DEPARTMENT OF ELECTRONICS AND COMMUNICATION
ENGINEERING
2 and 16 MARK QUESTIONS AND ANSWERS
SUBJECT CODE : EC1019
SUBJECT NAME : RADAR AND NAVIGATIONAL AIDS
Prepared by
S.M.RAMLEE (Lect/ECE)
M.SUCHARITHA(Lect/ECE)
2 Marks
1. What is a radar?
Radar is an electromagnetic system for the detection and location of
reflecting objects such as aircraft, ships, spacecraft, vehicles, people, and the natural
environment. It operates by radiating energy into space and detecing the echo signal
reflected from an object or target.
2. What do you mean by maximum unambiguous range?
Echoes that arrive after the transmission of the next pulses are called the
second time around echoes.The range beyond which the targets appear as secondtime-
around echoes is called the maximum unambiguous range,Run, and is given by
Run=cTp/2=c/2fp
3. What is the fundamental range equation?
Rmax=(PtGAe A 6min)^(1/4)
Pt=transmitted power , W
G= Antenna gain
Ae= Antenna effective aperture
Smin=Minimum detectable signal
4. What is a PPI?
A typical radar display for a surveillance radar is the PPI or Plan Position
Indicator.The PPI is a presentation that maps in polar coordinates the
location of the target in azimuth and range.
5. What are the applications of radar?
ƒ Military
ƒ Remotesensing
ƒ Air traffic control (ATC)
ƒ Law enforcement and highway safety
ƒ Aircraft safety and Navigation
ƒ Ship safety
ƒ Space
6. What are the main reasons for the failure of the simple form of the radar equation?
The failure of the simple form of the radar equation is due to
a. the statistical nature of the minimum detectable signal
b. fluctuations and uncertainties in the targets radar cross section
c. the losses experienced throughout the radar system
d. Propagation effects caused by the earth surface and atmosphere
7. Define minimum detectable signal?
The weakest signal that can just be detected by the receiver is the
minimum detectable signal.
8. What is called a false alarm?
If the target were set too low, noise might exceed it and be mistaken for a
target. This is called the false alarm.
9. What is called a missed detection?
If the threshold were set too high , noise might not be large enough to
cause false alarms, but weak target echoes might not exceed the threshold and
would not be detected .This is called as missed detection.
10. What is called threshold detection?
If the receiver output is not of sufficient amplitude to cross the threshold,
only noise is said to be present. This is called threshold detection
11. What is called a thermal noise?
If the radar were to operate in a noise free environment so that no external
sources of noise accompany the target signal, and if the receiver itself were so
perfect that it did not generate any excess noise, there would still be noise
generated by the thermal agitation of the conduction electrons in the ohmic
portion of the receiver input stages. This is called as thermal or Jhonson noise.
12. What is said to be the rayleigh region?
Radar cross section depends on the characteristic dimensions of the object
compared to the radar wavelength. When the wavelength is large compared to the
objects dimensions, scattering is said to be rayleigh scattering.
13. Give some examples of simple targets?
Some examples of simple targets are sphere, cylinder, flatplate, rod, ogive
and cone.
14. Define the term fluctuations?
$ UHODWLYH SKDVH VKLIW JUHDWHU WKDQ UDGLDQV FDQ \LHOG D VLJQLILFDQW
change in the resultant phase and amplitude of the composite echo signal which
results in target cross section fluctuations.
15. What is called frequency diversion?
It means that more than one transmitter, each at a different frequency is
utilized in parallel with each transmitter channel operating as a separate radar.
16. What is called frequency agility?
Pulse to Pulse change in frequency is called frequency agility.
17. What is called as revisit time?
It is the time that an antenna takes to return to view the same
region of space. It is also called as scan time.
18. What is a radome?
A typical ground based metal space frame radome might have a two-way
transmission loss of 1.2 db at frequency ban from L to X band.
19. Define a scan to scan fluctuation?
The echo pulses received from a target on any one scan are of constant
amplitude throughout the entire scan, but are independent from scan to scan. A
target echo fluctuation of this type is called scan to scan or slow fluctuations.
20. What are complex targets?
The radar cross section of complex targets such as aircraft, missiles, ships,
ground vehicles, fabricated structures, buildings and terrains can vary
considerably depending on the viewing angle and frequency.
21. What is clutter?
When detecting targets radars have to deal with more than receiver noise
since they can also receive echoes from the natural environment such as land ,sea
and weather.These echoes are called clutter since they can "clutter" the radar
display.
22. Write the four methods for reducing the effects of blind speeds.
1.operate the radar at long wavelengths.
2. operate with a high pulse repetition frequency
3. operate with more than one pulse repetition frequency
4. operate with more than one RF frequency.
23. Why do blind speeds occur?
Blind speeds occur because of the sampled nature of the pulse radar
waveform.Thus it is sampling that is the cause of ambiguities, or aliasing , in the
measurement of the doppler frequency .
24.Define MTI improvement factor.
The signal-to-clutter ratio at the output of the clutter ratio divided by the signalto-
clutter ratio at the input of the clutter filter , average uniformly over all target
radial velocities of interest.
25.What are bipolar and unipolar videos?
