Circular and Annular ring microstrip antennas

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). However narrow bandwidth is major concern of these antennas. There are various methods used to enhance the bandwidth of microstrip antennas. Of all the methods which are used in analysis of microstrip antennas the cavity model is simple, it is 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. Firstly a circular disc antenna with coaxial feeding is analysed. A simple numerical method is developed to calculate various parameters of the circular disc antenna. 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. Annular ring geometry has certain advantages over other geometries. So an