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RADAR UNWANTED EMMISSIONS. A personal view J R Holloway. ITU WP 8B Radar Seminar September 2005 GENEVA. All data in this presentation comes from public domain sources. Unwanted Emission Limits. Before 2003 no SE limit for radar From 2003 new radars must meet Cat A or Cat B SE limits
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RADAR UNWANTED EMMISSIONS A personal view J R Holloway ITU WP 8B Radar Seminar September 2005 GENEVA All data in this presentation comes from public domain sources
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
Current Unwanted Emission Limits Cat A&B Cat A Cat B
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
Design Aim Unwanted Emissions Cat A&B Cat A Cat B
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
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
Sensitivity of Equation for Bw-40 FM Pulsed • Bw-40dB gets large when • tr0 • Bc gets large
FM Trapezoidal Pulses vs Mask Mask 15 MHz Value 10 MHz
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 Practical Bandwidths
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
Trapezoidal Pulse • Two roll-off rates • 20 dB/dec • 40 dB/dec 20 dB/dec 40 dB/dec
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
Coaxial Magnetron: Cat B Limits Failure Zones
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
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
Practical Issues To Reduce Unwanted Emissions • Use High Compression ratios • Use slow rise and fall times • Shape pulses to remove discontinuities • Use Filters
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
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
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
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
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
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
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
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
END Thank you John Holloway