Reflective Liquid-Crystal Phase Shifter based on Periodically Loaded Differential Microstrip Lines

Abstract: High-performance phase control units are crucial in beamforming technology, which has gained substantial attention for its ability to manipulate the wireless propagation environment, thereby enhancing capacity and coverage in communication networks. This paper presents the design and fabrication of a 3.5GHz reflective liquid-crystal (LC) phase shifter. The phase shifter is constructed using coplanar differential lines, periodically loaded with floating electrodes. The LCs in the overlapping areas act as variable capacitors, and the continuous phase shift can be adjusted by applying AC to the permittivity in these areas. Both simulation and measurement results demonstrate impressive Figures of Merit (FoM) of 101.3 degrees per dB and 85.7 degrees per dB, respectively. The grounding issues typically associated with coplanar waveguides (CPWs) on glass substrates are effectively mitigated by employing the virtual ground in a differential pair configuration. The innovative reflective-type operation minimizes the unit cell size and allows for low-cost manufacturing of phase shifter arrays and advances the practical development of beamforming technology.