Research And Design Of The Frequency Reconfigurable Antennas With Band-notched And Dual-band Characteristics

Frequency reconfigurable antenna can work in various operating band. Therefore,the functions and capacities of the systems with frequency reconfigurable antennas areimproved. For some systems which can only operate at a particular frequency range orin a specific mode, frequency reconfigurable antenna means some importantengineering significances.In this dissertation, the band-notched ultra-wideband antennas, dual-bandantennas and frequency reconfigurable antennas are investigated. The frequencyreconfigurable antennas can work in the band-notched ultra wideband band ordual-band WLAN band. The main work and results of this dissertation are as follows:First, the basic structures and designing methods of the current dual-band antennaare studied. The design method of dual-band antenna is to create two various resonantpaths in the same antenna structure. When the lengths of the two resonant paths aredifferent, the antenna can work in two various operating band. According to thisconcept of design, the authors propose a new cross-slot dual-band antenna structure.The two operating frequencies of the antenna range respectively from2.9GHz to4.1GHz and from5.1GHz to5.9GHz, which cover exactly WiMAX and5GHz WLANband. Furthermore, on the operating frequency band, the antenna has a good radiationdirection.Secondly, the authors studied the current ultra-wideband band-notched antennastructure. In the ultra-wideband antenna, the slots or metal stubs which work as filtersare added into the ultra-wideband antenna structure to implement one or morestopbands. Based on this concept, the authors firstly design an ultra wideband antenna.And then, by adding one slot or several slots in the radiator or ground of the ultrawideband antenna, the single band-notched ultra-wideband antenna and the multi-bandnotched ultra-wideband antennas are achieved, one of them is dual band-notchedultra-wideband antenna with a stopband covering3.2-3.9GHz and4.8-5.9GHz.On the basis of the results of the dual-band antenna and band-notchedultra-wideband antenna, a novel frequency reconfigurable antenna is proposed. The antenna’s operating band can switch between dual-band WLAN band andband-notched ultra-wideband band. By adjusting the ideal switch between the "on"state and the "off" state, some parts of the antenna changes between the inverted L-typeradiation patch and the inverted S-shaped slot. As a reslut, the antenna can operate inthe band-notched ultra-wideband band and dual-band WLAN band. The experimentalresults show that in the dual-band WLAN mode, the measured-10dB impedancebandwidth of the lowest frequency band ranges from2.39to2.51GHz, and themeasured-10dB impedance bandwidth of the higher frequency band is from4.25to6.75GHz. In band-notched ultra-wideband mode, the antenna excited a stopbandfrequency band ranging from4.91to5.9GHz. Therefore, the antenna can not only beapplied in dual-band WLAN band, but also can work in band-notched ultra-widebandfrequency band.Finally, a summary and the future work are presented.