## 3 Results
### Fabrication and Measurement  
Following optimization via DH-BPSO, optimized and base IFAs were fabricated with ground clearance lengths of 9, 10, 12, and 14 mm using a LPKF S4 laser milling machine. The fabricated antennas with semi-rigid, 50 \(\Omega\) coaxial connectors attached are depicted in Figure 8. The reflection coefficient of each antenna was measured over a frequency range of 0.5 to 1 GHz using an Agilent E8364C PNA. Figure 7 compares the performance of the fabricated antennas with the simulations of the base and DH-BPSO-optimized designs. The optimized designs show good agreement between simulation and measurement results overall. The 14 mm ground clearance length IFA showed a measured bandwidth increase of 58.6%. The discrepancy from the simulated bandwidth increase can be attributed to fabrication tolerances. The measurements of the base IFA also show good agreement with the simulations, with a slight discrepancy of 6.83 MHz at 9 mm clearance length. Thus, the measurement results validate the results of the simulations and show that the DH-BPSO algorithm successfully found an optimal parasitic patch configuration to increase bandwidth of the IFA. The radiation patterns, peak gain, and radiation efficiency were measured using a Model 2100D anechoic chamber from The Howland Company. Figure 9 shows the measurement setup in the anechoic chamber. The simulated and measured radiation patterns are shown in Table 4 below. The omnidirectional radiation patterns were observed on the \(\varphi=90^{\circ}\) plane. In the \(\varphi=90^{\circ}\) plane, figure \"8\" shapes of radiation were measured, indicating characteristics of a dipole antenna. For the both principle planes, the simulated and measured results show good agreement. The DH-BPSO optimized IFA shows similar radiation characteristics as those of the base IFA despite the presence of parasitic patches. The simulated current distribution is also shown in Table 4. The current is strongest around the feed, grounding strip, and activated parasitic patches, whereas it is weakest at the end of the IFA arm and FR4 substrate. This supports the omnidirectional and figure \"8\" shape of radiation patterns. Figure 8: (**a**) The four IFA antennas with optimized parasitic patch configuration fabricated with attached connectors. (**b**) The four base IFAs measured as reference. Although the goal of the DH-BPSO algorithm was to improve the \(-10\) dB bandwidth, improvements in peak gain and efficiency are also observed. Figure 10 compares the peak gain and efficiency between the simulations and measurements. According to the simulated results, the DH-BPSO-optimized IFA shows a higher peak gain for all ground clearance lengths. The largest increase in peak gain is 5.8% observed at 14 mm ground clearance length. The peak gain slightly increases as the ground clearance becomes larger for both the simulated and measured results, as expected. The measured optimized peak gain varies from 2.9 to 3.2 dBi. In addition, the radiation efficiency of the optimized IFA improved by as much as 6.4% compared to the base IFA efficiency. The measured radiation efficiency ranges from 89% to 97% for 9 and 14 mm ground clearances, respectively. The discrepancy between the simulated and measured results can be attributed to fabrication tolerances. Thus, the radiation pattern, gain, and efficiency of the proposed IFA is suitable for mobile devices. Table 5 compares the bandwidth enhancement results of this article to those achieved in recent literature. [PERSON] and [PERSON] [31] make use of the Hybrid PSO (HPSO) algorithm, which makes use of both the real PSO algorithm [24] and the original binary PSO [14] to simultaneously optimize the configuration and spacing between parasitic patches surrounding a microstrip patch antenna. However, we achieve a markedly higher bandwidth improvement of 58.6% using DH-BPSO as opposed to the 16.3% achieved using HBPSO. [PERSON] et al. in [30] and [PERSON], et al. in [47] achieve bandwidth enhancement using curve fitting in conjunction with PSO.