TRANSMISSION LINE MODELLING OF COPLANAR WAVEGUIDE ANTENNA

Abstract

In this thesis, a rectangular coplanar waveguide antenna has been studied. Its resonance and radiation mechanism has been analysed based on a rectangular magnetic current loop assumption. From this point of view, the resonance has been interpreted as two parallel connected half-wavelength resonators and the radiation can be considered as originating from two main radiating slots. Therefore far field radiation patterns of the antenna have been derived by using aperture antenna theory. Agreement between experimental and theoretical results has been obtained for an antenna with a large ground plane. To analyse the input characteristics (input impedance and resonant frequency, etc.), a transmission line model is developed for the rectangular coplanar waveguide antenna. In this model, the antenna has been represented by a two-port network circuit with its two main radiating slots as loads. The two main radiating slots have been modelled by their self-admittance to incorporate radiation and open-end effects. Mutual coupling has been included in the model's equivalent circuit. Experiments have been performed for antennas with different substrates, different configurations and different dimensions. Good agreement between measurement and theoretical results has been obtained. The accuracy of the measured resonant frequency is within 5% of the calculated value. Some matching and tuning structures have also been tested to improve the antenna's performance. Finally, a feeding network configuration has been proposed and experimentally tested for coplanar waveguide antenna arrays. It consists of a microstrip line network and a coplanar-waveguide-microstrip-line-transition structure.