General theory of stratified media. Applied to the research of the correction of aircraft radome errors

Abstract

The problem treated in this paper is the radiation disturbances of a tracking radar antenna placed in the nose of a supersonic aircraft or engin which are due to the insertion of the radome between the antenna and its environment. The two essential reasons for the errors caused by the radome are: the taperd slim form given to the radome for to keep up with aerodynamic requirements. the rotating movement of the antenna about a point centered in the radiating surface. From these two particular points it is understood that the waves starting from the antenna may cross the radome wall with important and even grazing incidence angles. Amongst the radome errors deriving from this fact and being the most undesirable one is the axis deviation of a tracking radar which we call in the following the ? radome aberration ?. The different procedures employed up to now in order to correct this aberration (local thickness variations for an example) were not completely satisfying. Hence we had to look for and to try new methods in application of new ideas. So it seems a priori to be possible to dispose of a greater number of parameters for the correction of the radome aberration by increasing the number of dielectric layers used to built up a radome wall. But the theory of satisfied media, not being simple at its base, gets rapidly still more complicated by increasing the number of dielectric layers. In the first part of the paper a general theory of electromagnetic wave propagation in stratified media, divided into an arbitrary number of dielectric layers, is established. This theory is than appplied in the second part to the study of transmission and phase of a plane wave incident on a multilayer wall at grazing angles. The research has been directed to obtain good transmission and quasi zero phase variation versus incidence, the former in order to optimize energy transmission through the radome wall, the latter in order to facilitate the correction of radome aberration thanks to small phase variation and small phase variations cause poor transmission. It is finally shown that the best compromise for the design of a engin nose radome is the monolithic wall being adapted at the limit of grazing incidence and having a high dielectric constant.