# Compact Planar Super-Wideband Monopole Antenna with Four Notched Bands
## 2 Antenna Design
Similarly, as shown in Figure 2c, the interfering satellite communication X-band is notched using an inverted U-shaped slot. The length (\(L_{lli}\)) of the introduced U-shaped slot is estimated as  
\[L_{lli}=\left(2l_{3}+b_{3}+w_{3}\right)\approx 0.5\lambda_{gi}. \tag{6}\]  
Further, the interfering WLAN band is eliminated by introducing another inverted U-shaped slot at the center region of the circular patch, as shown in Figure 2d. The length (\(L_{ULo}\)) of the U-shaped slot is calculated as  
\[L_{ULo}=\left(2l_{4}+b_{4}+w_{4}\right)\approx 0.5\lambda_{gi} \tag{7}\]  
The interfering Wi-MAX band is rejected by forming a meandered slot in the upper region of the circular disc, as shown in Figure 2e. The length (\(L_{M}\)) of the meandered slot is estimated as  
\[L_{M}=\left(l_{5}+2b_{5}+2l_{6}+2b_{6}+2l_{7}+2b_{7}+2l_{8}+2b_{8}+2l_{9}+w_{5 }\right)\approx 0.5\lambda_{gi}. \tag{8}\]  
By introducing a meandered slot, two U-shaped slots, and SRR in the presented SWB monopole antenna, four notched bands are obtained at the frequencies 3.5 GHz, 5.5 GHz, 7.5 GHz, and 10.5 GHz, respectively. The calculated lengths of the notching elements are optimized to notch the entire Wi-MAX, WLAN, amateur radio, and satellite communication bands. The reflection coefficient curves in Figure 3a illustrate the behavior of Antenna-1, -2, and -3, whereas the curves in Figure 3b display the behavior of Antenna-4 and -5. In the SWB range, a single notch band (at 10.5 GHz) is obtained in the case of Antenna-2, while dual notch bands (at 10.5 GHz and 7.5 GHz) are noticed in the Antenna-3. Similarly, by loading three notching elements in the circular disc, three notch frequencies (at 10.5 GHz, 7.5 GHz, and 5.5 GHz) are achieved in the Antenna-4. In the same way, four elements are loaded in the Antenna-5 to notch four frequencies (at 10.5 GHz, 7.5 GHz, 5.5 GHz, and 3.5 GHz). The notch frequency can be controlled by varying the dimensions of the slot/resonator. Figure 3: \(Cont.\)  
Figure 2: Design steps of the proposed quad band-notched SWB antenna: (**a**) Antenna-1; (**b**) Antenna-2; (**c**) Antenna-3; (**d**) Antenna-4; (**e**) Antenna-5. Figure 4 illustrates the matching performance of the proposed SWB Antenna-1. The deviations in the real/imaginary values of the input impedance provide an approximate characteristic impedance of the feeding connector, which illustrates a good matching among them. Four notch elements are formed in the proposed antenna patch to remove interfering frequencies from the SWB. Figure 5 displays the surface current distribution on the proposed antenna at notch frequencies. It is noticed that the current is mainly concentrated around the SRR, inverted U-shaped slots, and meandered slot. As compared with the current direction on the radiator patch, the current around the notching element flows in the opposite direction at notch frequency. As the current is out-of-phase and flows in the opposite direction, it shows strong attenuation and cancellation of the radiating field. Figure 4: Input impedance of the SWB antenna. \[\lambda_{gi}\ =\frac{c}{f_{ri}}\left(\frac{1}{\sqrt{\varepsilon_{reff}}}\right) \tag{3}\]0 \(S_{11}\) of the proposed antenna design steps: (**a**) Antenna-1 to -3; (**b**) Antenna-4 to -5.