Primary Surveillance Radar (PSR) works on the pulse technique and echo principle which used electromagnetic waves to detect objects and detect their returning echoes. It provides bearing and distance information of detected objects. The radar relies on reflected signals but is not aware if they are received from aircraft or from other objects (e.g. terrain, buildings, clouds). Such reflections are called clutter.

Moving Target Indicator (MTI) technology is able to eliminate echoes from stationary objects such as terrain, buildings, etc. while leaving only relevant information displayed on the screen (aircraft). A target is therefore discriminated against clutter. MTI takes advantage of the Doppler effect:

• A moving target will be at different distance from the radar over a period of time. The reflection of radar pulses from a moving target will therefore occur at a varying distance with time - each successive pulse will be reflected from a different distance to the radar. The result will be a varying phase shift of the pulses due to a doppler effect. Stationary objects will reflect pulses at a constant phase shift.