending on their separation distance, so as to make the process numerically efficient.

In this paper we introduce a universal Method of Moment (MoM)-based formulation, which overcomes some of the drawbacks of conventional frequency domain techniques. Formulating the problem in a way that bypasses the evaluation of the electric field as a summation of scalar and vector potential terms enables us to overcome the low-frequency breakdown when applied to the solution of the Surface Electric Field Integral Equation (S-EFIE). The direct evaluation of the electric fields reduces the impedance matrix fill time compared to the conventional MoM. The Equivalent Medium Approach (EMA) can be applied in conjunction with the proposed formulation for the solution of microstrip circuits embedded in stratified environments.

In this paper, we describe a three-dimensional frequency-selective surface (FSS) element that generates a flat bandpass response over a wide band, as well as controllable low-pass angular response. The unit cell, which consists of a waveguide element with two connected cascaded radiating elements, exhibits a flat bandpass response over the frequency range 13 GHz to 24 GHz, i.e. a −3dB bandwidth (BW/f 0 ) of 66.6%. We show that the angular response of the FSS can be controlled by changing its periodicity, which, in turn, determines the angle at which the first higher-order Floquet harmonic begins to propagate.

In this paper we present a new numerically efficient and accurate technique for the analysis of doubly-infinite periodic arrays of elements, which find applications as Frequency Selective Surfaces (FSSs), Electronic Bandgap (EBGs) structures and Metamaterials (MTMs). The principal advantages of the proposed method, which is not based on the use of the Periodic Boundary Condition (PBC), are its versatility—since it can analyze 3D inhomogeneous elements—and its ability to handle arbitrary incidence angles in an efficient way, regardless of how large that angle is. It is well known that the Finite Difference Time Domain (FDTD)/PBC runs into difficulties for wide angles—requiring large computation times and becoming unstable for such angles.

In this paper we present a comparative study of flat and profiled lenses designed to operate in the GHz frequency range. Special attention is paid to focusing capabilities and bandwidth performance. Our results indicate that compared to the profiled lens, the flat lens with varying material parameters delivers a better performance in terms of scan capability and bandwidth.

In this paper we describe a novel technique for analyzing periodic structures that bypasses the use of the periodic boundary condition (PBC), and thus circumvents the slowness problem encountered in the construction of the periodic Green's function when using the Method of Moments (MoM), and the instability problem arising in the Finite Difference Time Domain (FDTD) analysis for wide angles of incidence. The basic strategy followed in the proposed approach is to generate the desired solution of the periodic problem by first analyzing a truncated version of the same, and then predicting the asymptotic limit of the solution of the truncated problem by using an efficient extrapolation technique that needs to work with only a moderate-size truncated structure to generate the desired solution of the doubly-infinite periodic configuration.

In this paper we present a new de-embedding algorithm for an efficient evaluation of the S-parameter for printed microwave circuits or antennas. The proposed technique is based on the Characteristic Basis Function Method (CBFM) with exponential type of Characteristic Basis Functions (CBFs) which can be exploited in order to mitigate the low frequency problems associated with the conventional de-embedding techniques. A numerical example that demonstrates the numerical accuracy and efficiency of the proposed method is included.

In this paper we present two numerically efficient and accurate techniques for the analysis of doubly-infinite periodic arrays, which find applications as Frequency Selective Surfaces (FSSs), Electronic Bandgap (EBGs) structures and Metamaterials (MTMs). The first method, suited for the analysis of periodic elements with fine features, processes the results of a truncated array, typically comprising of only four to six rings, to derive the response characteristics of its doubly-periodic infinite counterpart. The reduction of the matrix size to only two or three, combined with the use of Reciprocity Principle to compute the reflection and transmission coefficients of the array, leads to a considerable CPU time and memory saving. The second technique, which is formulated to address the analysis of arbitrary 3D periodic elements, utilizes a generalized version of the waveguide simulator (WGS) approach, which, in contrast to the conventional WGS approach, is designed to handle arbitrary angles of incidence.

In this paper, a novel technique for efficient electromagnetic simulation of microstrip circuits etched in layered media is presented. The proposed approach is useful for rapid prototyping of the desired circuit response and it uses closed-form expressions for the evaluation of the fields radiated by rooftop basis functions, applied in conjunction with an algorithm referred to herein as the Equivalent Medium Approach. Illustrative examples demostrating the reliability and the efficiency of the described procedures are included.

