Peter Petre

Planar near-field to far-field transformation using an equivalent magnetic current approach

An alternative method is presented for computing far-field antenna patterns from near-field measurements. The method utilizes the near-field data to determine equivalent magnetic current sources over a fictitious planar surface that encompasses the antenna, and these currents are used to ascertain the far fields. Under certain approximations, the currents should produce the correct far fields in all regions in front of the antenna regardless of the geometry over which the near-field measurements are made. An electric field integral equation (EFIE) is developed to relate the near fields to the equivalent magnetic currents. The method of moments is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient method, and in the case of a rectangular matrix, a least-squares solution for the currents is found without explicitly computing the normal form of the equation. Near-field to far-field transformation for planar scanning may be efficiently performed under certain conditions. Numerical results are presented for several antenna configurations. >

Planar near-field to far-field transformation using an array of dipole probes

A method is presented for computing far-field antenna patterns from measured near-field data measured by an array of planar dipole probes. The method utilizes the near-field data to determine some equivalent magnetic current sources over a fictitious planar surface which encompasses the antenna. These currents are then used to find the far fields. The near-field measurement is carried out by terminating each dipole with 50 /spl Omega/ load impedances and measuring the complex voltages across the loads. An electric field integral equation (EFIE) is developed to relate the measured complex voltages to the equivalent magnetic currents. The mutual coupling between the array of probes and the test antenna modeled by magnetic dipoles is taken into account. The method of moments with Galerkins type solution procedure is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient-fast Fourier transformation (CG-FFT) method exploiting the block Toeplitz structure of the matrix. Numerical results are presented for several antenna configurations to show the validity of the method. >

Integral equation solution for analyzing scattering from one-dimensional periodic coated strips

A set of integral equations based on the surface/surface formulation are developed for analyzing electromagnetic scattering by one-dimensional periodic structures. To compare the accuracy, efficiency, and robustness of the formulation, the electric field integral equation (EFIE), magnetic field integral equation (MFIE), and combined field integral equation (CFIE) are developed for analyzing the same structure for different excitations. Due to the periodicity of the structure, the integral equations are formulated in the spectral domain using the Fourier transform of the integrodifferential operators. The generalized-biconjugate-gradient-fast Fourier transform method with subdomain basis functions is used to solve the matrix equation. >

Near-field to far-field transformation using an equivalent current approach

The equivalent current approach for computing far-fields from measured near fields is presented. In this technique, the radiating antenna is replaced by equivalent currents which reside on a fictitious surface which encompasses the antenna. The measured near-fields are used to determine the equivalent currents. Accurate far-fields over large elevation and azimuthal ranges can be found from measurements on simple surfaces, such as a plane. Numerical results are presented.<<ETX>>

A planar near-field to far-field transformation using an equivalent magnetic current approach

A method is presented for computing far-field antenna patterns from near-field measurements. The method utilizes near-field data to determine equivalent magnetic current sources over a fictitious planar surface which encompasses the antenna, and these currents are used to ascertain the farfields. An electric field integral equation is developed to relate the near fields to the equivalent magnetic currents. A method of moments procedure is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient method (CGM), and, in the case of a rectangular matrix, a least-squares solution for the currents is found without explicitly computing the normal form of the equation. Near-field to far-field transformation for planar scanning may be efficiently performed under certain conditions by exploiting the block Toeplitz structure of the matrix and using CGM and the fast Fourier-transform (CGFFT), thereby drastically reducing computation and storage requirements. Numerical results are presented by extrapolating the far fields using experimental near-field data.<<ETX>>

Volume/surface formulation for analyzing scattering from coated periodic strips

A surface/surface formulation was used by Perte et al. (see IEEE Trans. Antennas. Propagat.) to analyze the scattering from periodic planar coated strips. This paper is an extension of that work where a combined volume/surface formulation has been used to solve the same problem. This formulation can be applied to problems which involve an inhomogeneous dielectric medium or/and a thick dielectric which requires the inclusion of the edge currents which were neglected as a simplification. Results obtained using the volume/surface formulation have been compared with the results published in the paper written by Petre et al. which were obtained using a surface/surface formulation. >

Spectral domain technique using surface wave excitation for the analysis of interconnects

