Introduction of radio navigation system

Equipment or systems used for radio navigation include radio compass, Vor navigation system, TACAN navigation system, Roland C navigation system, Omega navigation system, Doppler navigation system, satellite navigation system and the developing "Navigation Star" global positioning system.

Radio signals contain four electrical parameters: amplitude, frequency, time and phase. In the process of radio wave propagation, the parameters may change relative to the navigation parameters. By measuring this electrical parameter, the corresponding navigation parameters can be obtained. According to the different measured electrical parameters, the radio navigation system can be divided into amplitude type, frequency type, time type (pulse type) and phase type. According to the navigation parameters to be measured, the radio navigation system can also be divided into four types: angle measurement (azimuth or high and low angle), ranging, ranging difference and speed measurement. Modern radio navigation equipment can be divided into three types according to the main installation bases: ground-based (equipment is mainly installed on the ground or at sea), space-based (equipment is mainly installed on flying aircraft) and satellite-based (equipment is mainly installed on navigation satellites). According to the action distance, it can be divided into four types: short range, long range, ultra-long range and global positioning. Most of these systems work by using Doppler effect. The Doppler navigation radar installed on the plane emits radio signals in centimeter band to the ground in a narrow beam. Due to the Doppler effect, the signal frequency reflected by the ground is different from that of the transmitted signal, and there is Doppler frequency shift. By measuring the Doppler frequency shift, the speed of the aircraft relative to the ground can be obtained (see Doppler navigation system). Then, using the pitch angle and heading angle given by the vertical reference and heading reference on the aircraft, the radial velocity is decomposed into east velocity and north velocity, and the position of the aircraft at that time can be obtained by integrating the time respectively. The position line of Doppler velocimetry system is also a hyperbola, which is formed by the intersection of a cone with equal Doppler shift and the geocentric sphere at the altitude of the aircraft. Doppler navigation speed measuring system belongs to frequency type (see aircraft navigation system).