Reconfigurable Monopole Antennas with Circular Polarization

This thesis presents research on printed circularly-polarized monopole antennas and their application in reconfigurable monopole antennas. The proposed circularly-polarised monopole antennas benefit from advantages such as small size, low-cost, low-profile and simple designs. The first part of this thesis introduces three printed circularly-polarized monopole antennas for global navigation satellite systems and Wi-Fi applications. The primary focus is on the ground plane which is used as a radiating component in realizing circular-polarization. It is shown that by employing the ground plane as a radiator results in a wide axial ratio bandwidth. The radiation patterns of the antennas and their relationship with antenna ground plane sizes is investigated. Then, a frequency-reconfigurable monopole antenna with circular-polarization for wireless local area networks and global navigation satellite systems is presented. The ground plane current distribution, rearranged by a switch, enables the right-hand circularly-polarized band to move in frequency from the GPS band to Wi-Fi frequency bands.
Finally, a simple polarization reconfigurable printed monopole antenna for wireless applications is described. Once again, with the help of the ground plane and by changing its current distribution, linear-polarization, right-hand or left-hand circular-polarization is realized. The polarization agility is controlled by two PIN diodes, which alter the ground plane surface currents. The antenna is one of the few polarization-reconfigurable monopole antennas reported in the literature. For all the presented antennas, parametric studies of key geometric parameters are given for clear understanding of the circular-polarization radiation mechanism.