# A 3-D Metal-Printed Dual-Polarized Ridged Waveguide Slot Array Antenna for X-Band Applications
## 2 Antenna Array Configuration  
The proposed geometric configuration for the dual-polarized RWSAA is shown in Figure 1. The complete antenna structure is formed by a pair of linear RWSAAs with orthogonal polarization VP and HP arrays that operate simultaneously in the same X-band with a center frequency of 9.8 GHz. The radiation element of the two linear arrays is divided into two halves at the center of the waveguide, symmetrical in both the \(x\) and \(y\) directions with respect to VP but in the same direction with respect to the HP array as depicted in Figure 1a. The VP linear array is performed by eight longitudinal slots etched on the upper broad wall of the RWG. The HP linear array is produced by the inclination of both sides of the V-shaped slot and is cut into the ridged broad wall of the RWG. The V-shaped slot has a perpendicular electric field separated into VP and HP radiation components. The VP components are out-of-phase, so the radiation field is suppressed, while the in-phase HP components complement each other and achieve an ideal low cross-polarization level. The two linear arrays are interleaved with each other, so, in the \(z\) direction, the HP array is arranged one layer higher than the VP array to provide good polarization isolation and reduce the influence of mutual coupling between the radiation slot elements. Figure 1b illustrates the inside structure of the RWG for each of the VP and HP linear arrays with a central feeding technique for the eight-element slot array. The VP array uses a two-way equal-split divider, which is a T-junction between the coaxial-to-RWG transition and the radiated RWG with the top of the coaxial probe attached directly to the ceiling of the RWG, whereas the HP array attaches the coaxial probe to the ridge of the radiated RWG. A pair of irises is needed near the coaxial probe to obtain good impedance matching. From there, the detailed layer-by-layer structure of the proposed dual-polarized array is shown through the cross-section in Figure 1c. This feeding method enhances the operating bandwidth, and the uniform mechanical grid structure of the pair of linear arrays has robust and light profiting. Furthermore, both the VP and HP are excited by two commercial SMA connectors with the coaxial probe feed from the bottom through a coaxial-to-RWG transition. The simple and compact feed structure provides good mechanical stability with low voltage to avoid electrical breakdown [25]. The waveguide cross-sectional dimensions are denoted by \(w_{vr}\), \(h_{vr}\), and \(h_{ry}\) for the VP linear array, and \(w_{hr}\), \(h_{hr}\), and \(h_{hf}\) for the HP linear array. The waveguides are designed to be uniformly dimensioned with the same width and height to simplify the structure, reduce the hardware layer, and ease the manufacturing process. To contribute to the weight  
Figure 1: Geometry configuration of the proposed dual-polarization array. (**a**) 3-D view of complete structure. (**b**) View of the inside structure. (**c**) Cross section of the structure. (**d**) Top view of the radiating slots. reduction of the array, adjacent waveguides share the same wall with a thickness of \(t\). The waveguide resonant slot array is designed based on the strict requirement of spacing between radiated elements. Therefore, for dual-polarized RWSAA, the spacing between radiated slots needs to be considered simultaneously on both the VP and HP planes. This is to ensure radiation efficiency when combining dual polarized subarray models developed for a large array, and grating lobes are eliminated in the case of a scanned beam. For the WSAAs, the radiating slots should be arranged with an element spacing of \(0.5\lambda_{g}\) along the \(x\) and \(y\) directions for uniform illumination. In our design, for simplicity, both VP and HP arrays are configured to have the same guided-wavelength \(\lambda_{g}\).