Abstract

Ultra-wideband (UWB) technology is rapidly developing as a high speed, and high data rate wireless communication mode. There are many challenges in dealing with this new emerging technology. One of these challenges is how to design an antenna ele-ment that can operate effectively in the entire UWB frequency range. Another big chal-lenge is to design UWB antenna beamforming systems including suitable UWB compo-nents such as feed networks, transitions, crossovers, hybrid couplers and phase shifters to meet the UWB requirements.
This thesis is primarily focused on designing UWB antenna elements and other microwave components for UWB wireless communications applications. The thesis starts with designing and implementing different new UWB disc monopole and hybrid anten-nas with discussions covering their operation, electrical behavior and performance. An-tennas are developed using microstrip technology to achieve low profile and compatibil-ity with printed circuit board (PCB) technology. Different techniques for obtaining a bandstop function in the 5.0-6.0 GHz frequency band to avoid interference with other ex-isting wireless local area network (WLAN) systems are numerically and experimentally presented. A UWB feed network prototype based on a modified two-section Wilkinson power divider is then developed. The designed feed network has been used in construct-ing two-element and four-element antenna arrays. The two-element antenna array has a total directive gain of about 5.5–8.5 dBi within the whole UWB frequency band while for the four-element antenna array, the achieved total directive gain is about 7.5–11.5 dBi.
Two different UWB slot-coupled microstrip-to-microstrip vertical transitions are also addressed. The proposed transitions utilize trapezoidal- and butterfly-shaped mi-crostrip patches at the top and bottom layers. The broadside coupling between microstrip-coupled patches is achieved by cutting a rectangular-shaped slot in the mid-layer ground plane. The designed transitions are used to develop 3dB/90° hybrid couplers with good return loss, insertion loss, coupling and isolation characteristics across the desired fre-quency range. Then two different 45° phase shifters are developed to be used in building 4 × 4 Butler matrices for UWB beamforming applications.
Finally, two compact and inexpensive multiple beamforming network (M-BFN) prototypes are developed. The developed microwave components using multi-layer mi-crostrip PCB technology are used to design 4 × 4 Butler matrices. These matrices avoid using any crossing lines or crossovers and exhibit large bandwidth for UWB applications. To validate the proposed design, experimental prototypes of the proposed 4 × 4 matrices are designed, fabricated and tested. A four patch antenna array is connected to these ma-trices to form multiple beamforming array systems. Simulations are carried out on these beamforming systems and the obtained radiation characteristics are also presented and discussed.