| With the rapid development of modern communication technology, the volume of electronic elements is becoming miniaturized increasingly and the abitily of them to process information is intelligent and broadband day by day. Accordingly, higher and higher requirement have been presented to the antennas. Antennas should not only adapt to the miniaturized of the electronic elements but also meet the electrical characteristics index especially the bandwidth and efficiency. So the miniaturized,broadband and multiband characteristic are a general trend.Associated with research project, this dissertation makes deeply insight to the miniaturized and broadbandening of antennas and multiband/ultra-wideband printed antennas. The author's major contributions are as follows:1. The design of several sleeve antennas have been presented. Firstly, a double-choke sleeve antenna is proposed, which has slove the dependence to the ground plane of the antenna, thus act a positive role to the miniaturized of antenna. Secondly, a top-loading open sleeve antenna is proposed, using top-loading structure to decrease the height of the antenna. Since this open sleeve structure does not have rotational symmetry,the radiation patterns in the horizontal plane are slightly inferior. Considering the working requierment,we have improved the symmetry of the physical structure in order to improve the radiation pattern characteristic.2. Several multiband or broadband printed antennas in modern communication systems have been studied. Firstly, a top-loading multiband open sleeve printed antenna which supports WLAN systems has been proposed. The top-loading and open sleeve structures have realized multiband characteristic effectively. Secondly, a CPW-fed open sleeve printed antenna has been presented. The central feeder line and the ground plane of the CPW are both gradually changed structures. Open sleeve structure has been adopted and an inverted-L structure has also been used in this antenna to broaden the bandwidth. Thirdly, a combinational structure open sleeve antenna is proposed. The radiator is composed of three parts, and electromagnetic coupling feeding has been adopted to broaden the bandwidth in order to support several frequency band at the same time. Finally, a CPW-fed top-loading multiband printed antenna is proposed. Two pairs of zonal branch wire are adopted on the radiator and an inverted polygon is placed on the top of the radiator to act as a top-loading. The size of this antenna has been decreased effectively. The antennas proposed in this paper have been test and the measured results have verified the good radiation characteristic and practicality of those antennas.3. The band-notched characteristic of ultra-wideband and antenna with extremely bandwidth have bee studied. Firstly, obtain very large standing wave ratio during WLAN frequency band through embedding slot in the elliptic monopole printed antenna. The effects of the size of the slot on the band-notched characteristic have been studied. An ultra-wideband antenna with extremely bandwidth has been proposed. The bandwidth has been broadened by embedding slots in the radiator and the ground plane. The effects of the slot size on the bandwidth characteristic have also been discussed. The measured results shows good bandwith and pattern characteristics.4. Low profile antennas which have the radiation characteristics of monopole have been studied. A circular patch antenna which working at TM01 model is designed to work as a monopole. Shorting pins, electromagnetic coupling feeder and wideband matching network have been adopted to broaden the bandwidth of the circular patch antenna. Considering the feeblish withstanding power characteristic and the complex construction of matching network, another circular ring patch antenna has been proposed.The gradually changed feeding structure has made positive contribution to the bandwidth.
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