Felix Madjitey

__________________________________________________________________________________________ Cassegrain Reflector Antenna Design consists of various effects caused by blockage and diffraction and its overall effect on performance. The design condition for minimum center blockage results in geometry that offers lower amount of blockage and increased spillover past the subreflector. An asymptotic theory of the proper secondary diffraction integral is presented with which the reduction in the aperture efficiency caused by center blockage and diffraction from a subreflector edge was evaluated for the 32-m dual-reflector antenna in Ghana, which is being converted from a communications ground station to fully operational radio telescope instrument. The approximate analytical efficiency formulae from this theory were derived, studied and simulated using MATLAB 7.10.0 based programme. These formulae showed that subreflector diffraction and center blockage may present a significant aperture ef...

A LabVIEW model to calculate the Half Power Beam Width of the Kutunse antenna was developed. The Kutunse antenna as part of the AVN under the SKA is to do VLBI, to study masers and to train Ghanaians in Astronomy. The model produced an easy-to-use approach in calculating the Half Power Beam Width over the operating frequency range of 5.0 to 6.7 GHz of the antenna. The results indicated an angular width of 0.002249091 radians at 5 GHz and 0.001679611 radians at 6.7 GHz. The sensitive angular width at 6.7 GHz suitable for studying masers is 0.001679611 radians. This model is useful in providing a quick guide to scientists, engineers, technicians and students in using the radio telescope at Kutunse, Ghana.

__________________________________________________________________________________________ ABSTRACT The focus of the research was on developing parallel computing algorithm for solving eigen-values of the Boltzmann Neutron Transport Equation (BNTE) in a slab geometry using multi-grid approach. In response to the problem of slow execution of serial computing when solving large problems, such as BNTE, the study was focused on the design of parallel computing systems which is an evolution of serial computing that used multiple processing elements simultaneously to solve complex physical and mathematical problems. Finite Element Method (FEM) was used for the spatial discretization scheme while angular discretization was accomplished by expanding the angular dependence in terms of Legendre polynomials. The eigenvalues representing the multiplication factors in the BNTE were determined by the power method. MATLAB Compiler Version 4.1 (R2009a) was used to compile the MATLAB codes of BNTE. ...

Abstract
A LabVIEW model to calculate the Half Power Beam Width of the Kutunse antenna was developed. The
Kutunse antenna as part of the AVN under the SKA is study masers and to train Ghanaians in Astronomy. The
model produced an easy-to-use approach in calculating the Half Power Beam Width over the operating
frequency range of 5.0 to 6.7 GHz of the antenna. The results indicated an angular width of 0.002249091
radians at 5 GHz and 0.001679611 radians at 6.7 GHz. The sensitive angular width at 6.7 GHz suitable for
studying masers is 0.001679611 radians. This model is useful in providing a quick guide to scientists,
engineers, technicians and students in using the radio telescope at Kutunse, Ghana.
Keywords: Half power beam width, LabVIEW, frequency, wavelength, Kutunse, African VLBI Network
(AVN)

ABSTRACT
A high performance of an antenna defines the quality of service of a communication system. The most widely used narrow beam antennas in satellite communication systems for the past several decades are reflector types. Antenna feed system plays an important role in the overall antenna performance. The feed system is characterized by calculating the dish efficiency versus f/D ratio and the necessary subreflector dimensions needed to reshape the feedhorn pattern to properly illuminate the dish. The purpose of the study is to analyze the single conical corrugated feed system of the 32-m Cassegrain Dual Reflector Antenna for obtaining high performance of the antenna considering the effects of losses in the feed system due to the f/D ratio and the hyperbola dimensions of the subreflector. In this paper, a simulation based analysis of a conical corrugated feed horn is performed, using ICARA software which has been developed for the analysis and design of reflector antennas and the analysis concentrated on f/D ratio, subreflector dimensions and reduction of cross-polarization. From fig.3 (a-f), we realized that the focus of the 32-m Cassegrain antenna is located behind the vertex of the main parabolic reflector. This facilitates the primary feed in this location with a 2.6701 m diameter aperture incorporated in the main parabolic reflector design and high gain of 59.3702 dB. This configuration technically eliminates distribution associated with the primary feed blocking the main reflector. Also we found that the antenna’s subreflector diameter was greater than 10.0 wavelengths which is good to avoid degradation in efficiency caused by diffractive effects to the feed efficiency. Adaptation of this antenna geometry and feed system to the specific bands for smooth conversion for radio services presents excellent educational opportunities in using the facility and a success for the Africa Very Long Baseline Interferometry Network (AVN) initiates for Ghana.
                                                                                                      ©Emerging Academy Resources
KEYWORDS: Primary feed, Cassegrain Dual Reflector, subreflector dimensions, conical corrugated feed horn, ICARA