Radio Engineering

the science dealing with electromagnetic oscillations and waves in the radio-frequency range, that is, with methods of generating, amplifying, radiating, receiving, and using such waves; a branch of technology concerned with the use of electromagnetic oscillations and waves in the radio-frequency range for the transmission of information in such fields as radio communications, radio broadcasting, television, radar, and radio navigation, control and regulation of machines, mechanisms, and technological processes and in various scientific investigations. The radio-frequency range encompasses electromagnetic waves with wavelengths from tens of thousands of kilometers to tenths of a millimeter.

The development of radio engineering has been closely associated with advances in radio physics, electronics, the physics of semiconductors, electroacoustics, the theory of oscillations, information theory, and various branches of mathematics. Development has also been linked to, for example, advances in high-frequency measurements, vacuum and semiconductor technologies, and the manufacture of power-supply sources.

Radio engineering includes a number of divisions, among which are the generation, amplification, conversion, and control of electric oscillations. Other divisions include antenna technique, the propagation of radio waves in free space, in various media (ionosphere, soil) and in guiding systems (cables, wave guides), the filtration of electromagnetic oscillations, demodulation, and the reproduction of transmitted signals (speech, music, images, telegraph and other signals). Monitoring, control, and regulation through electromagnetic waves and oscillations (by means of electronic systems) are also divisions of radio engineering.

The history of radio engineering began with the work of M. Faraday, who laid the foundation for the doctrine of electric and magnetic fields (1837–46). Faraday advanced the idea that the propagation of electric and magnetic effects occurs with a finite velocity and constitutes a wave process. These ideas were further developed by J. C. Maxwell, who in 1864 mathematically described known electric and magnetic phenomena through a system of equations. These equations pointed to the possibility of the existence of an electromagnetic field capable of propagating through space in the form of electromagnetic waves, with light waves constituting a special case of such waves.

Electromagnetic waves in the radio-frequency range (with a wavelength of approximately 1 decimeter [dm]) were first obtained and studied by H. Hertz (1886–89). Hertz was able to generate and radiate these waves with the aid of an oscillator excited by a spark discharge. With the aid of a second oscillator, in which a spark would jump across a gap under the effect of a received wave, Hertz was able to detect electromagnetic waves. He showed that such waves, just as light waves, were capable of reflection, refraction, interference, and polarization, but he did not foresee the possibility of using electromagnetic waves to transmit information.

The phenomenon of resonance, which was studied in detail by V. F. K. Bjerknes in 1891, played a major role in Hertz’ experiments. A formula of great importance in the determination of the resonant frequency of an oscillatory circuit in the absence of damping (an ideal circuit) was obtained as early as 1853 by W. Thomson (Lord Kelvin). In 1890, E. Branley (France) discovered and studied the phenomenon of the decrease in the resistance of metal powder when acted upon by electric oscillations and the subsequent restoration of the powder’s original high resistance when tapped back. O. Lodge (Great Britain) used this phenomenon to detect electromagnetic waves when reproducing Hertz’ experiments in 1894. In this work, Lodge made use of a device, which he called a coherer, consisting of a glass tube filled with metal filings with electrodes at both ends.

A. S. Popov, in building on the work of Hertz and in trying to realize wireless communication through electromagnetic waves, refined the coherer. He did this by applying a system for restoring the coherer’s resistance; after being acted upon by electromagnetic waves, the coherer was automatically shaken. This automatic coherer was the basic component of the first apparatus for detecting and indicating signals (that is, for reception of signals) in a system for wireless communication. Popov also discovered that connecting a vertical conductor—an antenna—to the coherer resulted in an increase in the sensitivity of the receiving apparatus. Popov demonstrated the operation of his radio receiver, the world’s first, on Apr. 25 (May 7), 1895, at a meeting of the Physics Division of the Russian Physi-cochemical Society. Approximately one year later, G. Marconi offered a demonstration of the use of radio waves for wireless communication. The principal features of his apparatus coincided with those of the apparatus developed by Popov.

The early period of radio development, a period that saw the creation of simple transmitting and receiving radio sets operating at comparatively short wavelengths, was characterized by usage of strongly damped waves. These short waves were generated by a Hertz oscillator. The distance of radio communication gradually increased with the transition to longer wavelengths and the increase in the power of the transmitter and the dimensions of the antenna (height and number of wires). The use of either grounding or of a system of above-ground conductors (counterpoise) also contributed to an increase in transmission distance. Transmission distance and selectivity of reception were also substantially increased by the transition to auditory aural (with the aid of headphones) reception employing a detector (Popov’s co-workers P. N. Rybkin and D. S. Troitskii in 1899).

