Ultra-Wideband TEM Horns, Transient Arrays and Exponential Curves: A FDTD Look

This is a AIR FORCE INST OF TECH WRIGHT-PATTERSONAFB OH SCHOOL OF ENGINEERING report procured by the Pentagon and made available for public release. It has been reproduced in the best form available to the Pentagon. It is not spiral-bound, but rather assembled with Velobinding in a soft, white linen cover. The Storming Media report number is A787163. The abstract provided by the Pentagon follows: This research investigates the possibility of applying exponentially curved conducting plates to single-element Transverse Electromagnetic (TEM) horns and their transient arrays to enhance the UWB characteristics already experienced by these radiators. The first part of this study demonstrates the Finite-Difference Time-Domain (FDTD) method's ability to duplicate experimental data, and establishes the baseline models used throughout the remainder of the research. The baseline models consist of the typical flat-triangle shaped conducting plates. The exponential taper models incorporate the exponential curves in the height, the width, and both the height and width directions. One, two- and four-element baseline configurations are compared to their respective exponential-curved models. The comparisons are made in both the time-domain and the frequency-domain. The research concludes that reflection are not reduced by the application of exponential curves, but that the curves can increase or decrease the peak field strength depending on the input pulse width and the direction to which the curve is applied. This research also demonstrates, with the FDTD method, the major benefits realized when transient arrays are constructed from these elements. The final product of this research results from the exploration of methods to reduce FDTD run-times of these types of problems. The run-times are reduced by 96%, and approach the run-times necessary for interfacing the FDTD method with an optimizing algorithm.