## 3 Experiments and Discussion  
In this section, we experimentally validate the proposed phase shifter. The performance of the proposed LC-based phase shifter was analyzed by numerical finite difference time domain (FDTD) simulation. The prototype was fabricated by the ultraviolet light photoetching combined with the wet etching. The fabrication process consisted of the vacuum copper plating, photoresist spin coating, exposure, development, and wet etching. The sample and microscope image of the unit cell are shown in Figure 6, where it can be seen that the sample consisted of a 30 \(\times\) 30 unit cells, printed on the 40 \(\times\) 40 mm\({}^{2}\) area on a quartz substrate with the thickness of 520 mm and thickness tolerance of \(\pm\)10 \(\upmu\)m. The unit cell structure had a dimensional tolerance of \(\pm\)4 \(\upmu\)m on the wide side and \(\pm\)1 \(\upmu\)m on the narrow side. Figure 4: Operation principle of the reflectarray. Figure 5: Simulated static electric field strength and direction in the LC layer. Figure 6: Photograph of the fabricated prototype. The measurement setup used in the experiments is shown in Figure 7. An Agilent N5224A vector network analyzer (Keysight Technologies, Inc., Santa Rosa, CA, USA) with N5262 AW08 extender (Virginia Diodes, Inc., Charlottesville, VA, USA) was used to measure the spectral response of the fabricated structure. The free space measurements were used to obtain the scattering parameters in the frequency range from 110 to 140 GHz. In order to decrease the influence from the environment, the calibration was performed as follows: Firstly, calibrating the reflection amplitude on an ideal reflector. Secondly, the actual reflections from the sample were measured. Finally, compared the reflection from the sample and the reflection from the ideal reflector. In the experiments, a 1 kHz square wave with the maximum voltage of 10 V was energized between the ground and patches. The orientation of molecules decided the permittivity of the LC. The rotation speed of LC molecules, which is independent on testing frequencies, is mainly determined by external voltage. The response time of the LC was investigated by measuring voltage-transmission curves in transparent test cells made with the same spacers as were used in the unit cell samples. The transmission experiment was realized with a HeNe-laser source and photodetector. As expected in test cells with a relatively large cell gap, a response time of 200 ms was found. The response times can potentially be pushed by including a small amount of in-situ generated polymer or copolymer in the samples [25; 26; 27; 28]. The measured reflection amplitude at different voltages is presented in Figure 8a, wherein it can be seen that by increasing the bias voltage, the resonant frequency changed from 132 GHz (0 V bias) to 116 GHz (10 V bias). At the bias voltage of 10 V, most of the LC molecules were oriented parallel to the electric component of the static electric field, resulting in the relative permittivity similar to \(\varepsilon_{//}\). The loss of device is consisted of the ohmic loss in the copper layer, the absorption loss in the quartz plate and the LC layer, and resonant loss [29]. The test results also include the loss in free space, scattering loss, and receiving loss. As shown in Figure 8b, the simulation of reflection amplitude at different dielectric properties is obtained. Figure 7: Measurement setup of the reflectarray. The simulation and experimental results in the working frequency range are presented in Figure 9. All phases were normalized relative phases to the simulated 0 V phase curve.