## 4 Fabrication and Experimental Demonstration  
Figure 8 shows the proposed antenna fabricated sample to experimentally verify the concept. Figure 8a,b shows the circular disk and circular sector modes. The circular patch conductive pattern was implemented using copper tape. Ecoflex 00-30 was provided by Smooth-On, Inc (5600 Lower Macungie Road, Macungie, PA 18062, USA). The SMA spring employed was a commercial product, with 150 mm total length and 9 mm pitch. However, we only used a 5 mm section for the proposed kirigami-inspired structure. The spring was one-way with 10 N force (nominal) when pulled. Figure 8c shows that the SMA spring was pulled within 16-20 s by applying 0.68 V at 3 A was applied, confirming successful mode conversion. Figure 9 compares simulated and measured reflection coefficient for the proposed antenna in the circular disk and circular sector modes. The reflection coefficient was measured with an Anritsu MS2038C network analyzer. Simulated and measured reflection coefficient = \(-17.12\) and \(-12.81\) dB at 2.4 GHz, and \(-12.65\) and \(-22.43\) dB at 3.25 GHz for the circular disk and circular sector modes, respectively.  
Figure 7: (**a**) Kirigami-inspired structure with SMA rendered in COMSOL; (**b**) simulated von Mises stress; (**c**) total displacement with respect to time.  
Figure 10 shows simulated and measured normalized radiation patterns for the proposed antenna for each mode. Figure 10a,b shows normalized radiation patterns in \(XZ\) and \(YZ\) planes, respectively, in circular disk mode at 2.41 GHz, with simulated and measured peak gains = 4.9 and 4.26 dBi, respectively. Figure 10c,d shows normalized radiation patterns in \(XZ\) and \(YZ\) planes, respectively, in circular sector mode at 3.25 GHz, with simulated and measured peak gains = 5.95 and 6.41 dBi, respectively. The measured difference between co and cross-polarization = 15.49 and 18.47 dB in the boresight direction in the circular disk and circular sector modes, respectively. Figure 11a,b shows the simulated and measured radiation efficiency at different tangential losses for the circular disk mode and circular sector mode, respectively. Simulated and measured radiation efficiency = 65.55 and 51.44% at 2.41 GHz and 76.42 and 75.5% at 3.25 GHz for circular disk and circular sector modes, respectively. As shown in Figure 11, the radiation efficiency can be increased by decreasing the tangential loss of the substrate. In addition, the simulated efficiency is compared with the measured efficiency. The difference between the simulated and measured efficiency was due to the adhesive film from the copper tape.  
In Table 1, the proposed antenna was compared with other frequency reconfigurable antennas with different tuning technologies. It was observed that the mechanical and thermal tuning methods could achieve a wider frequency tuning range compared to  
Figure 8: Fabrication sample in (**a**) circular disk and (**b**) circular sector modes. (**c**) Measurement setup.  
Figure 9: Simulated and measured reflection coefficient for a proposed antenna in circular disk mode and circular sector mode.  
electrical and optical tuning methods because of their low parasitic capacitance. In this work, we sacrificed the tuning range for less stress of the SMA spring. Nevertheless, its tuning range can be increased with a longer SMA spring or larger mechanical deformation.  
Figure 10: Simulated and measured normalized radiation patterns for circular disk mode in the (**a**) \(XZ\) and (**b**) \(YZ\) planes; and circular sector mode in the (**c**) \(XZ\) and (**d**) \(YZ\) plane.