talk about radar system

1. Radar Basics
- Primary radar is very simple in principle
- However:
- high RF-energy is needed
- useful signals (echo or return) are very small
- interferences are very large
- useful signals contain significant information
- analysis and signal processing is quite complex
Simple in Concept – Complex in Reality
RAdio Detection And Ranging

2. Primary Radar Basics Principle
- pointing direction gives bearing of target
- time delay in received signal gives range of target

3. Co-ordinates
•Range and bearing describes a position in 2D-radar
•Range, bearing and elevation describes a position in 3D-radar
• Polar co-ordinates
• Cartesian co-ordinates

4. Radar Set Layout

5. Radar Set Layout (animated)

6. RADAR types

7. Radar Range Measurement
• tdelay
is the time taken for the signal to travel to the
target and return to radar site
• (therefore a half of this time is taken in account only)
• c0
is the speed of light (approximately 3·108
m/s)
0
2
delay
t c
R



8. Unambiguous Range
The expected time for receiving backscattered signal
must be smaller than the pulse repetition time!
If not, there are ambiguous returns!
• weak echo of actual period?
• strong echo of previous period?
 
0
2
unamb
c
R
 



9. Staggered PRF
• Previous period is not constant
• Ambiguous returns haven't a stable position

10. Ambiguous return on PPI
• Staggered PRT: ambiguous return is dotted:

11. Range Resolution
• The range resolution depends on the geometric dimension of
a range cell
• the (possibly compressed) pulse width therefore
0
2
c
R





12. Resolution Oscillogram

13. Example 1
• Distance between two targets is to small
Pulse width 1 microsecond
= 300 meters
Distance less than 150 meters

14. Example 2
• Distance between two targets is large enough
Pulse width 1 microsecond
= 300 meters
Distance more than 150 meters

15. Bearing Resolution
2 sin
2
A
S R

 
Spacing in azimuth depends on range R and beamwidth θ

16. Radar Resolution Cell
• The resolution cell depends on:
• Range resolution (function of time)
• Bearing resolution
(function of antenna’s beam width)

17. Radar coverage
• Cone of Silence: 2…3 times the height

18. • Influence of the curvature of the earth
Line of Sight
 
max 2 2
earth aim antenna
R r H H
 

19. • Influence of refraction
Radar Horizon
 
 
max aim antenna
max aim antenna
[km] ( in Meters)
[NM] ( in Feet)
4.12
1.23
H
H
R H H
R H H
 
 

20. Radar Service Availability
Sensor network provides overlapping cover – en route case
Closely located sensors mutually limit low coverage

21. Operational Availability
• Ratio of radars operational time
– in hours, or (e.g.: 1000 h)
– in percent (e.g.: 99.9 %)
in relation to the
• Non-operational time
– needed maintenance time
– probability of hardware faults

22. Time Scheduling

23. Transmitters Duty Cycle
Duty Cycle
i
P
P T

 

24. Dwell Time
60
360
AZ
D
T
n
 

 

25. Hits Per Scan
60
360
D AZ
m
T
n
T T
 
 
 

m= 1...4 m=15...25