# Potential of Liquid-Crystal Materials for Millimeter-Wave Application
## 4 Microstrip-Line-Type Liquid Crystal Phase Shifter
### Basic Performance of Antenna Array  
Figure 9 shows a schematic diagram of a twin module array consisting of an LC phase shifter and an antenna. One of the antenna electrodes was on the upper surface, which was connected to a signal electrode of the microstrip line; the other was on the bottom surface, which was connected to the ground electrode. Both electrodes were aligned symmetrically, as shown in Figure 9a. Figure 9b shows a configuration of the twin antenna array, in which the units were aligned vertically. A metal plate was mounted on a part of the dielectric substrate of each microstrip line to construct the LC cell structure using a thin insulating spacer. The LC material was introduced to the cell cavity to construct the LC phase shifter. Each end of the upper metal plate had four through-holes to connect with the ground electrode on the lower surface of the microstrip line. This worked as the conversion circuit, which could switch the MMW propagation path between the lower dielectric substrate and the upper LC layer; then, the LC material could modulate the propagation of MMW. The conversion circuit allowed the introduction of the LC material onto the surface of the substrate to develop an LC phase shifterusing a microstrip line. The planar-type antenna was also easily introduced onto the same substrate, as shown in Figure 9b, in which only the upper electrode of the planar antenna appeared. Initially, the spatial distribution properties of the MMW intensity radiating from the planar antenna were measured along the direction perpendicular to the substrate (\(y\)-direction), as shown in Figure 10a. The MMW (50 GHz) generated by the Gunn diode oscillator was fed to the left end of the planar antenna through the end launch connector. The spatial distribution of the radiated MMW intensity was measured by a diode detector mounted on the \(xy\) stage, which was set at a distance of 150 mm from the antenna. A short rectangular waveguide was mounted on the incident window of  
Figure 8: Changes in MMW focusing property of the LC composite Fresnel lens upon applying a magnetic field (**a**) parallel or (**b**) perpendicular to the electric field of the MMW. the diode detector; thus, it could only detect the MMW polarization direction parallel to the short arm of the waveguide aperture. It can be seen that the radiating MMW was strongly polarized horizontally (\(x\)-direction), because the vertical component (E\({}_{y}\)) was negligible. This result is reasonable if we consider that the electrodes of the antenna were aligned in the substrate plane. A symmetric distribution profile appeared along the direction perpendicular to the substrate plane, as shown in Figure 10a. Although we observed some asymmetric distribution along the direction parallel to the substrate, it was clear that the stack of the antennas along the \(y\)-direction was effective in checking the performance of the antenna array. Figure 10: (**a**) Radiation profile of an antenna along the direction perpendicular to the substrate. Radiation profiles of the twin array of antenna modules, whose distances are (**b**) 10 mm, (**c**) 20 mm, and (**d**) 30 mm. Figure 9: (**a**) Antenna electrode pattern, where both electrodes on the upper and lower surfaces are shown at the same time; (**b**) twin vertical array of antenna modules, which consists of a planar antenna and an LC phase shifter. Two units combining the LC phase shifter and planar antenna were aligned as their substrates became parallel to each other, as shown in Figure 9b. The radiated MMW intensity distribution properties of the twin antenna array were measured by changing the separation distance between them at 10 mm, 20 mm, and 30 mm, as shown in Figure 10b-d, respectively. It was observed that the MMW distribution profile became narrower and the intensity peak increased upon constructing the array. The main MMW beam tended to be narrower with increasing distance between the antennas; however, it was also observed that the side lobe tended to increase for the longer distance.