# A Frequency-Selective Reconfigurable Antenna for Wireless Applications in the S and C Bands
## 4 Experimental Results and Discussion  
The front and the back side of the fabricated multi-frequency reconfigurable patch antenna is shown in Figure 6. For the purpose of providing the biasing voltage to the PIN diode, two pins were soldered on the antenna, one next to the diode's anode, and the second to the side of the lower part of the ground plane. By varying the voltage on the diode, three modes arise with main resonances in the 2, 4, and 6 GHz bands, as dictated by the simulation results. Mode 1 corresponds to the best performance in the 2 GHz band, mode 2 in the 4 GHz band, and mode 3 in the 6 GHz band. Each mode is characterized by a forward-biasing voltage of 0, 550, and 740 mV, respectively. A Rohde & Schwarz ZVH8 Handheld VNA was used to experimentally validate the performance of the multifrequency reconfigurable patch antenna through S11 and VSWR. Figure 7a shows a snapshot of the S11 measurement for the multifrequency antenna before adding the PIN diode, while Figure 7b shows the S11 measurement for the reconfigurable antenna operating under mode 3 (6.22 GHz). The reconfiguration of the antenna is performed remotely through an Android application that changes the excitation voltage on the diode using a Raspberry platform. It is also essential to mention that, in our setup, we utilized a high-quality DAC as the voltage source for biasing the diode. The DAC's output has a low impedance of 1 Ohm, ensuring a stable DC bias voltage without significant AC components. Additionally, it provides exceptional isolation from AC signals, about 100 dB. Consequently, while the inclusion of chokes is essential in many cases, it was deemed non-critical for our application. The measurements of the antenna radiation pattern took place in a free-space lab environment in the university with dimensions of 5 m width by 10 m length. The free-space lab measurement plan appears in Figure 8. The fabricated prototype patch antenna was placed on top of a specific wooden positioning structure at a height of 1.5 m from the ground and at 6 m was the receiving antenna on a Tektronix RS3408A real-time spectrum analyzer. The fabricated patch antenna was stimulated using a signal generator, transmitting an unmodulated carrier at the frequency of three operation modes. The measurements for each operation mode were conducted at a 10-degree-step resolution, and to optimize the results, they were repeated five times. Each value on the antenna radiation pattern is the average value. Figure 9 shows a photograph of the measurement setup. Figure 6: Fabricated multi-frequency reconfigurable patch antenna (**a**) top side and (**b**) bottom side. Figure 8: Free-space lab measurement plan. Figure 7: S11 measurement setup for the antenna (**a**) before adding the PIN diode and (**b**) after adding the PIN diode, with the antenna operating in mode 3 (6.22 GHz). Figure 9: Measurement setup. The S11 and VSWR results are depicted in Figure 10. According to the experimental results in Figures 7 and 8, the antenna shows three excellent resonances in the 2, 4, and 6 GHz bands with a return loss well below \(-40\) dB and a VSWR no higher than 1.02 in all cases. Specifically, the primary resonance for mode 1 is found at 2.07 GHz, with a \(-43.1\) dB return loss, which is 15.6 dB lower than the return loss of a secondary resonance seen at 6.21 GHz. The VSWR at the 2.07 GHz resonance is 1.01, and the \(-10\) dB bandwidth is 327 MHz. Concerning mode 2, it shows a main resonance at 4.63 GHz. It has a return loss of \(-41.3\) dB, 17.1 dB lower than that of a secondary resonance at 6.17 GHz. The value of VSWR, in this case, is 1.02, and the \(-10\) dB bandwidth is 260 MHz. Finally, for mode 3, the primary resonance is found at 6.22 GHz, and the return loss is \(-45.6\) dB, 28.9 dB lower than that of a secondary resonance found at 2.07 GHz. The VSWR of the 6.22 GHz resonance is 1.01, and the bandwidth defined at \(-10\) dB return loss is found at 387 MHz.