# Fully Metallic Additively Manufactured Monopulse Horn Array Antenna in Ka-Band
## 2 Difference Pattern Hom Array Antenna Concept  
The design of the difference pattern horn array antenna must be conceptualized at the antenna system level, as it will be manufactured monolithically rather than as an integration of independent components. For this purpose, the methodology shown in Figure 1 is followed, where, in the first step, the design is divided into two subsystems: the array of radiating elements and the feeding network. The latter is further subdivided into each of the necessary RF components. Each RF component is designed independently, and once the specifications are met, they are progressively integrated to allow greater control over the feeding network integration. Typically, co-optimization of the RF component chain is performed during this process, requiring only minor dimension adjustments, as the independent designs establish a strong starting point. Once both subsystems are designed, they must be integrated, not only ensuring mechanical assembly but also maintaining RF performance. If any of the established figures of merit are affected by integration, a fine-tuning process is applied to the integrated model until the required specifications are met. Typically, this process requires only minor dimension adjustments; however, if, during integration, the performance deviates significantly from the specifications, the subsystems must be independently redesigned again. Translating this methodology to the array design itself results in a topology like the one shown in Figure 2. The feeding network consists of multiple \(H\)-plane waveguide dividers that directly feed the 16-element array, which is composed of square pyramidal horns, forming a square aperture array. The power dividers are 1:4, meaning 1 input and 4 outputs, with a septum included at the input to ensure good impedance matching and to enhance port isolation within the operating frequency range. The layout of the \(H\)-plane dividers is structured progressively. Initially, each antenna has a primary \(H\)-plane power divider with one input and two outputs. These outputs  
Figure 1: A flowchart of the difference pattern horn array antenna design process. then connect to additional dividers, creating an intermediate structure with one input and four outputs. Each of these four stacked outputs, in turn, connects to a divider with a 1:4 configuration, reaching the necessary 1:16 power divider to feed from the input port to the radiating elements. This feed configuration is not unique, as four \(E\)-plane waveguide dividers (perpendicular to the \(z\)-axis; see Figure 2) could be used instead to directly reach each of the 16 array inputs. However, using an \(H\)-plane divider allows for replication in both the vertical and horizontal parts of the network, reducing the overall design complexity. To connect the primary \(H\)-plane input divider of the feeding network to each of the four stacked dividers that feed the array, the ports need reorientation. Note that the output ports of the vertical divider are rotated 90 degrees relative to the input ports of the horizontal network dividers; that is, the \(E\)-plane of the primary divider output corresponds to the \(H\)-plane of the feeding network inputs. This misalignment is corrected by using a \(90^{\circ}\) twisted waveguide section. Each twist segment is defined by its length and the \(90^{\circ}\) rotation angle. Although these elements would not be necessary if using an \(E\)-plane divider, the addition of the twisted waveguides not only enables the use of a single \(H\)-plane design but also is responsible for generating a difference pattern. As shown in Figure 2, the twist segments are not identical: the top two twist segments rotate clockwise, while the bottom two rotate counterclockwise. This alternating configuration of twist segments in pairs allows the array's total aperture to be divided into two sub-apertures with respect to the \(H\)-plane, providing identical amplitude excitation across elements in each sub-aperture but with a 180-degree phase difference.