The Tactical Air Navigation or TACAN system is designed to work in a polar coordinate framework largely used to plot the directional properties of an antenna. This like the other navigation systems such as VOR and DME is a device which provides the pilot in an aircraft with the distance information from DME (a distance measuring equipment), and azimuth (coverage area). 

A TACAN system consists of two indicators or meters. One indicator provides the distance information of the aircraft from a ground station in nautical miles. The second indicator determines the direction of an aircraft, usually in degrees, relative to the geographical location of a ground station. 

With the help of information provided by the system installed in the aircraft, a pilot is able to either:

  • Fly directly towards that particular location or
  • Fix the location of an aircraft by utilizing the azimuth and distance information relative to a specific ground station

TACAN system working principle

This system usually calculates the distance on the basis of the concept of radar ranging techniques. As per the radar ranging technique, the distance is measured by calculating the round trip time traveled by a transmitted radio frequency wave or energy. The reflected or the return energy in a radar depends on the reflection of that particular radio wave. 

However, a TACAN system does not depend on the natural reflection, instead, the ground transponders or stations generate artificial replies. The aircraft or any airborne equipment propagates time stamped interrogation pulse pairs which is then received and decoded by a ground TACAN system. After adding a time delay of 50 microseconds, the ground transponder responds to the aircraft interrogator with a reply. The aircraft interrogator acknowledges that reply, and then performs computation to provide the pilot with an output in the form of distance from the ground transponder. Like a DME, it operates in the UHF spectrum in the range of 960 MHz to 1215 MHz, with a range of operation up to 320 km. 

Advantages 

  1. It rejects bounced signals
  2. It is a low power consumption device
  3. It is resistant to:
    • Shock and Vibration
    • Electromagnetic Interference 
  4. It is not affected in severe environmental conditions
    • Snow
    • Humidity 
    • Rain
    • Fungus
    • Sand and Dust
  5. Combines the bearing and distance capabilities 

Disadvantages 

  1. Outputs slant distance 
  2. Limited to the line-of-sight due to UHF band operation
An aircraft shot
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