This document provides an overview of moving target indication (MTI) and pulse Doppler radar systems. It describes the basic principles of MTI radar, including using Doppler shift to distinguish moving targets from clutter. It discusses different types of MTI radars and delay line cancellers. It also covers topics like blind speeds, staggered PRFs, range gated Doppler filters, and limitations to MTI performance. The key difference between MTI and pulse Doppler radar mentioned is that MTI radar operates with ambiguous Doppler but unambiguous range, while pulse Doppler radar has ambiguous range but unambiguous Doppler.

1. RADAR SYSTEMS
B.TECH (IV YEAR – I SEM)
Prepared by:
Mr. P.Venkata Ratnam.,M.Tech.,(Ph.D)
Associate Professor
Department of Electronics and Communication Engineering
RAJAMAHENDRI INSTITUTE OF ENGINEERING & TECHNOLOGY
(Affiliated to JNTUK, Kakinada, Approved by AICTE - Accredited by NAAC )
Bhoopalapatnam, Rajamahendravaram, E.G.Dt, Andhra Pradesh

2. Unit - III
MTI and Pulse Doppler Radar
➢Introduction
➢Principle of Operation
➢MTI Radar with Power Amplifier Transmitter
➢MTI Radar with Power Oscillator Transmitter
➢Delay Line Cancellers- Filter Characteristics
➢Blind Speeds

3. ➢Double Cancellations
➢Staggered PRFs
➢Range Gated Doppler Filters
➢MTI Radar Parameters
➢Limitations to MTI Performance
➢MTI vs. Pulse Doppler Radar

4. Introduction :
➢The Doppler frequency shift [fd =2Vr / λ] produced
by a moving target may be used in a pulse radar.
➢To determine the relative velocity of a target to
separate desired moving targets from undesired
stationary objects (clutter).
➢The target's relative velocity is made from the
Doppler frequency shift,
➢The use of Doppler to separate small moving
targets in the presence of large clutter has been of
greater interest.

5. ➢The pulse radar that utilizes the Doppler
frequency shift as a means of discriminating
moving targets from fixed targets is called a
MTI(moving target indication) or a pulse Doppler
radar.
➢The physical principle of MTI and Pulse Doppler
radar is same, but in practice there are differences
between them.
➢The MTI radar usually operates with ambiguous
Doppler measurement (so-called blind speeds)
but with unambiguous range measurement.
➢A pulse Doppler radar operates with ambiguous
range measurement but with unambiguous
Doppler measurement.

6. Salient Features of MTI:
➢MTI is a necessity in high-quality air-surveillance
radars that operate in the presence of clutter.
➢Its design is more challenging than that of a simple
pulse radar or a simple CW radar.
➢A MTI capability adds to a radar's cost and complexity
and often system designers must accept compromises
they might not wish to.
➢The chief factor that made this possible was the
development of reliable, small, and inexpensive digital
processing hardware.

7. Principle of Operation:
➢The MTI radar senses the target movement by
comparing the phase shift of the received signal with
respect to transmitting signal.
➢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 with those received during the
previous sweep.

8. ➢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.

9. Types of MTI Radars :
➢We can classify the MTI Radars into the
following two types based on the type of
transmitter that has been used.
1. MTI Radar with Power Amplifier Transmitter
2. MTI Radar with Power Oscillator Transmitter
➢Now, let us discuss about these two MTI Radars
one by one.

10. MTI Radar with Power Amplifier Transmitter :
➢MTI Radar uses single Antenna for both
transmission and reception of signals with the help
of Duplexer.
➢The block diagram of MTI Radar with power
amplifier transmitter is shown in the following
figure.
➢The function of each block of MTI Radar with
power amplifier transmitter is mentioned below.

12. ➢Pulse Modulator − It produces a pulse
modulated signal and it is applied to Power
Amplifier.
➢Power Amplifier − It amplifies the power levels
of the pulse modulated signal.
 Local Oscillator − It produces a signal having
stable frequency fl. Hence, it is also called stable
Local Oscillator.
 The output of Local Oscillator is applied to both
Mixer-I and Mixer-II.

13. ➢Coherent Oscillator − It produces a signal having
an Intermediate Frequency, fc. This signal is used
as the reference signal.
➢The output of Coherent Oscillator is applied to
both Mixer-I and Phase Detector.
➢Mixer-I − Mixer can produce either sum or
difference of the frequencies that are applied to it.
➢The signals having frequencies of fl and fc are
applied to Mixer-I.

