operations involving the use of radio aids to facilitate the movement of such objects as aircraft and ships and the guidance of controlled objects. Radio navigation is the scientific and technical discipline that considers the design principles of radio aids and develops methods of applying such principles to solve the problems of piloting moving objects along a specific trajectory (course) and guiding the objects to a given area at a given time (see and NAVIGATION, AIR).

In radio navigation, specialized radio aids are used in solving the basic problem of navigation—the determination of an object’s position and the navigation elements of the object’s movement; various techniques used in other fields of technology, such as in radar and radio broadcasting, may also be employed.

The operation of radio navigation aids is based on the use of the following important features of radio-wave propagation: radio waves propagate over the earth’s surface along the shortest (great-circle) distance between the radiating and receiving points; the propagation velocity is constant; and radio rays reflected from and incident upon the ionosphere lie in the same plane.

Various classifications and subcategories for radio navigation aids exist. Depending on the nature of the problems solved and the completeness of the solution, such aids may be classified as radio navigation devices or radio navigation systems. Examples of radio navigation devices are radio direction finders (including automatic direction finders), range-only radar, radio beacons, and radio sextants. Such devices may be employed in combinations, or they may make use of independent artificial or natural sources of radio radiation or the reflecting properties of the earth’s surface and the fixed objects situated on it. They are only used in solving particular navigational problems, usually the determination of one line (or plane) of position for a moving object. Radio navigation systems are used in solving complex navigational problems.

Radio navigation aids may also be classified according to the wavelength band used, in conformity with regulations governing radio communications, or according to a parameter of the radio signals used to measure navigational elements; this is the most common characteristic attribute, and the signal parameters include amplitude, phase, frequency, time, and combinations of parameters, such as amplitude and time or phase and time. Another classification is based on the method of determining a line of position, such as the angle-measuring (azi-muthal), range-measuring (panoramic), and combined aids; examples of combined aids are hyperbolic and polar-coordinate systems. According to the number of moving objects to which navigation information is provided, radio navigation aids may also be classified as having limited or unlimited traffic-handling capacity. Distinctions are also made according to the presence of other characteristics, resulting in such categories as self-contained and non-self-contained aids.

The use of radio navigation methods and aids has made it possible for moving objects to maintain course and arrive at a specified area with greater accuracy; the navigation of ships and the piloting of aircraft in adverse weather conditions has also been made much safer. In principle, combining various radio navigation devices into specific systems can ensure that all the basic problems of navigation are solved. However, with a view toward improving reliability and safety in piloting objects under the most complicated conditions, in practice such systems are employed within integrated systems jointly with non-radio aids, such as inertial navigation systems.