Scanning the Past: A History of Electrical Engineering from the Past
Submitted by Bob Morrison, Editor

Copyright 1996 IEEE. Reprinted with permission from the IEEE publication, “Scanning the Past” which covers a reprint of an article appearing in the Proceedings of the IEEE Vol. 84, No. 2, February 1996.

The Birth of the Term “Microwaves”

The term microwaves was used for the first time in an international journal in the October 1932 issue of the PROCEEDINGS OF THE INSTITUTE OF RADIO ENGINEERS (IRE) in an article by Nello Carrara: “The detection of microwaves” (the original manuscript was received by the Institute on April 2, 1932). .

This term has been, since then, commonly used to indicate those electromagnetic waves with wavelength ranging from 1 mm to 1 m. These limits have been arbitrarily defined: in practice they constitute an attempt to define the microwave frequency range as the one located between the frequencies of electromagnetic waves employed for radio and television broadcasting and those of infrared rays.

The steadily improving technology of this range of frequencies has characterized the development of telecommunications since the beginning of World War II. The demand for more and more high frequencies in telecommunications originated for various well known reasons, for the sake of brevity not discussed here, and attracted many researchers to this field. For example, Guglielmo Marconi (1887-1937), in the decade from 1919 to 1931, directed the attehtion of researchers to the potential of the microwave frequency range. The first radiowave broadcasting experiments with microwaves. were realized in 1931, by Marconi (at 50 cm) through the Tigullio Gulf in Liguria (Italy), and by Andre G. Clavier (at 17.6 cm) across the English Channel. Later on, in April 1932, Marconi realized the first microwave terrestrial link between Villa Mondragone (Monteporzio Catone, Rome, Italy) and the Vatican State.

This period of time was characterized also by the first theoretical studies on microwave propagation and the first experiments involving devices to generate and detect them. In this context worked the Italian physicist Nello Carrara (1900-1993) when he was with the RIEC (Regio Istituto Elettrotecnico e delle Comunicazioni [Royal Institute for Electrical Techniques.and Communications]) of the Italian Navy in Leghorn. The Institute, founded by Giancarlo Vallauri in 1916, housed the first Italian group of researchers in the fields of microwave engineering arid radar techniques. The RIEC maintained a prominent position in this field for many years.

In a paper dated March 1932, published in the first issue of the Italian journal Alta Frequenza (the journal was founded by Vallauri), Carrara stated that “un triodo, ad elettrodi cilindrici, con tensione di placca nulla o negativa e con tensione di griglia fortemente positiva, puoemettere onde elettromagnetiche di frequenza elevatissima (microonde)” [a triode with cylindrical electrodes, with a low anode potential and a highly positive grid potential, is capable of generating electromagnetic waves of a very high frequency (microwaves)] and explicitly related the term microwaves to electromagnetic waves with frequencies around 109 Hz.

Incidentally, it is worth emphasizing that in the same period many other terms were used to denote the range of frequencies now referred to as microwaves. Among others, the terms microrays and quasi-optical waves were introduced by Clavier and Eduard Karplus, respectively, but it was the term microwaves that was commonly adopted in scientific and technical terminology.

This contribution is a part of a paper, with iconographic material, to be published in the IEEE Microwave Theory and Techniques Newsletter.

Giuseppe Pelosi, Guest History Editor
Department of Electrical Engineering
University of Florence
Florence, Italy