VIJENDRASINGH RATHOR130170111092
CW and FM CW Radar
Contents
Basics of RadarClassification of RadarDoppler effectCW RadarFMCW radar
Radar Abbreviation
RA – RadioD – DetectionA – AndR – Ranging
Definition
Radar is an electromagnetic device and regarded to be a powerful electronic eye.
It is also an electromagnetic sensor.
What is done by Radar?
Radar can see the objects hidden anywhere in the globe or planet except some special cases like low altitude, shape changing the reflection direction, special fiber material etc.
Applications of Radar
Military purposeWeather forecastAirport controllingNavigationTo detect and measure objects under the
earthTo indicate speed of automobiles, cricket and
tennis balls etc.
Classification of Radar
Radar
Primary
CW
Modulate
d
Unmodulated
Pulse
MTI Doppler
Secondary
Doppler effect
If either the source of oscillation or the observer of the oscillation is in motion, an apparent shift in frequency will result. This is the Doppler effect and is the basis of the CW radar.
Doppler frequency
+- - +
observer
source
v = velocity of sound = 343 m/s at 20 degree Celsius
CW Radar
Doppler frequency for CW radar
fr= fo + fd … if target is comingfr= fo - fd … if target is moving away
Let R be the distance from radar to target.Let unit wavelength is for λ distance.So total no. of wavelength = 2R/λ (two way
path)One wavelength corresponds to 2п radian
phase.So total phase φ= 4пR/λ
Angular frequency is change in phase with respect to time.
Applications
To find the target’s bearing angle, elevation angle, velocity
To indicate the presence of moving targetsTo find radial velocity of moving targetsTo find whether an object is approaching or
moving away
Disadvantage
Does not give information about range
FMCW Radar
FMCW radar detects, measures range and radial velocity of objects.
It is a Frequency Modulated Continuous Wave radar in which the frequency of continuously transmitted wave is varied at a known rate and the frequency of reflected signals is compared with the frequency of transmitted signal
Block diagram
Stationary target
Beat frequency Rate of change of
carrier frequency is fo’
If the frequency is modulated at a rate fm over a range ∆f, the beat frequency is
Moving target
The beat frequency due to range fr can be calculated as,
Range equation
The distance R to the reflecting object can be determined by the following relations:
Applications
Slant range of the targetBearing and elevation angle of targetHeight of target
Thank You
References:
Radar EngineeringBy G. S. N. Raju
Introduction to Radar SystemsSecond EditionBy Merrill Skolnik