# A 3-D Metal-Printed Dual-Polarized Ridged Waveguide Slot Array Antenna for X-Band Applications
## 4 Experimental Results and Discussion
To see the effectiveness of electromagnetic wave radiation, another important parameter to be considered is the antenna efficiency. Figure 13 indicates the variation in the total antenna efficiency of the dual-polarized array with respect to frequency. From the figure, it can be seen that the efficiency of the antenna in both VP and HP polarization is almost uniform, and over 90% is achieved in the impedance bandwidth. Therefore, the antenna has good radiation efficiency and reduces the loss encountered while radiating. Figure 14 compares the measured and simulated results of normalized radiation patterns at three different frequencies of 9.4, 9.8, and 10.2 GHz in both the \(E\) plane and the \(H\) plane. The measurement was performed at elevation angles ranging from \(-90^{\circ}\) to \(+90^{\circ}\), for V and H polarizations along with cross-polarization. It can be seen that the measured radiation patterns have good agreement with the simulation. Due to the center feed structure, the main beam direction in the \(E\) and \(H\) planes stays in the broadside direction at all three frequencies. The radiation pattern of the VP array is shown in Figure 14a with measured first sidelobe levels in the \(H\) plane of \(-11.5\), \(-13.3\), and \(-10.3\) dB at the three frequencies of 9.4, 9.8, and 10.2 GHz, respectively. The cross-polarization level was better than \(-42\) dB at the boresight in both the \(E\) and \(H\) planes over the entire operating bandwidth. Similarly, Figure 14b shows the radiation pattern of the HP array, which, at the three operating frequencies, had measured first sidelobe levels in the \(E\) plane of \(-7.2\), \(-15.0\), and \(-13.6\) dB. The cross-polarization level in both the E and H planes was better than \(-40\) dB at the boresight. The antenna 3D radiation patterns are shown in Figure 15 at three different operating frequencies for both VP and HP linear polarization. Red represents the highest radiation level for the main lobe, and green represents the lower radiation level for the side lobe. The main lobe is at the boresight and remains stable throughout the wide operating bandwidth. Figure 13: The simulated efficiency of the dual-polarized antenna array. Figure 14: Simulated and measured normalized radiation patterns of the antenna in the \(E\) plane and \(H\) plane at three operating frequencies of 9.4, 9.8, and 10.2 GHz of: (**a**) VP linear array radiation pattern. (**b**) HP linear array radiation pattern. The performance comparison of various dual-polarized waveguide slot arrays is listed in Table 1. It can be seen that the proposed design has a much wider bandwidth for both VP and HP polarization when compared with the published designs, while maintaining good radiated efficiency over a wide frequency band with low cross-polarization better than \(-40\) dB on both \(E\) and \(H\) planes. Although the cross-polarization level mentioned in [17] is better than \(-60\) dB, this is only a simulation result that has not been verified by experimental measurements. Figure 15: Simulated 3D radiation patterns of the VP and HP linear arrays at three operating frequencies of 9.4, 9.8, and 10.2 GHz.