Radio Navigation System
Radio Navigation System
a set of several radio navigation aids of the same or different types that interact over radio channels or within a single unit, thereby making it possible to determine the position of moving objects and to solve other complex problems in navigation. Since the 1940’s and 1950’s, the most widely used types in radio navigation have been hyperbolic and polar-coordinate navigation systems.
Hyperbolic navigation systems use a phase-measuring or a pulse-phase-measuring method of determining the difference between distances. They consist of three or more ground transmitting stations and a special receiving-indicating device on board an aircraft or ship. One of the ground stations, called the master station, transmits operating signals that simultaneously serve as synchronizing signals for the two other (slave) stations. The slave stations transmit operating signals synchronized with those of the master station but with a certain artifical time delay. Ground stations in pulse-phase systems transmit operating signals in a pulse mode on one carrier frequency, while ground stations in phase systems usually transmit on different carrier frequencies with continuous-wave oscillation or with pulsed carrier oscillation. The signals transmitted by the ground stations are received on board the moving object, and their arrival times are compared, with allowance made for the delay. Two ground stations—the master and one of the slave stations —provide the means for measuring one line of position (a hyperbola), and three or more ground stations make it possible to determine a position and other navigational elements in the movement of objects.
Special charts are issued for each hyperbolic navigation system on which families of hyperbolas are plotted with high accuracy. Each hyperbola corresponds to a specific difference in the arrival time of signals from the corresponding master and slave stations located at known geographical points; the coordinates of an object are given by the point of intersection of two hyperbolas.
As of the mid-1970’s, long-wave hyperbolic pulse-phase systems and superlong-wave hyperbolic phase systems are most often employed for navigation at substantial distances (more than 500 or 600 km); each system has a minimum of three powerful ground stations. Long-wave systems operate in the frequency range from 70 to 130 kilohertz (kHz), and their ground stations have a pulse power of up to 4 megawatts. Distances between stations (the base line) of approximately 1,000 to 1,300 km provide an operating range of approximately 2,000 km when making measurements from surface waves and up to 5,000 km from sky waves. Within the service area of such systems, the accuracy (mean square error) in determining the position of an object using surface waves is between 600 and 1,250 m. Superlong-wave systems operate in the frequency range from 10 to 14 kHz, and their ground stations radiate a continuous power of approximately 100 kilowatts. With base lines of 2,000 to 4,000 km, the operating range provided is between 5,000 and 10,000 km. Within the service area of such systems, the accuracy (mean-square error) in determining a position is between approximately 1 and 2.5 km by day and one-half as high by night.
During the 1960’s and 1970’s, long-wave, pulse-phase systems became common using mobile ground stations on short base lines (of the order of 200 to 300 km) and having an operating range of 400 to 600 km. In addition to highly accurate navigation for aircraft and ships at short distances, these systems are also capable of providing highly accurate guidance for various types of ground objects because the frequencies used are approximately 100 kHz.
Polar coordinate radio navigation systems usually consist of omnidirectional ground radio beacons used for azimuth measurements (by a phase or pulse-phase method) and onboard pulse-type range-only radar used for range measurements. The position of an object is determined by measuring the azimuth and the distance from the object to the radio beacon. Such systems operate in the ultrashort-wave band at frequencies from approximately 0.1 to 1 gigahertz. In practice, the operating ranges are determined by line-of-sight capability; in air navigation at altitudes of 13 to 15 km, the operating range reaches 600 km. The maximum accuracy in determining the azimuthal line of position with these systems is approximately 0.25°, and for the range (circular) line of position, approximately 100 to 200 m on 50 percent of the measurements.
Satellite radio navigation systems developed in the 1960’s and early 1970’s may be of the azimuthal, ranging, or combination type. The classification depends on the equipment installed in the navigation satellite, the moving objects the satellite serves, and the measuring methods employed.
Of special importance in navigation are complex combination systems, including systems with navigation devices that do not interact with one another. Examples of such systems are the automatic control systems for air traffic on airways and in areas near airfields; these systems ensure the separation of aircraft with respect to altitude and in longitudinal and lateral directions, thereby facilitating aircraft identification and landing approaches and preventing midair collisions. Also important are systems used for landing aircraft on the deck of a ship and systems that provide safe sailing and piloting for ships in harbors and channels.
REFERENCESBelavin, O. V., and M. V. Zerova. Sovremennye sredstva radionavigatsii. Moscow, 1965.
Skiba, N. I. Sovremennye giperbolicheskie sislemy dal’nei radionavigatsii. Moscow, 1967.
Shuster, A. Ia. Sudovye radionavigatsionnye pribory. Leningrad, 1973.
Samoletnye navigatsionnye sistemy. Moscow, 1973. (Translated from English.)
M. M. RAICHEV