Performance Analysis of Diffraction Gain (Gd) Due to Presence of single and Multiple Knife-Edge as Compared to Free Space E- Field and Identifying the Position of Obstacle in a Fresnel Zone

This paper describes the concepts of diffraction, diffraction gain, diffraction loss, field strength at receiver due to single and multiple knife-edge obstacles between the propagation path of the signal i.e. b/w transmitter and receiver. Diffraction is the term used to describe the phenomenon of electromagnetic waves bending around the obstacles. This paper also present the complete idea of identifying the position of obstacle in a Fresnel zone, diffraction loss, position of obstacle with varying distances b/w source and field and varying heights of obstacles in a Fresnel-zones represented by tabular forms and appropriate charts. The calculation, based on an approximate evaluation of the contribution of individual Fresnel zones to the total field, leads to the Fresnel theorem: the total field is just one-half that due to the first zone alone. We show here that if the Fresnel zones are defined on a plane passing through the midpoint of the line joining the source point to the field point, the field due to each Fresnel zone may be calculated exactly. When the Fresnel zones are defined on a plane perpendicular to the line between the source and field points, the contribution of the first zone is equal to the total field multiplied by the factor 1+ (l+ /nd’)-2. Here, n is the wave number and d' is the distance separating source and field points. Thus, for this geometry, the Fresnel theorem holds only in the limit nd' 1; for arbitrary nd', the factor quoted must be used.