Some Studies on Circular and Annular Ring Microstrip Antennas

Abstract

Microstrip antennas are the class of antennas, which are widely used in GPS (Global Positioning system), SDARS (Satellite Digital Audio Radio Services), and WLAN (Wireless Local Area Networks). Modern communication systems often require compact antennas at low cost. Due to the lightweight microstrip antennas are well suited for airborne applications. In some applications operation at two or more discrete bands is desired with an arbitrary separation of bands. Further all the bands may be required to have the same polarization, radiation pattern and input impedance. It may not be possible to achieve these objectives from the basic microstrip antennas having regular shapes. These applications can be obtained by suitably loading the regular microstrip structures. newline In this thesis, a new analytical model is developed for antennas. The cavity model is simplest of all the models, which are used for the analysis of microstrip antennas. This model is also the approximate model, which leads to reactive input impedance and does not radiate any power. Thus the cavity model is used to predict frequency, input impedance and other important parameters of circular disc antenna, stacked antenna and ring antenna. newline Cavity model with circuital analysis is used for the development of these models. Firstly a circular disc antenna with coaxial feeding is analyzed. Different parameters of the circular disc antenna are obtained. The analysis is further extended to stacked circular disc antennas. The bandwidth and gain both are enhanced by stacking the antenna. It is observed that the stacking of elements input impedance is considerably reduced to the feed line impedance (50 ohms) or near it. newline