This document discusses different types of pulsed radar systems and moving target indication techniques. It describes coherent and non-coherent radar systems, with coherent systems able to use echo phase information to determine target range and velocity. It then focuses on phase processing moving target indication using a delay-line canceller. The canceller subtracts delayed and undelayed video signals, causing signals from stationary targets to cancel out while signals from moving targets remain. This allows the radar display to only show moving targets.

1. Chapter 3
Pulsed radar system & phase processing
MTI

2. Pulsed radar system
 The time-delay between the transmission of each
pulse and the reception of the echo of the same
pulse is proportional to the target range.
 The phase of the echo also depends on the target
range. And can be used to extract information
from it, if the phase of the transmitted signal is
stable from pulse to pulse.

3. Pulsed radar system
 Coherence
 A pulsed radar system where the transmitted signal is phase-stable
from pulse to pulse. The word coherent means “in-phase”
or maintaining a definite phase relationship with a
certain reference waveform. The phase of a coherent signal
at any point, relative to the reference signal is completely
predictable.

4. Pulsed radar system
 Non-coherence
 The phases of the transmitted signal are random from pulse to
pulse. The phases of their echoes cannot be used to predict
the range of the target.
 Conclusion:
 Coherent radar system: can use the round-trip time or the
echoes phases to detect the target range (the speed of the
target).
 No-coherent radar system: use only the round-trip time to
detect the target range.

5. Non-coherent radar
 The pulsed transmitted is usually high-power RF
oscillator, which is keyed on and off by a pulse
modulator.
 The phase relationship between successive
pulses in the transmitted signal is completely
random.
 The received RF signal is mixing with a local
oscillator to shift the RF signal down to the
intermediate frequency IF.

6. Non-coherent radar

7. Non-coherent radar
 The IF signal is amplified and filtered by the IF amplifier.
 The envelope detector produces an output signal whose level
corresponds to the envelope of the IF signal (linear detector,
square law detector, or logarithmic detector)
 All frequency and phase information is LOST.

8. Non-coherent radar
 Equation

9. Coherent pulsed radar
 Superheterodyne receiver
 Homodyne receiver

10. Coherent pulsed radar- Superheterodyne
receiver

11. Coherent pulsed radar- Superheterodyne
receiver
 Presence of a reference signal which is coherent with
the transmitted signal, and by the fact that the
transmitted RF signal itself is coherent (phase stable
from pulse to pulse).
 The coherence signal is generated by a stable
oscillator called COHO (coherent oscillator). The
frequency of the COHO is equal to the IF frequency
used in the receiver. The local oscillator is also a
stable oscillator called STALO. Its frequency is usually
near the transmitted frequency.

12. Coherent pulsed radar- Superheterodyne
receiver
 The phase detector output is a bipolar pulse signal
whose amplitude depends on the phase of the phase
detector input signal relative to the coherent reference
signal.(moving target change in phase )

13. Coherent pulsed radar- Homodyne
receiver
 Superheterodyne are commonly used in a radar
because it is usually more convenient to perform
phase detection at a relatively low IF frequency
than at the RF frequency.
 If    large bandwidth of the IF amplifier,
requires the using of higher intermediate
frequency: Impractical, circuit losses and
instability.

14. Coherent pulsed radar- Homodyne
receiver
 Equations……

15. Coherent pulsed radar- Homodyne
receiver

16. Fixed target

17. Moving target

18. Limitations
 Blind phases….
 Blind speeds….

19. Phase processing MTI
 The Doppler frequency shift can be used to allow the
radar to reject fixed targets (clutter) and detect only
moving targets. This type of signal processing is
called moving-target indication (MTI).
 One way of accomplishing moving-target indication is
to use the pulse-to-pulse change in amplitude at the
output of the phase detector to differentiate between
fixed and moving targets. This is called phase-processing
MTI and is implemented using a delay-line
canceller.

20. Phase-processing MTI

21. Phase-processing MTI
 The delay line canceller consists of a delay line and a summer. The
delay line delays the video signal by a time equal to the pulse-repetition
interval (sometimes called the PRF period) T=1/fp. The delay line
operates by sampling the video input signal at a high rate and storing
each sample for the required time. The delayed video signal is
subtracted from the undelayed video signal by the summer.
 The output of the delay-line canceller consists of the differences between
successive pulses in the video signal. If the target is not moving, the
amplitude of each pulse is the same as that of the previous pulse.
 The result of the subtraction is zero. If the target is moving, however, the
pulse amplitude changes from pulse to pulse. The result of the
subtraction is not zero; a residue remains in the form of a bipolar pulse
train. The bipolar pulse train is usually full-wave rectified before it is sent
to a PPI display. Since only moving targets produce a residue at the
canceller output, only these targets will be visible on the radar display.

22. Phase-processing MTI
 Frequency response

23. Phase-processing MTI

24. Phase-processing MTI

26. Blind phases
 Blind phases can cause nulls in the unipolar
video signal,This results in reduced sensitivity of
the radar. Even if the phases are such that no
pulses are completely cancelled, the fact that the
amplitude of the unipolar video signal drops
periodically causes a loss of sensitivity. The
problem of reduced sensitivity caused by blind
phases can be eliminated by using a quadrature
phase detector

27. Quadrature phase detector

28. Vector MTI processing