The output of the MTI radar is called bipolar video,since the signal has
negative as well as positive values.Unipolar video is rectified bipolar video with
only positive values.
26.Define doppler frequency in MTI radar?
In MTI radar ,the phase detector is a mixer-like device that combines the
received signal and the reference signal from the coho so as to produce the
difference between the received signal and the reference signal frequencies.This
difference is the doppler frequency.
27.What are stalo and coho?
Stalo (Stable oscillator) is the local oscillator of an MTI receiver which is used to
recognize the need for high stability.Coho stands for coherent oscillator to signify that it
is the reference signal that has the phase of the transmitter signal.
28.State the properties of single DLC that limit the utility of simple doppler filter.
1.The frequency response function also has zero response when moving targets
have doppler frequencies at the prf and its harmonis .
2.The clutter spectrum at zero frequency is not a delta function of zero width,but
has a finite width so that clutter will appear in the pass band of the Delay Line Canceler.
29.Define blind speeds.
The limitations of single DLC results in target speeds called blind speeds,where
the target will not be detected and there will be an uncancelled clutter residue that can
interfere with the detection of moving targets.
30.Why VHF is not considered as a desirable frequency cchoice for a long range airsurveillance
radar?
1.Resolution inrange and angle are poor due to narrow bandwidths and large
beamwidths.
2.This portionof electromagnetic spectrum is crowded with other than radar
services.
3.Low altitude coverage ally poor.
31.Define three-pulse canceler.
A canceler with two delay lines that has the same frequency response as the
double delay-line canceler,but which is arranged differently is known as three-pulse
canceler.
32.What are recursive filters?
Filter design using only zeros does not have the flexibility of filter design based
on poles as well as zeros.Poles can be obtained with delay line cancelers by employing
feedback.With both feedback and feed forward lines providing both poles and zeros
,arbitrary filter frequency response functions can be synthesized from cascaded delay
lines,within the limits of realizability.These are known as recursive filters or infinite
impulse response(IIR )filters.
33.State the methods for employing multiple prfs to avoid losing target echoes due to
blind speeds.
The prfs can be changed (1)scan to scan
(2)dwell to dwell or
(3)pulse to pulse(usually called stagered prf).
34.State two methods proposed for finding the effect of stagger periods.
The two methods are computer search and analytic formulation.The effect of the
stagger periods on the depth of the null is based on computer search and the MTI
improvement factor is based on analytic formulation.
35.What is clutter map?
It is used to detect crossing targets with zero radial velocity that would
otherwise be cancelled by any other MTI.
36.What is a saturation detector?
It is used to detect whether any of the ten pulses within a processing
interval saturates the A/D convertor and, if it does ,the entire ten pulses of that
particular CPI are discarded.
37. Define Navigation?
Navigation is the art of directing the movements of craft from one point to
another along a desired path.
38. What is the need of a Chronometer?
With the help of Chronometer, the navigator was able to determine his
longitude by noting the transit time of heavenly bodies.
39. Define electronic navigational aids?
Navigational systems which employ electronics in some way
40. What are the four methods of navigation?
1. Navigation by pilotage
2. Celestial or astronomical navigation
3. Navigation by dead –reckoning
4.Radio navigation
41. Define astronomical navigation?
Celestial navigation is accomplished by measuring the angular position of
celestial bodies.
42. Define navigation by dead reckoning?
The position of the craft at any instant of time is calculated from the
previously determined position, the speed of its motion with respect to earth along
with the direction of its motion and the time elapsed.
43. What is the important source of antenna effect?
The important source is the asymmetry of the loop antenna with respect to the
ground.
44. How the antenna effect is minimized?
To minimize the antenna effect, the centre of the loop is earthed and its output is
thereby balanced.
45. Give the disadvantage of loop direction finder?
1. The loop is small enough to be rotated easily. This results in a small
signal pick ups.
2. To facilitate manual operation, the loop is located near the receiver.
46. What are the errors arising in direction finders?
1. Errors due to abnormal polarization of the incoming wave
2. Errors due to abnormal propagation
3. Site errors
4. Instrumental errors
47. Define mountain effect?
In air borne direction finders, mountainous terrain may cause errors
when there is simultaneous reception of signal from the transmitter by a direct
path and by reflection from the mountain side. This is called mountain effect.
48. What is the need of Adcock direction finders?
The Adcock direction finders are designed to eliminate polarization
errors by dispensing with the horizontal members.
49. What are the types of automatic direction finders?
1. The radio compass
2. A VHF phase comparison automatic direction finders
50. What are the two types of radio ranges in use?
1. Low frequency four course radio range
2. VHF Omni directional radio range
51. What are the sources of errors in VOR system?
1. Ground station and aircraft equipment
2. Site irregularities
3. Terrain features
4. Polarization
52. Define hyperbolic system of navigation?
Hyperbolic systems are based on the measurement of the difference in
the time of arrival of electromagnetic waves from two transmitters to the receiver
in the craft.
53. What are the different hyperbolic navigational systems?
Different hyperbolic navigational systems are LORAN, DECCA and
OMEGA.
