Although the simple Fresnel zoneplate antenna with alternative reflective and transparent half-wave zones is easy to fabricate, its efficiency is too low for many practical applications. There are two factors that cause low efficiency to the simple Fresnel zoneplate. First, from a reception point of view, half of the energy intercepted by the aperture of a Fresnel zoneplate antenna is completely rejected. Second, the other half of the energy intercepted by the aperture is not efficiently focused into the feed, as the secondary radiation from a transparent half-wave zone does not add up completely in phase at the focal point. The first problem can be easily solved for reflection zoneplates, by placing a conducting plate at a quarter distance behind the simple zoneplate to form a phase reversal zoneplate reflector [4, 6]. The solution to the second problem is to apply phase correction techniques to the zoneplate surface . Since a continuous phase compensation is very difficult to achieve, two sub-optimal phase correction techniques have been used for high efficiency zoneplate antennas, the subzone phase correction and the optimal discrete phase correction [5, 14, 19]. This chapter is concerned with the first technique and the second one, which is to employ an array of discrete phase shifters, will be dealt with later in chapter 6.
KeywordsRadiation Pattern Phase Correction Dielectric Substrate Wave Zone Sidelobe Level
Unable to display preview. Download preview PDF.