Abstracts Computer Science

Analysis of a wire antenna of an arbitrary shape

by Shiu-keung Wong

The present state of software package for wire antenna analysis has been reviewed. Two important problems were found: The impotence of directly modeling a curved antenna and the difficulty in adding or modifying the functionality of existing antenna analysis software packages. To address these two problems, a software for analyzing wire antenna by moment method was constructed using object-oriented techniques. New algorithm to analysis curved antenna was also developed. The traditional straight segment modeling technique had been contemplated and generalized to a curve segment modeling technique. Necessary formulas for the analysis were developed by formulating the moment method in a general orthogonal coordinate system. Object-oriented design techniques and a client-server architecture were adapted in the design of the software. In the designed program, clear boundaries are seen between different software components; similar objects are grouped into the same class hierarchy. This produces a program design that is loosely coupled and highly cohesive, hence enhancements and modifications made to the software are simple and straightforward. Enhancements such as adding a new canonical element, adding the surface model can be done by deriving a new class from the existing hierarchy without affecting any existing software components. Extensive tests were carried out to verify the correctness of the algorithm and software. Wherein a study of various analysis methods for loop antenna had been conducted, results from Wu, Zhou and moment method were compared and their discrepancies were addressed. In the analysis, we have re-assured the divergent result from Wu's formula is due to the nonphysical delta excitation. A special form of wire antenna, called dumbbell antenna was designed for broadband application. A dumbbell antenna comprises of a folded dipole and two circular wire loop antennas. By appropriate adjusting the resonance frequencies of the dipole and the , loop antenna, the antenna bandwidth can be drastically increased. The validated software was used to optimize two dumbbell antennas: one of them operates in UHF band for TV reception and the other is a dual band antenna for receiving signals from UHF and VHF band. Genetic optimization was adapted to optimize the VSWR of the antenna calculated by moment method. With the exhaustive search mechanism provided by genetic optimization, the antenna can be completely designed by the computer without human intervention. A scaled model of the dumbbell antenna for TV reception had been made and measurement was taken. The result had been compared to the numerical calculated result and was found to be quite match. On the other hand, the design of dual band antenna has been considered to be failed inasmuch as the resultant antenna was too large for practical purpose. The software components developed in this research are found to be easy to modify, resilient to change and reusable. Hence, in the view of software ' functionality, maintainability and reusability, object-oriented…