4.5 Radio Navigation System
217
4.5.1 Ranging and Bearing Navigation System
The ranging and bearing navigation system is a kind of radio navigation system
which takes the distance and orientation of the movable object relative to the ground
stations as the basic observables to determine its position and velocity. It belongs to a
kind of short-range navigation system, commonly with the polar coordinate system,
and at the beginning is used in the navigation and approach landing of aircrafts. In
1912, the first radio navigation equipment, radio compass, was successfully developed according to the principle of amplitude direction-finding, with the working
frequency of 0.1−1.75 MHz. During the Second World War, the direction-finding
equipment, such as orientating plane, four-channel beacon and fan-shaped radiopointing beacon, had been developed. Afterward, a variety of ranging and directionfinding equipment have emerged, which improves the accuracy and safety for aircraft
navigating and landing. There are three typical ranging and bearing navigation
systems, Very High-Frequency (VHF) Omni-Directional Range (VOR), Distance
Measuring Equipment (DME) and Tactical Air Navigation System (TACAN). The
VOR is a type of short-range radio navigation system with the amplitude directionfinding for aircraft, enabling the aircraft with a receiving unit to determine its position
and stay on course by receiving radio signals transmitted by a network of fixed ground
radio beacons, with the VHF band of 108.00−117.95 MHz. In 1937, the VOR began
to be developed in the United States, and until 1946 it was deployed to use for aircraft
navigation. With the wide application of Global Positioning System (GPS), the VOR
ground stations are decreased gradually. For example, there were about 3,000 VOR
stations operating in 2000, while their number was reduced to 967 by 2013. The
DME is a radio navigation technology that measures the slant range between an
aircraft and a ground station by timing the propagation delay of radio signals in the
frequency band between 960 and 1215 MHz. As a result, the line of visibility between
the aircraft and the ground station is required. An airborne interrogator initiates an
exchange by transmitting a pulse pair, on an assigned channel, to the transponder at
the ground station, and the channel assignment specifies the carrier frequency and
interval between the pulses. After a known delay, the transponder replies by transmitting a pulse pair on a frequency that is offset from the interrogation frequency
by 63 MHz and having specified separation. The TACAN is a navigation system for
military aircrafts, providing the users with the bearing and slant range to a ground
or ship-borne station (as shown in Fig. 4.4), which is a more accurate version of
the VOR and DME. The DME portion of the TACAN system is available for civil
use, and at the VORTAC facilities where a VOR is combined with a TACAN, civil
aircraft can receive VOR/DME readings. The aircrafts equipped with the TACAN
avionics can use this system for en-route navigating and non-precision approaches
to landing. The navigation system for integrating the VOR and DME has become the
standard short-range navigation equipment stipulated by International Civil Aviation
Organization (ICAO), and the TACAN is the standard system for military aircrafts.
In addition, there is an aircraft approach and landing guidance system, which uses
radio equipment to guide the pilot or autopilot to make the aircraft land safely. The
217
4.5.1 Ranging and Bearing Navigation System
The ranging and bearing navigation system is a kind of radio navigation system
which takes the distance and orientation of the movable object relative to the ground
stations as the basic observables to determine its position and velocity. It belongs to a
kind of short-range navigation system, commonly with the polar coordinate system,
and at the beginning is used in the navigation and approach landing of aircrafts. In
1912, the first radio navigation equipment, radio compass, was successfully developed according to the principle of amplitude direction-finding, with the working
frequency of 0.1−1.75 MHz. During the Second World War, the direction-finding
equipment, such as orientating plane, four-channel beacon and fan-shaped radiopointing beacon, had been developed. Afterward, a variety of ranging and directionfinding equipment have emerged, which improves the accuracy and safety for aircraft
navigating and landing. There are three typical ranging and bearing navigation
systems, Very High-Frequency (VHF) Omni-Directional Range (VOR), Distance
Measuring Equipment (DME) and Tactical Air Navigation System (TACAN). The
VOR is a type of short-range radio navigation system with the amplitude directionfinding for aircraft, enabling the aircraft with a receiving unit to determine its position
and stay on course by receiving radio signals transmitted by a network of fixed ground
radio beacons, with the VHF band of 108.00−117.95 MHz. In 1937, the VOR began
to be developed in the United States, and until 1946 it was deployed to use for aircraft
navigation. With the wide application of Global Positioning System (GPS), the VOR
ground stations are decreased gradually. For example, there were about 3,000 VOR
stations operating in 2000, while their number was reduced to 967 by 2013. The
DME is a radio navigation technology that measures the slant range between an
aircraft and a ground station by timing the propagation delay of radio signals in the
frequency band between 960 and 1215 MHz. As a result, the line of visibility between
the aircraft and the ground station is required. An airborne interrogator initiates an
exchange by transmitting a pulse pair, on an assigned channel, to the transponder at
the ground station, and the channel assignment specifies the carrier frequency and
interval between the pulses. After a known delay, the transponder replies by transmitting a pulse pair on a frequency that is offset from the interrogation frequency
by 63 MHz and having specified separation. The TACAN is a navigation system for
military aircrafts, providing the users with the bearing and slant range to a ground
or ship-borne station (as shown in Fig. 4.4), which is a more accurate version of
the VOR and DME. The DME portion of the TACAN system is available for civil
use, and at the VORTAC facilities where a VOR is combined with a TACAN, civil
aircraft can receive VOR/DME readings. The aircrafts equipped with the TACAN
avionics can use this system for en-route navigating and non-precision approaches
to landing. The navigation system for integrating the VOR and DME has become the
standard short-range navigation equipment stipulated by International Civil Aviation
Organization (ICAO), and the TACAN is the standard system for military aircrafts.
In addition, there is an aircraft approach and landing guidance system, which uses
radio equipment to guide the pilot or autopilot to make the aircraft land safely. The