RADAR UNWANTED EMMISSIONS ITU WP 8 B Radar

RADAR UNWANTED EMMISSIONS ITU WP 8 B 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 n n n Before 2003 no SE limit for radar From 2003 new radars must meet Cat A or Cat B SE limits n Cat A -60 d. B n Cat B -100 d. B Class B being proposed to be adopted in Europe. OOB Definition of the extent by the emission masks n Current Mask n Design Aim Status of Limits n SE levels part of radio regulations n Boundary part of regulation n OOB mask is a recommendation n Design aim for new OOB 2006/2012 7

Current Unwanted Emission Limits Cat A&B Cat A Cat B 8

Design Aim n n When the OOB Mask was introduced a design aim was also introduced. This proposed to increase the Roll off to 40 d. B/dec If this is not agreed then the aim falls JRG is considering what should replace the design aim 9

Design Aim Unwanted Emissions Cat A&B Cat A Cat B 10

Problems With Current Mask n n n Mask perceived to be too relaxed at estimating – 40 d. B Bandwidth Mask perceived to be too relaxed in terms of Roll-off for trapezoidal pulses Magnetron Radars find it difficult to meet current mask n Impossible to meet design aim 11

Problems With Mask perceived to be too relaxed at estimating – 40 d. B Bandwidth n Mask perceived to be too relaxed in terms of Roll-off for trapezoidal pulses. n Magnetron Radars find it difficult to meet current mask n n Impossible to meet design aim 12

Sensitivity of Equation for Bw-40 FM Pulsed n Bw-40 d. B gets large when n n tr 0 Bc gets large 14

FM Trapezoidal Pulses vs Mask 15 MHz Value 10 MHz 15

Practical Bandwidths Measured MHz Calculated 16 MHz 3 d. B BW 20 d. B BW 40 d. B BW 2. 5 3. 6 10 2. 5 7. 8 25. 7 16

Problems With Mask perceived to be too relaxed at estimating – 40 d. B Bandwidth n Mask perceived to be too relaxed in terms of Roll-off for trapezoidal pulses. n Magnetron Radars find it difficult to meet current mask n n Impossible to meet design aim 17

Trapezoidal Pulse n n n Two roll-off rates 20 d. B/dec 40 d. B/dec 19

Problems With Mask perceived to be too relaxed at estimating – 40 d. B Bandwidth n Mask perceived to be too relaxed in terms of Roll-off for trapezoidal pulses. n Magnetron Radars find it difficult to meet current mask n n Impossible to meet design aim 21

Magnetron: Difficult to meet current OOB Limits Failure 22

Coaxial Magnetron: Cat B Limits Failure Zones 23

JRG Work on New Mask n n n Looking into how a better estimate of the reference bandwidth. n Non linear chirps n Limit excessive bandwidths due to n Large Chirps n Fast Rise Times Looking into what roll-off can be practically achieved n How Roll-off Relates to RB Looking into the special problems associated with. n Magnetron based radars n FM CW radars 24

Trade Off Reference Bandwidth vs Roll-off n n If the Reference Bandwidth is accurately calculated 20 d. B roll-off looks achievable 40 d. B roll-off looks difficult These are theoretical however in practice distortions make things worse 26

Practical Issues To Reduce Unwanted Emissions n n Use High Compression ratios Use slow rise and fall times Shape pulses to remove discontinuities Use Filters 27

Practical Issues cont n Magnetrons n Below rotation can use high Q filters n Multi pulse length systems have to use a filter wide enough to meet narrowest pulse n Above rotation systems have limited space n OOB match of filters could upset Magnetron and cause more emissions n Cost 28

Practical Issues Filters n n n n 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 n Linear Beam Tube Transmitters n Can use moderate compression ratios n Difficult to control rise and fall times n Single channel systems can use High Q channel Filters n Agile systems can only use band limiting filters n See Illustration 30

Practical Issues cont: n Solid State Lumped Transmitters n Can use higher compression ratios n Easier to control rise and fall times (slow down) n Single channel systems can use High Q channel Filters n Agile systems can only use band limiting filters of High Q 35

Practical Issues cont: n Solid State Distributed Transmitters n Can use higher compression ratios n Easier to control rise and fall times n Agile systems can only use band limiting filters with a moderate Q 36

Practical Issues n Active Array Systems n Can use very high compression ratios n Difficult to control rise and fall times n Agile systems can only use band limiting filters of very low Q n Or Low pass filters 37

Illustration: Solid State ATC n Can make use off Fixed Operating Frequencies n Long pulses n Slow rise & fall times n n Many radar applications cannot make use of all these advantages 38

Solid State ATC radar 39

Conclusions to Date n n Currently there is some scope for improving the mask Solid State systems are better than linear beam devices and cross field devices n Larger time bandwidth products There some scope for pulse shaping in Solid State transmitters OOB Filters are effective for fixed frequency systems n Agile systems are more problematic n Limited scope for OOB control not realistic in active arrays 40

END Thank you John Holloway 41