G. Dural

Closed-form Green's functions for general sources and stratified media

The closed-form Greens functions of the vector and scalar potentials in the spatial domain are presented for the sources of horizontal electric, magnetic, and vertical electric, magnetic dipoles embedded in general, multilayer, planar media. First, the spectral domain Greens functions in an arbitrary layer are derived analytically from the Greens functions in the source layer by using a recursive algorithm. Then, the spatial domain Greens functions are obtained by adding the contributions of the direct terms, surface waves, and complex images approximated by the Generalized Pencil of Functions Method (GPOF). In the derivations, the main emphasis is to put these closed-form representations in a suitable form for the solution of the mixed potential integral equation (MPIE) by the method of moments in a general three-dimensional geometry. The contributions of this paper are: 1) providing the complete set of closed-form Greens functions in spectral and spatial domains for general stratified media; 2) using the GPOF method, which is more robust and less noise sensitive, in the derivation of the closed-form spatial domain Greens functions; and 3) casting the closed-form Greens functions in a form to provide efficient applications of the method of moments. >

Clarification of issues on the closed-form Green's functions in stratified media

The closed-form Greens functions (CFGF), derived for the vector and scalar potentials in planar multilayer media, have been revisited to clarify some issues and misunderstandings on the derivation of these Greens functions. In addition, the range of validity of these Greens functions is assessed with and without explicit evaluation of the surface wave contributions. As it is well-known, the derivation of the CFGF begins with the approximation of the spectral-domain Greens functions by complex exponentials, and continues with applying the Sommerfeld identity to cast these approximated spectral-domain Greens functions into the space domain in closed forms. Questions and misunderstandings of this derivation, which have mainly originated from the approximation process of the spectral-domain Greens functions in terms of complex exponentials, can be categorized and discussed under the topics of: 1) branch-point contributions; 2) surface wave pole contributions; and 3) the accuracy of the obtained CFGF. When these issues are clarified, the region of validity of the CFGF so obtained may be defined better. Therefore, in this paper, these issues will be addressed first, and then their origins and possible remedies will be provided with solid analysis and numerical demonstrations.

Closed-form Green's functions for cylindrically stratified media

A numerically efficient technique is developed to obtain the spatial-domain closed-form Greens functions of the electric and magnetic fields due to z- and /spl phi/-oriented electric and magnetic sources embedded in an arbitrary layer of a cylindrical stratified medium. First, the electric- and magnetic-field components representing the coupled TM and TE modes are derived in the spectral domain for an arbitrary observation layer. The spectral-domain Greens functions are then obtained and approximated in terms of complex exponentials in two consecutive steps by using the generalized pencil of function method. For the Greens functions approximated in the first step, the large argument behavior of the zeroth-order Hankel functions is used for the transformation into the spatial domain with the use of the Sommerfeld identity. In the second step, the remaining part of the Greens functions are approximated on two complementary parts of a proposed deformed path and transformed into the spatial domain, analytically. The results obtained in the two consecutive steps are combined to yield the spatial-domain Greens functions in closed forms.

A new neural network approach to the target tracking problem with smart structure

The algorithm presented in this paper, namely the modified neural multiple source tracking algorithm (MN-MUST) is the modified form of the recently published work, a NN algorithm, the neural multiple-source tracking (N-MUST) algorithm, was presented for locating and tracking angles of arrival from multiple sources. MN-MUST algorithm consists of three stages that are classified as the detection, filtering and DoA estimation stages. In the first stage a number of radial basis function neural networks (RBFNN) are trained for detection of the angular sectors which have source or sources. A spatial filter stage applied individually to the every angular sector which is classified in the first stage as having source or sources. Each individual spatial filter is designed to filter out the signals coming from all the other angular sectors outside the particular source detected angular sector. This stage considerably improves the performance of the algorithm in the case where more than one angular sector have source or sources at the same time. Insertion of this spatial filtering stage is the main contribution of this paper. The third stage consists of a neural network trained for DoA estimation. In all three stages neural networks size and the training data are considerably reduced as compared to the previous approach, without loss of accuracy

