Design and analysis of compact CPW-FED multiband antennas incorporating UWB applications

Abstract

Over the past decade, there is a great demand for permission to transmit large bandwidth concurrent with existing narrowband signals. In 2002, the federal communications commission (FCC) decided to permit use of ultrawideband (UWB) systems. UWB systems are unique in their large instantaneous bandwidth and potential for lowcost digital design that enables a single system to operate in different modes as a communication device, radar etc. UWB systems aim at covering the frequency band of 3.1-10.6 GHz defined by the FCC. The addition of more and more features in each new generation communication system demands universal antennas suitable for operation in multiple bands. In this regard, designing a multiband antenna which also covers the UWB range without deteriorating the UWB performance is of great interest. Also, a significant issue in communication systems is to miniaturize the antenna size while providing good performance over the operation bands. The thesis presents three different designs of CPW-fed multiband antennas. The first design uses a fractal concept to achieve multiband operation. In the second and third designs, a slotted circular monopole and a spiral monopole are used respectively for multiband operation with UWB applications. For both these cases, variations from the basic antenna geometry are also proposed in which the frequency of operation is lowered without increase in overall antenna size. Design guidelines are developed for all antennas to facilitate design on substrates of different permittivity and thickness. The antennas are analyzed in both frequency and time domain for complete characterization