Research On The Band-botched Ultral-wideband Antennas

Since the frequency band 3.1-10.6 GHz has been released by FCC for commercial UWB applications, the development of ultra-wideband antenna has captured people’s attention. The key technology for UWB antenna design is to minimize the volume, reduce the loss and broaden the bandwidth at the beginning of the development of UWB. The printed monopole antenna is a preferred model for UWB antenna design owing to its advantages, such as small size, broad band, easy to fabricate and integrate and so on. The spectrum is finite, which leads to the overlap between the UWB operating band and other narrowband. It is necessary to design the UWB antenna with filter characteristics to reduce the electromagnetic interference between them. With the development of technology, to diminish the size of the communication system and realize its multi-function, combing the band-notched property with other antenna’s characteristic is one of the development trends for UWB antenna.The basic theory on antenna is introduced in this paper, and the common methods for broaden the band and producing notched bands are studied. And then a cup-shaped printed monopole UWB antenna with triple band-notched characteristic is proposed, which is fed by microstrip. The triple notched bands are generated by slitting a slot and introducing stubs on the antenna. The triple notched bands cover the frequency bands of 3.3-3.6 GHz, 5.15-5.825 GHz and 7.25-7.75 GHz. When comparing the simulated results and the simulated ones, one can find that the former coincide with the later except for little discrepancy between them.The reference knowledge of frequency reconfigurable antenna is studied by literature reading. Combing with the knowledge of UWB band-notched, a novel frequency reconfigurable antenna is presented. The antenna can work as a narrow band antenna or a UWB band-notched one which is controlled by changing the state of switches. The frequency range for narrowband mode is 5.7-6.5 GHz and for the UWB band-notched mode is 5.15-5.825 GHz. The return loss, radiation pattern and the maximum gain for both two modes are provided. The radiation patterns almost remain unchanged when the antenna works in narrowband mode and notched-band modes.