CW RADAR, FMCW RADAR, FMCW ALTIMETER, AND THEIR PARAMETERS

RADAR ENGINEERING Unit - 2
24-02-2024 DEPT. OF ECE, ADITYA ENGINEERING COLLEGE 1

Radar Engineering
RADAR ENGINEERING UNIT – II
CW AND FREQUENCY MODULATED RADAR
FM-CW RADAR
S Jagadeesh
Associate Professor
Dept. of ECE
Email: samudrala.Jagadeesh@aec.edu.in

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COURSE OUTCOMES
At the end of this course the learners will be able to:
CO1: Model the radar range equation.
CO2: Make use of the range equation in analytical problems.
CO3: Explain the different types of radars and its applications.
CO4: Classify the different tracking techniques
CO5: Explain the performance of radar receiver systems.

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MAPPING OF COURSE OUTCOMES WITH PROGRAM OUTCOMES:
CO/PO PO 1 PO 2 PO 3 PO 4 PO 5 PO 6 PO 7 PO 8 PO 9 PO 10 PO 11 PO 12
CO1 3 2 1 1 - - - - - - - -
CO2 3 2 2 1 - - - - - - - -
CO3 2 1 1 - - - - - - - - -
CO4 2 1 1 1 - - - - - - - -
CO5 2 1 1 - - - - - - - - -

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MAPPING OF COURSE OUTCOMES WITH PROGRAM SPECIFIC OUTCOMES:
CO/PSO PSO1 PSO2
CO1 3 -
CO2 3 -
CO3 2 -
CO4 2 -
CO5 2 -

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UNIT – II
CW AND FREQUENCY MODULATED RADAR
CW
➢Doppler Effect
➢CW Radar – Block Diagram
➢Isolation between Transmitter and
Receiver
➢Non-zero IF Receiver
➢Receiver Bandwidth Requirements
➢Applications of CW radar
➢Illustrative Problems.
FM-CW Radar
➢Range and Doppler Measurement
➢Block Diagram and Characteristics
➢FM-CW altimeter
➢Multiple Frequency CW Radar

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DOPPLER EFFECT
➢Doppler effect implies frequency of a wave when transmitted by a
source it is not necessarily same as the frequency of the transmitted
wave when picked up by a receiver
➢The received frequency depends on relative motion between
Transmitter and Receiver

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DOPPLER EFFECT
Source is Moving Destination is Moving
𝑭𝒓 > 𝑭𝒕
Source is Moving
Destination is Moving
Destination is
Stationary
Source is
Stationary
Source is Moving
Destination is
Moving
Source is Moving
Destination is
Stationary
Destination is
Moving
Source is
Stationary
𝑭𝒓 < 𝑭𝒕

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DOPPLER EFFECT
Depending on the relative motion between the source and destination,
the change in the received frequency at the destination is known as
“Doppler Shift”

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DOPPLER SHIFT
Doppler shift depends up on the
relative velocity between the source
and destination
𝐷𝑜𝑝𝑝𝑙𝑒𝑟 𝑆ℎ𝑖𝑓𝑡(∇𝑓) =
2𝑉𝑅
𝜆
=
2𝑉𝐶𝑜𝑠𝜃
𝜆
Here,
𝑉𝑅 = 𝑅𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦
𝜆 = 𝑂𝑝𝑒𝑟𝑎𝑡𝑖𝑛𝑔 𝑊𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ
𝑉 = 𝑇𝑎𝑟𝑔𝑒𝑡 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦
V
𝜽

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DOPPLER SHIFT
This principle used in Doppler Radar to find the velocity of the moving
targets

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PROBLEM 1
Find the doppler shift caused by a
vehicle moving towards a Radar at
96 KM/h, if the radar operates at
10 GHz.
13

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PROBLEM 2
What is the doppler shift when
tracking a car moving away from
Radar at 1000 Miles/Hr. The Radar
operates at 1GHz.
14