Analysis of interconnects is an area of prime importance in packaging since the characteristics of the interconnections eventually dictate the performance of the package. The analysis consists of two parts, namely, parameter extraction and package simulation where the former represents the computation of the line parameters such as resistance, inductance, capacitance, and conductance (R, L, C, G). At high frequencies, the line parameters vary with frequency which requires a complete solution to Maxwells equation for parameter extraction. This translates to the computation of the propagation constant as a function of frequency /spl beta/(/spl omega/) which is the focus of the work in this paper. Since packages typically consist of periodic structures, the spectral domain technique (SDT) lends itself to easy analysis and has therefore been used in this paper. A new method utilizing the surface wave excitation principle applied to the scattering problem has been used to compute /spl beta/(/spl omega/) which is different from the eigenvalue solution that has been used in the past. Using the present formulation, a single algorithm can be used both for the computation of wave propagation and scattering/radiation by changing the angle of the incident wave. >

Analysis of waveguides based on a surface integral formulation

An important constituent of any integrated circuit is the interconnections that carry the electrical signals between devices making up the circuit. At high frequencies, there is signal degradation due to skin effect and all the waveguide parameters are functions of the frequency at which the structure is operated. A time-harmonic analysis based on a complete solution to Maxwells equations is therefore necessary for waveguide analysis and characterization. A novel, simple, and efficient technique based on the surface equivalence principle is presented for computing and predicting the wave behavior. Both closed and open waveguides can be analyzed using the proposed formulation.<<ETX>>

Electromagnetic Scattering from Infinite Strip Grating with Inhomogeneous Material Coating using a Combined Surface and Volume Integral Equation Formulation

A combined-field integral equation is developed to analyse electromagnetic scattering from planar flat strip and infinite periodically located strip grating with homogeneous and/or inhomogeneous material coating. The equivalence principle is used to replace all conducting strips by equivalent surface electric currents and all dielectric coatings by equivalent volume electric and magnetic polarization currents. Utilizing the respective boundary conditions, an operator equation containing both volume and surface currents is constructed in the spectral domain and solved by the generalized BiConjugate Gradient (BiCG)-FFT method. Numerical results are presented for various geometries for both (transverse electric and transverse magnetic ) polarizations as well.

Theoretical Comparison of Modal Expansion and Integral Equation Methods for Near-Field to Far-Field Transformation

-STRICT A theoretical comparison for the application and derivation of modal expansion and integral equation methods is presented. It is shown that one formulation can be transformed into the other one using Fourier transform. From this point of view it can be stated that both method solves the same integral equation but for the modal expansion approach the integral equation is solved in the spectral domain while for the integral equation method the same equation is solved in the space domain. It is shown that for most of the practical antenna types the integral equation method gives more accurate far-field estimation than the modal expansion method, particularly in the planar scanning case. -ION Near-field antenna measurements have become widely used in antenna testing since they allow for accurate measurements of antenna patterns in a controlled environment. The earliest works based on the modal expansion method in which the fields radiated by the test antenna are expanded in terms of planar, cylindrical or spherical wave functions and the measured nearfields are used to determine the coefficients of the wave functions [l-31. The primary drawback of the modal expansion technique is that when Fourier transfonn is used, the fields outside the measurement region are assumed to be zero. Consequently the far-fields are accurately determined only over a particular angular sector which is dependent on the measurement configuration 143. The equivalent current approach which represents an alternate method of computing far-fields from measured near-fields has been recently explored t5-81. Thio method utilizes near-f ield data to determine equivalent electric, magnetic or both electric and magnetic current sources I over a fictitious planar surface which encompasses the aperture of the antenna. These currents are used to ascertain the far-fields. Under certain approximations the currents produce the correct f ar-f ields in all regions in front of the antenna regardless of the geometry over which the near-field measurements are made. In this paper it is shown that the formulation derived from the modal expansion method can be transformed into the formulation derived from the integral equation approach using twodimensional Fourier transform. The basic relationship between the plane wave representation and the integral representation, as an integral over the current distribution, of the fields is known [91. However a detailed comparison for the derivation and application of both method did not appear until now. The purpose of this paper is to clarify the limitation and validation for both method when they are applied for near-field to far-field transformation.