## 3 Experimental Results  
To prove the design of the proposed series-fed antennas, prototypes of each proposed antenna according to the beam tilting angle were manufactured, as shown in Figure 11. The manufactured prototype antennas have a size of \((6.22\lambda_{0}\times\ 0.78\lambda_{0}\times\ 0.015\lambda_{0}\), where \(\lambda_{0}\) is the free space wavelength at 5.84 GHz). The reflection coefficient was measured with an Agilent E8363B RF network analyzer. The AR and the radiation pattern were measured in an anechoic chamber designed for far-field measurements. A Linear Polarization (LP) standard gain horn antenna and antenna rotating technology were employed for testing, as shown in Figure 12.  
Figure 11: Photographs of the fabricated series-fed antennas prototype: (**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 10: Simulated impedance characteristics of matching network: (**a**) reflection coefficient and transmission coefficient of impedance-matching network, (**b**) input impedance of the broadside series-fed antenna, and (**c**) reflection coefficient of the broadside series-fed antenna. Figure 13 shows the simulated and measured reflection coefficient of the proposed series-fed antennas. The measured(simulated) reflection coefficients of broadside, \(15^{\circ}\), \(30^{\circ}\) and \(45^{\circ}\) beam tilt series-fed array antennas at 5.84 GHz are \(-22.5\) (\(-19.35\)) dB, \(-21.6\) (\(-21.8\)) dB, \(-20.24\) (\(-35.6\)) dB and \(-17.54\) (\(-29.1\)) dB in sequence. The measured (simulated) \(-10\) dB reflection coefficient bandwidth ranges are in a row: \(27.1\%\) (\(6.6\%\)), \(11.1\%\) (\(11.2\%\)), \(7.9\%\) (\(7.2\%\)), and \(6.3\%\) (\(6.4\%\)) in a same sequence. The simulated and measured axial ratios of each tilted angle are shown in Figure 14. The measured(simulated) axial ratios of broadside, \(15^{\circ}\), \(30^{\circ}\) and \(45^{\circ}\) beam tilt series-fed array antennas at 5.84 GHz are sequentially 2.71 (2.35), 2.12 (2.91), 3.44 (2.65) and 2.98 (2.69) dB. The measured results are quite consistent with the simulated results, but the measured axial ratio of \(\theta\) = \(30^{\circ}\) beam-tilted antenna at 5.84 GHz and its tilted angle is over 3 dB  
Figure 12: Measurement setup in an anechoic chamber. Figure 13: Simulated and measured reflection coefficient 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. level. The measured (simulated) 3 dB AR bandwidth ranges are 5.8-5.84 (5.8-5.84) GHz, 5.78-5.84 (5.79-5.85) GHz, 5.78-5.83 (5.79-5.84) GHz and 5.79-5.84 (5.8-5.85) GHz in a row. The corresponding AR fractional bandwidth is 1.03% (0.86%), 1.03% (1.03%), 0.86% (0.86%) and 0.86% (0.86%). Figure 15 shows simulated and measured results of realized gain patterns of the proposed series-fed antennas at 5.84 GHz. Each subplot represents different beam tilt angles of each tilted antenna, comparing RHCP and left-hand circular polarization (LHCP) gains in the \(\phi=90^{\circ}\) plane. Figure 15a is realized gain patterns of the broadside antenna, while Figure 15b-d shows realized gain patterns of antennas with \(15^{\circ}\), \(30^{\circ}\), and \(45^{\circ}\) beam tilts, respectively. There is 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). The maximum RHCP gains occur at angles \(\theta=0^{\circ}\), \(15^{\circ}\), \(30^{\circ}\), and \(45^{\circ}\), as designed, and the RHCP gain patterns tend to broaden as the beam tilting angle \(\theta\) increases. Figure 16 presents the simulated and measured radiation patterns of the proposed antenna from the main lobe's central axis in the \(\phi=0^{\circ}\) plane, comparing RHCP and LHCP gains at 5.84 GHz.