Developing Multi-Band And Ultra-Wide-Band Antennas

Recently, amount of data transmissions is sharply increased with development ofinformation society. One is consumingly interested in technology of ultra-wide-band wirelesscommunication. Lots of the practical applications have been investigated. As one of devices inthe communication system, antenna plays a very important role. It directly influences propertiesof the entire system. In this time, the communication system is upgraded continuously. Muchmore strict rules of the antenna design and manufacture have been proposed. In order to reducecoupling and interference between multiple working bands in the system, a strategy arises at thehistoric moment, which is tried to making use of only one antenna to cover all application bands.Whereas many interferences are existed from narrowband communication system within a wideband of3.1GHz-10.6GHz, some measures must be taken to filet out these interferences. Anultra-wide-band antenna must be designed with some band-notches; it may be used to solve theproblem better. Therefore, these antennas have been paid much attention to in this thesis. Startingfrom microstrip structure, we discuss its principle; then introduce parameters of the multi-bandand ultra-wide-band antennas. Design methods of these antennas have been given. Focus is onthe design of a multi-band antenna and an ultra-wide-band antenna with dual band-notches inthis project.To design above, the definition of the antenna is explained by radiation equation, and somemore important electric parameters have been discussed in details. Structures of microstripantenna and their radiation mechanism, as well as several feeders are discussed. Then therealization methods of the multi-band antenna have been analyzed. Combination of a specificinstance and simulation model, such as multi-chip, gap-loading, multi-branch, and fractalstructure techniques，the means of achieving multi-band have been described intuitively. Atri-band printed antenna is designed according to the actual requirement. The antenna iscomposed of three overlapped rectangular rings, fed by a microstrip line. It is studied that thesize of these rectangular rings has made an impact on reflecting coefficients of the antenna. Thechange of reflection coefficients have been observed when their sizes changed.Further, an ultra-wide band antenna is designed to verify the methods above. It isconstructed with rectangular and trapezoidal. One or more resonant structures have beendesigned to realize the band-notch. A slotting technique is adopted in both radiating body andground plate to reach a dual-band notches properties. The length of slot is approximately onefourth of the center wavelength. An U-shaped is slotted on the radiating patch locating at thesuitable position to stop the WiMAX signals; and the notched characteristic of the WLAN isachieved through two vertical narrow rectangular slots on the ground board.Finally, a tri-band and an ultra-wide-band printed antennas have been fabricated.Measurement results show that the designs are available.