Repeater, Passive

a device in the form of a mechanical structure of a definite shape, an artificially produced, electrically conductive medium, or a celestial body that is capable of dispersing or directionally reflecting the energy of radio waves; such repeaters are used as intermediate points in radio communications links. In radio-relay communications links, plane reflectors and antenna systems with reflector antennas serve as passive repeaters. In space communications, passive communications satellites may be used, such as the American Echo 2, a balloon 40 m in diameter, made of polymer film with a reflective aluminum coating; other means used include belts of needles, artificially produced clouds of metallic vapors ionized by radiation from the sun or by radio radiation from the earth, and the surface of the moon.

In contrast to an active repeater, a passive repeater can serve a communications network containing virtually an unlimited number of communications links operating at various, even closely adjacent, radio frequencies. Such operation is possible because a passive repeater reflects or disperses the energy of many simultaneously arriving signals without any mutual interference. With passive repeaters, the required energy level of the redirected signal is provided by increasing the power of the transmitter, increasing the dimensions of the antennas in transmitting and receiving stations, by narrowing the passband of the communications channel, and by reducing the speed of information transmission.