A computer model investigation of a quad log-periodic array

Abstract

This thesis investigates the possibility of developing a quad log-periodic array for use in military applications over a wide range of frequencies. The investigation of a uniformly periodic quad array was conducted utilizing the Numerical Electromagnetics Code (NEC). A numerical-experimental study of near field characteristics and far field radiation patterns for selected versions of the structure helped to identify necessary performance characteristics of a successful log-periodic version of the antenna. The near field investigation provided k versus /? information for a Brillouin diagram (/? was determined from the relative amplitude and phase of the near magnetic field created by the structure under various conditions). Far field radiation patterns provided a check on the results of the Brillouin diagram and identified the presence of end or truncation effects. The results of this study show the potential exists for designing a successful quad log-periodic antenna. Using NEC, a selected model was run in free space to obtain radiation patterns and element currents on the array. The NEC results indicate that a quad log-periodic array with a switched transmission line has desirable log-periodic characteristics and shows promise for military and commercial applications.