Liquid crystal mixed beam-switching and beam-steering network in hybrid metallic and dielectric waveguide technology

Future communication systems at W-band are demanding highly directive antenna systems with beam-steering capability. For the hardware implementation of analogue beam-steering at millimetre waves, the microwave liquid crystal (LC) technology is ideally suited. It takes advantage of specifically synthesised LCs for microwaves in combination with appropriate device and biasing concepts, where the orientation of the LC, and therefore, its effective permittivity can be continuously tuned. It has low dielectric losses above 10 GHz with a decreasing trend with increasing frequency. To exploit these unique characteristics, the focus of this scientific work is set for the first time on the investigation of an LC-based network with mixed discrete beam-switching and continuous beam-steering capability between the switching states for high-gain antennas at W-band. It consists of a Butler matrix combined with continuously tuneable phase shifters and a novel type of RF switch, an interference-based Single-Pole n-Throw (SPnT). The interference principle of the SPnT allows a continuously adjustable power splitting ratio, and hence, the generation of multiple beams. Different technologies are investigated for the realisation of this mixed network. Due to its high level of integrability and compact designs, the standard low temperature co-fired ceramic technology is examined, however, for a first proof-of-concept at Ka-band only. For W-band, two low-loss technologies are investigated: tuneable metallic and dielectric waveguides. The hybrid combination of metallic and dielectric waveguides reveals a high potential not only for the presented LC-based mixed beam-switching and beam-steering network, but also for LC-tuned continuous beam-steering networks at frequencies above 100 GHz.