RADAR UNWANTED
EMMISSIONS
ITU WP 8B Radar Seminar
A personal
view
J R Holloway
September 2005 GENEVA
All data in this presentation comes from public
domain sources
1
Unwanted Emission Limits





Before 2003 no SE limit for radar
From 2003 new radars must meet Cat A or Cat B SE limits
 Cat A -60 dB
 Cat B -100 dB
Class B being proposed to be adopted in Europe.
OOB Definition of the extent by the emission masks
 Current Mask
 Design Aim
Status of Limits
 SE levels part of radio regulations
 Boundary part of regulation
 OOB mask is a recommendation
 Design aim for new OOB 2006/2012
7
Current Unwanted Emission Limits
Cat A&B
Current Unwanted Emission Mask
Cat A
0
Power dB
-20
-40
-60
-80
-100
-120
0.1
1
10
Cat B
100
x BW-40dB Bandwidth
8
Design Aim




When the OOB Mask was introduced a
design aim was also introduced.
This proposed to increase the Roll off to
40 dB/dec
If this is not agreed then the aim falls
JRG is considering what should replace
the design aim
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Design Aim Unwanted Emissions Cat A&B
Power dB
"Design Aim" Unwanted Emission
Cat A
Mask
0
-20
-40
-60
-80
-100
-120
0.1
1
10
Cat B
100
x Bw-40dB
10
Problems With Current Mask



Mask perceived to be too relaxed at
estimating –40 dB Bandwidth
Mask perceived to be too relaxed in terms
of Roll-off for trapezoidal pulses
Magnetron Radars find it difficult to meet
current mask
 Impossible to meet design aim
11
Problems With Mask



Mask perceived to be too relaxed at
estimating –40 dB Bandwidth
Mask perceived to be too relaxed in
terms of Roll-off for trapezoidal
pulses.
Magnetron Radars find it difficult to
meet current mask

Impossible to meet design aim
12
Sensitivity of Equation for Bw-40 FM
Pulsed

Bw-40dB gets large when


tr0
Bc gets large
B40 

K
A
 2  Bc  
tr 
t  tr

14
FM Trapezoidal Pulses vs Mask
Mask
15 MHz
Value 10
MHz
15
Practical Bandwidths
Measured
MHz
Calculated
16 MHz
3 dB BW
20 dB BW
40 dB BW
3 dB BW
20 dB BW
40 dB
BW
2.5
3.6
10
2.5
7.8
25.7
16
Problems With Mask



Mask perceived to be too relaxed at
estimating –40 dB Bandwidth
Mask perceived to be too relaxed in
terms of Roll-off for trapezoidal
pulses.
Magnetron Radars find it difficult to
meet current mask

Impossible to meet design aim
17
Trapezoidal Pulse



Two roll-off rates
20 dB/dec
40 dB/dec
20 dB/dec
40 dB/dec
19
Problems With Mask



Mask perceived to be too relaxed at
estimating –40 dB Bandwidth
Mask perceived to be too relaxed in
terms of Roll-off for trapezoidal
pulses.
Magnetron Radars find it difficult to
meet current mask

Impossible to meet design aim
21
Magnetron: Difficult to meet current
OOB Limits
Failure
22
Coaxial Magnetron: Cat B Limits
Failure Zones
Meteorological Radar - Ground Based
C band Magnetron
0
Norm alised Power Measured in 511 KHz Bw (dB)
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
-110
5.3
5.3
5.4
5.4
5.5
5.5
5.6
5.6
5.7
5.7
5.8
5.8
5.9
5.9
6.0
6.0
Frequency (GHz)
23
JRG Work on New Mask



Looking into how a better estimate of the reference
bandwidth.
 Non linear chirps
 Limit excessive bandwidths due to
 Large Chirps
 Fast Rise Times
Looking into what roll-off can be practically achieved
 How Roll-off Relates to RB
Looking into the special problems associated with.
 Magnetron based radars
 FM CW radars
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Trade Off Reference Bandwidth vs
Roll-off

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If the Reference Bandwidth is accurately calculated
20 dB roll-off looks achievable
40 dB roll-off looks difficult
These are theoretical however in practice distortions make
things worse
26
Practical Issues To Reduce Unwanted
Emissions

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Use High Compression ratios
Use slow rise and fall times
Shape pulses to remove discontinuities
Use Filters
27
Practical Issues cont

Magnetrons
 Below rotation can use high Q filters
 Multi pulse length systems have to use a
filter wide enough to meet narrowest pulse
 Above rotation systems have limited space
 OOB match of filters could upset
Magnetron and cause more emissions
 Cost
28
Practical Issues Filters

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Are Lossy can contribute twice TX & RX
Can cause wild heat (active arrays)
Can take up space
Can cause oscillation out of band if not
well matched
Can distort want signal if too narrow
Limit the peak power due to arcing
Costly
29
Practical Issues

Linear Beam Tube Transmitters
 Can use moderate compression ratios
 Difficult to control rise and fall times
 Single channel systems can use High Q
channel Filters
 Agile systems can only use band limiting
filters
 See Illustration
30
Practical Issues cont:

Solid State Lumped Transmitters
 Can use higher compression ratios
 Easier to control rise and fall times
(slow down)
 Single channel systems can use High Q
channel Filters
 Agile systems can only use band limiting
filters of High Q
35
Practical Issues cont:

Solid State Distributed Transmitters
 Can use higher compression ratios
 Easier to control rise and fall times
 Agile systems can only use band limiting
filters with a moderate Q
36
Practical Issues

Active Array Systems
 Can use very high compression ratios
 Difficult to control rise and fall times
 Agile systems can only use band limiting
filters of very low Q
 Or Low pass filters
37
Illustration: Solid State ATC

Can make use off
Fixed Operating Frequencies
 Long pulses
 Slow rise & fall times


Many radar applications cannot
make use of all these advantages
38
Solid State ATC radar
39
Conclusions to Date


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Currently there is some scope for improving the mask
Solid State systems are better than linear beam
devices and cross field devices
 Larger time bandwidth products
There some scope for pulse shaping in Solid State
transmitters
OOB Filters are effective for fixed frequency systems
 Agile systems are more problematic
 Limited scope for OOB control
 OOB control not realistic in active arrays
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END
Thank you
John Holloway
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