54. Define LORAN?
LORAN is Long Range Navigational Aid and is a pulse system. The
ground station transmit a train of pulses with fixed time relation between them
and at the receiver, these pulses are identified and the delay between them is
measured on a cathode ray oscilloscope
55. What is the operating frequency of LORAN-C?
LORAN-C operates in the band 90-110 KHZ.
56. Define DECCA navigation system?
The measurement of the time difference in the reception of signals from two
stations is by measuring the phase difference between the signals of the two
stations, the radiations which are phase locked, instead of time interval between
pulses in the LORAN
57. What are the advantages of OMEGA system?
1. At low frequency in the 10KHZ range, the coverage is increased
2. Loss of power at this frequency is low.
58. Give the Secondary Radar systems?
1. DME (Distance Measuring Equipment)
2. TACAN (Tactical Air Navigation)
59. Define TACAN?
TACAN provides both range and bearing information with the same
radiation.
60. What are the types of landing aids?
1. Instrument landing system
2. Microwave Landing system
3. Ground controlled approach.
61. What is meant by Localizer?
The localizer operates in the VHF band (108-110 MHZ) and consists of a
transmitter with an antenna system. The radiation of which has two lobes, one
with a predominant modulation of 90 Hz and other with 150 Hz.
62. What are the types of Radar present in the Ground controlled approach systems?
1. Surveillance radar element
2. Precision approach radar
63. What are the disadvantages of ILS?
1. Provides a single approach path along the extended centre line of the
runway.
2. It is site sensitive and subject to distortion and bending of the approach
path due to site irregularities.
64. What are the basic elements of a MLS system?
1. Azimuth beam equipment
2. Elevation beam equipment
3. Distance measuring equipment
65. What is meant by Doppler navigation?
It employs the Doppler Effect to determine the velocity of the craft in a frame
of coordinates fixed with respect to the aircraft.
66. Define Frequency trackers?
The frequency tracker locates the centre of the noise like Doppler spectrum
and gives the output the pure signal of this frequency.
67. Define inertial navigation?
Inertial navigation is a system of dead reckoning navigation in which the
instruments in the craft determines its accelerations and by successive
integration, obtain its velocity and displacement.
68. What are the features of Navigation over earth?
1. The system of coordinated should be fixed with reference to earth.
2. The coordinate system most convenient for use is latitude and
longitude.
3. Avery large gravitational fields is present at the surface of the earth.
69. What are the components of inertial navigation systems?
1. Accelerometers
2. Gyros and stabilized platforms
70. Define DECTRA?
DECTRA is a Decca tracking and ranging. This is a long range
hyperbolic navigational system working at a frequency of about 70 KHz. The
system is designed to provide navigation information over a long route,
particularly along the sea.
71. Define CONSOL?
IT is a rotating beacon operating in the LF/MF band which employs a
system of three antennas producing a multi lobed pattern which is switched to
produce a number of equi signals as in the radio range.
72. Define CONSOLAN?
It is same as CONSOL except that a two antenna system is used instead of
three antennas .
73. What are Marker Beacons?
These are Radio beacons which are intended to mark some salient points.
74. Define SHORAN?
Short Navigation System is a secondary radar system in which fix is
obtained by the craft, which carriers the interrogator, by simultaneously
interrogating two ground beacons.
75. What is meant by Radio Sextant?
This is a Sextant operating on the radio frequency emission of heavenly
bodies, like a radio telescope.
76.What are the various system losses?
ƒ Microwave plumbing losses
ƒ Antenna losses
ƒ Signal processing losses
ƒ Collapsing losses
ƒ Operator losses
ƒ Equipment degradation
ƒ Propagation losses
ƒ Radar system losses
77. What are the disadvantages of low frequency four course radio range?
1. Limited number of courses (four)
2. Poor signal/noise ratio
3. Fatigue caused by listening to the tones
4. Difficulty of identifying the course
78. What are angel echoes?
Echoes produced by birds , insects
79. What is called velocity modulation?
The electrons getting accelerated and decelerated by the signal
producing bunching of electrons.
80. What are called Linear beam tubes and Cross field tubes?
The electric field and magnetic field are parallel to each other in linear
beam tubes and they are perpendicular to each other in cross field tubes.
81.Define Signal Processing?
Methods for the detection of desired signals and the rejection of undesired
noise, clutter and interference in radar are called signal processing
82.Define Matched filter?
Filter that maximizes the output signal to noise ratio of a radar receiver which
maximizes the delectability of a target.
83.What is meant by automatic detection?
Automatic delectation performs the operation required for the detection
decision without the operator intervention.
84.What is the need of integrator?
Integrator integrates or adds the energy from the received pulses
available from the target
85.Define moving window detector?
Continuous integration of the last n pulses at the output from the receiver
from each range resolution cell is accomplished with a moving window integrator
called as moving window detector.
86.Define binary integrator?
The use of a detection criterion that require m out of n pulses to be present in
the form of integration is called binary integrator
87.What is meant by Electromagnetic compatibility?
The elimination of interference from other radars and other electromagnetic
radiations that can enter the radar receiver.
88.What is the need of pulse compression?
Pulse compression is used to achieve high range resolution without the need
of high peak power.