In this paper, a novel MoM-based procedure is developed for efficient treatment of scattering problems over a wide frequency band, including very low frequencies where many of the conventional algorithms often fail. The proposed approach, based on closed-form expressions for the evaluation of the fields radiated by rooftop basis functions, is demonstrated to be universally applicable to conducting and dielectric objects without having to address the singularity issues associated with the conventional MoM approach. Furthermore, an equivalent rooftop type of basis function is introduced for handling curved surfaces. Illustrative examples demostrating the reliability and the efficiency of the described procedures are included.

The production of mitotic spindle disturbances and activation of the apoptosis pathway in V79 Chinese hamster cells by continuous 2.45 GHz microwaves exposure were studied, in order to investigate possible non-thermal cell damage. We demonstrated that microwave (MW) exposure at the water resonance frequency was able to induce alteration of the mitotic apparatus and apoptosis as a function of the applied power densities (5 and 10mW/cm(2)), together with a moderate reduction in the rate of cell division. After an exposure time of 15 min the proportion of aberrant spindles and of apoptotic cells was significantly increased, while the mitotic index decreased as well, as compared to the untreated V79 cells. Additionally, in order to understand if the observed effects were due to RF exposure per se or to a thermal effect, V79 cells were also treated in thermostatic bath mimicking the same temperature increase recorded during microwave emission. The effect of temperature on the correct assembly of mitotic spindles was negligible up to 41°C, while apoptosis was induced only when the medium temperature achieved 40°C, thus exceeding the maximum value registered during MW exposure. We hypothesise that short-time MW exposures at the water resonance frequency cause, in V79 cells, reversible alterations of the mitotic spindle, this representing, in turn, a pro-apoptotic signal for the cell line.

The Method of Moments (MoM) is the most commonly used technique for solving the Electric Field Integral Equation (EFIE) formulated for problems involving electromagnetic scattering from metallic objects. This formulation entails the expansion of the unknown current on the surface of the scatterer in terms of known basis functions [1, 2]. A key issue in the MoM solution is the evaluation of the singular integrals, which can be performed both by numerical and semi-analytical techniques [3]. A commonly used approach is to apply the singularity-extraction techniques, which is based upon subtracting the singular terms from the kernel and integrating them analytically. In this work, we propose a new method for the above field calculation, which utilizes the analytical expression for the near fields radiated by an electrically small dipole. The proposed method is found to be well suited for mitigating the problem of singularities encountered in the process of field computation while constructing the MoM matrix.

While the formulation of integral equations via the use of Green's functions is a well-established technique [1–3], it has been recognized that this formulation suffers from certain deficiencies. Some of these include low-frequency breakdown; need for special treatment of singularities of the E-field representation in terms of the Green's function; lack of a universal formulation for handling PEC and dielectric structures; and, difficulty with accurate treatment of fine features such as thin wires and surfaces, especially those with finite losses. The paper will begin by introducing the Dipole-Moment (DM) approach, and its application to the solution of the scattering from dielectric-coated structures. The Characteristic Basis Function Method (CBFM) will by applied over the DMA to accelerate the solution.

In order to investigate possible effects on cultured cells of Electromagnetic (EM) fields in the frequency range typical of mobile communications, a large variety of in vitro exposure systems have been designed and numerically characterized. Important requirements for in vitro experiments comprise a high homogeneity of the Specific Absorption Rate (SAR) distribution [1] and the possibility of performing experiments at SAR levels in the range of the actual safety standards of 2 W/kg [2] to achieve a low temperature rise in the cell monolayers. In this paper, a numerical dosimetric analysis has been carried out through CST Microwave Studio® 2009. The homogeneity of the SAR distribution and the coupling of EM fields within the liquid in the presence of a glass slide as support for living cells, has been investigated as a function of the incident field polarization.

