MICROSTRIP LINE AND COPLANAR WAVEGUIDE FED PARABOLIC MONOPOLES FOR UWB APPLICATIONS

Abstract

In this dissertation, three parabolic monopole antennas have been designed and optimized to operate over the 3.1 GHz -10.6GHz frequency band allocated for Ultra-wideband applications. One of these antennas is fed with a microstrip line and the other two are fed with a coplanar waveguide. One of the coplanar waveguide fed antennas has been designed to reject the 5.15 — 5.825 GHz band used by `802.1 la' Wireless-LAN. Various simulation and experimental results have been obtained for the designed antennas. Simulation results obtained during the design process of proposed antennas give an insight into the effects of change in various parameters of the antenna on its performance. The feed gap and the width of the ground plane have been found to have a significant effect on impedance matching and impedance bandwidth of the antennas. So, the feed gap and the width of the ground plane have been optimized to give best possible impedance matching over the desired frequency range. Monopole antennas exhibit tilting of the main beam away from the ground plane at higher frequencies, due to finite size of the ground plane. So, the microstrip line fed monopole antenna has been designed to reduce the tilting of the main beam by using a curved shape for the upper edge of the partial ground plane. The curvature was optimized to give minimum beam tilting. Coplanar waveguide (CPW) fed parabolic monopole antenna was found to have an impedance-matching better than that of microstrip line fed antenna. The fractional impedance bandwidth of CPW fed antenna was found to be 150% which is much higher than that of microstrip line fed antenna. The CPW fed, band-notched monopole antenna was designed to reject the 5.15-5.825 GHz frequency band by incorporating an inverted U-shaped slot in the parabolic radiating element. A parametric study was carried out to study the effect of change in the dimensions of the slot on the center frequency and width of the notched frequency band. Simulation results include variation of return loss, impedance, peak gain, bore-sight gain and side-sight gain with frequency, along with radiation patterns. Spatial dispersion of radiated signals has also been studied through simulations. The designed antennas have been fabricated and their return loss, bore-sight gain and azimuth radiation pattern have been measured. The measurement results have been compared with simulation results. 111