89.what are the basic radar measurements that can be achieved from a point target?
1.Range
2.Angle
3.Radial velocity
4.Tangential velocity.
90. What are the basic radar measurements that can be achieved from a Distributed
target?
1.Size and shape
2.Symmetry
3.Radial Profile
4.Tangential Profile.
91.What are the factors affecting the transmitted waveform by a radar?
1.Target detection
2.Accuaracy
3.resolution
4.Ambiguities
92.Define ECCM?
A short pulse radar can negate the effects of certain electronic
countermeasures such as range gate stealers, repeater Jammer and decoys.
93.What is meant by interdigital transducers?
The input/output devices arranged on the surface are known as interdigital
transducers.
94.Define apodization?
Amplitude shaping of the frequency response of a SAW filter can be obtained
by the amount of overlap of the electrodes of IDT is called as apodization.
95.What is meant by Doppler tolerant waveform?
A Doppler tolerant waveform is one whose signal to noise ration out of its
matched filter is independent of the Doppler frequency shift. Such waveforms are
called as Doppler invariant
96.What is meant by Welti codes?
These are related to Golay complementary codes in that they are used in pairs
that are subtracted from one another to obtain autocorrelation functions with zero side
lobes,
97.Define synthetic Aperture radar?
SAR produces a high-resolution image of a scene of the earth’s surface in
both range and cross range. It can produce images of scenes at long range and in
adverse weather that are not possible with infrared or optical sensors.
98.What are the different radar cross section modulations?
1.Propeller modulation
2.Helicopter Blade modulation
3.Jet engine modulation
99.What are the target recognition applications?
1.Military combat identification
2.Ballistic missile target discrimination
3.Meterological observation
4.Battlefield surveillance
100.Define Point clutter?
Buildings and other constructed objects can result in large echoes known as
discretes or point clutter.
16 marks
1. Explain the radar block diagram?
Block diagram
Explanation
2. Derive the simple form of the radar equation?
3. Explain about the Receiver noise and derive the signal to noise ratio?
Noise figure
Minimum detectable signal
Maximum range
4. Explain about the radar cross section of targets?
Simple targets
Complex targets
5. Explain the various system losses?
Microwave plumbing losses
Antenna losses
Signal processing losses
Collapsing losses
Operator losses
Equipment degradation
Propagation losses
Radar system losses
6.Explain the four methods of navigation in detail?
1. Navigation by pilotage
2. Celestial or astronomical navigation
3. Navigation by dead –reckoning
4.Radio navigation
7. Explain the errors arising in direction finders?
1. Polarization Errors
2. Errors due to abnormal propagation
3. Site errors
4. Instrumental errors
8. Explain briefly the Automatic Direction finders?
1.The radio compass
2. A VHF phase comparison automatic direction finders
-------Block diagram and explanation
9. Briefly discuss the VHF Omni Directional Range (VOR)?
Block diagram
Modulation Eliminator
VOR receiver
Range and Accuracy
10. Explain hyperbolic system of Navigation?
1. LORAN –A
Equipment
Range and precision
2. LORAN-C
3. DECCA navigation system
Block diagram
Range and Accuracy
4. OMEGA system
11. Briefly explain the secondary radar systems?
1. DME
2. TACAN
12. Explain the Instrument LANDING systems?
1. Localizer
2. Glide slope system
3. Receiving equipment
4. Course sharpness and width
5. Marker beacon
13. Discuss the Doppler navigation with a neat block diagram?
Doppler Effect
Doppler frequency equations
Block diagram and explanation
14. Explain the concept of inertial navigation systems?
1. Accelerometers
2. Gyros and stabilized platforms
Explanation
15. Discuss the Satellite Navigational systems in detail?
GPS
Explanation
16.Explain the operation of cavity magnetron and discuss the importance of
performance chart and Ricke Diagram
Magnetron construction
Explanation
Pi –mode
Ricke diagram
17.Explain the principle of Parabolic antennas
Reflector antennas –basic concept
Various feeds
Radiation patterns
18.Explain the principle of Cassegrain antennas
Cassegrain antennas-basic concept
Various feeds
Feed support
19.Draw the block diagram of two co-ordinate mono-pulse tracking radar and its
operation.
Block diagram
Two coordinate explanation
Hybrid rings
20.Draw the block diagram of one co-ordinate mono-pulse tracking radar and its
operation.
Block diagram
One coordinate explanation
Hybrid rings
21.Draw the block diagram of conical scan radar and sequential lobing tracking radar
and its operation.
Block diagram
conical scan radar explanation
sequential lobing explanation
22.Explain Superheterodyne receivers. Add notes on Receiver noise figure.
Block diagram
Operation
Explanation of each block
Noise figure
23.Draw the block diagram of conical scan radar , one-coordinate monopulse tracking
and explain its operation.
Block diagram
conical scan radar explanation
24.Explain blind speed and the methods for reducing the effects of blind speeds.
Explanation
1.operate the radar at long wavelengths.
2. operate with a high pulse repetition frequency
3. operate with more than one pulse repetition frequency
4.operate with more than one RF frequency.
