T.K. Sarkar

Bio: T.K. Sarkar is an academic researcher. The author has contributed to research in topics: Matrix (mathematics) & Radiation pattern. The author has an hindex of 1, co-authored 1 publications receiving 234 citations.

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

Abstract: 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. >

Near-field to near/far-field transformation for arbitrary near-field geometry utilizing an equivalent electric current and MoM

Abstract: Presented here is a method for computing near- and far-field patterns of an antenna from its near-field measurements taken over an arbitrarily shaped geometry. This method utilizes near-field data to determine an equivalent electric current source over a fictitious surface which encompasses the antenna. This electric current, once determined, can be used to ascertain the near and the far field. This method demonstrates the concept of analytic continuity, i.e., once the value of the electric field is known for one region in space, from a theoretical perspective, its value for any other region can be extrapolated. It is shown that the equivalent electric current produces the correct fields in the regions in front of the antenna regardless of the geometry over which the near-field measurements are made. In this approach, the measured data need not satisfy the Nyquist sampling criteria. An electric field integral equation is developed to relate the near field to the equivalent electric current. A moment method procedure is employed to solve the integral equation by transforming it into a matrix equation. A least-squares solution via singular value decomposition is used to solve the matrix equation. Computations with both synthetic and experimental data, where the near field of several antenna configurations are measured over various geometrical surfaces, illustrate the accuracy of this method.

Reconstruction of Equivalent Currents Distribution Over Arbitrary Three-Dimensional Surfaces Based on Integral Equation Algorithms

Abstract: A technique for the determination of the equivalent currents distribution from a known radiated field is described. This Inverse Radiation Problem is solved through an Integral Equation algorithm that allows the characterization of antennas of complex geometry both for near field to far field (NF-FF) transformation purposes as well as for diagnostic tasks. The algorithm is based on the representation of the radiating structure by means of a set of equivalent currents over a three-dimensional (3D) surface that can be fitted to the arbitrary geometry of the antenna. The innovative formulation uses an integral equation involving the electric field due to the currents tangential components to the represented antenna 3D surface. For that purpose, both the magnetic and electric equivalent currents are considered in the integral equations. Regularization techniques are also introduced to improve the convergence of the proposed iterative solution. The paper concludes with several results related to the practical verification of the Equivalence Principle and the characterization of a horn antenna.

Modeling Magnetic Radiations of Electronic Circuits Using Near-Field Scanning Method

Abstract: In this paper, a simple method to obtain the equivalent radiation emitting sources of an electronic circuit using the near-field scanning method is presented. The model is based on a set of elemental dipoles that substitutes the electronic circuit and radiates the same magnetic field. Two different approaches are presented: a set of electric dipoles and a set of magnetic dipoles. In order to build the model, both the magnitude and phase of the magnetic field are required. These measurements are carried out using the "near-field scanning method," and two procedures are presented: using the vector network analyzer and the spectrum analyzer. Finally, the model is applied to two different cases: to obtain the radiated near-field of a component (microcontroller) and to obtain the field of a complete electronic board.

Field And Source Equivalence In Source Reconstruction On 3D Surfaces

Abstract: This paper describes in detail difierent formulations of the inverse-source problem, whereby equivalent sources and/or flelds are to be computed on an arbitrary 3-D closed surface from the knowledge of complex vector electric fleld data at a specifled (exterior) surface. The starting point is the analysis of the formulation in terms of the Equivalence Principle, of the possible choices for the internal flelds, and of their practical impact. Love's (zero interior fleld) equivalence is the only equivalence form that yields currents directly related to the flelds on the reconstruction surface; its enforcement results in a pair of coupled integral equations. Formulations resulting in a single integral equation are also analyzed. The flrst is the single-equation, two-current formulation which is most common in current literature, in which no interior fleld condition is enforced. The single-current (electric or magnetic) formulation deriving from continuity enforcement of one fleld is also introduced and analyzed. Single-equation formulations result in a simpler implementation and a lower computational load than the dual-equation formulation, but numerical tests with synthetic data support the beneflts of the latter. The spectrum of the involved (discretized) operators clearly shows a relation with the theoretical Degrees of Freedom (DoF) of the measured fleld for the dual-equation formulation that guarantees extraction of these DoF; this is absent in the single-equation formulation. Examples conflrm that single- equation formulations do not yield Love's currents, as observed both with comparison with reference data and via energetic considerations. The presentation is concluded with a test on measured data which shows the stability and usefulness of the dual-equation formulation in a situation of practical relevance.

Improved-Accuracy Source Reconstruction on Arbitrary 3-D Surfaces

Abstract: This paper presents a novel formulation of the source reconstruction problem on arbitrary three-dimensional (3-D) surfaces based on integral equations. Rigorous boundary integral field identities are employed to enforce that the two unknown currents are Maxwellian on the reconstruction surface; this leads to a dual integral-equation formulation, in contrast to the single-equation formulation found in literature. Numerical tests against reference currents allow a quantitative assessment of the improvements in accuracy afforded by the novel formulation, with important benefits in diagnostic applications.