## 2 Antenna Design Stages
### Antenna Design and Configuration  
The dielectric substrate selection plays a pivotal role in determining the microstrip antenna impedance characteristics, bandwidth, and radiation efficiency, particularly at mmWave frequencies. To minimize signal attenuation [18] while maintaining structural stability, this study employs Rogers RT/duroid 5880, a well-established high-frequency substrate with a dielectric constant (\(\epsilon_{\rm{r}}\)) of 2.2 and a low loss tangent (tan \(\delta\) = 0.0009). The substrate thickness (h) was set to 1.6 mm to ensure a balance between mechanical robustness and optimal electromagnetic performance. The Rogers RT/duroid 5880 is particularly advantageous for millimeter wave applications, where excessive propagation losses can significantly degrade antenna efficiency. The low-loss properties of this material make it highly suitable for 5G and other systems, in which maintaining signal integrity and minimizing power dissipation are paramount. Once the dielectric material was selected, the physical dimensions of the radiating patch, specifically its width (W) and length (L), were determined using well-established microstrip antenna design principles [19]. Achieving dual-band operation in single-element microstrip antennas requires approaches beyond classical mathematical models. The most commonly used techniques in the literature include slot configurations, the incorporation of notches in the patch geometry to achieve similar effects, the use of multiple resonant structures on the patch, the integration of short-circuit pins, and adjustments to the feed line configuration. For the designed antenna to operate at dual-band frequencies of 28/38 GHz, the effect of notches on the patch is analyzed using slot configurations. The resonant frequencies (f\({}_{\rm{mn}}\)) for a classic rectangular microstrip antenna are given in Equation (1) [19; 20; 21]. \[\rm{f}_{mn}=\frac{c}{2\sqrt{\epsilon_{eff}}}\sqrt{\left(\frac{m}{L_{eff}} \right)^{2}+\left(\frac{n}{W_{eff}}\right)^{2}} \tag{1}\]  
where \(\epsilon_{\rm{eff}}\) is the effective relative permittivity of the patch, \(c\) is the speed of light in free space, and \(m\) and  
The effective relative permittivity (\(\epsilon_{\text{eff}}\)) accounts for the nonuniform electric field distribution between the patch and the ground plane and is determined using the equation provided by [PERSON] [22; 23]. \[\epsilon_{\text{eff}}=\frac{\epsilon_{\text{r}}+1}{2}+\frac{\epsilon_{\text{r}} -1}{2}\bigg{[}1+12\frac{\text{h}}{\text{W}}\bigg{]}^{-\frac{1}{2}} \tag{4}\]  
Due to the presence of fringing fields, there is difference between the electrical and physical dimensions of the antenna. The extension length \(\Delta\)L caused by these fields can be estimated using the equation provided by [PERSON] [22; 23]. \[\Delta\text{L}=0.412\;\text{h}\frac{(\epsilon_{\text{eff}}+0.3)\Big{(}\frac{ \text{W}}{\text{h}}+0.264\Big{)}}{(\epsilon_{\text{eff}}-0.258)\Big{(}\frac{ \text{W}}{\text{h}}+0.8\Big{)}} \tag{5}\]  
These extensions influence resonance and impedance matching, necessitating precise adjustments in the final design [24; 25]. Adding slots or notches to a rectangular microstrip patch antenna changes the surface current paths and increases the antenna's electrical length, creating additional resonant frequencies. This approach is widely used for dual-band or multiband operation [26]. Creating an upper gap at the radiation edge is particularly effective for achieving dual resonance. A compact microstrip patch antenna with inverted C-shaped and U-shaped slots functions as two connected resonators of different sizes. These slots guide meandering currents, generating multiple resonances. Dual-band operation can be achieved by strategically placing slots on the radiating patch, ground plane, or feed line, with the slot dimensions manually tuned to optimize performance [27]. Slots positioned at the radiation edge primarily influence higher-order modes, while center slots play a key role in generating a secondary frequency by extending the current path.