## 2 Delta-Stub-Based Wilkinson Power Divider (WPD) Design Configuration and Characterization Results  
The WPD [8] is characterized as a three-port lossless network, which provides isolation between the output ports when they are matched; only the reflected power is typically dissipated. The power to the input port-1 can be split into two ports with the same amplitude. In order to realize a two-way equal-split in signal power, quarter-wave (\(\lambda\)/4 impedance) transformers with a characteristic impedance of \(Z_{o}\) are used. The equivalent circuit of the conventional WPD is shown in Figure 1a. The simulated design of the proposed WPD using CST Microwave Studio is shown in Figure 1b, whereas the fabricated prototype is shown in Figure 1c. FR4 glass epoxy substrate (\(\varepsilon_{r}\) = 4.3 and \(h\) = 1.66 mm) is selected for this purpose.  
The three ports of the WPD are labeled as port-1, port-2, and port-3, respectively, as shown in Figure 1a-c. The straight quarter-lambda split Section 1 \(\times\) 2 WPD is the conventional design, which is initially presented in Figure 1a. In the WPD, the power at the output ports, port-2 and port-3, is half the power of the input from port-1. Therefore, the insertion loss at each of the output ports is \(-\)3 dB. The width of the 50 \(\Omega\) transmission line is taken as 3 mm, whereas the length and width of the quarter-wave transformers with an impedance of 70.71 \(\Omega\) are taken as 7 mm \(\times\) 1.5 mm. The fabricated prototype of the WPD has overall dimensions of 20 \(\times\) 36 mm, as shown in Figure 1c. Two delta-stubs with a length \(\times\) width of 2.38 \(\times\) 0.74 mm are introduced on both sides of the quarter-wave transformers for improved impedance matching and wide bandwidth characteristics of the WPD.  
Figure 2a,b shows the simulated and measured S-parameter response of the delta-stub-based 1 \(\times\) 2 WPD at the bandwidth of 3.5-6.5 GHz. It can be observed from the results in Figure 2b that there is almost equal power division between the two output ports, port-2 and port-3, respectively.  
The return loss \(S_{1I}\) (dB) and \(S_{22}\) (dB) at port-1 and port-2, as shown in Figure 2a, also refers to the fact that the designed delta-stub-based 1 \(\times\) 2 WPD has a wide bandwidth of  
Figure 1: Shows (**a**) transmission-line circuit of an equal-split WPD [8], (**b**) simulated design, and (**c**) fabricated prototype of delta-stub-based 1 \(\times\) 2 WPD.  
Figure 2: Shows the S–parameter response of the WPD (**a**) simulated and measured return loss (\(S_{1I}\)) at port-1 and (\(S_{22}\)) at port-2, and (**b**) simulated and measured insertion loss (\(S_{2I}\)) between port-1 and port-2, and isolation loss (\(S_{32}\)) between port-2 and port-3, respectively.  
3 GHz. Figure 2b shows the simulated and measured insertion loss \(S_{21}\) (dB) between port-1 and port-2, and isolation loss \(S_{32}\) (dB) between port-2 and port-3, respectively. It can be observed from the WPD measured response that there is an isolation of 14 dB between the two output ports and an insertion loss of \(-4\)\(\pm\) 1 dB between port-1 and port-2.  
Single-Element Minkowski-Sierpinski Fractal Antenna and Four-Element Antenna Array Design and Characterization Results