VOR (Very High Frequency Omnidirectional Range) is a system of aid to navigation area, widely used. It operates in the VHF band VHF, from 108.00 MHz to 117.95 MHz
In the navigation instrument (IFR), the VOR allow dial lines (or "radial") for that route.
When a pilot (or autopilot) tunes the frequency of a VOR radio beacon, the aircraft receives the reference signal and the directional antenna pointing east. Comparing both signals yields the variable signal delay compared to the reference, and this shift indicates that the beacon radio we are.
Formerly in the 50s, is mechanically rotated antennas using a directional motor elements.
In the busiest commercial air routes, like roads in land, there are intersections and cornering.
Under these "crosses" and "curves" are typically installed these VOR stations. The "aerial highway" is the radial degrees of XXX starting with a VOR and VOR normally come to another or even a runway.
The pilot can direct the automatic pilot, "Follow the 115 degree radial of the VOR transmitting frequency 109.75Mhz." And the plane automatically when crossing with the radial 115, will continue to fly over the VOR.
The modern VOR beacons are also fitted with DME (Distance Measuring Equipment). Electronic system that measures the distance the plane being oblique and direct assistance on the ground. By tuning in VHF VOR frequency is tuned to another frequency also UHF (linked to the preceding through a mathematical formula). In this, the aircraft transmits a signal with a code to the receiver VOR DME and it returns another sign with the same code. From the time that the plane take to get the rebound to calculate the distance to the VOR beacon
(1 mile = 12.36 microseconds).
With this technique, the plane can know how long it takes to fly a radio beacon (and then rotate or enter another path). If the beacon is located at an airport, the pilot will know how many miles is this and what course should be followed to achieve it.
Strangely enough, say VOR systems do not work when the plane flies just above. This is because the signals are radiated laterally.
Well, I hope this information is helpful.