Entegre mast yapısının gemi radar kesit alanı üzerindeki etkilerinin incelenmesi
Investigation of integrated mast module impacts on radar cross section of a battleship
Yazar: SEYHAN ÇAKAL
Danışman: DR. ÖĞR. ÜYESİ MUSTAFA HELVACI
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / İletişim Sistemleri Ana Bilim Dalı / Uydu Haberleşmesi ve Uzaktan Algılama Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Mühendislik Bilimleri = Engineering Sciences

Özet:
Düşük görünürlük teknolojilerinde, uçar, yüzer ve kara platformlarının radar, kızılötesi ve sonar gibi algılayıcı sistemler tarafından tespitinin önlenmesi amaçlanmaktadır. Askeri açıdan bakıldığında düşük görünürlük kavramı, platform veya platorma ait alt sistemlerin düşman radar sistemleri tarafından tespitine, teşhis ve takibine yakalanmadan ilerlemesi platformlara avantaj sağlamaktadır.
Yüzer, uçar ve kara platformları düşük görünürlük teknolojisi konsepti dahilinde incelendiğinde bahse konu platformlar için "Radar Kesit Alanı" kavramının önemine değinmek gerekmektedir. Kabaca bir cismin radar kesit alanı, hedefin elektromanyetik sinyali yansıtıcılığının bir ölçütü olarak tanımlanır. Platformun radar kesit alanını azaltmak, hem platformun savaş gemilerine konuşlandırılan radar sistemleri tarafından geç algılanmasını sağlamakta hem de teşhis ve takibini zorlaştırmaktadır. Bu nedenle, radar kesit alanı savaş gemileri için önemli bir tasarım kavramı haline gelmektedir.
Savaş gemileri gelişen radar teknolojisinden faydalanarak, tehdit platformları kolaylıkla tespit edebilmektedir. Ancak roller değiştiğinde platformların yeni nesil radar sistemleri tarafından fark edilmeden hedefine ilerlemesi oldukça zordur. Gemiler üzerine yerleştirilen antenler, silah sistemleri ve birçok sensör platformların radar kesit alanını artırmaktadır. Görülmeden gören platformlar geliştirmek için literatürde çeşitli yöntemler mevcuttur. Bu yöntemlerden nispeten maliyet etkin bir yöntem olan şekillendirme, gemilerin radar kesit alanı üzerinde önemli bir etkiye sahiptir. Günümüzde, gemi üzerinde çeşitli mevkilerde konuşlanmış radar sistemlerinin radar kesit alanı üzerindeki etkisinin azaltmak maksadıyla geliştirilen entegre mast sistemlerinden faydalanılmaktadır.
Bu çalışmada, platformlarda yerini almaya başlayan yeni nesil entegre mast yapılarının gemilerin radar kesit alanları üzerinde etkilerinin incelenmesi amaçlanmıştır. Çalışma kapsamında ilk olarak, iki farklı mast yapısı tasarlanmış, gemi üzerindeki etkisini incelemek amacıyla 3 boyutlu gemi modeli oluşturulmuş ve son olarak her bir mastın etkisini incelemek maksadıyla gemi üzerine konuşlandırılarak analizler koşulmuştur. Bahse konu analizlerde radar kesit alanı tahmin yazılımları tarafından sıklıkla kullanılan "fiziksel optik" yöntemi kullanılmış, elektromanyetik propagasyonda kaybın en düşük olduğu iki farklı frekans bölgesi seçilmiş ve yanca/yükseliş açıları için çeşitli açı değerleri seçilerek çalışmalar yapılmıştır. Analizler neticesinde; nispeten daha düz yüzeylerin geminin radar kesit alanına ne yönde katkı sağladığı ve tasarlanan iki farklı mast yapısının platformun radar kesit alanı üzerindeki etkisinin bakış açısına (yanca/yükseliş), polarizasyona ve frekansa bağlı olarak nasıl değiştiği incelenmiş ve grafiklerle sergilenmiştir.

Abstract:
Stealth technologies are about preventing the detection of flying, floating, and landing platforms by sensor systems such as radar, infrared, and sonar. From a military perspective, the concept of low visibility provides an advantage to platforms because platform subsystems or the platform itself can move without being detected, diagnosed, and tracked by enemy radar systems.