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CW RADAR WORKING PRINCIPLE
➢It is possible to detect moving targets
by radiating un-modulated continuous
wave (CW).
➢Radar makes the use of Doppler Shift
for target speed measurement.
➢Note: If a common antenna serves for
both Transmitter and Receiver, then a
“Circulator” will be used for the purpose
of isolation of both Transmitter and
Receiver.
Frequency Response

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CW RADAR - ADVANTAGES
➢CW Radar has no blind speeds
➢CW Radar is able to give accurate relative velocity
➢It operates at low power levels
➢It is used for small and large ranges with high degree of efficiency
➢Radar performance is not effected by stationary object

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CW RADAR - DISADVANTAGES
➢CW radar cannot determine the target range
➢If more number of targets are present, there is a chance of ambiguity
in measurement

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CW RADAR - APPLICATIONS
➢CW radar can be used in traffic counters
➢CW radar serves as a intruder alarm in security systems
➢CW radar serves in monitoring the runway of an airport
➢CW radar will be used in measuring the ball speed in sports such as Cricket.

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ISOLATION BETWEEN TRANSMITTER AND RECEIVER
Isolation between transmitter and receiver is an important aspect to be
studied and addressed in simple CW radars where a single antenna
serves the purpose of both transmission and reception.
A moderate amount of Transmitter leakage (reference signal from the
transmitter to the receiver) entering the receiver along with the echo
signal supplies the reference necessary for the detection of the doppler
frequency shift.

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There are two practical effects which limit the amount of transmitter
leakage power which can be tolerated at the receiver. They are:
1. The maximum amount of power the receiver can withstand.
2. The amount of transmitter noise which enters the receiver from the
transmitter.

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Example:
The safe value of the receiver power : 10 milli watt
The transmitter power : 1K Watt
The minimum amount of isolation between the transmitter and receiver should
be:__________
A. 100 dB
B. 50 dB
C. 120 dB
D. 10 dB

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For a long range CW radar the isolation is determined the noise that
accompanies the transmitter leakage rather than, by any damage
caused by high power.
Example: for a certain long range CW Radar the transmitter leakage
power is 10 mW, minimum detectable signal power is 10-13watt. Then
what should be the limit of transmitter noise in dB ??
Ans: Below -130 dB

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IF RECEIVER
In simple CW radar receiver, the local oscillator is replaced by a transmitter leakage
signal this concept is called as “Homodyne Receiver” (Zero IF Receiver)
But these kind of receivers are very sensitive to “flicker noise”
The super heterodyne receivers (Non-zero IF receiver) are able to over come the
problem of flicker noise by using an intermediate frequency high enough to make the
flicker noise small compared with normal receiver noise

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IF RECEIVER

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RECEIVER BANDWIDTH REQUIREMENTS

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(SPECTRUM BROADENING OF IF AMPLIFIER)
1. The spread in the spectrum due to antenna scanning
Let an antenna beam width is : 𝜃𝐵
Antenna scanning rate: 𝜃𝑆
Then, the spread in the spectrum of the received signal : 1/
𝜃𝐵
𝜃𝑆
Hz
Example: Find the spread in the spectrum of the received signal if the antenna beam
width is 20 and antenna scanning rate is 36 degrees/sec.

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2. Target cross section fluctuations
3. Modulation of Echo due to propeller (Ex: due to propeller of helicopter)
4. Variation on target relative velocity
Let 𝑎𝑟 is the acceleration w.r.t Radar
Then, the signal will occupy a bandwidth of
𝜵𝒇𝒅 =
𝟐 𝒂𝒓
𝝀
𝟏/𝟐

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Example: find the doppler signal bandwidth if a target acceleration is due to gravity
and the operating wavelength is 10 CM.
𝜵𝒇𝒅 =
𝟐 𝒂𝒓
𝝀
𝟏/𝟐

