# A Compact, Low-Profile, Broadband Quasi-Isotropic Antenna for Non-Line-of-Sight Communications
## 4 Measurements with the Built Prototype  
The proposed antenna is built on the same substrate used in the simulation for experimental verification, as shown in the photos in Figure 11. Each metallic arm is etched at the top and bottom sides of the substrate. The proposed antenna is fed using a coaxial cable surrounded by ferrite beads, also used in the simulation, to eliminate the current flows in the outer conductor of the cable. A quarter dollar coin is placed next to the antenna as a size reference in Figure 11a. The measured reflection coefficient can be found in Figure 7, where one can see a good agreement with the simulation. The radiation performance of the proposed antenna was measured in an anechoic chamber. The elevation (\(xz\)-plane) and azimuth (\(yz\)- and \(xy\)-planes) radiation patterns of the simulated and measured results are presented in Figure 12. Only the radiation patterns at 2.0, 2.6, 3.2, and 3.6 GHz are shown for the brevity of the paper. From this, it can be clearly seen that the proposed antenna shows an omni-directional radiation pattern at the \(xz\)- and \(yz\)-planes with a good quasi-isotropic radiation pattern at the \(xy\)-plane for the observed broad range of frequencies. The simulated and measured results generally agree with each other. The spherical radiation pattern measurement results are plotted in Figure 13. They show a similar trend to the computed ones, as displayed in Figure 8, although there is a deviation in the absolute gain values. The measured gain deviations across the frequencies can be found in Figure 7. The proposed quasi-isotropic antenna shows a maximum gain deviation in the range of 8.4 to 11.2 dB for the frequency range of 1.9 to 3.5 GHz from the measurement. When compared with the simulated gain deviation, which is in the range of 6.2 to 9.2 dB, the measured gain deviation is a bit higher around 2 dB and is in the range of 8.4 to 9.8 dB at frequencies from 1.9 to 3.3 GHz, where a gain deviation of less than 10 dB is observed. In addition, for frequencies around 1.8, 3.4, and 3.5 GHz, the gain deviations are 12.6, 11.2, and 10.7 dB, respectively. As expected from the simulation results of the different feeding methods shown in Figure 9, the feeding cable will surely affect the measured radiation performance of the antenna. Even though the material properties of the ferrite beads were characterized in the simulation setup, they could vary from those of real products. Another possible reason for the deviation might be from the anechoic chamber measurement setups, including the dielectric supporters, and not perfectly shielded measuring cables. Not only in this design, but also in most cases, quasi  
Figure 11: Photos of the built antenna. (**a**) Top view. (**b**) Bird’s eye view. isotropic antennas are quite sensitive to their feeding cables [18; 20; 25; 26]. Even though the measured gain deviation is higher than the simulation results, it is still within the acceptable range of the 10 dB criterion over the broadband frequencies. As illustrated in Figure 14, the measured peak gain is mostly in the range from 2 to 3 dBi, and the efficiency is around 90% from 1.9 to 3.3 GHz. Figure 12: Simulated and measured radiation patterns: (**a**) _xz_-plane at 2.0 and 2.6 GHz, (**b**) _yz_-plane at 2.0 and 2.6 GHz, (**c**) _xy_-plane at 2.0 and 2.6 GHz, (**d**) _xz_-plane at 3.2 and 3.6 GHz, (**e**) _yz_-plane at 3.2 and 3.6 GHz, and (**f**) _xy_-plane at 3.2 and 3.6 GHz. Figure 13: Measured spherical gain deviations of the proposed antenna: (**a**) 2.0 GHz, (**b**) 2.6 GHz, (**c**) 3.2 GHz, and (**d**) 3.6 GHz.