In recent years reflectarray has received more and more attention and it has been considered as a suitable candidate to replace the traditional reflectors due to its high-gain, low profile and low cost features. Reflectarray also eliminates the lossy feed network and costly transmitting and receiving modules when comparing with phased array antenna. It is desired to implement these functionalities with simple and effective techniques. Narrow bandwidth is the main issue which restricts the applications of the microstrip antennas, including the microstrip reflectarray. A broadband singlelayer reflectarray is introduced as the solutions to the issue of narrow bandwidth. A combination of two types of element configurations, including (i) ring elements and (ii) circular patch elements with ring boundary, enlarges the reflection phase range to more than 360◦ and thus enables the broadband operation of reflectarray. Blockage effect is another issue with the center-fed reflectarray. Certain obstacles, such as the feed horn, subreflector, and their supports, exist in reflectarray antennas. When these obstacles are in front of the reflectarray, the reflected wave is blocked, and the feed’s absorption also weakens the reflected power. An accurate prediction of this blockage effect in reflectarray design is essential. Five modeling schemes to account for the blockage effects in a reflectarray are described and also compared in terms of simulation time and consumed computing resource. In addition, another reflectarray with mainbeam direction steered 18◦ off broadside is also introduced to mitigate the blockage effect. Low cross-polarization performance is required for some reflectarray applications. For example, in dual-polarized weather radar the precipitation detection relies on complete isolation of orthogonal components of the fields, and thus negligible levels of cross-polarized radiation along the beam axis need to be maintained. A reflectarray design with suppressed cross-polarization is introduced in this dissertation. The directions of the surface currents can be changed by cutting gaps on the double-ring elements, so that the co-polar components of the surface currents enhance each other while the cross-polar components cancel each other, and thus a low cross-polarization level can be achieved. An X/Ku dual-band microstrip reflectarray with cosecant squared shaped beams has also been developed. The two operation frequency bands, 10 GHz and 15 GHz, are very close to each other. Thus the radiation interference between the two bands is taken into consideration and design is optimized to suppress the interference as much as possible. A dual-layer structure with cross-dipoles on the top layer and double-rings on the lower layer is adopted to suppress the interband couplings. Moreover, the dual-band elements are arranged in an interleaved manner in order to minimize element blockage. In addition, a phase-only synthesis technique is also introduced to obtain the two cosecant squared shaped beams for each operation frequency band. In summary, this dissertation presents a series of new research developments for reflectarray antennas. The results should have many applications for the modern wireless communications and radar systems.