25. Draw the block diagram of MTI radar and explain in detail?
MTI radar
Block diagram
Explanation
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ENGINEERING
2 and 16 MARK QUESTIONS AND ANSWERS
SUBJECT CODE : EC1019
SUBJECT NAME : RADAR AND NAVIGATIONAL AIDS
Prepared by
S.M.RAMLEE (Lect/ECE)
M.SUCHARITHA(Lect/ECE)
2 Marks
1. What is a radar?
Radar is an electromagnetic system for the detection and location of
reflecting objects such as aircraft, ships, spacecraft, vehicles, people, and the natural
environment. It operates by radiating energy into space and detecing the echo signal
reflected from an object or target.
2. What do you mean by maximum unambiguous range?
Echoes that arrive after the transmission of the next pulses are called the
second time around echoes.The range beyond which the targets appear as secondtime-
around echoes is called the maximum unambiguous range,Run, and is given by
Run=cTp/2=c/2fp
3. What is the fundamental range equation?
Rmax=(PtGAe A 6min)^(1/4)
Pt=transmitted power , W
G= Antenna gain
Ae= Antenna effective aperture
Smin=Minimum detectable signal
4. What is a PPI?
A typical radar display for a surveillance radar is the PPI or Plan Position
Indicator.The PPI is a presentation that maps in polar coordinates the
location of the target in azimuth and range.
5. What are the applications of radar?
ƒ Military
ƒ Remotesensing
ƒ Air traffic control (ATC)
ƒ Law enforcement and highway safety
ƒ Aircraft safety and Navigation
ƒ Ship safety
ƒ Space
6. What are the main reasons for the failure of the simple form of the radar equation?
The failure of the simple form of the radar equation is due to
a. the statistical nature of the minimum detectable signal
b. fluctuations and uncertainties in the targets radar cross section
c. the losses experienced throughout the radar system
d. Propagation effects caused by the earth surface and atmosphere
7. Define minimum detectable signal?
The weakest signal that can just be detected by the receiver is the
minimum detectable signal.
8. What is called a false alarm?
If the target were set too low, noise might exceed it and be mistaken for a
target. This is called the false alarm.
9. What is called a missed detection?
If the threshold were set too high , noise might not be large enough to
cause false alarms, but weak target echoes might not exceed the threshold and
would not be detected .This is called as missed detection.
10. What is called threshold detection?
If the receiver output is not of sufficient amplitude to cross the threshold,
only noise is said to be present. This is called threshold detection
11. What is called a thermal noise?
If the radar were to operate in a noise free environment so that no external
sources of noise accompany the target signal, and if the receiver itself were so
perfect that it did not generate any excess noise, there would still be noise
generated by the thermal agitation of the conduction electrons in the ohmic
portion of the receiver input stages. This is called as thermal or Jhonson noise.
12. What is said to be the rayleigh region?
Radar cross section depends on the characteristic dimensions of the object
compared to the radar wavelength. When the wavelength is large compared to the
objects dimensions, scattering is said to be rayleigh scattering.
13. Give some examples of simple targets?
Some examples of simple targets are sphere, cylinder, flatplate, rod, ogive
and cone.
14. Define the term fluctuations?
$ UHODWLYH SKDVH VKLIW JUHDWHU WKDQ UDGLDQV FDQ \LHOG D VLJQLILFDQW
change in the resultant phase and amplitude of the composite echo signal which
results in target cross section fluctuations.
15. What is called frequency diversion?
It means that more than one transmitter, each at a different frequency is
utilized in parallel with each transmitter channel operating as a separate radar.
16. What is called frequency agility?
Pulse to Pulse change in frequency is called frequency agility.
17. What is called as revisit time?
It is the time that an antenna takes to return to view the same
region of space. It is also called as scan time.
18. What is a radome?
A typical ground based metal space frame radome might have a two-way
transmission loss of 1.2 db at frequency ban from L to X band.
19. Define a scan to scan fluctuation?
The echo pulses received from a target on any one scan are of constant
amplitude throughout the entire scan, but are independent from scan to scan. A
target echo fluctuation of this type is called scan to scan or slow fluctuations.
20. What are complex targets?
The radar cross section of complex targets such as aircraft, missiles, ships,
ground vehicles, fabricated structures, buildings and terrains can vary
considerably depending on the viewing angle and frequency.
21. What is clutter?
When detecting targets radars have to deal with more than receiver noise
since they can also receive echoes from the natural environment such as land ,sea
and weather.These echoes are called clutter since they can "clutter" the radar
display.
22. Write the four methods for reducing the effects of blind speeds.
1.operate the radar at long wavelengths.
2. operate with a high pulse repetition frequency
3. operate with more than one pulse repetition frequency
4. operate with more than one RF frequency.
23. Why do blind speeds occur?
Blind speeds occur because of the sampled nature of the pulse radar
waveform.Thus it is sampling that is the cause of ambiguities, or aliasing , in the
measurement of the doppler frequency .
24.Define MTI improvement factor.
The signal-to-clutter ratio at the output of the clutter ratio divided by the signalto-
clutter ratio at the input of the clutter filter , average uniformly over all target
radial velocities of interest.
25.What are bipolar and unipolar videos?
