Conductors on multilayer media as radiating elements

ABSTRACT CONDUCTORS ON MULTILAYER MEDIA AS RADIATING ELEMENTS Ö?ÜCÜ, Gölge Hatice PhD. in Electrical and Electronics Engineering Department Supervisor: Prof. Dr. Tuncay EGE Co-Supervisor: Assist. Prof. Dr. Lale ALATAN December 2004, 122 pages Although the microstrip antennas are placed on finite substrate and ground plane in practice, most of the analysis methods developed are based on the assumption that both the ground plane and the substrate layer are infinite. However, if the finiteness of the substrate and the ground plane is considered in the mathematical models, the characteristics of the antennas will be found more accurately. In this thesis, a method is proposed to analyze efficiently the microstrip antennas placed on a finite grounded dielectric substrate. The method is based on the solution of the spatial domain mixed- potential integral-equation (MPIE) formulation of the antenna using the method of moments (MoM) procedure. Because the spatial domain MPIE involve the Green's functions of the vector and scalar potentials spatial domain, and because the Green's functions of the vector and scalar potentials for a point source placed on a finite grounded dielectric substrate do not exist in literature, the main contribution of this thesis is the development of the approximate spatial domain closed-form Green's functions of the vector and scalar potentials for a horizontal electric dipole (HED) on a finite grounded dielectric medium. To obtain the approximate Green's functions for the finite structure, the closed- form Green's functions for a HED placed in multilayered infinite geometry are modified by including the reflected surface waves from the air-dielectric interface at the truncated edge. The reflection coefficient at the interface is found by using the iiiedge admittance values that are obtained as a function of the incident angle. The closed-form expressions of the reflection coefficients are then derived by means of generalized pencil of function (GPOF) method. The resulting approximate Green's functions are obtained as the sum of the Green's functions for the infinite case and the reflected surface wave contributions. Another contribution of this work is the use of the approximate Green's functions in the MoM solution of the microstrip patch antennas on the finite structure. By the proposed method, it is possible to include the effect of the finiteness of the structure in the calculation of the surface current density on the antenna. The surface currents are used in the computation of the input impedance of the antenna and the results are provided to be compared with the numerical and experimental results in literature. The radiation pattern and scattering parameters of the antenna are also analyzed and the numerical results are compared with the measured results to discuss the efficiency of the proposed method. Keywords: Approximate Green's Functions, Method of Moments, Reflected Surface Waves, Edge Admittance, Antenna Parameters IV