## 3 Experimental Results
There is also a good correlation between the simulated RHCP and LHCP gains (solid and dotted lines) and the measured RHCP and LHCP gains (dashed and dot-dashed lines), similar to realized gain patterns in the \(\phi=90^{\circ}\) plane. Additionally, since proposed series-fed array antennas are linear array antennas not for the \(\phi=0^{\circ}\) plane, but for \(\phi=90^{\circ}\) plane, the patterns of Figure 16 are similar to the radiation pattern of the unit cell in the \(\phi=0^{\circ}\) plane shown in Figure 2d, with differences observed in the magnitude of the gains. Figure 14: Simulated and measured axial ratio of the proposed series-fed antennas: (**a**) broadside antenna, (**b**) \(\theta=15^{\circ}\) beam-tilted antenna, (**c**) \(\theta=30^{\circ}\) beam-tilted antenna, and (**d**) \(\theta=45^{\circ}\) beam-tilted antenna. Figure 16: Simulated and measured radiation patterns of the proposed antennas in \(\phi=0^{\circ}\) plane at 5.84 GHz: (**a**) broadside antenna, (**b**) \(\theta=15^{\circ}\) beam-tilted antenna, (**c**) \(\theta=30^{\circ}\) beam-tilted antenna, and (**d**) \(\theta=45^{\circ}\) beam-tilted antenna. Figure 15: Simulated and measured radiation patterns of the proposed antennas at 5.84 GHz in \(\phi=90^{\circ}\) plane: (**a**) broadside antenna, (**b**) \(\theta=15^{\circ}\) beam-tilted antenna, (**c**) \(\theta=30^{\circ}\) beam-tilted antenna, and (**d**) \(\theta=45^{\circ}\) beam-tilted antenna. Figure 17 shows the simulated and measured RHCP gain patterns and ARs within the angular range of \(\pm 10^{\circ}\) from tilted angle, in \(\phi=90^{\circ}\) planes and at the operational frequency of 5.84 GHz. The measured ARs from each tilted angle stay below 3 dB within the HPBW for the proposed broadside antenna, \(\theta=15^{\circ}\), \(\theta=45^{\circ}\) beam-tilted antenna. The measured AR of \(\theta=30^{\circ}\) beam-tilted antenna is slightly above 3 dB at \(\theta=28.3\)-\(30^{\circ}\). The observed discrepancies between the simulated and measured results could be attributed to losses in the connecting cables and variations introduced during the manufacturing process. Figure 18 shows both the simulated and measured RHCP gains for each angle of beam tilt, along with the radiation efficiencies as functions of frequency. Figure 18a details the RHCP gains for the broadside series-fed array antenna at a \(\theta\) of \(0^{\circ}\). Figure 18b-d show the RHCP gains for beam tilt antennas at \(\theta=15^{\circ}\), \(30^{\circ}\), and \(45^{\circ}\), respectively, in the \(\phi=90^{\circ}\) plane. At the central frequency of 5.84 GHz, the measured RHCP gains of broadside series-fed array antenna, \(15^{\circ}\), \(30^{\circ}\) and \(45^{\circ}\) beam tilt antennas are 14.59 dBic, 13.09 dBic, 12.07 dBic and 10.71 dBic, respectively, which closely align with the simulated RHCP gains of 15.52 dBic, 13.75 dBic, 12.99 dBic and 11.76 dBic in sequence. The radiation efficiencies of the antennas at 5.84 GHz range from 80.3% to 84.8% in measurements, and the simulated radiation efficiencies at 5.84 GHz are in the range of 81.9% to 86.0%. The highest RHCP gains and efficiencies are centered around the frequency of 5.84 GHz. Table 2 summarizes the measured performance of the proposed series-fed antennas operating at 5.84 GHz, with data on impedance bandwidth, AR bandwidth, gain at tilted angles, HPBW in \(\phi=90^{\circ}\) plane, and AR 3-dB bandwidth in \(\phi=90^{\circ}\) plane. As the angle of beam tilting increases, both the impedance bandwidth and AR bandwidth narrow, and the gain at tilted angles decreases. Conversely, The HPBW and AR 3-dB bandwidth in the \(\phi=90^{\circ}\) plane both widen  
Figure 12.0 Simulated and measured AR and RHCP gain patterns of the proposed antennas at 5.84 GHz in \(\phi=90^{\circ}\) plane at the tilted angles: (**a**) broadside antenna, (**b**) \(\theta=15^{\circ}\) beam-tilted antenna, (**c**) \(\theta=30^{\circ}\) beam-tilted antenna, and (**d**) \(\theta=45^{\circ}\) beam-tilted antenna.