The output of the MTI radar is called bipolar video,since the signal has
negative as well as positive values.Unipolar video is rectified bipolar video with
only positive values.
26.Define doppler frequency in MTI radar?
In MTI radar ,the phase detector is a mixer-like device that combines the
received signal and the reference signal from the coho so as to produce the
difference between the received signal and the reference signal frequencies.This
difference is the doppler frequency.
27.What are stalo and coho?
Stalo (Stable oscillator) is the local oscillator of an MTI receiver which is used to
recognize the need for high stability.Coho stands for coherent oscillator to signify that it
is the reference signal that has the phase of the transmitter signal.
28.State the properties of single DLC that limit the utility of simple doppler filter.
1.The frequency response function also has zero response when moving targets
have doppler frequencies at the prf and its harmonis .
2.The clutter spectrum at zero frequency is not a delta function of zero width,but
has a finite width so that clutter will appear in the pass band of the Delay Line Canceler.
29.Define blind speeds.
The limitations of single DLC results in target speeds called blind speeds,where
the target will not be detected and there will be an uncancelled clutter residue that can
interfere with the detection of moving targets.
30.Why VHF is not considered as a desirable frequency cchoice for a long range airsurveillance
radar?
1.Resolution inrange and angle are poor due to narrow bandwidths and large
beamwidths.
2.This portionof electromagnetic spectrum is crowded with other than radar
services.
3.Low altitude coverage ally poor.
31.Define three-pulse canceler.
A canceler with two delay lines that has the same frequency response as the
double delay-line canceler,but which is arranged differently is known as three-pulse
canceler.
32.What are recursive filters?
Filter design using only zeros does not have the flexibility of filter design based
on poles as well as zeros.Poles can be obtained with delay line cancelers by employing
feedback.With both feedback and feed forward lines providing both poles and zeros
,arbitrary filter frequency response functions can be synthesized from cascaded delay
lines,within the limits of realizability.These are known as recursive filters or infinite
impulse response(IIR )filters.
33.State the methods for employing multiple prfs to avoid losing target echoes due to
blind speeds.
The prfs can be changed (1)scan to scan
(2)dwell to dwell or
(3)pulse to pulse(usually called stagered prf).
34.State two methods proposed for finding the effect of stagger periods.
The two methods are computer search and analytic formulation.The effect of the
stagger periods on the depth of the null is based on computer search and the MTI
improvement factor is based on analytic formulation.
35.What is clutter map?
It is used to detect crossing targets with zero radial velocity that would
otherwise be cancelled by any other MTI.
36.What is a saturation detector?
It is used to detect whether any of the ten pulses within a processing
interval saturates the A/D convertor and, if it does ,the entire ten pulses of that
particular CPI are discarded.
37. Define Navigation?
Navigation is the art of directing the movements of craft from one point to
another along a desired path.
38. What is the need of a Chronometer?
With the help of Chronometer, the navigator was able to determine his
longitude by noting the transit time of heavenly bodies.
39. Define electronic navigational aids?
Navigational systems which employ electronics in some way
40. What are the four methods of navigation?
1. Navigation by pilotage
2. Celestial or astronomical navigation
3. Navigation by dead –reckoning
4.Radio navigation
41. Define astronomical navigation?
Celestial navigation is accomplished by measuring the angular position of
celestial bodies.
42. Define navigation by dead reckoning?
The position of the craft at any instant of time is calculated from the
previously determined position, the speed of its motion with respect to earth along
with the direction of its motion and the time elapsed.
43. What is the important source of antenna effect?
The important source is the asymmetry of the loop antenna with respect to the
ground.
44. How the antenna effect is minimized?
To minimize the antenna effect, the centre of the loop is earthed and its output is
thereby balanced.
45. Give the disadvantage of loop direction finder?
1. The loop is small enough to be rotated easily. This results in a small
signal pick ups.
2. To facilitate manual operation, the loop is located near the receiver.
46. What are the errors arising in direction finders?
1. Errors due to abnormal polarization of the incoming wave
2. Errors due to abnormal propagation
3. Site errors
4. Instrumental errors
47. Define mountain effect?
In air borne direction finders, mountainous terrain may cause errors
when there is simultaneous reception of signal from the transmitter by a direct
path and by reflection from the mountain side. This is called mountain effect.
48. What is the need of Adcock direction finders?
The Adcock direction finders are designed to eliminate polarization
errors by dispensing with the horizontal members.
49. What are the types of automatic direction finders?
1. The radio compass
2. A VHF phase comparison automatic direction finders
50. What are the two types of radio ranges in use?
1. Low frequency four course radio range
2. VHF Omni directional radio range
51. What are the sources of errors in VOR system?
1. Ground station and aircraft equipment
2. Site irregularities
3. Terrain features
4. Polarization
52. Define hyperbolic system of navigation?
Hyperbolic systems are based on the measurement of the difference in
the time of arrival of electromagnetic waves from two transmitters to the receiver
in the craft.
53. What are the different hyperbolic navigational systems?
Different hyperbolic navigational systems are LORAN, DECCA and
OMEGA.
