Radio Physics

the field of physics that studies the physical processes associated with radio-frequency electromagnetic oscillations and waves. It investigates not only the processes of excitation, propagation, reception, and frequency conversion but also the accompanying interactions of electric and magnetic fields with charges in a vacuum and in matter. Radio physics took shape in the 1920’s and 1930’s through the consolidation of the branches of physics that had developed for the study of the problems of radio engineering and radio electronics.

There are three principal areas of research in radio physics. The first encompasses theoretical and experimental studies of electrical oscillations in oscillatory systems with lumped parameters (seeOSCILLATORY SYSTEMS and OSCILLATORY CIRCUIT) and in continuous media with distributed parameters. These studies are the basis for the development of new methods of generating, amplifying, and converting oscillations with frequencies from 1–2 hertz to 10¹¹ hertz or more (seeSELF-OSCILLATIONS, GENERATION OF ELECTRICAL OSCILLATIONS, and PARAMETRIC EXCITATION AND AMPLIFICATION OF ELECTROMAGNETIC OSCILLATIONS). This area is also concerned with the influence of random (fluctuation) processes on electrical oscillations in actual devices and with methods of discriminating an information-carrying signal from a group of intelligence signals and random signals, such as noise. Both problems are closely connected with the general mathematical theory of oscillations, automatic control theory, information theory, and cybernetics, which constitute an extension of the laws studied in radio physics to processes occurring in, for example, various mechanical, electrical, and biological systems.

The second area of research studies interactions of electrical oscillations and electromagnetic waves in the radio-frequency range with charge carriers in a vacuum, in gases, and in solids. The study of the interaction of electromagnetic fields with electron fluxes in a vacuum has made it possible to develop and improve both electron tubes (with static control of electron fluxes) and microwave electronic devices, such as the magnetron, klystron, traveling-wave tube, and backward-wave tube. Research on the interaction of electromagnetic fields with ionized gas has led to the development of gas-discharge devices, such as the thyratron and trigatron, that are extensively used in electronic systems. Such research borders on general investigations of the physical properties—in particular, the oscillatory properties —of plasmas and on investigations of wave processes in the natural plasma of near-terrestrial and interplanetary space.

The construction of a variety of devices has been made possible by the study of the interaction of electrical oscillations and radio-frequency waves with electronic processes in semiconductors, p-n junctions, heterostructures, a number of dielectric crystals, and some superconductors. Such devices include solid-state generators, amplifiers, and converters of electrical oscillations of different frequencies—from the very lowest frequencies to frequencies in the optical region. Examples are the transistor and the semiconductor diode (see alsoGUNN DIODE. JOSEPHSON EFFECT, and QUANTUM ELECTRONICS).

The third area of research is the radiation and propagation of radio waves. An important role in the design of radio-communications systems and transmitting and receiving equipment has been played by theoretical and experimental research on the radiation of various types of antennas, on the electrody-namic design of antennas, and on radio-wave propagation in various guiding systems—such as radio wave guides and feeders—and slow-wave circuits. When radio physics studies radio-wave propagation above and below the earth’s surface and takes into account specific conditions resulting from the inconstancy of geophysical and space phenomena, it borders on geophysics. The characteristics of radio-wave propagation over terrestrial and space paths can be investigated only if information is systematically accumulated on the properties of the troposphere, ionosphere, near-terrestrial space, and interplanetary space and on the variability of these properties over time. On the other hand, many properties of geophysical objects are studied primarily by radio-physical techniques, that is, on the basis of observations of the characteristics of radio-frequency wave and oscillatory processes.

The development of radio physics has been accompanied by the discovery of new phenomena that have found practical application and have formed the basis for such new areas of study as quantum electronics. Some branches of radio physics have become independent fields of physics—for example, radio astronomy, radio-frequency spectroscopy, and radio meteorology. In such fields, the methods of radio physics are used only as a means of studying phenomena that lie beyond the range of radio physics. The application of radio-physical methods in optics has played a special role (seeNONLINEAR OPTICS).