| Summary: | 碩士 === 大同大學 === 通訊工程研究所 === 95 === The purpose of this work is to study the antenna structure for wideband application. A wideband DTV (Digital TV) antenna with a multiple-structure of transmission line antenna is designed firstly. A technique of varying the width of transmission line antenna is developed firstly to shorten its length. By adding three individual transmission line antennas for different bands together, a wideband characteristics is achieved in the UHF band. This is suitable for digital TV reception, especially for the DVB-T, which is based on the OFDM technique, because of its near omni-directional pattern. Monopole antenna is the most popular type of antennas used in varied applications including military, industrial and civil wireless communications. This work also intends to design a wideband monopole antenna used for a Wireless LAN application, in which, the antenna is working with a USB-based transceiver. This design is applied in a Microsoft XBOX 360 game station. In theory, the length of a monopole is designed to be a quarter-wavelength ( ) in free space of the frequency of system. Consequently, the multiple- behavior may happen in frequency response. This response of return loss of a monopole antenna usually looks like an one of multi-band, if the propriety of the associated radiation patterns is not concerned. Also, since the monopole antenna is a -based design, its individual band is narrow in characteristics. Other than its natural multi-band, if an assigned dual-band is necessary and one of this dual-band is needed to be ultra wide, such a design will be difficult. Present work is to aim at such a goal. This specification in terms of band is wanted in some countries, for example, Japan or Korea, where the WLAN adopting IEEE 802.11j uses the spectra that are not exactly the same as that used in northern America or Europe; yet overlapping on each other is possible.
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