# Design of Two Compact Wideband Monopoles Through Loading with Linear Approximated Lumped Components
## 3 Experiments and Results  
The optimized loaded monopole is fabricated as Figure 10a,b show. A copper tube is divided into eight segments producing seven gaps for arranging seven load circuits for the lower monopole. And the yellow plastic tube is employed as a bracket for keeping the linear structure of the lower loaded monopole. Since the material of this plastic tube is identical to an ordinary radome, there is little effect on the electric property of the antenna. The load unit of the lower monopole is composed of patch resistance, patch capacitance, and the coil inductor made of the outer surface of the outer conductor of the coaxial feeding line, as Figure 10c shows, which corresponds to the design depicted in Figure 4. The attenuator with 1.5 dB attenuation for the lower monopole is shown in Figure 10d. Ferrite beads choke the current to the ground while working as part of the attenuator at the same time, as Figure 5 depicts.  
Figure 10: Fabricated prototypes. (**a**) Two loaded monopoles in colinear structure; (**b**) upper monopole; (**c**) unit of load circuit; (**d**) attenuator for lower monopole.  
Figure 9: The simulated radiation patterns of the upper monopole. (**a**) At 1000 MHz. (**b**) At 1800 MHz. (**c**) At 2600 MHz.  
The experiment is carried out in outdoor open half-space environment, as shown in Figure 11. The transmitting and the receiving antenna are separated 100 m away for measurement of the far field at 30 MHz by employing the criterion of 10\(\lambda\) for far-field judgment. The measured and simulated VSWR of the lower monopole are shown in Figure 12a. It can be seen that the lower monopole covers a wide band of 30-750 MHz with a VSWR < 3.5. Acceptable agreement between the simulation and measurement can be found. The differences between the simulation and measurement may come from the fact that the practical load circuit possesses a certain square in contrast to the point load in the simulation. The measured and simulated gain of the lower monopole are shown in Figure 12b. Since it is unavoidable that multiple interferences appear in outdoor measurements, the measured gain vibrates slightly across the band. However, there is still acceptable agreement between the simulation and measurement. For the upper monopole, the plots of the measured and simulated VSWR and the measured and simulated gain are shown in Figure 13a,b, respectively. Since the feed line of the upper monopole traveled through the lower tube over 2 m, 2.5 dB attenuation is effectively introduced on the port of the upper monopole, which results in a better VSWR (<2), while the gain has not deteriorated yet. The introduced attenuator and loaded resistor absorb some power feed on the antenna port for matching across a wide bandwidth. The radiation efficiency of the lower monopole and the upper monopole shown in Figure 14 is acceptable in ultra-wide-band loaded monopole applications.  
Figure 11: Experiment in outdoor open half-space environment.  
Figure 12: Electrical property of lower monopole. (**a**) Measured and simulated VSWRs. (**b**) Measured and simulated gains.