The exposure of the antenna beams of radio-relay systems to emissions from communication satellites is geometrically predictable when such satellites have circular orbits with recurrent earth tracks but is only predictable statistically for inclined circular orbits of arbitrary periods. A phased system of these recurrent earth-track satellites can be made to follow a single earth-track and such systems are of increasing interest for communication. Geostationary satellites are a special case, since the equator constitutes the earth-track of all equatorial orbits.