Antennas for communications

Attention is given to the demands being made on antennas because of spectrum congestion. In the microwave bands employed by satellites, the antenna characteristics must now be good enough for frequencies to be reused. At HF, broadband performance is required even of structures of a limited physical size; in all bands, adaptive antennas are needed to minimize interference from unwanted transmissions. Developments in communications antenna technology that are enabling these and other goals to be achieved are discussed. It is pointed out that because of more powerful launch vehicles, satellites carry larger, more directional antennas which can link directly to smaller, less expensive ground terminals. Also discussed are low-profile, HF, active, small, and adaptive antennas.