B.P. Kumar

Bio: B.P. Kumar is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Antenna aperture & Radiation pattern. The author has an hindex of 1, co-authored 1 publications receiving 16 citations.

A technique of synthesizing the excitation currents of planar arrays or apertures

Abstract: A technique of synthesizing or reconstructing the excitation currents of a planar array of aperture-type antennas from the known near-field patterns of the radiating source is presented. This technique uses an exact solution to the fields radiated by the aperture antenna without disregarding the source currents. Typical numerical computations have been carried out to validate the analytical technique developed. Sensitivity and stability of the numerical computations performed have been studied. The available iterative bandlimited signal extrapolation technique is used to reconstruct the aperture excitation currents only if the far-field patterns of the radiating source are known. Far-field patterns of aperture antennas measured in the laboratory were also used to reconstruct the aperture electric field distribution in the principal plane. >

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.

Reduction of Truncation Errors in Planar Near-Field Aperture Antenna Measurements Using the Gerchberg-Papoulis Algorithm

Abstract: A simple and effective procedure for the reduction of truncation errors in planar near-field measurements of aperture antennas is presented. The procedure relies on the consideration that, due to the scan plane truncation, the calculated plane wave spectrum of the field radiated by the antenna is reliable only within a certain portion of the visible region. Accordingly, the truncation error is reduced by extrapolating the remaining portion of the visible region by the Gerchberg-Papoulis iterative algorithm, exploiting a condition of spatial concentration of the fields on the antenna aperture plane. The proposed procedure is simple and computationally efficient; it does not require any modification of the measurement procedure and it allows for the usual probe correction. Far-field patterns reconstructed from both simulated and measured truncated near-field data demonstrate its effectiveness and stability against measurement inaccuracies.

Design, simulation and experimental study of near-field beam forming techniques using conformal waveguide arrays

Abstract: Microwave hyperthermia is rapidly evolving as a fourth modality in the fight against cancer, along with surgery, radiation and chemotherapy. This form of cancer treatment utilises a narrow microwave beam to heat the tumour volume to a temperature of ∼42°C; however, with minimal energy delivery to neighbouring healthy tissue, which is one of the main challenges in hyperthermia technology. Potentially, this application can be achieved by using a phased array of apertures or dipoles to generate and control the beam focus within the near-field treatment region. This paper describes another approach to near-field beam forming by using of a conformal waveguide array, operating in the K band (18–26 GHz). The array comprises a central movable element that acts as the focusing element, and surrounding fixed directing elements. The focusing element gives conformal property to the array and serves two purposes: firstly to obtain a sharp focus at a prescribed near-field location, and secondly the added flexibility to move the beam around the tumour. Several simulations and measurements have been performed on linear and planar configurations, which demonstrate the ability of the array to achieve beam widths as small as∼4 mm, with a maximum beam movement range of ∼15 mm.

Reduction of truncation errors in planar near-field aperture antenna measurements using the method of alternating orthogonal projections

Abstract: A simple and effective procedure for the reduction of truncation error in planar near-field to far-field transformations is presented. The starting point is the consideration that the actual scan plane truncation implies a reliability of the reconstructed plane wave spectrum of the field radiated by the antenna only within a certain region inside the visible range. Then, the truncation error is reduced by a Maxwellian continuation of the reliable portion of the spectrum: after back propagating the measured field to the antenna plane, a condition of spatial concentration of the primary field is exploited to define a convergent iterative process which is also stable against moderately noisy data. Far-field patterns reconstructed from both simulated and measured near-field data demonstrate the effectiveness of the proposed procedure.