# Design and Analysis of Pattern Reconfigurable Antenna Based on RF MEMS Switches
## 2 Antenna Structure Design
### RF MEMS Switch Design  
Compared to other RF switches, MEMS switches have benefits such as low insertion loss and excellent isolation. They play a crucial role in performance tuning for antenna reconfigurability in this paper. Figure 7 depicts the structure of the MEMS shunt capacitive switch, with the beam thickness being 1 \(\upmu\)m and the distance \(g_{0}\) between the beam and the dielectric layer being 1.5 \(\upmu\)m. The MEMS switch works by utilizing the electrostatic force generated by the DC voltage to change the distance \(g_{0}\), thereby controlling the on-off of the RF signal. When the electrostatic force causes the beam and the dielectric layer to contact, the MEMS switch is closed and in the down state, and the RF signal is cut off. When no DC voltage is applied, the switch is in the up state, and the beam and dielectric layer maintain a distance of 1.5 \(\upmu\)m, allowing the RF signal to pass through the transmission line below the beam. In addition, a fan-shaped microstrip line was utilized, with a length of approximately one quarter wavelength of the center frequency. The use of fan-shaped microstrip lines has two functions. One is to make the RF signal see an open circuit at the  
\begin{table}
\begin{tabular}{c c c} \hline
**Symbol** & **Description** & **Value** \\ \hline \(W_{0}\) & width of the main patch & 900 \(\upmu\)m \\ \(L_{0}\) & length of the main patch & 1500 \(\upmu\)m \\ \(W_{1}\) & width of the sub-patch & 400 \(\upmu\)m \\ \(L_{1}\) & length of the sub-patch & 890 \(\upmu\)m \\ \(W_{2}\) & width of the parasitic patch & 300 \(\upmu\)m \\ \(L_{2}\) & length of the parasitic patch & 450 \(\upmu\)m \\ \(W_{\mathrm{m}}\) & width of the impedance transformer & 110 \(\upmu\)m \\ \(L_{\mathrm{m}}\) & length of the impedance transformer & 1300 \(\upmu\)m \\ \(W_{\mathrm{n}}\) & width of the 50 \(\Omega\) microstrip line & 190 \(\upmu\)m \\ \(L_{\mathrm{n}}\) & length of the 50 \(\Omega\) microstrip line & 380 \(\upmu\)m \\ \(W_{\mathrm{b}}\) & width of the switch beam & 90 \(\upmu\)m \\ \(L_{\mathrm{b}}\) & length of the switch beam & 340 \(\upmu\)m \\ \(W_{\mathrm{h}}\) & width of the hole & 54 \(\upmu\)m \\ \(L_{\mathrm{h}}\) & length of the hole & 72 \(\upmu\)m \\ \(a\) & length of releasing hole & 8 \(\upmu\)m \\ \(r\) & length of the sector stub & 575 \(\upmu\)m \\ \(\delta\) & angle of the sector stub & 25\({}^{\circ}\) \\ \end{tabular}
\end{table}
Table 2: The physical size of the antenna.  
Figure 6: Top view of the antenna.  
end of the fan-shaped microstrip line so that the RF signal in the MEMS switch anchor area can smoothly pass through this fan-shaped microstrip line and short-circuit to ground. Another function is to reduce the size of the impedance transformer branch, making the structure of the entire antenna element more compact.  
The MEMS switch loaded with the fan-shaped microstrip line was simulated separately and the simulated insertion loss and isolation are shown in Figure 8. Figure 8 shows that, at 35 GHz, the MEMS switch's isolation can reach 20 dB while its insertion loss is only approximately 0.3 dB, which meets the design requirements and can ensure the performance of the reconfigurable antenna.