Studies of the optimum isolation in a multi-mode PDA phone are presented in this thesis. Firstly, we analyze the optimum isolation between the DCS and GPS antennas embedded in a dual-mode PDA phone. Then, we change the antenna types of the DCS system to study again the behavior of the optimum isolation. Secondly, we analyze the optimum isolation between a DCS antenna and a WLAN antenna embedded in a dual-mode PDA phone. Finally, we propose a multi-mode PDA phone for DCS, GPS, and WLAN operations with good isolation among the three internal antennas.

In this dissertation, many novel low-cost planar antenna designs are presented for on-vehicle applications. Promising planar antennas showing the desired broadside and omnidirectional radiation patterns and having low-profile configurations are demonstrated. Also, studies on controlling the radiation patterns are conducted. Details of the measured and simulated results of the studied antennas are presented and discussed.

In this thesis, a comparison of the body SAR value of five planar WLAN antennas including two coupled-fed shorted monopole antennas, a coupled-fed loop antenna, a monopole antenna, and a monopole slot antenna for tablet PC applications are presented. A required minimum distance between the antenna and the testing flat phantom to meet the 1-g body SAR requirement of 1.6 W/kg has been determined. Results show that the body SAR results of the coupled-fed loop antenna are lowest among the five tested antennas. Detailed results and discussion are presented in this thesis. Also, a comparison of the body SAR value of a planar antenna and an antenna with 3-D bent structure are presented.

The rapidly growing demand for UWB as high data rates wireless communications technology, since the Federal Communications Commission (FCC) allocated the bandwidth of UWB from 3.1GHz to 10.6 GHz. Antenna also plays an essential role in UWB system. However, there are some difficulties in designing UWB antenna as compared to narrowband antenna. The primary requirement of UWB antennas is be able to operate over frequencies released by the FCC. Moreover, the satisfaction of radiation properties and good time domain performance over the entire frequency range are also necessary. In this thesis, designing and analysing printed crescent shape monopole antenna, Planar Inverted F-L Antenna (PIFLA) and Planar Inverted FF Antenna (PIFFA) are focused. A Planar Inverted FF Antenna (PIFFA) can be created to reduce the potential for interference between a UWB system and other communications protocols by using spiral slot. The antennas exhibits broadside directional pattern. The performances such as return loss, radiation pattern and current distribution of the UWB antennas are extensively investigated and carried out. All the results have been demonstrated using simulation and experimentally whereby all results satisfy the performance under - 10dB point in the bandwidth of UWB. In addition the miniaturization of MIMO/diversity Planar Inverted-F antenna (PIFA) which is suitable for pattern diversity in UWB applications is presented. This antenna assembly is formed by two identical PIFAs, a T-shaped decoupling structure which connects the two PIFAs and a finite ground plane with a total compact envelope dimension of 50 x 90 x 7.5mm³. The radiation performance of the proposed MIMO antenna was quite encouraging and provided an acceptable agreement between the computed and measured envelope correlation coefficient and channel capacity loss.