Comparative evaluation of absorbing boundary conditions using Green's functions for layered media

Absorbing boundary conditions are comparatively studied using the Greens functions of the vector and scalar potentials for multilayer geometries and general sources. Since the absorbing boundaries are introduced as additional layers with predefined reflection coefficients into the calculation of the Greens functions, this approach provides an absolute measure of the effectiveness of different absorbing boundaries. The Greens functions are calculated using different reflection coefficients corresponding to different absorbing boundaries and compared to those obtained with no absorbing boundary. It is observed that the perfectly matched layer (PML) is by far the best among the other absorbing boundary conditions whose reflection coefficients are available.

Mutual Coupling of Printed Elements on a Cylindrically Layered Structure using Closed-Form Green's Functions

This paper examines the mutual coupling between two strips on a cylindrical multilayer medium using closed-form Greens function with method-of-moments (MoM). The computational efficiency of the evaluation of the matrix elements of MoM is significantly increased using our hybrid method when evaluating the matrix entries of MoM in a mutual coupling application on a cylindrical multilayer medium

Comments on the problems in DCIM

For the rigorous analysis of multilayer printed geometries, numerical algorithms based on the method of moments (MoM) are widely favored. The application of the MoM in either the spectral or the spatial domain, requires knowledge of the Greens functions in the corresponding domain. In the spatial domain, the Greens functions for stratified media are traditionally represented by the Sommerfeld integral. However, this representation of the Greens functions is not computationally efficient for use in conjunction with the MoM. To overcome this numerical inefficiency for obtaining the spatial-domain Greens functions, they have been approximated by complex images using the Sommerfeld identity; hence, the method is named the discrete complex image method (DCIM). As is the case for most approximations, the closed-form Greens functions have some limitations. Closed-form Greens functions are accurate for small and moderate distances, but for distances larger than a few wavelengths, they deteriorate violently. Three possible sources of this problem are discussed and misunderstandings are clarified.

A numerically efficient technique for the analysis of slots in multilayer media

A numerically efficient technique for the analysis of slot geometries in multilayer media is presented using closed-form Greens functions in spatial domain in conjunction with the method of moments (MoM). The slot is represented by an equivalent magnetic-current distribution, which is then used to determine the total power crossing through the slot and the input impedance. In order to calculate power and current distribution, spatial-domain closed-form Greens functions are expanded as power series of the radial distance /spl rho/, which makes the analytical evaluation of the spatial-domain integrals possible, saving a considerable amount of computation time.

A novel neural network method for direction of arrival estimation with uniform cylindrical 12-element microstrip patch array

In this study a new neural network algorithm is proposed for real time multiple source tracking problem with cylindrical patch antenna array based on a previously reported Modified Neural Multiple Source Tracking Algorithm(MN-MUST). The proposed algorithm, namely Cylindrical Microstrip Patch Array Modified Neural Multiple Source Tracking Algorithm (CMN-MUST) implements MN-MUST algorithm on a cylindrical microstrip patch array structure. CMN-MUST algorithm uses the advantage of directive pattern of microstrip patch elements by considering only a part of array elements for a chosen sector. This reduces neural network sizes and also improves the spatial filtering performance. The proposed algorithm improves MN-MUST algorithm in the sense of accuracy and speed while covering the full azimuth range. It is observed that the CMN-MUST algorithm provides an accurate and efficient solution to the target-tracking problem in real time.

Cavity model analysis of spherical-rectangular printed antennas by employing basic spherical vector transformation techniques

In this study, an analytical method is proposed for the derivation of radiation characteristics of spherical-rectangular printed antenna arrays without suffering from rectangular grid alignment. The far-field solutions obtained by the spherical cavity model are transformed with respect to the geometrical locations of each rectangular antenna on the conducting sphere. The transformations are realized by using the spherical vector rotation techniques. Then, the superposition of far-field solutions is implemented to obtain the total far-field pattern and the result is compared with pattern of the antenna array that conforms to the rectangular grid alignment.