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Ec1019-Radar and Navigational Aids | Navigation | Radar

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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 b
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  DEPARTMENT OF ELECTRONICS AND COMMUNICATIONENGINEERING 2 and 16 MARK QUESTIONS AND ANSWERSSUBJECT CODE : EC1019SUBJECT NAME : RADAR AND NAVIGATIONAL AIDSPrepared byS.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 naturalenvironment. It operates by radiating energy into space and detecing the echo signalreflected 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 thesecond time around echoes.The range beyond which the targets appear as second-time-around echoes is called the maximum unambiguous range,R un, and is given byR un =cT p  /2=c/2f  p 3. What is the fundamental range equation?R max =(P t GA e  A6 min )^(1/4)Pt=transmitted power , WG= Antenna gainAe= Antenna effective apertureSmin=Minimum detectable signal4. What is a PPI?A typical radar display for a surveillance radar is the PPI or Plan PositionIndicator.The PPI is a presentation that maps in polar coordinates thelocation 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  Space6. 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 toa. the statistical nature of the minimum detectable signalb. fluctuations and uncertainties in the targets radar cross sectionc. the losses experienced throughout the radar system  d. Propagation effects caused by the earth surface and atmosphere7. Define minimum detectable signal?The weakest signal that can just be detected by the receiver is theminimum detectable signal.8. What is called a false alarm?If the target were set too low, noise might exceed it and be mistaken for atarget. 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 tocause false alarms, but weak target echoes might not exceed the threshold andwould 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 detection11. What is called a thermal noise?If the radar were to operate in a noise free environment so that no externalsources of noise accompany the target signal, and if the receiver itself were soperfect that it did not generate any excess noise, there would still be noisegenerated by the thermal agitation of the conduction electrons in the ohmicportion 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 objectcompared to the radar wavelength. When the wavelength is large compared to theobjects 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, ogiveand 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 whichresults in target cross section fluctuations.15. What is called frequency diversion?It means that more than one transmitter, each at a different frequency isutilized 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 sameregion 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-waytransmission 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 constantamplitude throughout the entire scan, but are independent from scan to scan. Atarget 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 varyconsiderably depending on the viewing angle and frequency.21. What is clutter?When detecting targets radars have to deal with more than receiver noisesince they can also receive echoes from the natural environment such as land ,seaand weather.These echoes are called clutter since they can clutter the radardisplay.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 frequency3. operate with more than one pulse repetition frequency4. operate with more than one RF frequency.23. Why do blind speeds occur?Blind speeds occur because of the sampled nature of the pulse radarwaveform.Thus it is sampling that is the cause of ambiguities, or aliasing , in themeasurement of the doppler frequency .24.Define MTI improvement factor.The signal-to-clutter ratio at the output of the clutter ratio divided by the signal-to-clutter ratio at the input of the clutter filter , average uniformly over all targetradial velocities of interest.25.What are bipolar and unipolar videos?The output of the MTI radar is called bipolar video,since the signal hasnegative as well as positive values.Unipolar video is rectified bipolar video withonly positive values.26.Define doppler frequency in MTI radar?
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