There exists a great need to develop numerical techniques for efficient solution of multiscale electromagnetic problems, regardless of the computational electromagnetics (CEM) method currently being used to tackle them, be it FEM, FDTD or MoM. Dealing with multiscale objects, which have features that are both small and large compared to the wavelength, is highly challenging and often forces us to compromise the accuracy (relaxing the numerical discretization process when attempting to capture the small-scale features) in order to cope with the limited available resources in terms of CPU memory and time. In this paper, we introduce a new scheme that combines the Recursive Update Frequency Domain (RUFD) method with the Dipole Moment (DM) method, to solve multiscale problems in a numerically efficient manner.

Although thermal effects of Radio Frequency (RF) electromagnetic fields on biological tissue are well established in the literature, any possible non-thermal effects are currently being investigated. In-vitro exposure in conjunction with an accurate numerical modeling can be used in determining whether this effects exist and to establish a dose response curve. We would require such exposure to produce a uniform Specific Absorption Rate (SAR) throughout the sample, to avoid artifacts due to thermal hot-spots and to provide accurate dosimetry. The in-vitro uniformity exposure of blood tissue in the far field region of a horn antenna has been numerically investigated employing a FDTD code. The electric field distribution in a cylindrical test tube has been derived, furthermore the biological material has been exposed among two metal parallel plates to improve SAR uniformity. Further modifications, as the introduction of a polypropylene septum at its interior have been analyzed.

Results of in vitro studies on EM field risks provide the most convincing evidence of direct RF exposure effects on biological cells, even if the mechanisms for such effects remain uncertain [1-2-3].

This paper shows the importance of using realistic cell shapes with the proper geometry and orientation to study the mechanism of direct cellular effects from RF exposure. For this purpose, the electric field distribution is computed, using the FDTD technique, in realistic cell models exposed to a linearly polarized plane wave of frequencies 900 MHz and 2.45 GHz. Furthermore, an insight on the mutual interactions between erythrocyte cell models shows that polarizing effects significantly affect the values of field intensity within the cell.

A frequency selective surface with a new type of three-dimensional element which produces a quasi-elliptic bandpass response is presented. The element exhibits an elliptic bandpass response with a −3 dB bandwidth (BW/f 0) of ∼ 70%, where f 0 is the centre frequency. The design has been adapted to a form that can be conveniently fabricated by utilising printed technology. The measured results for the frequency response show good agreement with those predicted via numerical simulations.

In this study the authors present a novel technique in the context of the characteristic basis function method (CBFM) for the efficient analysis of microstrip circuits and antennas printed on layered media. The proposed approach, defined herein as spectral domain CBFM (SP-CBFM), improves the CBFM performance by providing a fast and accurate method to reduce the total computational time required to generate the reduced matrix. Numerical examples are presented to demonstrate the reliability and the efficiency of the described procedure in terms of accuracy and time saving.

An efficient technique for the analysis of microwave circuits and antennas etched on a layered medium is presented. The proposed method, based on the recently introduced equivalent medium approach, yields accurate results and yet reduces computational time in comparison with the conventional method of moments algorithm. A numerical example which demonstrates the accuracy and numerical efficiency of the proposed technique is included.

A method of moments (MoM)-based procedure is developed for efficient treatment of scattering problems over a wide frequency band where many of the conventional algorithms often fail. The proposed method uses a type of basis function whose radiated field is expressible in a convenient closed-form. This, in turn, circumvents the need to either employ the Green's function to formulate the problem, or having to deal with the singularities of the same. Furthermore, since the formulation deals with the electric fields generated by the basis functions directly, without involving the vector and scalar potentials typically employed in the conventional MoM formulation, it is possible to use a uniform formulation over a much wider frequency range without having to resort to special basis functions, for example, the loop-stars. Numerical results validating the accuracy and the numerical efficiency of the proposed method both in the near- and in the far-field regions are included in this study.

In this letter, we present a technique for an efficient evaluation of the reduced matrix in the context of the characteristic basis function method (CBFM) for the simulation of microstrip circuits printed on layered media. The underlying concept is to evaluate the off-diagonal terms of the reduced matrix, which vary much less rapidly then the diagonal ones, in the spectral domain, while the self-interactions are computed in the conventional way. Numerical examples are presented to demonstrate that the fill-time of the reduced matrix is reduced by working in the spectral domain, as compared to the spatial domain evaluation in the conventional CBFM, while maintaining the computational accuracy of the results. Furthermore, the efficiency of the present approach increases rapidly as the number of unknowns in each block is increased .