1. Information Warfare Technologies Inc. Calibration Techniques for Amplitude DF Systems AOC SYMPOSIUM OCTOBER 2005 Mr. Al Evans President Information Warfare Technologies Inc.

2. Agenda Amplitude AOA Measurement Background Uninstalled Performance Error Sources Typical Installed AOA Performance Performance Modeling Error Correction Methods AOA Performance Improvement Results Conclusions

3. Information Warfare Technologies Inc. Typical Amplitude DF Installation 45º 135º225º 315º Four Antennas On Intercardinal Axis Boresights Are Commonly Used

4. Information Warfare Technologies Inc. Typical Well Behaved DF Antenna Patterns 3 dB Beamwidth = 80º (nominal) DF Slope = 2.5 deg/dB Mid Band 4.0 deg/dB Low Band 7 Degree RMS DF Accuracy Is Possible With A Good Installation

5. Information Warfare Technologies Inc. Error Sources Antenna Deviation From Gaussian Pattern Polarization Error Aircraft Antenna Installation Effects Aircraft Cabling Imbalance Receiver Channel Imbalance Quantization Error

6. Information Warfare Technologies Inc. Above Average Average Below Average Fuselage Blockage Impacts Antenna Pattern Wingtip External Stores Impacts Antenna Pattern DF Performance Impacts of Aircraft Installation Radome Impacts Adjacent Antenna Axial Ratio

7. Information Warfare Technologies Inc. Installed Antenna Patterns Wingtip External Stores Impacts Antenna Pattern Fuselage Blockage Impact on Antenna Pattern Fuselage Blockage Impact on Antenna Pattern No Stores Antenna Pattern No Stores Antenna Pattern Bias Error @ Pattern Crossover Due to Pattern Ripple Bias Error @ Pattern Crossover Due to Squint Large Errors @ Pattern Secondary Crossover

8. Information Warfare Technologies Inc. Forward = 3.98 dB With Bias Impact of Forward Fuselage It Is Degraded to = 5.27 dB Over -5º to +20º Elevation Forward = 3.98 dB With Bias Impact of Forward Fuselage It Is Degraded to = 5.27 dB Over -5º to +20º Elevation AFT = 2.99 dB With Bias Impact of Wingtip Stores It Is Degraded to = 3.71 dB Over ± 20º Elevation AFT = 2.99 dB With Bias Impact of Wingtip Stores It Is Degraded to = 3.71 dB Over ± 20º Elevation Antenna Pattern Effect On DF Slope & Bias Antenna Channel to Channel Imbalance: dB Delta per 5 Degree Step dB Variation Due to Pattern Ripple and Axial Ratio

9. Information Warfare Technologies Inc. Typical Aircraft Installed Performance Uncorrected installed performance can be severely degraded by –Blockage / pattern deviation from gaussian –Multipath (quantified by degradation in axial ratio) F MID/HIGH F LOW

10. Information Warfare Technologies Inc. Performance Modeling Model the DF performance based on Y=MX+B Add rules for dominant backlobe conditions STD DEV of error denotes random error components Compare RMS Error w/ STD DEV to assess magnitude of BIAS errors RSS A kit and B kit random error contributions to calculate uncorrected system DF performance Model the DF performance based on Y=MX+B Add rules for dominant backlobe conditions STD DEV of error denotes random error components Compare RMS Error w/ STD DEV to assess magnitude of BIAS errors RSS A kit and B kit random error contributions to calculate uncorrected system DF performance Azimuth 0 – 360 degrees Degrees Error The Results May Be Shocking !

11. Information Warfare Technologies Inc. First Order Amplitude DF Correction Methods Limitations –DF Curves Must Remain Monotonic –Assume Linear DF Function –Assume Fixed Polarization Calculate Optimum Y=MX+B Slope and Intercept Calculate Corrected DF Error Azimuth 0 – 360 degrees Degrees Error Optimized DF Curve: Slope = 2.8 deg/dB Bias @ 270 az = 12 degrees A Kit = 3.36 deg B Kit = 4.2 deg Antenna = 7.7 deg Total Error = 9.4 deg Optimized DF Curve: Slope = 2.8 deg/dB Bias @ 270 az = 12 degrees A Kit = 3.36 deg B Kit = 4.2 deg Antenna = 7.7 deg Total Error = 9.4 deg The Results May Look Good @ Some Frequencies !

