## 2 Design and Simulation Results
### Structural Analysis  
Etching the slot resonators is one of the most effective techniques in designing the UWB antenna with multi-rejection bands without any size increase. After adequately calculating the initial value of the design variables for the band-notched frequency bands, it can be further optimized through parametric analysis and a step-by-step design procedure. To more clearly demonstrate the design process of this quintuple band-notched UWB antenna, Figure 3 presents the subsequent design process of the proposed quintuple band-notched UWB antenna and the corresponding frequency response at each sequence. In the beginning, a single band-notched UWB antenna is designed to reject the WiMAX (3.5 GHz) frequency band. The structure of this antenna is shown in Figure 3a and termed as Antenna_1 which comprises of a single slot resonator using Equation (1), and optimized using the parametric analysis with HFSS. Then, a dual band-notched UWB antenna is designed by integrating another rectangular slot resonator within the first resonator. The dimensions of this resonator are also calculated from Equation (1) and further optimized at the center frequency of 4.5 GHz for notching the INSAT frequency band. This antenna along with its frequency response is shown in Figure 3b and termed as Antenna_2. Similarly, repeating the same procedure, we obtain the triple band-notched UWB antenna, and the quad band-notched UWB antenna termed as Antenna_3 and Antenna_4 by rejecting lower WLAN (5.25 GHz), and upper WLAN (5.7 GHz), respectively. Finally, a pair of RSRRs is placed in the vicinity of the feedline to obtain a broad notched frequency band at ITU 8.2 GHz (whose dimensions are calculated using Equation (3)), and optimized with HFSS. The final antenna is termed as the proposed antenna, and its frequency response is also presented in Figure 3e which shows the combined graph of all antennas and the variations within one plot. This independent behavior of the slot resonator also makes the proposed antennas structure advantageous to be used for single, dual, triple quadruple and quintuple band rejection capabilities depending on the application requirements. By using the R-CSRR and RSRR, we can quickly set the multiple notches to the desired frequencies by selecting the length and width of the resonators according to Equations (1) and (3). Figure 3: \(Cont.\)Simulated Input Voltage Standing Wave Ratio (VSWR) (Return-Loss) and Antenna Gain (Radiation Efficiency)  
The proposed quintuple band-notched UWB antenna is simulated using HFSS. Figure 4 shows the simulated reflection coefficient \(\Gamma_{in}\) and VSWR (Voltage Standing Wave Ratio) of the proposed antenna which reveals the effective filtering behavior at 3.5, 4.5, 5.25, 5.7, and 8.2 GHz for WiMAX, INSAT, lower WLAN, upper WLAN, and ITU 8 GHz frequency bands, respectively. The simulated antenna peak gain (\(G_{0}\)), radiation efficiency (\(\eta\)), and realized antenna gain (\(G_{r}=G_{0}(1-1\,\Gamma_{in}\,|^{2})\) are presented in Figure 5, which shows proper suppression occurs in the primary radiator represented by the antenna gain (\(G_{0}\)) as well as at the antenna input in the form of the impedance mismatch (\(\Gamma_{in}\)) at the notched bands. To further evaluate the quintuple band-notching function resulting from R-CSRR and RSRR, the surface current distributions for the proposed antenna have been simulated at 3.5, 4.5, 5.25, 5.7,  
Figure 3: Design steps of the proposed antenna with the corresponding reflection coefficient results at each stage. The left column shows the antenna structure under design at different stages (**a**) Step 1: adding notch at Worldwide-Interoperability for Microwave-Access (WiMAX; 3.5 GHz); (**b**) Step 2: adding notch at Indian National Satellite (INSAT; 4.5 GHz); (**c**) Step 3: adding notch at the lower wireless local area network (WLAN; 5.25 GHz); (**d**) Step 4: adding notch at upper WLAN (5.7 GHz); (**e**) Step 5: adding notch at ITU 8 GHz (8.2 GHz).