History of Radio Engineering from Maxwell to the Present

The Scottish physicist and mathematician James Clerk Maxwell (1831-1879) predicted the existence of electromagnetic waves. He combined Gauss' law for electric and magnetic fields, Ampere's law for magnetic fields, and the Faraday-Henry law of electromagnetic induction, and added displacement current to Ampere's law. He formulated a set of equations, which he published in 1864. These equations showed the interrelation of electric and magnetic fields. Maxwell proposed that visible light is formed of electromagnetic vibrations and that electromagnetic waves of other wavelengths propagating with the speed of light were possible.

The German physicist Heinrich Hertz (1857-1894) was the first to prove experimentally the existence of radio waves, thus verifying Maxwell's equations [3]. In 1888, he released the results of his first experiments. The transmitter was an end-loaded dipole antenna with a spark gap. A current oscillating back and forth was produced as the charged antenna was discharged across the spark gap. The receiver consisted of a loop antenna and a spark gap. With this apparatus operating at about 50 MHz, Hertz was able to show that there are radio waves. Later he showed the reflection, diffraction, and polarization of radio waves, and he measured the wavelength from an interference pattern of radio waves.

The first person to use radio waves for communication was the Italian inventor Guglielmo Marconi (1874-1937). He made experiments in 1895 and submitted his patent application ''Improvements in transmitting electrical impulses and signals and in apparatus therefor'' in England in 1896. In 1901, Marconi, using his wireless telegraph, succeeded in sending the letter S in Morse code from Poldhu in Cornwall across the Atlantic to St. Johns in Newfoundland. Because the distance was over 3,000 km, this experiment demonstrated that radio waves could be sent beyond the horizon, contrary to the common belief of that time. The Russian physicist Alexander Popov (1859-1906) made experiments nearly simultaneously with Marconi. He demonstrated his apparatus in 1896 to a scientific audience in St. Petersburg.

Hertz used a spark gap between antenna terminals as a receiver. In 1891, the French physicist Edouard Branly (1846-1940) published a better detector, a coherer. It was based on the properties of small metal particles between two electrodes in an evacuated glass tube. Both Marconi and Popov used coherers in their early experiments. The invention of vacuum tubes was a great step forward toward better transmitters and receivers. In 1904, the British physicist John Ambrose Fleming (1849-1945) invented the rectifying vacuum tube, the diode. In 1906 the American inventor Lee De Forest (1873-1961) added a third electrode, called a grid, and thereby invented the triode. The grid controlled the current and made amplification possible. The efficiency of the electron tubes was greatly improved by using concentric cylinders as electrodes. One of the first inventors was the Finnish engineer Eric Tigerstedt (1886-1925), who filed his patent application for such a triode in 1914.

De Forest and the American engineer and inventor Edwin Armstrong (1890-1954) independently discovered regenerative feedback in 1912. This phenomenon was used to produce a continuous carrier wave, which could be modulated by a voice signal. Armstrong invented also the superheterodyne receiver. These techniques made broadcasting possible. AM stations began broadcasting in 1919 and 1920. Regular TV transmissions started in Germany in 1935. Armstrong's third great broadcasting invention was FM radio, but FM broadcasting was accepted not until after World War II.

Communication was not the only application of radio waves. Karl Jansky (1905-1950), while studying radio noise at Bell Labs in 1932, detected a steady hiss from our own galaxy, the Milky Way. This was the beginning of radio astronomy. The invention of microwave tubes, of klystron in 1939, and of magnetron in 1940 was essential for the development of microwave radar during World War II. The principle of radar had been introduced much earlier by the German engineer Christian Hulsmeyer (1881-1957), who made experiments in 1903. Due to the lack of financing, the idea was abandoned until 1922, when Marconi proposed using radar for detecting ships in fog.

The Radiation Laboratory, which was established at the Massachusetts Institute of Technology during World War II, had a great impact on the development of radio engineering. Many leading American physicists were gathered there to develop radar, radionavigation, microwave components, microwave theory, electronics, and education in the field, and gave written 27 books on the research conducted there.

The rectifying properties of semiconductors were noted in the late nineteenth century. However, the development of semiconductor devices was slow because vacuum tubes could do all the necessary operations, such as amplification and detection. A serious study of semiconductors began in the 1940s. The high-frequency capabilities of the point-contact semiconductor diode had already been observed. The invention of the transistor by Bardeen, Brattain, and Shockley started a new era in electronics. Their point-contact transistor worked for the first time in 1947. The principle of the bipolar junction transistor was proposed the next year.

The subsequent development of semiconductor devices is a prerequisite for the radio engineering of today. The continuous development of components and integrated circuits has made it possible to pack more complex functions to an ever-smaller space, which in turn has made possible many modern systems, such as mobile communication, satellite communication, and satellite navigation systems.


[1] Radio Regulations, Vol. I, Geneva, Switzerland: International Telecommunication Union, 2001.

[2] Paul, C. R., Introduction to Electromagnetic Compatibility, New York: John Wiley & Sons, 1992.

[3] Levy, R., (ed.), "Special Issue Commemorating the Centennial of Heinrich Hertz,'' IEEE Trans. on Microwave Theory and Techniques, Vol. 36, No. 5, 1988, pp. 801—858.

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