An engineering approach for site shielding calculations

In this paper, two models to approximately calculate the field distribution in the vicinity of a perfectly conducting finite width screen are discussed. The first model is based on the geometrical theory of diffraction (GTD), and is simplified such that the magnitude of the individual ray contributions can be easily calculated. The second model is based on a graphical approach. Coefficients that are representative for the dimensions of the obstacle and the relative position of the observation point are used together with standardized equations to calculate the field strength in the shadow region behind the screen. Also a modification of the current CCIR procedure for knife‐edge diffraction is proposed, such that it can be applied to a finite width screen. Results of all models are compared with more accurate and complex results from a model based on the uniform theory of diffraction (UTD). All models proposed are simple to apply and present an essential extension to currently available engineering models. It is found that the GTD model has the best performance with respect to the UTD approach. The graphical method, however, is more user friendly than the GTD model, because fewer intermediate results need to be calculated. Moreover, the use of this method yields a field‐strength distribution for the whole shadow region of the obstacle instead of the field at just a single point. Further, it is found that the modified CCIR approach can also be used with good accuracy. The models discussed answer some questions formulated by the CCIR concerning site shielding, and extend the currently available engineering models for this interference reduction technique.