# A 3-D Metal-Printed Dual-Polarized Ridged Waveguide Slot Array Antenna for X-Band Applications
###### Abstract  
A compact three-dimensional (3-D) metal-printed ridged waveguide slot array antenna with wideband, dual linear polarization and low cross-polarization is presented for X-band applications. The proposed design achieves a compact structure due to the method of using a ridged waveguide (RWG). A vertically linear polarized (VP) array is realized through eight longitudinal shunt slots etched on the non-ridged broad wall of the RWG, while a horizontally linear polarized (HP) array is realized through eight V-shaped slots cut on the ridged broad wall of the RWG. To extend the operating bandwidth, each \(1\times 8\)-element linear array is separated into two \(1\times 4\)-element sub-arrays through a central feeding technique. The two sub-arrays of the VP array are excited with equal amplitude and are \(180^{\circ}\) out-of-phase through a T-junction power divider, which connects the coaxial feed and the radiated waveguide, while the two HP subarrays are directly excited by a coaxial feed with equal amplitude and remain in phase. The feed structure uses coaxial probes directly attached to the RWG to provide good mechanical stability and low voltage around the feed. An optimized \(2\times 8\)-element dual-polarized array is fabricated using 3-D metal-printing technology for experimental verification. The measured \(-10\) dB impedance bandwidth of the VP array is 1.2 GHz (12.2%) and, of the HP array, is 1.1 GHz (11.2%) with maximum gains of 14.6 and 15.5 dBi, respectively. There is good polarization purity over the entire operating bandwidth with a cross-polarization level better than \(-40\) dB in the main beam direction. The isolation between two orthogonal polarized arrays is greater than 40 dB over the whole band. 3-D metal-printed; wideband slot array antenna; ridged waveguide; dual-polarized; low cross-polarization +
Footnote †: journal: Applied  
In [14; 15], dual polarization was produced on the same waveguide structure, with the input electronic signal traveling via the coupling slot and into the cavity. The complex structure with many overlapping layers included feed networks, coupling slots, electromagnetic field conversion cavities, and radiation slots. Making dual-polarized array antennas highly configurable and difficult to fabricate requires powerful fixation techniques based on sophisticated brazing and bonding facilities. For the sake of simplicity, the dual polarization of the WSAA is designed separately on two different waveguides. Conventional rectangular waveguides have broad wall dimensions larger than \(0.7\lambda_{0}\), so interlacing them on the same aperture to produce dual polarization is a significant obstacle as the distance between the radiating slot elements in the plane perpendicular to the waveguide axis are larger than \(1\lambda_{0}\). This decreases the effectiveness of the dual-polarized array due to the formation of grating lobes during the scanning of the electromagnetic beam [16]. In other words, it is difficult to produce effective radiation patterns in a dual-polarized array using conventional rectangular waveguides so that the grating lobes are not visible. An adopted structure that reduces the standard waveguide size is the ridged waveguide developed for both vertical and horizontal polarization. In [17], a VP array was produced from longitudinal slots engraved on the broad wall, and an HP array was produced from transverse slots on the narrow wall. The transverse slots have the advantage of producing a low degree of cross-polarization, which increases the polarization purity. However, this has the major disadvantage of having to be excited through the position and dimensions of the additional iris inside the waveguide near the transverse slots. However, integrating the auxiliary excitation elements inside the waveguide leads to a very difficult fabrication process because of the high machining accuracy requirements and the expensive manufacturing cost.