14. ➢Here, the Mixer-I is used for producing the output,
which is having the frequency fl + fc.
➢Duplexer − It is a microwave switch, which
connects the Antenna to either the transmitter
section or the receiver section based on the
requirement.
➢Antenna transmits the signal having
frequency fl + fc when the duplexer connects
the Antenna to power amplifier.
➢ Similarly, Antenna receives the signal having
frequency of fl + fc ±fd when the duplexer
connects the Antenna to Mixer-II.

15.  Mixer-II − Mixer can produce either sum or
difference of the frequencies that are applied to it.
 Here, The signals having frequencies fl + fc ±fd and
fl are applied to Mixer-II.
 Here, the Mixer-II is used for producing the output,
which is having the frequency fc ± fd
 IF Amplifier − IF amplifier amplifies the Intermediate
Frequency (IF) signal.

16. ➢The IF amplifier shown in the figure amplifies the
signal having frequency fc ± fd.
➢ This amplified signal is applied as an input to Phase
detector.
➢Phase Detector − It is used to produce the output
signal having frequency fd from the applied two input
signals.
➢Which are having the frequencies of fc ± fd and fc .
➢The output of phase detector can be connected to
Delay line canceller.

17. MTI Radar with Power Oscillator Transmitter :
➢A block diagram of MTI radar using a power
oscillator is shown in Fig.

18. ➢A portion of the transmitted signal mixed with the
Stalo output to produce an IF beat signal whose
phase is directly related to the phase of the
transmitter.
➢This IF pulse is applied to the coherent (Coho) and
cause the phase of the Coho CW oscillation to
“lock” in step with the phase of the IF reference
pulse.
➢The phase of the Coho is then related to the phase
of the transmitted pulse and may be used as the
reference signal for echoes received from the
particular transmitted pulse.

19. “BUTTERFLY” Effect in MTI Radar :
➢Moving targets may be distinguished from
stationary targets by observing the video output on
an A-scope (amplitude vs. range).

20. ➢A single sweep on an A-scope might appear as in
Fig. (a).
➢This sweep shows several fixed targets and two
moving targets indicated by the two arrows.
➢On the basis of a single sweep, moving targets
cannot be distinguished from fixed targets.
➢Successive A scope sweeps (pulse-repetition
intervals) are shown in Fig. (b) to (e).

21. ➢Echoes from fixed targets remain constant
throughout but echoes from moving targets vary
in amplitude from sweep to sweep at a rate
corresponding to the Doppler frequency.
➢The superposition of the successive A-scope
sweeps is shown in Fig. (f).
➢The moving targets produce, with time, a butterfly
effect on the A-scope.

22. Delay Line Cancellers- Filter Characteristics :
➢Delay line canceller is a filter, which eliminates
the DC components of echo signals received from
stationary targets.
➢This means, it allows the AC components of echo
signals received from non-stationary targets, i.e.,
moving targets.
➢Delay line cancellers can be classified into the
following two types based on the number of delay
lines that are present in it.
1. Single Delay Line Canceller
2. Double Delay Line Canceller

23. Single Delay Line Canceller :
➢The simple MTI delay-line canceller shown in Fig.
is an example of a time-domain filter.
➢The combination of a delay line and a subtractor is
known as Delay line canceller.
➢The block diagram of MTI receiver with single
Delay line canceller is shown in the figure below.

24. ➢The mathematical equation of the received echo
signal after the Doppler effect as −
➢The output of Delay line canceller, by
replacing t by t−TP in Equation 1

25. ➢Then the subtractor output by subtracting
Equation 2 from Equation 1.

26. ➢The output of subtractor is applied as input to Full
Wave Rectifier.
➢Therefore, the output of Full Wave Rectifier looks
like as shown in the following figure.
➢It is nothing but the frequency response of the
single delay line canceller.

27. ➢From Equation 3, we can observe that the
frequency response of the single delay line
canceller becomes zero, when πfdTP is equal
to integer multiples of π.
➢This means, πfdTP is equal to nπ, it can be written
as

28. Blind Speeds :
➢Single Delay line canceller eliminates the DC
components of echo signals received from
stationary targets, when n π is equal to zero.
➢In addition to that, it also eliminates the AC
components of echo signals received from non-
stationary targets,
➢When the Doppler frequency fd is equal to
integer (other than zero) multiples of pulse
repetition frequency fP

29. ➢So, the relative velocities for which the frequency
response of the single delay line canceller becomes
zero are called blind speeds.
➢Mathematically, we can write the expression for
blind speed vn as

30. Double Delay Line Canceller :
➢A single delay line canceller consists of a delay line
and a subtractor.
➢If two such delay line cancellers are cascaded
together, then that combination is called Double
delay line canceller.
➢The block diagram of Double delay line canceller is
shown in the following figure.