The next important step in the development of radio engineering was made by C. F. Braun, who proposed (1899–1900) to separate the antenna from the spark discharger. With this design, the discharger was located in a closed oscillatory circuit, and the antenna was inductively coupled to the circuit with the aid of a high-frequency transformer. Braun’s scheme made it possible to radiate into space a significantly larger fraction of the energy stored in the primary oscillatory circuit. A substantial part of this energy, however, returned from the antenna to the circuit and excited a new spark, thus causing a loss of energy. In 1906, M. Wien (Germany) designed a special discharger to prevent a return of energy from the antenna to the oscillatory circuit. With this design, the oscillations in the antenna were only weakly damped and almost all the energy was radiated as radio waves.

A further step in the development of radio equipment was the use of undamped radio waves generated by arc oscillators and high-frequency alternators. V. P. Vologdin successfully constructed prototypes of high-frequency alternators of the inductor type in the years 1912–34. Vologdin’s alternators were used in 1925 to establish the first radio communication between Moscow and New York. During the early 1920’s, O. V. Losev used crystal detectors for the generation of electromagnetic oscillations.

The development and use of electron tubes brought fundamental changes to all areas of radio engineering. The first electron tube detector was proposed by J. A. Fleming in 1904. This detector made use of the Edison effect, that is, the unidirectional flow of electrons in a vacuum from an incandescent filament (cathode) to a metal plate (anode). However, this detector, as well as L. De Forest’s three-electrode electron tube, was less sensitive than the crystal detector. Crystal detectors were widely used until the mid-1920’s, becoming obsolescent only after receiving tubes had been perfected.

An electron tube generator of undamped oscillations was invented almost simultaneously by several scientists. A. Meissner (Germany), however, is regarded as the first (1913). Important contributions to the theory and development of electron tubes and the circuits incorporating them were made by M. V. Shulei-kin, I. G. Freiman, M. A. Bonch-Bruevich, A. I. Berg, A. L. Mints, L. I. Mandel’shtam, and N. D. Papaleksi, as well as by H. Barkhausen and H. Muller. In the USSR, in the period 1918–28, the Nizhny Novgorod Radio Laboratory became a center for research on receiving and oscillator tubes; in 1928 the laboratory was incorporated into the Central Radio Laboratory. Reliable reception of undamped radio waves in the presence of various types of interference became possible with the advent of the heterodyning method. However, the introduction of the regenerative reception and, later, of superheterodyne reception represented an important step toward increasing the sensitivity of radio receivers (E. H. Armstrong, 1913, 1918; L. Levy, France, 1918). The theory of radio reception was developed in the works of Armstrong and V. I. Siforov.

The development of radio engineering was accompanied by the use of various frequency ranges of radio waves. The period from the invention of radio to the introduction of arc oscillators and alternators was associated with a gradual increase in the wavelength of radio waves from several decimeters to several kilometers. An increase in wavelength meant an increase of the transmission distance and an improved stability of radio communication. This result was caused both by more favorable conditions for the propagation of radio waves and by an increase in transmitted power. The use of radio tubes facilitated an efficient generation of radio waves in a range from hundreds of meters to several kilometers.

The early 1920’s saw the development of both radiotelegra-phy and radio broadcasting. The increase in the number of broadcasting and communications stations and the desire to operate at long wavelengths led to mutual interference and a “congestion in the air.” These conditions required rigid adherence to international agreements on the allocation of radio waves. Radio amateurs, to whom wavelengths shorter than 100 m were assigned, discovered that it was possible with these waves to establish long-distance communication using transmitters of low power. An investigation of the laws governing the propagation of radio waves in the shortwave range led to the use of these waves in communications and radio broadcasting. Special radio tubes for the short and ultrashort (meter) wavelength ranges were devised, as were special circuits, special antennas, and feeders for coupling antennas to transmitters and receivers.

