Principle:

• When it is desired to remove the clutter due to stationary targets an MTI radar is employed.
• The basic principle of MTI radar is to compare a set of received echoes witrh those received during the previous sweep.
• Moving targets will give change of phase and are not cancelled. Thus clutter due to stationary targets both manmade and natural is removed from the display and this allows easier detection of moving targets.

• Mixer-2 in block diag generates the transmitter frequency $(f_0 + f_c)$ which is obtain by the sum of frequency produced by two oscillators the STALO and COHO (coherent oscillator producing $f_c$).

• Echo pulse from the target is received by the MTI radar antenna. If the echo is due to moving target, the echo pulse undergoes Doppler frequency shift.

• The received echo pulse is then passed through mixer-1 which mix $(f_0 + f_c)$ with $f_0$ and produce a difference frequency fc at its output.
• The detector output is proportional to phase difference between two signals.
• Phase difference is constant for all stationary targets but varies for moving targets. Thus Doppler frequency shift is there as per phase difference.
• This delay line acts as high pass filter to separate Doppler shifted echo signal of moving target from stationary clutter.

Limitations for MTI radar:-

1. Doppler shift may results in blind speed.
2. For MTI radar, Reduction in Doppler shift may results in loss of information.