A passive radio link deflection, or passive repeater is a plant for the implementation of a microwave link, in which because of an obstacle in the signal path no direct line of sight microwave link is possible. It has the advantage over the installation of a microwave radio relay station with active components, that at the place of the installation no electricity supply is required and that no further frequencies are needed (at repeater stations with active components usually different frequencies for reception and transmission are used, in order to prevent feedbacks). The corresponding disadvantage is that the returned signal is significantly weaker.
Passive radio relay link deflection systems in the vertical level can be realized by receiving the signal with a parabolic antenna and leading it through a waveguide to a second parabolic antenna, where it is radiated. For passive microwave radio relay link deflections in the horizontal plane, flat surfaces of metallic material are used, arranged so that the angle of incoming beam corresponds to the angle of the outcoming signal. The resulting structure resembles a billboard. For small deflection angles, cavity prisms can be used.
Similar systems are used also occasionally for TV relay transmitters or as tunnel transmitter. Here a Yagi antenna receives the signal of the transmitter and supplies it by way of a coaxial cable to a second antenna.