Much of the investigative work into the laws governing the propagation of radio waves was done by B. A. Vvedenskii, A. N. Shchukin, V. A. Fok, and A. Sommerfeld. Present-day radio broadcasting is carried out at ultrashort, short, medium, and long waves. The USSR (A. L. Mints) leads the world in the design of high-power radio broadcasting stations and synchronized broadcasting networks. The advent of electronic television, which by the middle of the 20th century had become a mass medium, was of great importance. In the transmission of moving images, a large volume of information can only be conveyed with the aid of oscillations of very high frequency, corresponding to meter and even shorter wavelengths. In addition to television broadcasting, television apparatus are also used for monitoring processes that occur under conditions that are inhospitable to man, for example, in outer space, at great depths, and in zones of intensive radiation. Television apparatus are also useful where the intensity of illumination is low, such as in astronomical observations and in observations conducted at night.

Radar and radio navigation are special divisions of radio engineering. Radar, which is based on the reception of radio waves that are reflected by an object (target), made its appearance during the 1930’s (Iu. B. Kobzarev, D. A. Rozhanskii). Radar techniques permit a determination of the location and velocity of distant objects and, in some cases, an identification of the objects. Radar techniques are now being successfully applied to planets (V. A. Kotel’nikov). Radar uses the shortest wavelengths (from meter to millimeter). Meter waves are used mainly in measuring long distances; millimeter waves are used for a precise determination of short distances and for the detection of small objects (in radio altimeters and in the docking devices of space vehicles). Radar has stimulated a rapid development of all the components required for the generation, radiation, and reception of meter waves and those even shorter. Among the components so developed were coaxial cables, wave guides, coaxial cavities, and cavity resonators. In the proper frequency range, these new components replaced twin feeders and resonant oscillatory circuits. New, beam antennas were also constructed; these included multi-unit antennas, equipped with special reflectors or shaped like a paraboloid, with a diameter of several tens of meters. Special duplexers permitted the use of the same antenna both for transmitting the scanning pulse and receiving the pulses reflected by the target. The special radio tubes developed for use in radar sets included triodes with electrodes of a planar shape and with coaxial terminals suitable for use with coaxial cavities. Other special tubes were based on new principles and included magnetrons, klystrons, traveling-wave tubes, and backward-wave tubes.

Because of the requirements of radar, crystal detectors underwent a further development and formed the basis for semiconductor diodes. Improvements in these diodes led to the appearance of transistors and later to the development of semiconductor microcircuits (thin-film and integrated) and the introduction of semiconductor parametric amplifiers and oscillators. As a result of advances made in semiconductor electronics, radio tubes were replaced in a variety of fields by semiconductor components. New, advanced electron beam instruments appeared, and among them were models with multiple-color phosphor screens, which made for the advent of color television. The requirements of radar also stimulated the development of quantum electronics and of cryogenic electronics.

Radio navigation and the closely associated science of radio geodesy, which have undergone a prolonged development (A. S. Popov, 1897; N. D. Papaleksi, 1906, 1930; I.I. Rengarten, 1912; and L. I. Mandel’shtam, 1930), are vital for navigation on the sea, in the air, and in outer space, for cartography, and for geodetic surveys. Radio techniques permit a determination of the position and velocity of a particular object with the highest possible accuracy; in a number of cases, the error does not exceed one-millionth or even one hundred-millionth of the quantity being measured. Passive techniques of radio navigation, where the moving object merely receives signals from a reference, ground-based radio station, are distinguished from active techniques, where the moving object can itself employ radar. The systems that are most widely used in radio navigation are either passive or combined. However, in the landing of space vehicles on the moon or on planets of the solar system, active, independent systems are used, which receive from the earth only initiating commands.

Modern radio engineering enters into practically all areas of human activity. Radio communication through conventional telegraphy or high-speed teletypewriters, radiotelephony, and the transmission of images, drawings, sketches, newspaper matrices, and facsimiles are all possible now irrespective of distance. Investigations of outer space have required the establishment of reliable radio communication with artificial satellites circling the earth and with space probes that are either enroute to a planet or are located on a planet’s surface. Radio communication allows the transmission of commands to the probes and the transmission of scientific information and images from the probes back to earth. The importance of radio engineering for manned space flights is well known. But artificial satellites circling the earth are themselves components of communication links. Functioning as retransmitting stations, the satellites provide reliable communication between distant points and transmit television programs and exact time signals. Since ultrashort waves do not follow the earth’s curvature to any appreciable extent, long-distance communication and the transmission of television images must be carried out with the aid of radio-relay systems, special high-frequency cable lines and such retransmission units, including those mounted in satellites.

