# Wideband-Narrowband Switchable Tapered Slot Antenna for Breast Cancer Diagnosis and Treatment
## 3 Simulation and Measurement Results  
As mentioned earlier, a meander line resonator was printed on the backside of the TSA. To achieve frequency switchable characteristics, an SMV 1231 PIN diode switch was inserted in the middle of the meander line resonator to control the current induced by the flared slot, as shown in Figure 9a. In Figure 9b, the measurement configuration with a fabricated breast phantom and supporting structure is represented. The DC biasing line was connected to the DC power supply through the inductors for RF choking, and the bias voltage was 0.8 V in order to activate the diode. When the PIN diode was in the OFF state, the transmission line that connected the two sides of the symmetric meander line resonator was terminated, and the current was not induced. In this case, the proposed antenna operated as a conventional wideband antenna in the frequency range of 3.1-10 GHz, as shown in Figure 10a. The simulated reflection coefficients both with and without the meander line were compared to verify that the designed meander lines did not degrade the wideband impedance matching characteristic. There were mismatches for the reflection coefficient between the simulated and measured results around 4 and 6.5 GHz. It could be seen that there were some deviations in the measurement condition, such as antenna fabrication errors, coaxial cable utilization in the experiment, soldering effects, and the variation of dielectric properties of the RF-4 substrate within tolerance levels. However, the measured reflection coefficient was acceptable for the entire frequency band. On the other hand, when the PIN diode was in the ON state, the EM energy was transferred to the transmission line between the meander lines and the current induced in the meander line resonators. In this case, the TSA operated as a narrowband antenna, as shown in Figure 10b. In Figure 10b, several resonances are shown in other frequency bands caused by the harmonics of the meander line. Therefore, multiple resonances occurred even in the narrowband mode because of the band-pass characteristic of meander line resonators. However, in this paper, for microwave hyperthermia we only used 2.45 GHz as a power  
Figure 9: Fabricated frequency switchable TSA: (**a**) front and back, and (**b**) antenna measurement configuration with the fabricated breast phantom and supporting structure. source. Current distributions are presented in Figure 11, verifying the resonance and traveling-wave modes, both of which depended on the PIN diode. Table 2 compares the proposed antenna with the existing research in terms of the type and size of the wideband antenna, the number of switching elements, and the shape and size of the narrowband structure. To compare the electrical size of the narrowband structure with other papers, the resonance frequency and relative dielectric constant of the substrate were considered to calculate the size of the narrowband structure in \(\lambda_{\mathrm{r}}\). The results suggested that the proposed antenna exhibits a frequency switching characteristic with the smallest number of PIN diodes as well as the smallest electrical size for the narrowband structure. Figure 11: Simulated current distributions: (**a**) resonance mode at 2.45 GHz with the PIN diode in the ON state and (**b**) traveling-wave mode at 5, 7, and 9 GHz with the PIN diode in the OFF state. Figure 10: The simulated and measured reflection coefficients: (**a**) wideband mode for microwave imaging and (**b**) narrowband mode for microwave hyperthermia.