54. Define LORAN?
LORAN is Long Range Navigational Aid and is a pulse system. The
ground station transmit a train of pulses with fixed time relation between them
and at the receiver, these pulses are identified and the delay between them is
measured on a cathode ray oscilloscope
55. What is the operating frequency of LORAN-C?
LORAN-C operates in the band 90-110 KHZ.
56. Define DECCA navigation system?
The measurement of the time difference in the reception of signals from two
stations is by measuring the phase difference between the signals of the two
stations, the radiations which are phase locked, instead of time interval between
pulses in the LORAN
57. What are the advantages of OMEGA system?
1. At low frequency in the 10KHZ range, the coverage is increased
2. Loss of power at this frequency is low.
58. Give the Secondary Radar systems?
1. DME (Distance Measuring Equipment)
2. TACAN (Tactical Air Navigation)
59. Define TACAN?
TACAN provides both range and bearing information with the same
radiation.
60. What are the types of landing aids?
1. Instrument landing system
2. Microwave Landing system
3. Ground controlled approach.
61. What is meant by Localizer?
The localizer operates in the VHF band (108-110 MHZ) and consists of a
transmitter with an antenna system. The radiation of which has two lobes, one
with a predominant modulation of 90 Hz and other with 150 Hz.
62. What are the types of Radar present in the Ground controlled approach systems?
1. Surveillance radar element
2. Precision approach radar
63. What are the disadvantages of ILS?
1. Provides a single approach path along the extended centre line of the
runway.
2. It is site sensitive and subject to distortion and bending of the approach
path due to site irregularities.
64. What are the basic elements of a MLS system?
1. Azimuth beam equipment
2. Elevation beam equipment
3. Distance measuring equipment
65. What is meant by Doppler navigation?
It employs the Doppler Effect to determine the velocity of the craft in a frame
of coordinates fixed with respect to the aircraft.
66. Define Frequency trackers?
The frequency tracker locates the centre of the noise like Doppler spectrum
and gives the output the pure signal of this frequency.
67. Define inertial navigation?
Inertial navigation is a system of dead reckoning navigation in which the
instruments in the craft determines its accelerations and by successive
integration, obtain its velocity and displacement.
68. What are the features of Navigation over earth?
1. The system of coordinated should be fixed with reference to earth.
2. The coordinate system most convenient for use is latitude and
longitude.
3. Avery large gravitational fields is present at the surface of the earth.
69. What are the components of inertial navigation systems?
1. Accelerometers
2. Gyros and stabilized platforms
70. Define DECTRA?
DECTRA is a Decca tracking and ranging. This is a long range
hyperbolic navigational system working at a frequency of about 70 KHz. The
system is designed to provide navigation information over a long route,
particularly along the sea.
71. Define CONSOL?
IT is a rotating beacon operating in the LF/MF band which employs a
system of three antennas producing a multi lobed pattern which is switched to
produce a number of equi signals as in the radio range.
72. Define CONSOLAN?
It is same as CONSOL except that a two antenna system is used instead of
three antennas .
73. What are Marker Beacons?
These are Radio beacons which are intended to mark some salient points.
74. Define SHORAN?
Short Navigation System is a secondary radar system in which fix is
obtained by the craft, which carriers the interrogator, by simultaneously
interrogating two ground beacons.
75. What is meant by Radio Sextant?
This is a Sextant operating on the radio frequency emission of heavenly
bodies, like a radio telescope.
76.What are the various system losses?
ƒ Microwave plumbing losses
ƒ Antenna losses
ƒ Signal processing losses
ƒ Collapsing losses
ƒ Operator losses
ƒ Equipment degradation
ƒ Propagation losses
ƒ Radar system losses
77. What are the disadvantages of low frequency four course radio range?
1. Limited number of courses (four)
2. Poor signal/noise ratio
3. Fatigue caused by listening to the tones
4. Difficulty of identifying the course
78. What are angel echoes?
Echoes produced by birds , insects
79. What is called velocity modulation?
The electrons getting accelerated and decelerated by the signal
producing bunching of electrons.
80. What are called Linear beam tubes and Cross field tubes?
The electric field and magnetic field are parallel to each other in linear
beam tubes and they are perpendicular to each other in cross field tubes.
81.Define Signal Processing?
Methods for the detection of desired signals and the rejection of undesired
noise, clutter and interference in radar are called signal processing
82.Define Matched filter?
Filter that maximizes the output signal to noise ratio of a radar receiver which
maximizes the delectability of a target.
83.What is meant by automatic detection?
Automatic delectation performs the operation required for the detection
decision without the operator intervention.
84.What is the need of integrator?
Integrator integrates or adds the energy from the received pulses
available from the target
85.Define moving window detector?
Continuous integration of the last n pulses at the output from the receiver
from each range resolution cell is accomplished with a moving window integrator
called as moving window detector.
86.Define binary integrator?
The use of a detection criterion that require m out of n pulses to be present in
the form of integration is called binary integrator
87.What is meant by Electromagnetic compatibility?
The elimination of interference from other radars and other electromagnetic
radiations that can enter the radar receiver.
88.What is the need of pulse compression?
Pulse compression is used to achieve high range resolution without the need
of high peak power.
89.what are the basic radar measurements that can be achieved from a point target?
