DEPARTMENT OF ELECTRONICS AND COMMUNICATION
ENGINEERING
2 and 16 MARK QUESTIONS AND ANSWERS
SUBJECT NAME : RADAR AND NAVIGATIONAL AIDS
Prepared by
S.M.RAMLEE (Lect/ECE)
M.SUCHARITHA(Lect/ECE)
www.Vidyarthiplus.com
, www.Vidyarthiplus.com
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 second-
time-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 A6min)^(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?
Military
Remotesensing
Air traffic control (ATC)
Law enforcement and highway safety
Aircraft safety and Navigation
Ship safety
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
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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?
$UHODWLYHSKDVHVKLIWJUHDWHUWKDQ UDGLDQVFDQ\LHOGDVLJQLILFDQW
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.
www.Vidyarthiplus.com
ENGINEERING
2 and 16 MARK QUESTIONS AND ANSWERS
SUBJECT NAME : RADAR AND NAVIGATIONAL AIDS
Prepared by
S.M.RAMLEE (Lect/ECE)
M.SUCHARITHA(Lect/ECE)
www.Vidyarthiplus.com
, www.Vidyarthiplus.com
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 second-
time-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 A6min)^(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?
Military
Remotesensing
Air traffic control (ATC)
Law enforcement and highway safety
Aircraft safety and Navigation
Ship safety
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
www.Vidyarthiplus.com
, www.Vidyarthiplus.com
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?
$UHODWLYHSKDVHVKLIWJUHDWHUWKDQ UDGLDQVFDQ\LHOGDVLJQLILFDQW
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.
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