Projeto e otimização de antenas helicoidais não uniformes

Abstract

In this dissertation, uniform helical antennas are used as a starting point to generate nonuniform optimized antennas . Improvements in the gain and input impedance are obtained by varying the helix shape using a second order polynomial function. The the polynomial approximation coefficients are found using the deep-cut version of the ellipsoidal optimization algorithm. The use of the well known formulae and diagrams for the design of uniform helical antennas as a initial point of the deterministic method can reduce the search domain and provides a fast convergence rate. To simulate the behavior of the antennas, the Method of Moments (MoM) is applied to the Electric Field Integral Equation-EFIE. The antennas are fed using a Delta-Gap voltage source and the conducting plane at the base of the antennas are represented by the Image Theory. Results are presented for WiFi application using a center frequency of 2.45 GHz. It shows that the input impedance and the antenna length can be considerably improved using a simple and efficient parametrization.