# Fully Metallic Additively Manufactured Monopulse Horn Array Antenna in Ka-Band
## 1 Introduction  
Additive manufacturing, also known as 3D printing, has had a significant impact on different engineering fields, particularly by presenting a new manufacturing process that enables innovative designs, providing substantial advancements that were not achievable with conventional manufacturing methods. More specifically, AM has had a major impact on the development of antenna concepts in the millimeter-wave (mm-Wave) band. Two key points should be highlighted. First, AM allows the fabrication of intricate designs with complex geometries, achieving relatively high precision, while also enabling novel antenna concepts by utilizing more complex shapes. Secondly, AM enables the rapid prototyping of antennas, not only reducing manufacturing times and costs but also allowing for fast iterations to fine-tune designs, leading to highly optimized solutions. Moreover, AM has opened the door to the use of new materials, ranging from polymers to ceramics and even metals, enabling more cost-effective solutions, as well as designs with reduced volume or weight. Therefore, AM has emerged as an alternative to traditional subtractive manufacturing methods, like Computer Numerical Control (CNC) milling, offering speed, precision, and cost-effectiveness [1]. However, the most important feature that AM provides is the ability to create complex and arbitrary geometries. Thus, it has attracted interest beyond mechanical engineering, notably in antenna engineering. There are three methodologies that involve manufacturing with AM for antenna and microwave devices. The first method entails the use of dielectric materials for graded-index lenses [2; 3; 4], metasurfaces [5], and transmitarrays [6; 7; 8]. The second method involves manufacturing dielectric components and subsequently applying metallic coatings, suchas nickel [9; 10] or copper [11; 12; 13; 14]. Finally, the third method involves metal-only AM techniques, such as AM Laser Powder-Bed Fusion (LPBF), Binder Jetting (BJ), or Directed Energy Deposition (DED), which is ideal for space applications due to its dielectric-loss-free properties and better structural properties. However, AM is not limited solely to radiating elements; it also enables the development of feeding network components, which include various RF devices in waveguide technology, such as filters, twists, or OMTs [1; 15; 16]. Therefore, AM allows for the development of RF devices that incorporate both the feeding network and radiating elements. To manufacture these designs, a combination of dielectric-material-based fabrication followed by coating can be used to achieve the desired electromagnetic properties. This approach involves dividing the system into multiple parts, ensuring clear access to internal surfaces for coating application. This method presents two potential sources of error. First, it is challenging to guarantee uniform coating throughout the entire structure. Second, the subsequent assembly may introduce minor alignment errors or mismatches, which can cause current leakage and therefore degrade device performance. A second method that eliminates both sources of error is monolithic fabrication. In this approach, access to internal faces is not possible, so metal-based manufacturing (such as LPBF, BF, or DED) is needed. In particular, LPBF AM has been used to develop monolithic microwave components, like waveguide filters [17; 18], horn antennas [19], and shaped parallel plate lenses [20; 21; 22]. Moreover, the use of monolithic components manufactured by means of this technique has been probed to address and solve alignment issues encountered in milling processes [23], being a suitable technique for designing antenna systems. Conversely, the role of difference pattern antennas spans various critical applications where precise signal discrimination is essential. In radar systems, they enable the accurate tracking of targets such as aircraft, ships, or weather phenomena by analyzing differences in phase and amplitude among signals received by array elements [24].