Past exam of the physics A course of the University of Cambridge / 2010 / Paper 1 / Section B / B9 / a / Solution

The grazing-gap signal is the chord from $F(0)=0$ to $F(1.768)$, approximately $(0.3245,0.4818)$ in the (C,S) plane. Its squared length determines received power after applying the same propagation normalization used for the open field. Reversing which gap edge grazes the ray reflects both limits and leaves the power unchanged.