posted on 2010-11-17, 11:12authored byYan Wah Chia
The thesis deals with the analysis of a microwave Frequency Selective Surface (FSS) on a conical dielectric radome illuminated by a feed hom located at the base. Two approaches have been adopted to solve this problem. The first approach is to calculate the element currents under the assumption that the surface is locally flat. Consequently, the element current at that locality can be determined by employing Floquet modal
analysis. The local incidence has been modelled from the radiation pattern of the
source or the aperture fields of the feed. Three types of feed model were used to account for the field illumination on the radome. The transmitted fields from the curved surface are obtained from the sum of the radiated fields due to the equivalent
magnetic and electric current sources distributed in each local unit cell of the conical
surface. This method treats the interaction of neighbouring FSS elements only. In the
second approach the curvature is taken into account by dividing the each element into
segments which conform to the curved surface. An integral formulation is used to
take into account the interaction of all the elements. The current source in each FSS
element from the formulation is solved using the method of moments (MOM) technique. A linear system of simultaneous equations is obtained from the MOM and has been solved using elimination method and an iterative method which employs
conjugate gradients. The performance of both methods has been compared with regard to the speed of computations and the memory storage capability. New formulations using quasi static approximations have been derived to account for thin dielectric backing in the curved aperture FSS analysis. Computer models have been developed
to predict the radiation performance of the curved(conical) FSS. Experiments were performed in an anechoic chamber where the FSS cone was mounted on a jig resting on a turntable. The measuring setup contained a sweep oscillator that supplied power to a transmitting feed placed at the base of the cone. Amplitude and phase values of the
far field radiation pattern of the cone were measured with the aid of a vector network
analyser. Cones with different dimensions and FSS element geometries were
constructed and the measured transmission losses and radiation patterns compared
with predictions.
History
School
Mechanical, Electrical and Manufacturing Engineering