| The objective of this research is to investigate and develop a novel measurement method of microwave holography for the situation where the subreflector or feed may not be easily displaced or when the system is desired to be measured in-place, that is to characterize a particular alignment. Other potential advantages unique to this technique will also be discussed. Since the primary effect of the slight defocusing is a phase shift between ray paths reflecting on the antenna surface, a microwave lens may be employed as an alternative method of defocusing the antenna. As part of this study, different types of microwave lenses have been studied, designed, and implemented to achieve this primary purpose, and measurements have been performed to demonstrate and explore the potential and feasibility of the proposed method. This method is well suited to those facilities that are not able or willing to move the subreflector or feed, or cannot move them a sufficient amount, and do not wish to set up a coherent reference antenna. In addition, this method affords the possibility of examining the effects of a feed or subreflector at a specific position on the system as a whole. As another advantage, utilization of the lens also allows the freedom to select the profile and amount of the phase variation over the aperture, which according to the preliminary study may result in some advantages in obtaining accurate results or in probing specific effects. |
