## 2 Antenna Design and Analysis  
In this unit, the configuration of circularly polarized RDRA is elucidated. In Section II-A, the focus is on designing and optimizing a linearly polarized DRA at its maximum possible impedance bandwidth with a single conformal metal strip Moreover, further changing the single metal strip to cross shape feed with optimized parameters in order to excite the orthogonal waves for the generation of circular polarization. In Section II-B, to provide good AR bandwidth, a metal strip structure is introduced and optimized at top of the RDRA. Finally, desired antennas are designed with desired dual CP performance as depicted in Figure 1.  
Linear Polarized DRATo initiate with, singly fed simple DRA which is made up of a Rectangular DR excited through singly feed mechanism is designed. DR is made of ECCOSTOCK HIK with \(\varepsilon\)r = 9.8 and tan\(\delta\) = 0.002, mounted on the PEC ground plate. Figure 2 depicts the proposed antenna's geometric development process. Figure 2a shows the three-dimensional and cross-sectional views of an RDRA. The dimensions of the rectangular DR are kept similar as in [20], with a height (H), width (B), and depth of (C) 26.1 mm, 25.4 mm, and = 14.3 mm, respectively. Figure 1: The geometry of the singly fed RDRA (3-D View) 5G Sub6 GHz Applications. The dimensions of proposed DRA are given in Table 1. The initial model was designed and analyzed using the dielectric waveguide model [8]. By placing the DRA on a ground plane even modes will be short-circuited and only the odd modes can exist [7]. Because of this principle, TE modes (odd modes) are excited. In parallel, the resonant frequency of the fundamental mode, TE\({}_{111}\), is calculated by means of the equations [9] where. _kx_, _ky_, and _kz_ respectively denote the wavenumbers in the \(x\), \(y\), and \(z\) directions inside the DRA, as shown in Equation (1). \[f_{0}=\frac{c}{2\pi\sqrt{\epsilon\tau}}\sqrt{k_{x}^{2}+k_{y}^{2}+k_{z}^{2}} \tag{1}\]  
\[k_{x}=\frac{\pi}{c} \tag{2}\]  
\[k_{z}=\frac{\pi}{2H} \tag{3}\]  
Moreover, the 3-dB AR is defined by:  
\[\frac{E_{y}}{E_{x}}=\frac{\left|E_{y}\right|}{\left|E_{x}\right|}\ *\ e^{i\phi}\]  
The electric field vector's y-directed component is _Ey_, while the x-directed component is _Ex_. The difference in phase between _Ex_ and _Ey_ the amplitude ratio is 1, and the phase difference (\(\phi\)) is 90\({}^{\circ}\) for pure circular polarization's standard performance. The single feed RDRA (Figure 2b) can obviously achieve dual-band operation, but it does not have a CP mode. The optimized parameter for the single conformal metal strips of the RDRA based on rigorous parametric analysis using the CST tool is mentioned in Table 2. This presents the impedance matching bandwidth; the aforementioned bandwidth is sensitive to the strip height, as changing the height may deteriorate the results. The dimensions of the strip were  
Figure 2: Evolution of the RDRA (3-D View) (**a**) Simple RDRA, (**b**) Linear polarized DRA, (**c**) circularly polarized RDRA, (**d**) desired RDRA. optimized based on running the parametric sweep, and the optimized dimensions of the individual strips were found to be h1 = 11.75 mm, and b1 = 1 mm. The optimized feed parameters provide S11 bandwidths of ~7.19%. The impedance matching bandwidth (S11) of the RDRA can be controlled and optimized by adjusting the position of the feed as well. Therefore, a parametric study was conducted for different values of d1 as well. As depicted in Figure 2b schematic diagram of the optimum value of d1, while Figure 3 shows the various reflection coefficient characteristics of the single element DRA with the different values of d1 = 7.5 mm, 8.0 mm, and 8.5 mm from the edge. It is observed that each value of \"d1\" produces a different value of the reflection coefficient. As the value changes, the resonant frequency is shifted upward (higher frequencies), and the best return loss is achieved when keeping the distance at d1 = 8 mm.