  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.