Warships can easily detect threat platforms using evolving radar technology. However, as missions change, it is very difficult for platforms to move toward their targets without being detected by the new-generation radar systems. Antennas, weapons systems, and many sensors placed on vessels increase the radar cross section, which is a measure of the scattering electromagnetic energy returned from platforms. Several methods for developing platforms without line of sight can be found in the literature. Of these methods, shaping, which is a relatively inexpensive method, has a significant impact on the radar cross section of ships. Nowadays, integrated mast systems are used to reduce the impact of radar systems placed at different locations on the ship on the radar cross section.
This thesis aims to examine the effects of an integrated mast structure on the radar cross section (RCS) of a ship, specifically at X and Ka bands. The integration of various antennas, sensors, and communication systems within the mast structure has become a common practice in modern naval vessels. However, this integration can potentially impact the ship's RCS, which is a crucial factor in determining its detectability and susceptibility to radar systems.
The study begins by providing the reason for choosing this subject, its purpose, and its contribution to the literature. Then, it gives an overview of the radar basics, the concept of radar cross section and its significance in naval operations. It highlights the importance of minimizing a ship's RCS at specific frequency bands, such as X and Ka, to enhance stealth capabilities and reduce vulnerability to enemy radar detection in these bands.
Next, the research focuses on the design and implementation of two distinct mast configurations for the ship. Each configuration incorporates different arrangements. In the study, two different mast structures were first designed, a CAD model of the ship was created to study the effects on the ship, and finally analyses were performed by placing them on the ship to study the effects of each mast.
To evaluate the effects of the two mast configurations, "the physical optics" method commonly used by commercial software are utilized. Two different frequency ranges with the lowest losses in electromagnetic propagation were selected, and the studies were performed by choosing different angular values in the azimuth and elevation. Specialized software tools are employed to model the ship's geometry, materials, and the integrated mast structures for both configurations. The simulations enable the calculation of the RCS at X and Ka bands for various incident angles and polarization states, allowing for a comprehensive analysis.
The obtained results from the simulations are then compared and analyzed to determine the differences in the ship's RCS between the two mast configurations at X and Ka bands. The thesis discusses the factors contributing to RCS reduction or enhancement in each configuration, considering the size, shape, and composition of the integrated components.
Furthermore, the research explores potential mitigation strategies to minimize the RCS impact of the integrated mast structures in both configurations at X and Ka bands. Techniques such as radar-absorbent materials, coatings, and shaping optimization are evaluated to identify their effectiveness in reducing the ship's radar signature. Especially, the research aims to show shaping's which is one of the radar cross section reduction techniques basics for the warship designer.
In conclusion, this thesis presents a comparative analysis of the effects of two integrated mast structures on the ship's radar cross section specifically at X and Ka bands. Moreover, it is investigated how relatively flatter surfaces contribute to the radar cross section of the ship and how the effect of two differently designed mast structures on the radar cross-sectional area of the platform changes depending on the viewing angle (the azimuth and elevation angle), polarization, and frequency. By the way, the findings contribute to the understanding of how different mast configurations can influence the ship's detectability in radar systems operating in these frequency bands. To summarize briefly the following articles;
 It is necessary to define the element that will threaten the platform to be designed. For example operating frequency, polarization, viewing angle to target platform etc.
 Since the radar cross section reduction is roughly increasing the angle of the incoming signal with the surface normal, it is necessary to avoid flat surfaces that will create a mirror effect.
 When the analysis results in X and Ka bands are examined, it is seen that the radar cross section pattern of the platform is similar in both frequency bands, which can give an idea about the upper bands for designers who have the ability to make predictions for the lower frequency band.
 According to the results of the analyzes, it is seen that integrated mast structures are really viable structures for ships beyond just futuristic designs and can produce optimum solutions for platforms with low visibility technology when appropriate design criteria are taken into account.
 It should be considered to resort to other radar cross section reduction methods, such as the application of radar absorbing material, in order to achieve radar cross section reduction methods in areas where shaping does not produce an optimum solution.
The research also identifies potential avenues for further investigation in optimizing mast designs to achieve reduced RCS in X and Ka bands for naval applications.