1 radar unwanted emmissions a personal view j r holloway all data in this presentation comes from...
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RADAR UNWANTED EMMISSIONS
A personal viewJ R Holloway
All data in this presentation comes from public domain sources
ITU WP 8B Radar Seminar
September 2005 GENEVA
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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
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Current Unwanted Emission Limits Cat A&B
Current Unwanted Emission Mask
-120
-100
-80
-60
-40
-20
0
0.1 1 10 100
x BW-40dB Bandwidth
Po
we
r d
B
Cat A
Cat B
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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
"Design Aim" Unwanted Emission Mask
-120-100
-80-60-40-20
0
0.1 1 10 100
x Bw-40dB
Po
we
r d
B
Cat A
Cat B
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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
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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
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Sensitivity of Equation for Bw-40 FM Pulsed
Bw-40dB gets large when tr0 Bc gets large
rc
r t
AB
tt
KB 240
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FM Trapezoidal Pulses vs Mask
Mask 15 MHz
Value 10 MHz
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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
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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
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Trapezoidal Pulse
Two roll-off rates 20 dB/dec 40 dB/dec
20 dB/dec
40 dB/dec
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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
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Magnetron: Difficult to meet current OOB Limits
Marine Navigation Radar X band Magnetron - Short Pulse Mode
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
8.00 8.25 8.50 8.75 9.00 9.25 9.50 9.75 10.00 10.25 10.50 10.75
Frequency (GHz)
Radar Antenna Fixed
Radar Antenna Rotating
Mask
Failure
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Coaxial Magnetron: Cat B Limits
Meteorological Radar - Ground BasedC band Magnetron
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
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)
No
rmal
ised
Po
wer
Mea
sure
d in
51
1 K
Hz
Bw
(d
B)
Failure Zones
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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 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
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Practical Issues To Reduce Unwanted Emissions
Use High Compression ratios Use slow rise and fall times Shape pulses to remove
discontinuities Use Filters
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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
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Practical Issues Filters
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
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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
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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
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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
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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
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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
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Solid State ATC radarCivil Air Traffic Control Radar - Ground Based
S band Solid StateKnown interference signals removed
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
2 3 4 5 6 7 8 9 10 11 12 13 14
Frequency (GHz)
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Conclusions to Date Currently there is some scope for improving the
mask Solid State systems are better than linear beam
devices and cross field devices L arger 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 youJohn Holloway