# Design and Analysis of Pattern Reconfigurable Antenna Based on RF MEMS Switches
## 4 Measurement and Results  
After the antenna design and simulation were completed, the layout of the antenna was made and processed. A 400 \(\upmu\)m thick, 11.9 relative permittivity, high-resistivity silicon surface was used to create the antenna structure. First, a thermal oxidation method was used to form a SiO\({}_{2}\) thin film with a thickness of 0.3 \(\upmu\)m on the surface of the high-resistivity silicon as an insulating layer. Second, 0.2 \(\upmu\)m thick aluminum was deposited on the silicon wafer and formed into direct current bias feeding points according to the preset pattern. Next, SiAl with a thickness of about 0.05 \(\upmu\)m was used to make the bias lines. Then, a dielectric layer with a thickness of 1500 A of Si\({}_{3}\)N\({}_{4}\) was prepared by PECVD on top of the electrodes and bias lines. After that, evaporation was performed to form a MEMS switch anchor area with a thickness of 1.5 \(\upmu\)m. Then, chemical mechanical polishing (CMP) was used to reduce the thickness of the polyimide sacrificial layer from 5 \(\upmu\)m to 1.3 \(\upmu\)m and aluminum with a thickness of 0.6 \(\upmu\)m was used to make the MEMS switch beam. Finally, plasma dry release technology was used for full-chip release to ensure that the switch beam would not collapse. Figure 11 shows the antenna after fabrication. Figure 11: Physical picture of the antenna. (**a**) Antenna with a test fixture; (**b**) An enlarged view of the antenna. Figure 10: Radiation pattern of the reconfigurable antenna. (**a**) Theoretical calculation results of the radiation pattern; (**b**) Simulation results of the radiation pattern. The pattern reconfigurable antenna designed in this paper works at 35 GHz, a frequency point at which impedance matching is critical for antenna performance. The return loss of the antenna needs to be measured, which is carried out by a vector network analyzer (R&S ZVA50, Rohde&Schwarz, Munich, Germany). Figure 12 shows the simulation and measurement results of the return loss of the antenna. According to the simulation results, the antenna is capable of switching among three working modes while maintaining a return loss greater than 20 dB in all three modes. When both switches are in the on state, the 10 dB bandwidth is about \((36-33.2)/35=8\%\), which far exceeds the design requirements. It is worth noting that the measurement results indicate a return loss greater than 17 dB in all three modes, and the 10 dB bandwidth is approximately \((36.1-35.25)/35=2.4\%\). The shapes of the return loss curves in both simulation and measurement results are very similar, which verifies the correctness of this design. Due to the use of fixtures in the test and the influence of processing technology and other factors, the return loss of the measurement results is not as good as the simulation effect, which is the main reason for the gap. The radiation pattern of the reconfigurable antenna in each working mode was tested in the microwave anechoic chamber after the return loss of the antenna was evaluated. For the antenna gain measurement in this paper, we adopted the comparison method. The test steps are as follows. 1. Connect the test system according to Figure 13 and power on the instrument equipment for preheating;
2. Calibrate the instrument and set the instrument parameters correctly, set the signal source and make the radiation direction of the transmitting antenna point to the gain reference antenna and the direction of the pattern reconfigurable antenna to be tested, turn on the DC bias power supply and make the pattern reconfigurable antenna enter one of the reconfigurable working modes;
3. Turn on the transmitting antenna and make it emit a constant power signal, adjust the position of the antenna to be tested so that its direction faces the direction of the signal transmitted by the transmitting antenna, and record the signal power intensity \(P_{AUT}\) received by the spectrum analyzer connected to the reconfigurable antenna to be tested.