RADAR UNWANTED EMMISSIONS

1. 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

2. 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

3. Current Unwanted Emission Limits Cat A&B Cat A Cat B

4. 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

5. Design Aim Unwanted Emissions Cat A&B Cat A Cat B

6. 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

7. 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

8. Sensitivity of Equation for Bw-40 FM Pulsed • Bw-40dB gets large when • tr0 • Bc gets large

9. FM Trapezoidal Pulses vs Mask Mask 15 MHz Value 10 MHz

10. 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

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. Trapezoidal Pulse • Two roll-off rates • 20 dB/dec • 40 dB/dec 20 dB/dec 40 dB/dec

13. 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

14. Magnetron: Difficult to meet current OOB Limits Failure

15. Coaxial Magnetron: Cat B Limits Failure Zones

16. 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

17. 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

18. Practical Issues To Reduce Unwanted Emissions • Use High Compression ratios • Use slow rise and fall times • Shape pulses to remove discontinuities • Use Filters

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. Solid State ATC radar

27. 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

28. END Thank you John Holloway