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To improve the efficiency and reduce the effect of noise, the filter banks are used

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FREQUENCY MODULATED CW (FM-CW) RADAR
The system transmits a continuous wave at a certain frequency, which is then
modulated over a period of time T. This gives the transmitted signal a “time
stamp". The signal travels then to the target and part of it is reflected back.
The radar will detect the reflected signal and compare it to the original one
by mixing them and processing the resulting signal. A simplified schematic is
presented here
Courtesy of Renesas Electronics

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FM-CW RADAR WORKING PRINCIPLE
Courtesy of Renesas Electronics

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RANGE MEASUREMENT
In the frequency-modulated CW radar (abbreviated FM-CW), the
transmitter frequency is changed as a function of time in a known
manner. Assume that the transmitter frequency increases linearly with
time. If there is no doppler shift (in case of stationary target) the beat
frequency is a measure of the target’s range.

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RANGE MEASUREMENT

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DOPPLER MEASUREMENT
A Doppler frequency shift will be superimposed on the FM range beat
note and an erroneous range measurement results. The Doppler
frequency shift causes the frequency-time plot of the echo signal to be
shifted up or down. On one portion of the frequency-modulation cycle
the beat frequency is increased by the Doppler shift, while on the other
portion, it is decreased.

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DOPPLER MEASUREMENT

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FM-CW RADAR BLOCK DIAGRAM

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FM-CW ALTIMETER
Courtesy of Mathworks

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FM-CW ALTIMETER
(USING SIDEBAND SUPER HETERODYNE RECEIVER)

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Courtesy of Mathworks

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MULTIPLE FREQUENCY CW RADAR
▪The Transmitted signal sin 2𝜋𝑓0𝑡
▪Received Echo Signal sin 2𝜋𝑓0(𝑡 − 𝑇)
▪In a phase detector,
▪∇∅ = 2𝜋𝑓0𝑇 ⇒ 2𝜋𝑓0
2𝑅
𝐶
=
4𝜋𝑓0𝑅
𝐶
▪Therefore,
▪𝑹 =
𝑪𝜵∅
𝟒𝝅𝒇𝟎
=
𝝀
𝟒𝝅
𝜵∅
▪When the maximum phase difference 𝛻∅ = 2𝜋
▪The maximum range is 𝑅𝑚𝑎𝑥 =
𝜆
4𝜋
2𝜋 =
𝜆
2
▪Hence the maximum range depends on radar operating
wave length, and its limited and very small in case of
lower operating wavelengths.
▪Hence in a a multiple frequency radar with frequencies
𝑓1, 𝑓2
▪The range, 𝑹 =
𝑪𝜵∅
𝟒𝝅(𝒇𝟏−𝒇𝟐)
⇒ 𝑹𝒎𝒂𝒙 =
𝑪
𝟐(𝒇𝟏−𝒇𝟐)
.
▪Here the maximum radar range depends on the
difference between the frequencies of operation.

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SUMMARY OF RADAR SYSTEMS

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PREVIOUS YEAR QUESTION PAPERS
AR20 Aug 2023
Supply

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AR20 June 2023
Regular

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AR 19June 2023
Supply

Radar Engineering
AR 19 Aug 2022
Supply

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AR 19 June 2022
Regular

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EXTERNAL LINKS FOR UNDERSTANDING OF
CRITICAL CONCEPTS
FM CW Radar Applications in automobiles (Matlab Tech Talks)
https://www.youtube.com/watch?v=-N7A5CIi0sg&t=3s

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THANK YOU…
All the Best for Sessional and End Semester Examinations…
S Jagadeesh,
Associate Professor
Dept. of Electronics and Communication Engineering
Aditya Engineering College(A)

CW RADAR, FMCW RADAR, FMCW ALTIMETER, AND THEIR PARAMETERS

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CW RADAR, FMCW RADAR, FMCW ALTIMETER, AND THEIR PARAMETERS