The Electromagnetic Characteristics of a Loop Antenna Positioned Coaxially on AN Infinitely Long Dielectric Circular Cylinder
An analysis of the electromagnetic characteristics of a loop antenna which is positioned coaxially on the surface of an infinitely long dielectric circular cylinder has many applications in the areas of antenna design, fibre -optics, millimeter wave devices, and bioelectromagnetics. Such an analysis, focussing primarily upon input impedance, surface wave behaviour, and radiation characteristics, is the subject of this thesis. The antenna is modelled with the aid of the thin wire approximation as an f(phi)delta(z) electric current distribution situated on the free space-dielectric interface. A Debye potentials based formulation is employed to obtain formal exact expressions for all electromagnetic field components which result from said current distribution. The formulation for the fields is extended to obtain expressions for input impedance and current distribution, surface wave characteristics, and radiation characteristics. The input impedance is evaluated using numerical quadrature and residue theory. The surface wave behaviour is studied with the aid of residue theory. The far field, or radiation characteristics, are studied with the aid of the steepest descent technique. Numerical results are provided for the three main characteristics of interest and a number of interesting features are shown from these results. In particular, the input impedance of the antenna is shown to consist of two terms, a radiation term and a surface wave term. Extensive investigation into these terms illustrate the relative impact of each term on the overall behaviour of the loop's input impedance. The field amplitudes of a selected number of surface wave modes are studied. Finally, the radiation characteristics of the antenna are extensively investigated and the extent to which the cylinder affects the radiation from the antenna is thoroughly presented.
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- Engineering: Electronics and Electrical; Physics: Electricity and Magnetism; Physics: Radiation