Friis' first important publications were his 1923 Institute of Radio Engineers (IRE) paper on radio transmission measurements, 1925 IRE paper on directional antennas, and 1928 IRE paper on oscillographic observations of propagation phenomena. These papers documented studies of field strength and noise over a wide range of frequencies and stressed the importance of the signal to noise ratio (SNR) in receivers rather than simple field strength.
During the early 1930s Friis helped design the radio receiver used by Karl Jansky for radio astronomy, and with Edmond Bruce invented the rhombic antenna widely used for shortwave communications. In 1938 Friis became the director of the Holmdel Radio Laboratory developing microwave systems, where he and Alfred C. Beck designed a horn reflector antenna; AT&T's national microwave relay network was subsequently based on this work. During World War II, Friis invented a "rocking horse" mechanical scanner for radar used to locate enemy mortars. He also authorized research into the first germanium diodes (Teal, 1942).
In 1946 Friis published his well-known analytic formula for transmission loss, the Friis transmission equation, which is still widely employed. In 1958 he retired but continued as a research consultant to the Hewlett-Packard Company as a friend of David Packard. He held 31 U.S. patents. Friis died in 1976 at age 83.[1]
Reference: http://en.wikipedia.org/wiki/Friis_transmission_equation
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