Manufacturing and testing of liquid crystal phase shifters for an electronically steerable array

In 2011 TU-Munich together with TU-Darmstadt started to develop a novel phased array antenna with liquid crystal phase shifters for space applications (Lisa-ES). The antenna design and manufacturing is based on the precursor Lisa-MS (mechanically steered). Both antennas are designed for inter-satellite links in the Ka-Band (23/27 GHz). The novel part in this antenna is a phase shifter that uses liquid crystals that are placed within a waveguide. Several of these liquid crystal phase shifters are than placed in-between the distribution network of the array antenna and each horn. The phase shift is controlled by the orientation of the liquid crystals and thus by the variation of the relative permittivity. In this case the orientation of the liquid crystals is controlled by an electric field. The liquid crystal phase shifters design is very sensitive to air gaps and air bubbles within the waveguide. Therefore, the non-conductive polystyrene container is vapor-metallized (400 nm silver) and then electroplated with 600 μm copper to achieve a gap-free conductive surface (= waveguide). The process for the antenna was well established from a precursor project. Finding the appropriate integrated manufacturing sequence and processes was much more time-consuming and challenging than originally expected at the start of this project. The process remains complex and error-prone. Environmental tests in addition to further high frequency performance tests are designed to prove the viability of the selected design. Despite the complexity and unavoidable losses within the phase shifter, the concept has advantages over alternate designs and could become a viable option for selected applications.