A single receiver picking up a signal only knows from which direction it comes — a bearing, in other words a line on the map, not a point. Triangulation (cross-bearing) solves this: if you measure the same source from two or more spatially separated receivers, the bearings intersect — and the intersection is the position of the source.
Key points:
- Geometry matters: if the receivers are far apart (long baseline) and the bearings intersect at a wide angle, the fix is accurate. If they intersect at a sharp angle (the source almost in line with the receivers), the error ellipse becomes long and inaccurate.
- More receivers = better: three or more bearings shrink the error ellipse and absorb measurement errors.
- Related alternative: TDOA (Time Difference Of Arrival) locates a source from the differences in arrival time at several receivers — often more accurate than angle bearings, but it requires tight time synchronisation.
EW relevance
Triangulation is the tool of ESM/ELINT (Electronic Support Measures) for geolocating an enemy radar or jammer — the first step towards engaging it with an anti-radiation missile or artillery. It is also the reason why transmitting is dangerous: every emission (radar, jammer, radio) can be cross-fixed. A network of RWR/ESM platforms sharing the same threat turns bearings into a firing solution.