1.Range
2.Angle
3.Radial velocity
4.Tangential velocity.
90. What are the basic radar measurements that can be achieved from a Distributed
target?
1.Size and shape
2.Symmetry
3.Radial Profile
4.Tangential Profile.
91.What are the factors affecting the transmitted waveform by a radar?
1.Target detection
2.Accuaracy
3.resolution
4.Ambiguities
92.Define ECCM?
A short pulse radar can negate the effects of certain electronic
countermeasures such as range gate stealers, repeater Jammer and decoys.
93.What is meant by interdigital transducers?
The input/output devices arranged on the surface are known as interdigital
transducers.
94.Define apodization?
Amplitude shaping of the frequency response of a SAW filter can be obtained
by the amount of overlap of the electrodes of IDT is called as apodization.
95.What is meant by Doppler tolerant waveform?
A Doppler tolerant waveform is one whose signal to noise ration out of its
matched filter is independent of the Doppler frequency shift. Such waveforms are
called as Doppler invariant
96.What is meant by Welti codes?
These are related to Golay complementary codes in that they are used in pairs
that are subtracted from one another to obtain autocorrelation functions with zero side
lobes,
97.Define synthetic Aperture radar?
SAR produces a high-resolution image of a scene of the earth’s surface in
both range and cross range. It can produce images of scenes at long range and in
adverse weather that are not possible with infrared or optical sensors.
98.What are the different radar cross section modulations?
1.Propeller modulation
2.Helicopter Blade modulation
3.Jet engine modulation
99.What are the target recognition applications?
1.Military combat identification
2.Ballistic missile target discrimination
3.Meterological observation
4.Battlefield surveillance
100.Define Point clutter?
Buildings and other constructed objects can result in large echoes known as
discretes or point clutter.
16 marks
1. Explain the radar block diagram?
Block diagram
Explanation
2. Derive the simple form of the radar equation?
3. Explain about the Receiver noise and derive the signal to noise ratio?
Noise figure
Minimum detectable signal
Maximum range
4. Explain about the radar cross section of targets?
Simple targets
Complex targets
5. Explain the various system losses?
Microwave plumbing losses
Antenna losses
Signal processing losses
Collapsing losses
Operator losses
Equipment degradation
Propagation losses
Radar system losses
6.Explain the four methods of navigation in detail?
1. Navigation by pilotage
2. Celestial or astronomical navigation
3. Navigation by dead –reckoning
4.Radio navigation
7. Explain the errors arising in direction finders?
1. Polarization Errors
2. Errors due to abnormal propagation
3. Site errors
4. Instrumental errors
8. Explain briefly the Automatic Direction finders?
1.The radio compass
2. A VHF phase comparison automatic direction finders
-------Block diagram and explanation
9. Briefly discuss the VHF Omni Directional Range (VOR)?
Block diagram
Modulation Eliminator
VOR receiver
Range and Accuracy
10. Explain hyperbolic system of Navigation?
1. LORAN –A
Equipment
Range and precision
2. LORAN-C
3. DECCA navigation system
Block diagram
Range and Accuracy
4. OMEGA system
11. Briefly explain the secondary radar systems?
1. DME
2. TACAN
12. Explain the Instrument LANDING systems?
1. Localizer
2. Glide slope system
3. Receiving equipment
4. Course sharpness and width
5. Marker beacon
13. Discuss the Doppler navigation with a neat block diagram?
Doppler Effect
Doppler frequency equations
Block diagram and explanation
14. Explain the concept of inertial navigation systems?
1. Accelerometers
2. Gyros and stabilized platforms
Explanation
15. Discuss the Satellite Navigational systems in detail?
GPS
Explanation
16.Explain the operation of cavity magnetron and discuss the importance of
performance chart and Ricke Diagram
Magnetron construction
Explanation
Pi –mode
Ricke diagram
17.Explain the principle of Parabolic antennas
Reflector antennas –basic concept
Various feeds
Radiation patterns
18.Explain the principle of Cassegrain antennas
Cassegrain antennas-basic concept
Various feeds
Feed support
19.Draw the block diagram of two co-ordinate mono-pulse tracking radar and its
operation.
Block diagram
Two coordinate explanation
Hybrid rings
20.Draw the block diagram of one co-ordinate mono-pulse tracking radar and its
operation.
Block diagram
One coordinate explanation
Hybrid rings
21.Draw the block diagram of conical scan radar and sequential lobing tracking radar
and its operation.
Block diagram
conical scan radar explanation
sequential lobing explanation
22.Explain Superheterodyne receivers. Add notes on Receiver noise figure.
Block diagram
Operation
Explanation of each block
Noise figure
23.Draw the block diagram of conical scan radar , one-coordinate monopulse tracking
and explain its operation.
Block diagram
conical scan radar explanation
24.Explain blind speed and the methods for reducing the effects of blind speeds.
Explanation
1.operate the radar at long wavelengths.
2. operate with a high pulse repetition frequency
3. operate with more than one pulse repetition frequency
4.operate with more than one RF frequency.
25. Draw the block diagram of MTI radar and explain in detail?
MTI radar
Block diagram
Explanation
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