Research And Design Of Ultra-Wideband Antenna And Band-Notched Characteristics

With the flourishing development of ultra-wideband communication technology, UWB printed antenna inspire researchers’interest due to its merits such as low profile, simple fabrication and ease of integration with circuits, and lots of UWB antenna with excellent performance have been proposed. But some of the existing narrowband communication systems, such as WiMAX and WLAN, are located in the civil UWB frequency band allocated by Federal Communications Commission, which will inevitably lead to interference from different systems. In order to realize system compatibility, UWB antenna with band-notched characteristics has gradually become a hot topic. This paper mainly focus on the achievement of UWB antenna and band-stop function, specific contents include the following two aspects:First of all, based on the principle of UWB antenna, four miniature UWB printed antennas have been designed. With the help of electromagnetic simulation software, how the important parameters of antennas affect impedance matching is analyzed, at the same time two designed antennas are fabricated and measured. The simulated and measured results agree well with each other. All the printed antennas could provide sufficiently wide impedance bandwidth(VSWR<2) covering entire UWB frequency band. They also demonstrate stable radiation patterns and flat gain across the whole operating bandwidth, which can satisfy requirements of UWB applications. In addition, transfer function and group delay indicate that aforementioned antennas are suitable for transmitting and receiving UWB signal in terms of time-domain characteristics.Then, quarter-wavelength and half-wavelength slots are respectively embedded into the ground plane and feed line of the UWB slot antenna to filter out WiMAX and WLAN bands. The measured result shows that VSWR is greater than 2 in the frequency range of 3.24-3.7GHz and 5.33-6GHz. According to predicted current distributions, the reason of generating band-rejection has been discussed, meanwhile equivalent circuits corresponding to different working conditions have been given also. In order to avoid waste of useful frequencies owing to the wide notched bands, complementary stepped impedance ring resonators are employed to generate dual notched bands at the lower and higher WLAN bands(5.15～5.35GHz,5.725～5.825GHz). Furthermore an open-circuited stub was attached to feed line so as to suppress WiMAX band. The final antenna exhibit tri-band rejected characteristic. There is good agreement between simulated and measured results, and the structures to produce band-notched characteristics have little effect on behavior of the UWB slot antenna outside notched bands. Lastly performance of this tri-band notched antenna which is used to transmit and receive UWB pulse has been evaluated from the perspective of transfer function and group delay.