INVESTIGATION OF SMALL ANTENNAS FOR PERSONAL HANDY PHONE USE
In this thesis, three types of small antennas for personal handy phone (PHP) use have been designed and analyzed using the Numerical Electromagnetics Code (NEC). First is the Modified Transmission Line Antenna (MTLA). It can provide a good impedance matching to 50Q at a very broad frequency band by selecting the total length of MTLA around 0.561. The input impedance and gain can be controlled by properly choosing the size of the respective part of the MTLA. Effects of a human body on the characteristics of an antenna are relatively small. The numerical and experimental results of input impedance and radiation patterns agree well confirming the valid of wire-grid model. This antenna can realize the functions of receiving and transmitting at the same time. Because of the limitation of MTLA for application at higher frequency, we have designed a new type of antenna array for PHP use. A 2-way hybrid power divider with in-phase outputs is used for antenna feeding. It has the same interesting features with MTLA for PHP use at 900 MHz and 1.9 GHz and even more flexible. The gain is higher than a quarter-wavelength and half-wavelength monopole according to numerical results. The numerical results are found to agree well when compared with the measurement results. Finally, we have investigated the effects of parasitic wire elements (PWE) on a monopole antenna mounted on a conducting box. The one and two PWEs are used for this study. It is found that effects are similar to one or two Yagi-Uda antenna array. A surface-patch model is used for the analysis and agrees well with the experimental results. However, there are some limitations when using a surface patch model for obtaining the accuracy results for input impedance.
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