The most common form of Fresnel zone reflectors and lenses is the circular zoneplate. The design of the simple circular zoneplate is well documented in the open literature, and experiments at various frequencies and with various configurations had been reported from time to time since late nineteenth century [1–7]. However, no serious attention was paid to the offset or elliptical zoneplate until the 1980s [2, 9]. This might be due to the fact that “offset feeding” is mainly a microwave antenna concept and flush mounting a zoneplate to a chosen surface was not regarded as an important issue for optical and millimetre devices. In this chapter, a thorough study on the geometrical characteristics of offset zoneplates is presented and explicit design equations of offset zoneplate antennas are given. Then, based on the physical optics approximation, formulae for calculating the radiation pattern of offset Fresnel lens antennas are derived . Owing to the asymmetry caused by the offset configuration, calculation of the radiation integral can be time-consuming, so solutions to this problem are also provided in this chapter. Finally, an experiment on the offset Fresnel lens antenna is reported.
KeywordsZone Boundary Fresnel Zone Observation Angle Maximum Radiation Fresnel Lens
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