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Characteristic-impedance (Z 0

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terns at 2.5, 3.5, and 5.5 GHz, which are the center operating frequencies of the three possible frequency bands (licensed 2.5-and 3.5-GHz bands and unlicensed 5-GHz band) between 2 and 6 GHz proposed for WiMAX operation [9]. By comparing the radiation patterns at 5.5 GHz to those at 2.5 and 3.5 GHz, it was observed that the radiation patterns at 5.5 GHz are more like those of the conventional monopole antenna mounted on a large horizontal ground plane. This characteristic is exhibited largely because the main ground plane at 5.5 GHz has a relatively much larger wavelength dimension and thus performs less like a radiator than in the cases at 2.5 and 3.5 GHz. Figure 6 shows the measured radiation patterns at 1575 MHz. Comparable E and E components are observed, which are expected to be advantageous for application in a heavy multipath environment for E911 operation [3]. CONCLUSIONAn antenna system comprising a wideband stubby metal-plate monopole antenna for WiMAX operation in the frequency bands between 2 and 6 GHz and an internal GPS antenna at 1575 MHz for the E911 function have been proposed. The antenna system applied to a mobile phone has been successfully implemented. The experimental results indicate that good radiation characteristics over the WiMAX and GPS bands were obtained. Good isolation between the WiMAX and GPS antennas was also achieved.