Radiation from resonant frequency selective horn antennas

The research involves the analysis and design of a new band of horn antennas, namely Frequency Selective Horns (FSHs). Folding a Frequency Selective Surface (FSS) into a shape of a cone makes a FSH. The stimulus behind this research emanates from an idea to use the FSH as a microwave camera for medical diagnostic purposes. FSHs with dipole geometries have been modelled using existing software. A quasi-static approximation models the dipole elements with a dielectric backing as dielectrically loaded cylindrical conducting elements. The curvature of the surface is taken into account by dividing the elements into segments that conform to the curved surface. An integral equation takes into account the interactions between all the elements. The current due to the incident electromagnetic incidence is solved using the Method of Moment (MoM) technique. The author modified the model in order to speed up the computational time by utilising the symmetries in the impedance matrix. The predicted results of the conical FSH with dipole elements have been compared with experimental results carried out in an anechoic chamber. The comparisons include E and H-plane radiation patterns and the frequency response. Furthermore, current distributions on the surface of the cone have been predicted and return-loss measurements have been produced. Five FSHs with different geometries are presented in this thesis. The near field of the horn is modelled by sub-dividing the feed aperture into small patches and summing the fields generated by each patch in order to find the total field from the circular waveguide. Predicted results of the radiation patterns for the feed have also been produced and compared with measurements. (author)