# Wideband Printed Wide-Slot Antenna with Fork-Shaped Stub
## Antenna Design and Analysis  
### Antenna Configuration  
The proposed printed WS antennas with two different tuning stubs are illustrated in Figure 1. Both of the designs were improved from the normal slot antenna with a fork-shaped stub [20]. For the normal printed WS antenna with a fork-shaped tuning stub, the slot and the feeding line were printed on different sides of the dielectric substrate. For the comparison with the proposed antennas, a normal antenna with a fork-shaped stub was taken as a reference, as shown in Figure 2. The reference antenna was designed on a FR4 substrate, dimensions of 220 mm \(\times\) 220 mm \(\times\) 1.5 mm, permittivity (\(\varepsilon_{r}\)) of 4.4, and a loss tangent of 0.02. The dimensions of the slot were 108 mm \(\times\) 108 mm. The parameters of the normal fork-shaped stub were: \(l_{0}\) = 11.12 mm, \(w_{0}\) = 6.12 mm, \(d_{0}\) = 20.0 mm, \(r_{0}\) = 3.88 mm, \(r_{\mathrm{s}}\) = 6.0 mm, \(w_{1}\) = 3.06 mm, and \(d_{1}\) = 4.0 mm. Note that all the rectangular corners shown in the structure (see Figure 2) have been replaced by round corners, considering that a smooth transition contributes to better impedance matching [11]. It is well known that a half-wavelength variation in current can be observed along the boundary of the slot at the lowest resonant frequency [24]. Hence, the perimeter (\(p\)) of the slot boundary OP, which is shown by dashed lines in Figure 2, is appropriately related to the wavelength (\(\lambda_{1}\)) at the lowest resonant frequency as  
\[\lambda_{1}/2=p=2L_{1}+L_{2}+\pi r_{1} \tag{1}\]  
The lowest resonant frequency \(f_{\mathrm{L}}\) can be expressed as  
\[f_{\mathrm{L}}(\mathrm{GHz})=\frac{300}{p\sqrt{\varepsilon_{eff}}} \tag{2}\]  
with  
\[\varepsilon_{eff}=\frac{(\varepsilon_{r}+1)}{2} \tag{3}\]  
Figure 1: Top views of the two types of proposed antenna. Figure 2: Geometry and configuration of the normal printed WS antenna with a round corner on the stub and ground plane. where the unit of perimeter (\(p\)) is in millimeters. In the design, the parameters of the rectangular slot were: \(L_{1}\) = 44 mm, \(L_{2}\) = 88 mm, \(r_{1}\) = 10 mm, \(d_{x}\) = 56 mm, and \(d_{y}\) = 56 mm. It was found that the lowest resonant frequency \(f_{L}\) was about 0.9 GHz. This will be validated in a subsequent simulation. According to the 3 GPP standard (the 3 rd Generation Partnership Project), the 5G frequency range (the 5 th generation mobile communication technology) at low frequency is from 450 MHz to 6 GHz. Most of its usable frequencies range from 900 MHz to 6 GHz. Although the normal WS antenna with a fork-shaped stub can obtain a wide impedance BW, it is still not enough. Therefore, to further improve the BW, a multiple-resonance technique for the printed WS antenna with a fork-shaped stub is proposed. It has been found that incorporating multiple tuning stubs into a planar WS antenna can excite more resonant modes. However, before the effective tuning, the multiple resonant frequency bands do not overlap nor are they impedance matched. By appropriately tuning the position and dimensions of the stubs, the overlap and impedance matching of these resonances can be promoted to realize the large impedance bandwidth. The proposed antenna design was developed on this basis. The wideband performance was achieved by adding an extra tuning stub and optimizing the position and dimensions of the stub. In addition, the added variables of the extra stub increase the tuning degrees of freedom for the impedance matching. The geometries and configurations of the two kinds of proposed antennas are shown in Figure 3. Two different design proposals, marked antenna A and antenna B, were created by setting the added stubs in different positions. The added stub had a similar shape to the main fork-shaped stub. For antenna A, the bottom edge of the added stub coincided with that of the main stub. For antenna B, the bottom edge of the added stub was lower than that of the main stub.