Beam steering reflectarrays using liquid crystal substrate

Radar acquisition and tracking systems often require the generation of single or multiple dynamically reconfigurable beams, which must be steered rapidly within the scan volume. Microstrip phased arrays are often used for these applications because this type of antenna can normally be designed to satisfy the pattern shape and coverage requirements and the beam can be scanned simply by varying the phase of the individual elements in the periodic structure. In this paper we present the preliminary results of a study to exploit the electrical properties of anisotropic nematic liquid crystal (LC) substrate in order to create a phase shifter which is suitable for beam scanning reflectarray antennas. A finite element computer model is used to establish the relationship between the LC thickness and the obtainable reflection phase range for a patch element, where the change in material permittivity can be obtained by applying a DC voltage between the patch and the ground plane. Waveguide simulator measurements are used to demonstrate the validity of the predictions.