Today, conformal antennas are widely used in airborne radar applications. One of the important issues related to these antennas are calculating radiation pattern and mutual coupling between antennas mounted on aircraft platform. Because these antennas are usually mounted on surfaces whose radius of curvature is larger than wavelength, numerical methods are not practical in these cases. Furthermore to reduce radar cross section (RCS) of aircrafts, their bodies are usually coated with absorbing material. One of the most common used radar absorbing materials (RAM) is ferrite coatings. Due to tensor permeability of these materials calculations in the presence of coatings are much more complicated. To solve problems including geometries larger than wavelength asymptotic methods such as uniform theory of diffraction (UTD) are used. This method is highly efficient as compared to the conventional numerical methods such as method of moment (MOM). More importantly, it provides useful physical insights into the antenna radiation and coupling mechanisms. To use asymptotic methods we need Green’s function in an accurate and simple form. But for ferrite coated cylinder calculation of Green’s function is difficult and therefore approximate methods must be used. A common and simple approximate method in electromagnetic and also acoustic problems is impedance boundary condition (IBC). With this method electromagnetic fields is solved only for outer region of ferrite layer and as a result complexity of calculation reduced considerably. Impedance boundary conditions are widely used to analyze problems with dielectric structures but this method has not been used for analyzing ferrite layers. In this thesis we first derive impedance boundary condition for ferrite layers. To do this fields in ferrite medium are expanded using Taylor series and then appropriate impedance boundary condition is derived. The resulting condition is general and can be used in every orthogonal curvilinear coordinate. The validity and accuracy of computed IBC is also examined. We observed that by increasing radius of cylinder accuracy of our approximate impedance boundary condition increased. In addition accuracy of our method is decreased by increasing ferrite layer thickness. Using this impedance boundary condition, Green’s function of ferrite coated cylinder is calculated. Because Green’s function is in infinite series form and converges slowly specially for surface fields we expand it with asymptotic methods. First by using Watson transform we transform infinite series solution to integ Key Words Ferrite coating, Dyadic Green’s function, Impedance boundary condition, Asymptotic method, Uniform Theory of Diffraction (UTD), Surface fields, Far field