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