# A Compact Monopole Wideband Antenna Based on DGS
## 2 Antenna Design Methodology and Optimization Process
### Reconfiguration and Characterization of Antenna  
To enhance radiation performance and achieve a compact size, the conventional rectangular patch antenna, Figure 1a, was reconfigured into asymmetric U-shaped and G-shaped designs. The total area of the original antenna was 20 \(\times\) 23 mm\({}^{2}\). To obtain the G-shaped antenna involved removing 23.70% (109 mm\({}^{2}\)) of the total area, while the asymmetric U-shaped antenna reduced the total area by 18.04% (83 mm\({}^{2}\)), Figure 1b. The dimensions of the U-shaped patch, L-slot, and semi-circular slot of the G-shaped patch are obtained by the trial-and-error method.  
Figure 1: Overview of the initial antenna design stages for evolution.  
Characterization was performed on both reconfigured designs mounted on a substrate-sized ground plane of 28 \(\times\) 34 mm\({}^{2}\) with a 50 \(\Omega\) impedance-matched stepped feed line. The simulated reflection coefficient (S11) plots are shown in Figure 2d. The G-shaped antenna exhibited notch bands at 8.79-8.93 GHz and 15.03-17.60 GHz, resulting in a total bandwidth of 2.71 GHz. In contrast, the asymmetric U-shaped patch displayed bands at 6.50-6.65 GHz, 16.37-16.63 GHz, and 19.83-20.48 GHz, with a total bandwidth of 1.06 GHz.  
Based on these results, the G-shaped patch is preferred for further characterization and evolution due to its superior impedance matching and wider bandwidth. The use of a DGS was then explored to enhance bandwidth and gain. The DGS geometry incorporates two slots (L-slot and semi-circle slot), improving antenna performance by altering surface current distribution and modifying transmission line characteristics, including inductance and capacitance. The proposed antenna with a conventional ground plane and optimized DGS is illustrated in Figure 3a-c. The S\({}_{11}\) responses for both configurations are presented in Figure 3d, highlighting the transformation of notched bands into a passband, which is essential for achieving wideband characteristics. Thus, the parametric analysis will focus on the DGS structure evolution.  
Figure 3: Layout of the proposed antenna: (**a**) front view; (**b**) conventional ground plane; (**c**) proposed DGS; and (**d**) S11 of conventional ground plane and S11 with DGS (proposed antenna).  
Figure 2: Antennas for characterization and its S\({}_{11}\): (**a**) asymmetrical U-shape patch; (**b**) G-shaped patch antenna; (**c**) conventional ground plane; and (**d**) S\({}_{11}\) response of the characterization process.  
Using DGS in the ground plane alters the surface current distribution in a microstrip antenna, leading to a wider operating frequency band. This disturbance affects transmission line characteristics by modifying parameters such as inductance, capacitance, and resistance between the feed line and the slot. Specifically, having a DGS beneath the feed line changes its effective capacitance and inductance due to the added slot effects. Consequently, the resonance frequency of a DGS-based antenna differs from that of a standard ground plane. Notably, the effective capacitance is inversely related to the DGS slot area, while the effective inductance is directly proportional to it.