Soumyabrata Chakrabarty

Removal of Beam Squinting Effects in a Circularly Polarized Offset Parabolic Reflector Antenna Using a Matched Feed

This paper presents the design of a tri-mode matched feed horn to remove the beam squinting effects in a circularly polarized offset parabolic reflector antenna. In a conical horn, three modes i.e., TE11, TM11 and TE21 are combined in proper amplitude and phase proportion to obtain a tri-mode matched feed configuration. The proposed tri-mode horn is then used as a primary feed device to illuminate the circularly polarized offset parabolic reflector antenna. The simulated data on radiation characteristics of the offset reflector are used to estimate the magnitude of beam squinting and the results are compared with that of a conventional potter horn fed offset reflector. The experimental results on secondary radiation pattern are also incorporated in the paper. Corresponding author: D. A. Pujara (dapujara@yahoo.com).

Multifrequency waveguide orthomode transducer

This paper presents the design and development of a multifrequency probe-coupled orthomode transducer (OMT) using a circular waveguide as the primary waveguide and a rectangular waveguide as the secondary waveguide. Design is presented for a common OMT operating at 6.6, 10.65, 18, and 21 GHz using four cascaded circular waveguide sections with different cross-sectional dimensions. An innovative design technique is used to minimize the inter-port coupling and to maximize the power in the dominant mode to get the required radiation performance at all the frequency bands using a common radiating aperture. The simulated and measured parameters of the OMT and the horn fed by this OMT have been presented.

Electrostatic Analysis of an Artificial Orbiting Satellite for Absolute Charging

This paper presents the evaluation of a capacitance matrix and the temporal body potential of an artificial orbiting satellite considering a metallic cuboid, parabolic reflector antennas, and solar panels. Integral equations are formed by relating the unknown charge density on the metallic conductor and are solved using the method of moments, in which the pulse functions are used as basis functions and the delta functions are used as testing functions. The surfaces of the conducting structure are meshed using nonuniform triangular subareas. The matrix equations are solved using an iterative generalized minimum residual algorithm. The numerical data on the capacitance matrix and the charge distribution of these structures have been presented. The validity of this analysis has been established by comparing the data on capacitance available in the literature for the metallic cuboid with the data on capacitance computed by the present method for similar structures. The temporal behavior of body potential of the satellite is computed for different cases.

Investigation of Different Basis and Testing Functions in Method of Moments for Electrostatic Problems

This paper presents comparative studies on difierent types of basis and testing functions used in Method of Moments (MoM) in terms of analytical complexity, convergence and condition number of the co-e-cient matrix when applied to electrostatic problem of evaluating capacitance and charge distribution of conducting bodies. A thin conducting cylinder of flnite length has been taken as a representative case study to evaluate the capacitance and charge distribution. The basis and testing functions which have been studied for this problem are pulse-delta, pulse-pulse, triangular- delta, triangular-pulse and triangular-triangular functions respectively. Numerical data on capacitance and charge distribution has been presented for each set of basis and testing functions in terms of condition number and convergence.

Analysis of a Post Discontinuity in an Oversized Circular Waveguide

This paper presents the analysis of scattering characteristics of a radially directed thin post in a circular waveguide using the method of moments. Electric type dyadic Greens function has been used to compute the scattered field in a circular waveguide considering variation of current only in the axial direction of the post. Simulated data on return loss and power coupling in the dominant mode and higher order modes have been compared with the data computed using Ansofts High Frequency Structure Simulator. The data on return loss and coupling for the incident TE11 mode have been compared with experimental data.

Improving the Beam Efficiency of an Offset Parabolic Reflector Antenna for Spaceborne Radiometric Applications

This paper presents a novel technique to improve the cross- polarization and the beam e-ciency of an ofiset parabolic re∞ector antenna used for space borne radiometric applications. A special multi-mode primary feed (tri-mode conjugate matched feed) is used to illuminate the ofiset parabolic re∞ector antenna. The simulated data on the radiation characteristics of the ofiset parabolic re∞ector antenna with a matched feed has been compared with that of a conventional Potter horn. It is observed that the tri-mode feed suppress the unwanted high cross-polarization of an ofiset re∞ector antenna and improves the beam e-ciency.

EFFECT OF SOLAR ILLUMINATION ON ESD FOR STRUCTURE USED IN SPACECRAFT

This paper presents the effect of solar illumination on the differential potential generated on the surfaces of spacecraft body in space. Two geometrical cases are considered: 1) Cylindrical symmetry and 2) Tilted metallic plates forming an angle with the adjacent side. The capacitance required for estimation of the body potential is computed by Method of Moment. Nonuniform triangular meshing is used for both the geometrical structures. The differential potential generated on surfaces of a geometrical body due to photoelectric effect results in electrostatic discharge. In the case of the tilted plates, the differential potential at various tilt-angles is computed along with the capacitance computation. In the case of the cylindrical object, the estimation of potential at the day-night interface is shown. The variation in the potential for different incident angles of the solar photons and the changing (h/r) ratio is analyzed. The validity of the analysis is established with that obtained in open literature.

Computation of Capacitance Matrix of Orbiting Spacecraft Bodies

ABSTRACT This paper presents the method of moments (MoM)-based analysis for the computation of capacitance matrix and charge distribution of a three-dimensional spacecraft body. The integral equations which are formed by relating the unknown charge density on the satellite body represented by metallic cuboid and solar panel consisting of two rectangular plates to the potential on the surface of these bodies are solved using MoM. In order to apply the MoM, the surfaces of the metallic bodies are discretized using non-uniform triangular subsections. The numerical data on the capacitance and charge distribution of this structure are presented. The validity of this analysis has been established by comparing the data on capacitance available in the literature for metallic cuboid with metallic plates with the data on capacitance computed by the present method for similar structures.

Absolute charging analysis of space-craft bodies using method of moments (MoM)

Absolute charging analysis of space-craft bodies using MoM has been presented. Integral equations are formed by relating the unknown charge density on the metallic conductor. Pulse functions are used as basis functions and the delta functions are used as testing functions. The surfaces of the conducting structure are meshed using non-uniform triangular sub-areas. The matrix equations are solved by using iterative algorithm. The numerical data on the capacitance matrix and charge distribution of these structures have been presented. The temporal behavior of body potential of the satellite is computed.

Electrostatic Modeling of Coupled Metallic Bodies in the Shape of a Funnel

Abstract This article presents the evaluation of capacitance of two coupled metallic funnels. Two cases have been considered: (1) two skewed funnels and (2) two coaxial funnels. Integral equations are formed by relating the unknown charge density on the cylinders to the corresponding potential on the conductors. The integral equations are solved using the method of moments using pulse functions as basis functions and delta functions as testing functions. The numerical data on capacitance for both configurations have been presented. The validity of the analysis has been presented by comparison of data presented on capacitance considering a case study published in open literature.