## 4 Results and Discussion  
A prototype antenna of the inverted L-shaped patch antenna with a corner-truncated partial ground plane diagonally adjoined with a square branch (Antenna IV) was fabricated and experiments were carried out (Figure 17a,b). During the fabrication, the relative  
Figure 16: The simulated reflection coefficient and axial ratio under variable distance between the radiating patch and the edge of the substrate (\(d\)). Figure 15: The simulated reflection coefficient and axial ratio under variable horizontal length (\(L_{4}\)) of radiating patch. permittivity of the actual substrate was characterized using a near-field transmission-line measurement technique implemented by a modified complementary square ring resonator (CSRR) [21]. A 50 \(\Omega\) transmission line acted as a sensor with the Minkowski fractal pattern of CSRR. The extraction result of FR-4 (TLM140) was the relative permittivity of 4.308 at 1.5 GHz (average of 5 measurements, as shown in Table 3). The accuracy of the method used for characterization was limited by the air gap effect between the material under test (MUT) and CSRR, therefore the extracted values of relative permittivity could be obtained by a number of measurements. In addition, the resonant frequency and magnitude response of CSRR were dependent on the thickness of the substrate. Therefore, substrate thickness must be reasonably chosen to yield the sufficient accuracy of the measured relative permittivity and loss tangent of the material under test (MUT). In the experiment in an anechoic chamber, the antenna prototype on a rotating table was used as the receiving antenna, and a standard CP reference antenna (ETS-Lindgren's Model 3102 Conical Log Spiral series) was used as the transmitting antenna (Figure 17c). The results were measured by a vector network analyzer (model E5061B, Agilent, Santa Clara, CA, USA). The performance metrics included the reflection coefficient, AR, gain, and radiation pattern. Figure 18 compares the simulated and measured reflection coefficients of the proposed antenna. The simulated and measured RLBWs (\(\mid\)S\({}_{11}\mid\leq-10\) dB) were 53.12% (1.106-1.906 GHz) and 62.37% (1.07-2.04 GHz), with the center frequency of 1.55 GHz. Figure 19 compares the simulated and measured AR of the proposed antenna. The simulated and measured ARBWs (AR \(\leq\) 3 dB) were 70.88% (1.02-2.14 GHz) and 77.87% (1.09-2.48 GHz). The simulation and measured results were agreeable. However, there are some discrepancies between the simulated and measured reflection coefficients and  
Figure 17: The prototype of the inverted L-shaped patch antenna with a corner-truncated partial ground plane diagonally adjoined with square branch: (**a**) front, (**b**) rear, (**c**) in anechoic chamber. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Measurements** & **1 st** & **2 nd** & **3 rd** & **4 th** & **5 th** & **Average** \\ \hline
**Extracted Values** & 4.32 & 4.27 & 4.35 & 4.31 & 4.29 & 4.308 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The extracted values for the relative permittivity of FR-4 (TLM140) at 1.5 GHz. axial ratios. The degradation of the measured reflection coefficient in the upper L-band frequency (1.8-2.0 GHz) and the improved measured reflection coefficient in the lower L-band frequency (1.0-1.5 GHz) could be attributed to the soldering of the SMA in the antenna fabrication. The same rationale also affected the simulated and measured axial ratios of the proposed antenna. On the other hand, the simulation was carried out under ideal conditions in the absence of soldering. Figure 20 compares the simulated and measured gains of the proposed antenna. The simulated and measured maximum gains were 3.0 dBi at 1.7 GHz and 2.76 dBi at 1.6 GHz, respectively. The simulation and measured results were in good agreement. The simulation and measured radiation patterns of the proposed antenna at the center frequency (1.5 GHz) are illustrated in Figure 21a,b.