Design Of Band Notched And Miniaturized Ultra-wideband Antennas

As a promising new technique, UWB (Ultra-wideband) is finding a myriad of applications nowadays, mainly in wireless communication and microwave imaging (MI). This is due to its capability of providing high data throughput and reasonable good image resolution, respectively. Antenna design for UWB applications offers significant challenges, since a number of design constraints should be satisfied. This thesis addresses the omini-directional and directional band notched UWB antennas for wireless communication systems and MI, as well as miniaturized portable antennas for UWB communications. By using electromagnetic simulations and measurements, four novel UWB antenna designs as follows are pursued and described in details.Firstly, a novel microstrip-line fed monopole dual band-notched antenna with tapered slot for UWB applications is presented. The tapered slot, making the antenna have a scissors-like shape, is utilized to enhance the wideband characteristics. In addition, by inserting slots on the ground plane and adding circle arc stubs on the radiating patch, the dual band-notched characteristic of this design has been achieved. Secondly, a novel Vivaldi antenna for MI is proposed. The wide impedance bandwidth is realized by using a quarter-wave impedance transformer of 3 steps combined with a double-Y balun for microstrip/slot-line transition. Meanwhile, by inserting slot onto the strip-line, a suitable notched band has been obtained.Thirdly, a novel miniaturized strip-line fed UWB antenna with band-notched function is presented. By employing a balanced antipodal structure and strip-line feed with the low relative permittivity dielectric substrate, the physical and electric dimensions of this antenna have been reduced significantly. Moreover, a slot is added onto the radiating patch of the mid metalisation layer to realize the band-notched function.Finally, a small internal 2.4GHz/UWB (Ultra-wideband) antenna suitable for integration with printed circuit board (PCB) of a wireless universal serial-bus (WUSB) dongle is proposed. The overall size of this design is very compact and approximately equal to that of a normal USB flash disk. Experimental results of the constructed prototype show that the impedance bandwidth of the proposed antenna is covering the whole WLAN and UWB operating bands with good radiation characteristic. Furthermore, the influence of the laptop, the wood desk as well as the wood desk on the performance of the antenna is also studied and discussed.