81-Element single-layer reflectarray with double-ring phasing elements for wideband applications

Abstract

A microstrip reflectarray antenna utilizes a planar array of printed patch elements and a conventional prime or offset feed to form an alternative to the parabolic reflector [1]. It transforms the spherical wave of the feed into the planar wave by employing microstrip patch elements as radiators and phase shifters. Due to the use of planar technology, it offers a good balance between conventional reflector antennas and phased arrays. Because it uses many radiating elements it provides flexibility with respect to radiation pattern formation [2-4]. Its disadvantage is a limited operational bandwidth, which for the case of moderate gain is mainly due to a limited phase range and a high phase slope of the elements. In the wave transformation process, a full phasing range of 360° is desirable for unit cells containing patch elements. However, a variable size patch antenna developed on a single layer substrate offers a phasing range of about 300°. To overcome this problem, multilayer substrates including stacked variable-size patches for phasing the unit cells of a reflectarray have been devised to extend the phase range to multiples of 360°. The multi-layer approach with stacked patches not only extends the phase range but also reduces the slope of the phase curve as a function of patch dimensions [5-6]. However, the use of multi-layer substrates means that in practice layers of the reflectarray have to be manufactured separately and the assembly should leave no air gaps. This results in an elaborate and expensive manufacturing process. To overcome this problem, printed double-ring elements to form a single-layer reflectarray have been proposed. The double rings improve the phasing range of unit cells by utilizing multi-resonance behaviour. The extended range for unit cells containing double-ring elements has been demonstrated for the case of normal (TEM) wave incidence [7]. The assumption of normal incidence is less accurate for peripheral elements. Therefore in [8], TE and TM waves were considered to obtain an oblique incidence to obtain more accurate phasing characteristics of unit cells. © 2010 IEEE