12. Information Warfare Technologies Inc. Second Order Amplitude DF Correction Methods Limitations –DF Curves Must Remain Monotonic –Assume Best Fit NonLinear DF Function –Assume Fixed Polarization Calculate Optimum Y=f(X) Curve Calculate Corrected DF Error Left Hemisphere: Slope = 2.0 deg/dB Bias @ 270 az = 12 degrees A Kit = 2.4 deg B Kit = 3.0 deg Antenna = 10.7 deg Total Error = 11.3 deg Left Hemisphere: Slope = 2.0 deg/dB Bias @ 270 az = 12 degrees A Kit = 2.4 deg B Kit = 3.0 deg Antenna = 10.7 deg Total Error = 11.3 deg Right Hemisphere: Slope = 2.0 deg/dB Bias @ 90 az = 0 degrees A Kit = 2.4 deg B Kit = 3.0 deg Antenna = 5.1 deg Total Error = 6.4 deg Right Hemisphere: Slope = 2.0 deg/dB Bias @ 90 az = 0 degrees A Kit = 2.4 deg B Kit = 3.0 deg Antenna = 5.1 deg Total Error = 6.4 deg It Gets Worse @ Other Frequencies !

13. Information Warfare Technologies Inc. Some Results (25.1 deg Error Baseline) Azimuth 0 – 360 degrees Degrees Error Left Hemisphere: Slope = 3.9 deg/dB Bias @ 270 az = 20 degrees A Kit = 1.2 deg B Kit = 1.5 deg Antenna = 17 deg Total Error = 18.6 deg Left Hemisphere: Slope = 3.9 deg/dB Bias @ 270 az = 20 degrees A Kit = 1.2 deg B Kit = 1.5 deg Antenna = 17 deg Total Error = 18.6 deg Right Hemisphere: Slope = 3.9 deg/dB Bias @ 90 az = 0 degrees A Kit = 1.2 deg B Kit = 1.5 deg Antenna = 11.4 deg Total Error = 13.7 deg Right Hemisphere: Slope = 3.9 deg/dB Bias @ 90 az = 0 degrees A Kit = 1.2 deg B Kit = 1.5 deg Antenna = 11.4 deg Total Error = 13.7 deg 20º Note: Right Hemisphere Error ~ 8.7º If 5 Deg Bias Correction Applied

14. Information Warfare Technologies Inc. What to Do With Polarization Errors Polarization Errors Are Major Error Contributors – You Cannot Accept Them Unless There Is No Other Alternative Most Emitters Are Fixed Polarization And The Threat ID Will Allow You To Pick The Polarization DF Table To Use Fortunately, Even With Massive Polarization Error (Axial Ratio), The Installed Interferometer Effects Are At Least Equal. So At Least The Polarization Error Gets Rss’d With The Rest Of The Errors. Understand That The Peak Polarization Errors Are In The Proximity Of Antenna Boresights. –That Is Why An 8 Antenna System Will Cut Errors By More Than 50% Use A Quadrant/Octant Mode To Overcome Polarization Errors If They Are Too Large !

15. Information Warfare Technologies Inc. Smoothing / Integration Improvements Airborne Platforms Can Integrate DF Over Short Time Intervals Slope = 3.9 deg/dB Single Pulse RMS Error = 8.6 deg Integrated RMS Error = 6.9 deg Slope = 3.9 deg/dB Single Pulse RMS Error = 8.6 deg Integrated RMS Error = 6.9 deg Instantaneous DF Error 10:1 Integrated DF Error Applied to 0.5º Resolution Data

16. Information Warfare Technologies Inc. Conclusions Amplitude DF Systems Can Be Calibrated To Achieve 7 To 15 Degrees RMS Performance In Spite Of Bad Installations Amplitude DF Systems Can Be Calibrated To Achieve 5 To 8 Degrees RMS Performance In Good Installations Integration Of DF Data Offers Significant Benefit In Improved DF Report Accuracy BUT MOST OF ALL: Installed Antenna Patterns Are The Pre-requisite To Implementing Improved Installed Performance Amplitude DF Systems Can Be Calibrated To Achieve 7 To 15 Degrees RMS Performance In Spite Of Bad Installations Amplitude DF Systems Can Be Calibrated To Achieve 5 To 8 Degrees RMS Performance In Good Installations Integration Of DF Data Offers Significant Benefit In Improved DF Report Accuracy BUT MOST OF ALL: Installed Antenna Patterns Are The Pre-requisite To Implementing Improved Installed Performance

17. Information Warfare Technologies Inc. 3 Things To Do Monotonic Nonlinear Model of Installed Antenna Pattern 8 Antenna Quadrant / Octant Uses Best Part of Installed Antenna Pattern Noise Source Calibration of A- Kit and Receiver Channels You Can Make a 5 Degree Installed Performance System 123

18. Information Warfare Technologies Inc. QUESTIONS ? Contact Data: Information Warfare Technologies Inc. P.O. Box 800 Middletown DE 19709 www.iw-tech.org email: al.evans@iw-tech.org Contact Data: Information Warfare Technologies Inc. P.O. Box 800 Middletown DE 19709 www.iw-tech.org email: al.evans@iw-tech.org