High frequency performance extending to millimeter-waves in inverted-microstrip-line-type LC phase shifter

Various liquid crystal (LC) phase shifters that operate in the super-high-frequency electromagnetic-wave regions have been investigated using planar-type excellent waveguides such as the microstrip line (MSL) and coplanar waveguide (CPW). First planar-type LC phase shifters were constructed using MSL, which was developed as an excellent planar waveguide for super-high-frequency electromagnetic waves. CPW-type LC phase shifters have attracted continued attention, because when they are used, all the signal and ground electrodes are at the same surface, which leads to ease in integration for constructing various functional devices. However, they suffer from an essential drawback of degradation in the phase shift magnitude, which is because the propagating electromagnetic waves encounter the permittivity of both the substrate and the LC materials, which reduces the modulation effect of the LC materials to less than half. In this work, a novel MSL-type LC phase shifter is investigated to achieve excellent phase shifting performance while maintaining ease in integration, as offered by the CPW-type phase shifter. Several device structural parameters are investigated to improve the transmission and phase shifting properties. Some LC materials are also tested for further improvement in the high-frequency operation extended to the millimeter-wave region.