Presentation on CW Radar with the design related details.pdf

CW Radar material

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CW Radar
DR Sanjeev Kumar Mishra
Lecture 21

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Radar classification
Based on
Antenna type
Based on
frequency band
Based on waveform
utilized
Based on mission
and/or functionality
of the Radar

 HF

 VHF

 UHF

 L - Band

 S - Band

 C - Band

 X - Band

 Ku - Band

 K - Band

 Ka - Band
 mmW

 Continuous
Wave (CW)
 Pulse Radar
(PR)

Low PRF

Medium PRF

High PRF

 Weather

 Acquisition & Search

 Tracking

 Track while -Scan

 Fire control

 Early warning

 Over the horizon

 Terrain following

 Terrain avoidance

 Mono static

 Bi - static
 Phased
Array

 Ground Based

 Airborne

 Spaceborne

 Shipborne

· Imaging
· Non-Imaging

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•Continuous Wave Transmission
•Pulse Transmission.
Introduction

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CW Transmission
Discriminator
AMP
Mixer
CW RF
Oscillator
Indicator
OUT
IN
Transmitter Antenna
Antenna

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Monostatic CW RADAR
Switching Time
Transmitter Leakage
•the maximum amount of power enter into the receiver input circuitry
•the amount of transmitter noise enters into the receiver:
•reduces the receiver sensitivity
•Thus Proper isolation is required.

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Frequency spectrum of CW oscillation
(a) infinite duration and (b) finite duration

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Bi-static CW RADAR

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Doppler filter bank:
•The effective radar Doppler bandwidth is N
FFTf/2.
•N
FFT is the Doppler filter bank size and
•f is the individual NBF bandwidth (FFT bin),
•Thus, The reason for the one-half factor is to account for both negative
and positive Doppler shifts.
•Since the NBF bank is implemented by an FFT, only finite length data
sets can be processed at a time.
•The length of such blocks is normally referred to as the dwell time or
dwell interval.
•It is also known as Time on Target (T
i)

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•The dwell interval (T
Dwell) determines the frequency resolution or the
bandwidth of the individual NBFs. More precisely, iDwell
T
f
T 


1
•Therefore, once the maximum resolvable frequency by the NBF bank
is chosen the size of the NBF bank is computed as f
B
N
FFT


2 B
N
T
FFT
Dwell
2
 FFTN
Bf2 
iav
o
TP
FLkTR
G
SNR
43
22
4


The CW radar equation can now be derived from the high PRF radar
equation given
CW RADAR Equation

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
iav
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TP
FLkTR
G
SNR
43
22
4


The CW radar equation can now be derived from the high PRF radar
equation given
In the case of CW radars, P
av is replaced by the CW average transmitted
power over the dwell interval P
CW, and T
i must be replaced by T
Dwell .
Thus CW Radar equation will be 
DwellCW
wino
rt
TP
FLLkTR
GG
SNR
43
2
4


Where, G
t and G
r and are the transmit and receive antenna gains,
respectively.
The factor L
win is a loss term associated with the type of window (weighting)
used in computing the FFT.

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Sign of the radial velocity
•If the echo frequency is greater than the carrier, the target is
approaching
•If the echo-signal frequency lies below the carrier, the target is
receding;

(a) No doppler shift, no relative target motion; b) approaching target; c) receding target.
Spectra of received signals.

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CW RADAR Applications
•Un-modulated CW radar is for the measurement of the relative velocity
of a moving target, as in the police speed monitor or in the previously
mentioned rate-of-climb meter for vertical-take-off aircraft.
•In support of automobile traffic, CW radar has been suggested for the
control of traffic lights, regulation of toll booths, vehicle counting, as a
speedometer in vehicle testing, as a sensor in antilock braking
systems, and for collision avoidance.
•For railways, CW radar can be used as a speedometer to replace the
conventional axle-driven tachometer.
•CW radar is also employed for monitoring the docking speed of large
ships.
•It has also seen application for intruder alarms and for the
measurement of the velocity of missiles, ammunition, and baseballs.

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