## 4 Measured Results  
The prototype of the proposed dual-circularly polarized microstrip antenna is exhibited in Figure 9a,b with the front and back views, respectively. The measured results of the reflection coefficient were obtained with the aid of the Amitec VNA40 network analyzer to be compared with the simulation results. The measurement setup of the reflection coefficient is revealed in Figure 10a. On the other hand, the measurement setup of the axial ratio, radiation patterns, and gain in the Amitec VNA40 anechoic chamber is illustrated in Figure 10b. Figure 11a,b shows the simulated and measured results of the S-parameters (\(S_{11},S_{21}\)) and the broadside AR, respectively, when port 1 is excited. Due to the structure's symmetry, port 2 gives the same results as port 1 but with a reversed direction of rotation. The simulated \(-10\) dB reflection coefficient bandwidth is equal to 500 MHz (13.5%) along the range (3.35-3.85 GHz), while the measured impedance bandwidth is 390 MHz (10.6%) from 3.46 to 3.85 GHz. The transmission parameter \(S_{21}\) has reduced values (\(|S_{21}|<-10\) dB)  
Figure 10: The measurements setup of (**a**) S11 and (**b**) radiation patterns, AR, and the gain. Figure 9: The prototype of the proposed circularly polarized microstrip antenna: (**a**) front view and (**b**) back view. along the range of operation of the antenna, and this verifies the good isolation between the two ports. There are many techniques that are used to reduce the mutual coupling between the ports [31; 32; 33; 34]. Due to the symmetry of the design of the hybrid coupler, both reflection coefficients at port 1 and 2 (\(S_{11},S_{22}\)) are intuitively identical, so \(S_{22}\) does not appear in Figure 11. The simulated 3 dB ARBW is 330 MHz (9%) along the range (3.48-3.81 GHz), whereas the measured 3 dB ARBW is 300 MHz (8.2%) along the range (3.50-3.80 GHz). Therefore, this dual-CP antenna properly covers the standard LTE43 5G mid-band applications. The differences between the measured and simulated results are caused by the imperfect SMA connectors soldering, the fabrication imperfections, and the reflections coming from the equipment or objects inside the anechoic chamber. Figures 12 and 13 illustrate the simulated and measured results of the realized gain and the normalized power patterns of the proposed antenna at the center frequency of f = 3.7 GHz, respectively. Figure 12 shows an acceptable value of the realized gain along the intended 5G frequencies (3.6-3.8 GHz). The co- and cross-polarization radiation patterns (when port 1 is excited) are demonstrated in Figure 13 in YZ and XZ-planes to verify the presence of the circular polarization (CP) in the broadside direction (\(\theta=0^{\circ}\)). For both simulation and measured patterns, the difference between the values of the co- and cross polarization patterns is less than 3 dB in the broadside direction. This is clear evidence for the presence of the circular polarization in the broadside direction with gain values larger than 1.3 dBi along the impedance bandwidth of the antenna. The difference between the measured and simulated results of the axial ratio is attributed to the same reasons of the distortions in the radiation pattern measurement, which are due to the reflections coming from the surrounding objects inside the anechoic chamber. This is because the axial ratio is measured in the same environment that was used for measuring the radiation pattern and gain. Table 1 reveals a comparison between the proposed antenna and other dual CP designs. The antenna's dimensions are given with respect to the free-space wavelength \(\uplo\) at the center frequency f\({}_{\rm o}\). As given in this table, the presented antenna has a simple structure, large impedance and axial ratio bandwidths as compared with the other proposed antennas with comparable antenna dimensions and a single element realized gain.