Radiation of spiral antennas in the presence of BOR radome structure based on physical optics analysis

Spiral antennas are popularly employed in radar direction-finding systems. Due to the presence of radome structures, the antenna performance tends to degrade. In order to evaluate the performance, numerical analysis is very effective. Among the techniques, which include ray tracing and the method of moments, a physical optics (Pathak, P.H., 1988) approximation, based on geometrical optic fields, is very straightforward and requires no complicated and intensive computational procedures or resources. The paper employs PO to analyze the antenna radiation in the presence of a body of revolution (BOR) radome structure. Detailed formulations are presented, particularly for the multi-arm spiral antenna. Due to the fact that each mode of the spiral antenna radiation results in a cylindrical wave mode (Penno, R.P. and Pasala, K.M., 1999), analysis can be relatively simplified. Furthermore, based on a cylindrical mode expansion, the presented procedure can be further extended in a straightforward fashion to treat relatively arbitrary antenna radiation. Numerical examples are presented.