4. COMPUTING THE EFFECT OF ANTENNA LOCATIONS ON THE RADIATION PATTERN ON BOARD COMPLEX PLATFORMS Soner KARACA, 2004

Key Words : Antenna, physical optics approximation, radiation pattern, surface currents, scattering, scattered fields, radar cross section

Complex platforms such as modern aircraft and ships, are equipped with many sensors and communication systems. The performances of these systems are not determined only by the types and structures of the antennas. The interactions between the antennas and superstructures of the complex platforms also influence the performance. Basically, the interaction between the antenna and the superstructure of a platform may cause blind sectors. Ideally, the exact results for a real platform can be determined by measurements. However, this is an expensive method incurring high costs as well as technology. Analysis of the antenna performance by software is an alternate method.

While evaluating the radiation performance of an antenna on board a complex platform, the radiation of the antenna should be considered together with the platform‑induced radiation (scattered electromagnetic field), which is the result of the interaction between the antenna and the platform. The radar cross section (RCS), is a special situation for the radiation pattern in which only the scattered electromagnetic field, caused by surface currents on the platform, is evaluated.

The scattered electromagnetic fields can be evaluated exactly by analytical formulas only for a few simple geometric objects. Therefore, for the complex platforms, such as ships and aircraft, the scattered electromagnetic fields are evaluated by numerical quadrature. The radiation integrals need to be evaluated for computation of scattered fields, when the surface currents induced on the platform are resolved. In this thesis, an analytical technique for accurate and rapid computation of electromagnetic fields, whose sources are the induced currents obtained with the physical optics approximation, is developed. Since the developed analytical technique is valid only in the far-field, a hybrid method that is applicable when the antenna is in the vicinity of the platform is also proposed. Finally, a software which evaluates the radiation performance of an antenna on board a complex platform with minimum cost and visualizes the results, is designed. An RCS evaluation and plotting opportunity is added to the software as an option.