# Shape Optimization of an Integrated Mast for RCS Reduction of a Stealth Naval Vessel
## 2 Analysis Procedure  
The SBR method is a well-known high frequency approximation technique that is efficiently capable of predicting the RCS of large objects such as naval ships based on the determination of the equivalent current densities induced on the surface of an illuminated perfect electric conductor (PEC) plane [23; 24; 25]. In this study, The RCS was simulated using commercial electromagnetic (EM) software based on the SBR method and the diffraction fields at the edges were also considered. The integrated mast can dramatically reduce the RCS of a naval vessel. In the stealth design of a naval vessel, not only the RCS of the naval ship but also the RCS of the integrated mast itself is very important. This is because enemy radars in distant areas may only detect the integrated mast located on top of the naval ship due to the curvature of the earth. Therefore, it is essential to design the integrated mast with low RCS characteristics in the stealth design of a naval vessel. The goals of shaping are to have specular reflections of the EM field in a direction away from the enemy radar and this technique is the most representative and effective technique that can be used to reduce the RCS [2]. The shaping technique is usually used first to design the shape of the integrated mast with low RCS properties before other techniques such as RAM/RAS are applied. In other words, the shape of the integrated mast is one of the most important factors in the stealth design of a naval ship and must be considered in the early stages of the concept/design. Figure 1 shows an overall procedure to design the integrated mast shape. As the integrated mast mounted on a naval ship must have stable structural characteristics, the base width and length are determined by the superstructure of the naval ship. In addition, the ranges of the size and slope of the surface of the integrated mast are determined by the size, performance and installation concept of the many antennas and sensors to be installed on the surface of the integrated mast. In other words, the basic size and shape of the integrated mast are set by the naval ship and the antennas and sensors and the ranges of the size and shape that can be redesigned are constrained. Therefore, the shape of the integrated mast is optimized within these constraints by the iterative redesign. First of all, the cardinal points, which are the exceptional angle regions and the expected threats such as the frequencies, polarizations and detection ranges of enemy radars, are defined for operational requirements. In a naval ship, the main concerns are generally radar signals coming from distant patrol aircraft, other ships and sea-skimming anti-ship missiles with radar seekers usually near or slightly above the horizon as seen from the ship. In other words, the threat regions are usually 0\({}^{\circ}\) to 360\({}^{\circ}\) in the azimuth plane and very limited in the elevation plane. The RCS of the integrated mast should be reduced in all azimuth planes due to the defined threat regions but RCS reduction cannot be achieved for all incident angles in the spherical coordinate system. As mentioned above, this is because shaping is limited because of the dozens of radars, sensors and antennas installed on the integrated mast. Therefore, a definition of the cardinal points that are exceptional angle ranges are also needed with considerations for the operational environments of the naval vessel such as the shape of the ship and the radar signals coming from the enemy radar. Figure 2 shows an example of the cardinal points of a naval ship. As shown in Figure 2, the cardinal points for the naval ship in the azimuth plane are generally in the regions of the bow, the starboard, the port and the stern. After that, the RCS of an initial model of the integrated mast is calculated and analyzed. In order to evaluate the RCS of the integrated mast, the RCS pattern and the representative RCS values such as the geometric mean and the arithmetic mean [3,4,21,22] are used.