# Extremely Low-Profile Monopolar Microstrip Antenna with Wide Bandwidth
## 3 Implementation and Measurement Results  
The proposed antenna, denoted as \"MK4\", was fabricated as shown in Figure 5. Using a finite element method-based full-wave electromagnetic simulator of Ansys High Frequency Structure Simulator (HFSS), the proposed antenna was finalized with physical dimensions, as summarized in Table 1. The 0.254 mm-thick substrate of Rogers RT/duroid 5880 with a dielectric constant of 2.2 and loss tangent of 0.0009 was used, and the substrate diameter, \(D\), was set as 70 mm. All of the dimensions of the proposed antenna were optimized to maximize the operating bandwidth with the thin substrate and to minimize the fabrication errors that occur in the antenna manufacturing process. In addition, the parameters of the antenna prototype ensure process reliability. After the etching process of the antenna prototype, a commercial semi-rigid standard coaxial cable was installed with a cable length of 3 mm, excluding the SMA female connector part. Figure 6 shows photos of the measurement setup environment of the antenna prototype for the reflection coefficient test with the E5071C Vector Network Analyzer (Keysight Technologies, Winnersh, UK) and for the three-dimensional far-field radiation pattern test. The radiation patterns were measured in a well-defined and calibrated electromagnetic anechoic chamber with a width of 5.5 m, length of 5.5 m and height of 5 m. The anechoic chamber guarantees the capability to directly measure far-field conditions from 800 MHz to 8 GHz. Figure 7 illustrates the reflection coefficients and realized antenna gains of the proposed antenna. For the simulation, the 10-dB impedance bandwidth was observed at 1016 MHz from 4.910 GHz to 5.926 GHz with respect to approximately 18.75% at the center  
Figure 5: Photos of the implemented antenna: (**a**) top front side and (**b**) ground bottom side. Figure 6: Photos of the measurement setup for the implemented antenna: (**a**) side view for reflection coefficient test and (**b**) front view for three-dimensional far-field radiation pattern test in anechoic chamber. frequency of 5.418 GHz. Additionally, the measurements were taken according to the 10 dB impedance bandwidths of 855 MHz from 5.184 GHz to 6.039 GHz with respect to approximately 15.24% at the center frequency of 5.612 GHz. The difference between the simulation and the measurement is the result of the inexact alignment between the top patch plane and bottom mesh ground surfaces in the process. In addition, errors occurred as the flatness of the extremely thin substrate was not maintained in a flat state where an isolated support was not used. In other words, in the reflection coefficient measurement experiment, it is judged that the extremely thin substrate is warped due to the surrounding air condition, which is different from the simulation result. The analysis result represented by the red dotted line considering the process error and the warpage of the substrate shows the same result as the measurement result. Therefore, it is judged that our analysis was very accurate. However, the measurement results of the fabricated antenna agreed well with the simulations of the proposed antenna for validating the degenerated TM\({}_{02}\) modes. The realized antenna gains of the proposed antenna are shown in Figure 7b. The realized antenna peak gains were measured from 5.20 GHz to 5.84 GHz with 6410 MHz-stepped test frequencies. The realized antenna gains of 6.71 dBi were maximally observed at 5.57 GHz in 1.5-wavelength resonant TM\({}_{02}\) mode. For the simulation, the realized antenna gain was 5.21 dBi at 5.81 GHz. Due to the characteristics of the wideband operating frequency, the observed realized antenna gains were 3.28 dBi at 5.20 GHz and 6.46 dBi at 5.84 GHz. As can be seen, the stable realized antenna gains were produced in a whole operating frequency band. As expected, the measurement antenna gains are almost in agreement with the simulations.