Harald Friis

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Harald Trap Friis (born February 22, 1893 in Næstved ; † June 15, 1976 ) was an American engineer of Danish origin who worked in various areas of high-frequency technology .


Friis was born in Næstved , Denmark in 1893 . In 1916 he received his electrical engineering diploma from the Polytechnic Institute in Copenhagen . After working at the Royal Cannon Factory for two years, he moved to the United States in 1919 and continued his studies at Columbia University . The following year he started working for the Western Electric Company , which was taken over by Bell Laboratories in 1925 .

Friis, who had in the meantime taken on his US citizenship, retired in 1958, but continued to work as a consultant at Hewlett-Packard through personal acquaintance with David Packard . In 1971 he published his autobiography "Seventy Five Years in an Exciting World" .

Friis has filed 31 patents over the course of 50 years . He died in 1976.


Friis had given valuable impulses to various areas of high frequency technology.

First he dealt with the propagation of radio waves in different frequency ranges, whereby he also developed a heterodyne receiver . With the corresponding radio measurements, he made it important to measure not only the signal strength but also the noise, because the intelligibility of the transmitter is ultimately determined by the ratio of these two variables.

During this activity, Friis developed the theoretical fundamentals of the noise figure , which can be used to determine the signal-to-noise ratio of an amplifier. The name of the Friis formula goes back to this work . In the 1930s, together with Karl Jansky , he designed receivers for galactic noise, which paved the way for radio astronomy .

Friis was also active in the field of directional antennas . As early as 1925 he had published research results in this area. Together with Edmond Bruce he invented the rhombus antenna , which was very suitable for shortwave . Friis later designed a steerable directional antenna that consisted of several rhombuses.

From 1938 Friis was department head in the Bell laboratory in Holmdel. His duties included developing microwave and radar equipment that would later be used by US forces during World War II. Together with Alfred Beck , Friis designed a horn antenna . In 1946 he published an equation that describes the relationship between the transmission and reception power of two antennas in a vacuum, which is known as the Friis transmission equation . After the war, Friis was able to publish some research results, which then paved the way for commercial microwave links in the USA.


Friis has received numerous awards, including the Morris Liebmann Prize from the IRE , the Valdemar Poulsen Medal from the Royal Danish Academy of Sciences , the IRE Medal of Honor, the Ballentine Medal from the Franklin Institute and the Mervin Kelly Prize from the IEEE .

Web links

Individual evidence

  1. Harald Friis: A note on a simple transmission formula . In: Proceedings of the IRE . tape 34 , Issue 5, 1946, pp. 254-256 , doi : 10.1109 / JRPROC.1946.234568 ( online [PDF]). online ( Memento of the original from August 12, 2014 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / dsc.ufcg.edu.br