31.  We will get the following mathematical relation
from first delay line canceller.
 The output of the first delay line canceller is
applied as an input to the second delay line
canceller.
 Hence, q(t) will be the input of the second delay
line canceller.


32. ➢ Let r(t) be the output of the second delay line
canceller.
➢ Now, Replace t by t−TP , we get,
➢ Substitute in r(t) equation, we get,

33. ➢The advantage of double delay line canceller is that
it rejects the clutter broadly.
➢The output of two delay line cancellers, which are
cascaded, will be equal to the square of the output
of single delay line canceller.
➢So, the magnitude of output of double delay line
canceller, which is present at MTI Radar receiver
will be equal to 4 A2 (sin[πfdTP]) 2

34. Multiple or Staggered PRFs :
➢The use of more than one PRF offers additional
flexibility in the design of MTI Doppler filters.
➢ It not only reduces the effect of the blind speeds,
but it also allows a sharper low-frequency cut off in
the frequency response.
➢The blind speeds of two independent radars
operating at the same frequency will be different if
their PRF’s are different.

35. ➢Instead of using two separate radars, the same
result can be obtained with one radar which time-
shares its PRF between two or more different
values.
➢The PRF might be switched every other scan or
every time the antenna is scanned a half
beamwidth, or the period might be alternated on
every other pulse.
➢When the switching is pulse to pulse, it is known
as a staggered PRF

36. ➢Suppose the first PRF is F1 shown in bold line and
the speed of second PRF is F2 shown in dotted
lines.
➢If we observed the figure, it is clear that at
particular position when 2f1 = 3f2, both the PRFs
have the same blind speed.

37. Range gated Doppler Filters :
➢In order to separate moving targets from stationary
clutter, the delay line canceller has been widely
used in MTI radar.
➢Quantizing the time in to small interval can
eliminate the loss of range information and
collapsing loss.
➢This process is known as the range gating where
width depends on range accuracy desired.
➢After quantizing the radar return interval, the
output from each gate is applied to narrow band
filter.

38. ➢MTI radar using multiple range gates followed by
clutter rejection filter is shown in Fig.
➢The output of the phase detector is sampled
sequentially by the range gates.

39. ➢Each range gate opens in sequence just long enough
to sample the voltage of the video waveform.
➢The range gate acts as a switch or a gate which opens
and closes at the proper time.
➢ The range gates are activated once each pulse-
repetition interval.
➢An echo from a moving target produces a series of
pulses which vary in amplitude according to the
Doppler frequency.

40. ➢The output of the range gates is stretched in a
circuit called the boxcar generator, or sample-
and-hold circuit.
➢The purpose is to filtering and detection process
and eliminating harmonics of the PRF.
➢The clutter rejection filter is a band pass filter
whose bandwidth depends upon the extent of the
expected clutter spectrum.
➢The filtered output from the Doppler filter is
further fed to a full wave linear detector which
convert the bipolar video.

41. ➢The output of the integrator is applied to a
threshold-detection circuit.
➢Only those signals which cross the threshold are
reported as targets.
➢Following the threshold detector, the outputs from
each of the range channels must be properly
combined for display on the PPI or A-scope.
➢The frequency-response characteristic of the range
gated MTI appears as in Fig.

42. MTI Performance:
➢ MTI improvement factor: The signal-to-clutter ratio at
the output of the MTI system divided by the signal-to-
clutter ratio at the input.
➢ Sub clutter visibility : It is defined as the ability of MTI
radar to detect the moving target, if the target is
superimposed over the clutters.
➢ Clutter visibility factor : The signal-to-clutter ratio, after
cancellation or Doppler filtering that provides stated
probabilities of detection and false alarm.
➢ The improvement factor (I): Is equal to the sub clutter
visibility (SCV) times the clutter visibility factor(VOC).

43. Limitations to MTI Performance :
➢Equipment instabilities
➢Internal fluctuation of clutter
➢Antenna scanning modulation

44. Pulse Doppler Radar Vs MTI :
➢A Pulse radar that extracts the Doppler frequency
shift for the purpose of detecting moving targets in
the presence of clutter is either a MTI Radar or a
Pulse Doppler Radar.
➢MTI usually refers to a Radar in which the PRF is
chosen low enough to avoid ambiguities in range.
➢The pulse Doppler radar, on the other hand, has a
high PRF that avoids blind speeds.

47. Thank you