Harald Trap Friis (22 February 1893 – 15 June 1976), who published as H. T. Friis, was a

Danish-American Danish Americans () are Americans who have ancestral roots originated fully or partially from Denmark. There are approximately 1,300,000 Americans of Danes, Danish origin or descent. Most Danes who came to the United States after 1865 did so ...

radio Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...

engineer whose work at

Bell Laboratories Nokia Bell Labs, commonly referred to as ''Bell Labs'', is an American industrial research and development company owned by Finnish technology company Nokia. With headquarters located in Murray Hill, New Jersey, the company operates several lab ...

included pioneering contributions to

radio propagation Radio propagation is the behavior of radio waves as they travel, or are wave propagation, propagated, from one point to another in vacuum, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio w ...

radio astronomy Radio astronomy is a subfield of astronomy that studies Astronomical object, celestial objects using radio waves. It started in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation coming from the Milky Way. Subsequent observat ...

, and

radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

. His two Friis formulas remain widely used.

Background

Friis was born in

Næstved Næstved () is a town in Næstved Municipality, the municipality of the same name, located in the southern part of the island of Zealand (Denmark), Zealand in Denmark. Næstved has several adult education centers, five Primary education, elemen ...

Denmark Denmark is a Nordic countries, Nordic country in Northern Europe. It is the metropole and most populous constituent of the Kingdom of Denmark,, . also known as the Danish Realm, a constitutionally unitary state that includes the Autonomous a ...

. In 1916, he received his electrical engineering degree from the

Technical University of Denmark The Technical University of Denmark (), often simply referred to as DTU, is a polytechnic university and school of engineering. It was founded in 1829 at the initiative of Hans Christian Ørsted as Denmark's first polytechnic, and it is today ran ...

. After a stint at the Royal Gun Factory, in 1919 he received a

Columbia University Columbia University in the City of New York, commonly referred to as Columbia University, is a Private university, private Ivy League research university in New York City. Established in 1754 as King's College on the grounds of Trinity Churc ...

fellowship to study radio engineering under John H. Morecroft. In 1920 Friis joined a

Western Electric Company Western Electric Co., Inc. was an American electrical engineering and manufacturing company that operated from 1869 to 1996. A subsidiary of the AT&T Corporation for most of its lifespan, Western Electric was the primary manufacturer, supplier, ...

research group which in 1925 became part of Bell Laboratories. There he remained for his entire professional career.

Career

Friis' first important publications were his 1923

Institute of Radio Engineers The Institute of Radio Engineers (IRE) was a professional organization which existed from 1912 until December 31, 1962. On January 1, 1963, it merged with the American Institute of Electrical Engineers (AIEE) to form the Institute of Electrical ...

(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 Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in deci ...

(SNR) in receivers rather than simple field strength. During the early 1930s Friis helped design the radio receiver used by

Karl Jansky Karl Guthe Jansky (October 22, 1905 – February 14, 1950) was an American physicist and radio engineer who in April 1933 first announced his discovery of radio waves emanating from the Milky Way in the constellation Sagittarius. He is consider ...

for

, and with

Edmond Bruce Edmond Bruce (September 28, 1899 – November 28, 1973) was an American radio pioneer best known for creating the rhombic antenna and Bruce array. Bruce was born in Saint Louis, Missouri, and raised in Cambridge, Massachusetts, Brooklyn, and Was ...

invented the

rhombic antenna A rhombic antenna is made of four sections of wire suspended parallel to the ground in a diamond or "rhombus" shape. Each of the four sides is the same length – about a quarter-wavelength to one wavelength per section – converging but not to ...

widely used for shortwave communications. In 1938 Friis became the director of the Holmdel Radio Laboratory developing

microwave Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...

systems, where he and Alfred C. Beck designed the horn reflector antenna, which was widely used in

AT&T AT&T Inc., an abbreviation for its predecessor's former name, the American Telephone and Telegraph Company, is an American multinational telecommunications holding company headquartered at Whitacre Tower in Downtown Dallas, Texas. It is the w ...

's national microwave relay network in the 1960s. 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 diode A diode is a two- terminal electronic component that conducts electric current primarily in one direction (asymmetric conductance). It has low (ideally zero) resistance in one direction and high (ideally infinite) resistance in the other. A ...

s (

Teal alt=American teal duck (male), Green-winged teal (male) Teal is a greenish-blue color. Its name comes from that of a bird—the Eurasian teal (''Anas crecca'')—which presents a similarly colored stripe on its head. The word is often used ...

, 1942). In 1946 Friis published his well-known analytic formula for power transfer between two antenna, the

Friis transmission equation The Friis transmission formula is used in telecommunications engineering, equating the power at the terminals of a receive antenna as the product of power density of the incident wave and the effective aperture of the receiving antenna under i ...

, which is still widely employed. In 1958 he retired but continued as a research consultant to the

Hewlett-Packard Company The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company. It was founded by Bill Hewlett and David Packard in 1939 in a one-car garage in Palo Alto, Californ ...

as a friend of

David Packard David Packard ( ; September 7, 1912 – March 26, 1996) was an American electrical engineer and co-founder, with Bill Hewlett, of Hewlett-Packard (1939), serving as president (1947–64), CEO (1964–68), and chairman of the board (1964–68 ...

. He held 31 U.S. patents. Friis died on 15 June 1976, at age 83, of a stroke in

Palo Alto, California Palo Alto ( ; Spanish language, Spanish for ) is a charter city in northwestern Santa Clara County, California, United States, in the San Francisco Bay Area, named after a Sequoia sempervirens, coastal redwood tree known as El Palo Alto. Th ...

Awards

Friis received the IRE Morris N. Liebmann Award in 1939, the IRE Medal of Honor (now the

IEEE Medal of Honor The IEEE Medal of Honor is the highest recognition of the American Institute of Electrical and Electronics Engineers (IEEE). It has been awarded since 1917, and is presented to an individual or team of up to three who have made exceptional contri ...

) in 1955, the Valdemar Poulsen Gold Medal of the in 1956, the

Stuart Ballantine Medal {{Refimprove, date=February 2018 The Stuart Ballantine Medal was a science and engineering award presented by the Franklin Institute, of Philadelphia, Pennsylvania, USA. It was named after the US inventor Stuart Ballantine. Laureates *1947 - Ge ...

from the

Franklin Institute The Franklin Institute is a science museum and a center of science education and research in Philadelphia, Pennsylvania. It is named after the American scientist and wikt:statesman, statesman Benjamin Franklin. It houses the Benjamin Franklin ...

in 1958 and the Mervin Kelly Award of the IEEE in 1964.

Selected works

* ''Seventy Five Years in an Exciting World'', (1971) * ''Antennas: Theory and Practice'', (1952) – with Sergei A. Schelkunoff * ''Proceedings of the IRE'', vol. 34, p. 254, (1946) –

* ''A New Directional Receiving System'', (1925) * ''High Frequency Amplifiers'', (1924)

Work papers

The papers of Harald Trap Friis span the years 1921-1976. These documents are available to the public and are maintained at the Manuscript Division, Library of Congress, Washington, D.C.

References

Other sources

* {{DEFAULTSORT:Friis, Harald T. 1893 births 1976 deaths American electrical engineers Radio pioneers IEEE Medal of Honor recipients Valdemar Poulsen Gold Medal recipients Scientists at Bell Labs Danish emigrants to the United States People from Næstved Municipality 20th-century American engineers Microwave engineers American telecommunications engineers 20th-century Danish engineers