Design of a Reflectarray Antenna at 300 GHz Using Parallel Dipoles of Variable Size Printed on a Quartz Wafer

Reflectarray antennas can offer a suitable technology for antennas in the sub-millimetre wave range, because the metallic patches can be realized by selectively wet etching a thin copper conductive layer deposited on an optical quality quartz wafer, as described in [1]. This process ensures very small tolerances for the patch dimensions and a very good flatness for the reflectarray antenna. However, a reflectarray made of a single layer of varying sized-patches is constrained by a narrow frequency band. It was proved that the use of stacked patches significantly improves the bandwidth [2], at the cost of a more complex manufacturing process derived from the bonding of different reflectarray layers. The simplification of the manufacturing process is particularly important in the case of sub-millimetre and THz ranges, where the manufacturing tolerances must be kept in the order of a few microns. In the present work, first we propose a reflectarray elementary cell made of three parallel dipoles printed on the same side of a 110-µm Quartz wafer, which is coated with a conductive layer on the back side to form the ground plane. The relative lengths of the three dipoles in the elementary cell are adjusted to improve the bandwidth of the reflectarray element (i.e. to provide a phase-curve very linear with the length of the dipoles) in a similar manner as in stacked patches, but in this case the three dipoles are on the same surface, as proposed in [3]. After some adjustments, a very linear phase response was obtained for the reflectarray cell. It has been demonstrated that the phase-shift produced by this reflectarray cell is very insensitive to the angle of incidence for angles up to 30 degrees. Based on these results, a reflectarray antenna has been designed using the data for normal incidence and the radiation patterns are shown in a 13% bandwidth.