UWB Antenna design for Communication System Performance Optimization

Traditional antenna performance descriptors such as input port impedance, radiation pattern or effective antenna length generally face strong frequency dependence. In this context the traditional narrowband approach to antenna design is no more appropriate for UWB antennas. Such antennas behave as spatial and temporal filters, distorting the radiated waveforms. Indeed, the radiated signal distortion is an inherent UWB antenna issue, usually assessed qualitatively. Consequently the need for a compact frequency and direction-independent antenna distortion descriptor was identified. For this purpose the first objective of the thesis is to define and analyze new direction-independent UWB antenna descriptors that should assess the antenna performance in terms of transmitted UWB pulse fidelity. As a second objective of the thesis, a critical analysis of the proposed UWB descriptors measurement methods is developed. Namely, spatially averaged fidelity (SAF) descriptors and radiation efficiency measurement methods in ultra wideband frequency range are shown. A demonstration of the practical use of the newly defined UWB direction-independent antenna descriptors is shown through the design and optimization of impedance loaded linear monopoles. For this purpose an evolutionary optimization technique, Particle Swarm Optimization (PSO) was used. Finally, the optimized monopole performances were verified experimentally.