Introduction to RADAR systems

1. By:
Amjad Hassan Khan MK
Lecturer in Electronics
Kristu Jayanti College, Bengaluru

2. • Introduction-RADAR principles,
• frequencies and powers used in RADAR,
• maximum unambiguous range,
• detailed block diagram of pulsed RADAR
system, RADAR range equation, derivation,
• factors influencing maximum range,
• Effect of ground on RADAR , antenna
characteristics,
• Doppler effect, MTI RADAR, Block diagram,
• CW RADAR, Block diagram, advantages,
applications and limitations,
• FM CW RADAR, block diagram,
• Numerical examples where ever applicable.

3. RAdio Detection And Ranging

5. Band designation Nominal frequency range Maximum Available Peak Power
MW
UHF 0.300 – 1GHz 5.0
L 1 – 2 GHz 30.0
S 2 – 4 GHz 25.0
C 4 – 8 GHz 15.0
X 8 – 12 GHz 10.0
Ku 1 2– 18 GHz 2.0
K 18 – 27 GHz 0.6
Ka 27 – 40 GHz 0.25
V 40-80 GHz 0.12
N 80-170 GHz 0.01

6. There are two main types of RADAR:
1)Primary Radar
 Continuous wave Radar
 Pulse Radar
2)Secondary Radar

7. 1)CONTINUOS WAVE RADAR:
Continuous-wave radar system is a radar system where a known stable
frequency continuous wave radio energy is transmitted and then received
from any reflecting objects. The return frequencies are shifted away from
the transmitted frequency based on the Doppler effect if they are moving.
The main advantage of the CW radars is that they are not pulsed and
simple to manufacture.
CW radars also have a disadvantage because they cannot measure range.
2)PULSE RADAR:
Pulse radar is the more conventional radar, which transmits a burst of
radar energy and then waits for the energy (or echo) to be reflected
back to the antenna. After a specific period of time (depending on how
far the radar is searching) another pulse will be sent followed by
another listening period. Since radar waves travel at the speed of light,
range from the return can be calculated

8. The distance of the target can be calculated from
the total time (T) taken by the pulse to travel to
the target and return to its original initial point.
Assuming ‘ c ‘ to be the velocity of light in free
space, the distance traversed by pulse is ‘cT’
meters. Now this is 2 times the target distance,
hence the distance to the target
R = cT/2 meters.

9. Pulse repetition frequency (PRF): The frequency
that pulses are transmitted, measured in hertz (s-1)
Pulse repetition period (Tr
): The time between pulses
(typical value is 1 ms)
Maximum Unambiguous Range (Rmax
): The
maximum distance that an object can be located
such that a pulse arriving at the object can return to
the radar before another pulse is emitted.
)(22
max
PRF
ccT
r r


11. Let the power radiated by an isotropic antenna be Pt
Power density at a distance R from the transmitting antenna is
P
But the antenna is not isotropic, but unidirectional
Where Ap is maximum power gain

12. Let S be effective area of the target
The power incident on the target will be
The power density of the radiation
from the target at the receiving
antenna is

13. The power received by the antenna depends on the
cross-sectional area(effective area) of the receiving antenna.
The received power will be
If the same antenna is used for both transmission and reception, then

14. The range will be maximum, when the received power is minimum
This is called radar range equation

15. • Transmitted power (Pt)
• Radar cross-section area of the target
• Cross sectional area of the receiving antenna
• Frequency or wavelength
• Minimum received signal power Pr (min)

18. The Doppler effect, named after Christian Doppler, is the change in
frequency and wavelength of a wave due to the relative motion between
the observer and the source.
It is commonly heard when a vehicle sounding a siren approaches,
passes and recedes from an observer

19. If frequency increases than the transmitted frequency then the
source and observer are approaching each other.
If the frequency decreases than the transmitted frequency than
the source and observer are going away from each other.
Change in frequency is called Doppler shift in frequency and
change in wavelength is called Doppler shift in wavelength

22. • Uses low transmitting power
• Circuitry is simple
• Power consumption is small
• Size is small
• Performance is not affected by stationary objects
• Capable of measuring target speeds of long range quickly and
accurately
• Limit to the maximum power
• Limit to the maximum range
• Gets confused by more targets
• Can show only speed not the range

23. Amplifier
Limiter
Sawtooth
generator
Frequency
counter
Indicator
Frequency
modulatorMixer
CW
Transmitter
Oscillator