Many of the systems for automatic control and data processing are based on the techniques of radio engineering. Since electronic computers are complex assemblies of the components used in radio engineering, improvements in computer hardware are closely bound up with improvements in these components.

Radio engineering is widely used in the national economy. High-frequency induction heating is used in melting metals of high purity in a vacuum or in an atmosphere of inert gases. This heating technique has also been successfully used, for example, for the surface-hardening of steel parts, for drying wood, ceramics, and grain, for preserving and preparing food, and for various medical purposes.

Radio engineering is intertwined with various branches of science. Radio meteorology is a prime example. Here, the influence of such meteorological processes as the motion of clouds and the fall of precipitation on the propagation of radio waves is studied, and the techniques of radio engineering, in this case radar, are used for meteorological investigations. A. S. Popov used his storm indicator, the world’s first radio-meteorological instrument, to study the phenomena that occur during a thunderstorm; in so doing, he laid the foundation for the science of radio meteorology.

Investigations of atmospheric interference with radio reception resulted in the science of radio astronomy (K. Jansky, USA, 1931). Radio astronomy employs techniques for observing celestial bodies located at distances that exceed the range of optical telescopes. Radio telescopes have made possible, for example, the discovery of pulsars, a detailed investigation of the obscured nucleus of our galaxy, and investigations of quasars, the solar corona, and the solar surface.

The techniques and devices of radio engineering are used in designing instruments and apparatus for scientific investigations. Accelerators of charged particles are, in essence, powerful generators of radio-frequency oscillations equipped with modulators, transmission lines, and special cavities in which the process of particle acceleration occurs. Most installations for investigating elementary particles and cosmic rays consist of complex, radio-engineering circuits and assemblies that make possible an identification of particles from the observed results of the particles’ interaction with a substance. Complex data-processing systems, often incorporating electronic computers, permit a computation of such characteristics as the energy, charge, and mass of a particle. Techniques of isotopic analysis and magnetometry based on radio engineering are used in archaeology for a scientific determination of the age of archaeological objects. Apparatus of various types used in radio spectroscopy, including those designed for investigations of electron, nuclear, and quadrupole resonances, are radio-engineering devices. These apparatus are used in physics, chemistry, and biology to determine the characteristics of atomic nuclei, atoms, and molecules and to study chemical reactions and biological processes.

Developments in radio engineering paved the way for elec-troacoustics, which investigates and implements processes for conversion of sound into electric oscillations and vice versa. Electroacoustics is also concerned with various systems for sound recording and reproduction (magnetic and optical sound recording) and with systems that utilize ultrasonics in such areas as medicine and technology. Examples are ultrasonic underwater communication and ultrasonic materials processing and cleaning. Apparatus used in ultrasonic technology are essentially radio apparatus, namely, oscillators, converters, and amplifiers.

Radio engineering has given rise to a vigorous radio manufacturing industry, which produces such things as radios and television sets for mass consumption, communications equipment, radio and television broadcasting equipment, apparatus for communication trunk lines, industrial and scientific radio equipment, and radio components.

International societies and intergovernmental bodies as well as scientific journals have played an important role in the development of radio engineering. The International Scientific Radio Union, one of the oldest scientific societies, brings together the leading scientific organizations of many countries. Soviet scientists have actively participated in the union’s activities since 1957. The union meets every three years in a general assembly, where advances in radio engineering are summarized and new avenues of research are proposed. The union also periodically schedules symposia on selected topics. The most important intergovernmental bodies for regulating the activities of member countries in the areas of radio communications and radio broadcasting are the International Radio Consultative Committee and the International Frequency Registration Board. The Soviet Union takes an active part in the work of both groups.

In the USSR, the A. S. Popov Scientific and Technical Society for Radio Engineering, Electronics, and Communications has a broadly based membership, and its sections and local chapters are active in many cities throughout the Union republics. The best known radio-engineering society abroad is the Institute of Electrical and Electronics Engineers (USA).

In the USSR, the All-Union journals that appear regularly are Radiotekhnika i elektronika (Radio Engineering and Electronics), Radio tekhnika (Radio Engineering), and Radio. Abroad, the periodicals that deal with topics in radio engineering include IEEE Proceedings, L’Onde Electrique, QST, Alta Frequenza, Hochfrequenztechnik und Elecktroakustik and Wireless Engineer.