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Pattern Synthesis and Antenna Receiver Design for Passive Coherent Location

Pattern Synthesis and Antenna Receiver Design for Passive Coherent Location. Gunther Lange Radar Remote Sensing Group University of Cape Town Supervisor: Professor Mike Inggs. Presentation Outline. Brief overview of passive coherent location (PCL) Motivation for study

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Pattern Synthesis and Antenna Receiver Design for Passive Coherent Location

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  1. Pattern Synthesis and Antenna Receiver Design for Passive Coherent Location Gunther Lange Radar Remote Sensing Group University of Cape Town Supervisor: Professor Mike Inggs

  2. Presentation Outline • Brief overview of passive coherent location (PCL) • Motivation for study • Objectives and Methodology • Signal environment of the Cape Town region • Geometry of the problem • Discussion of possible transmitters for target illumination • Pattern synthesis of an antenna array • Beam forming and null placement • Simulation of pattern synthesis method • Work in progress • Conclusion © CSIR 2006 www.csir.co.za

  3. Overview of Passive Coherent Location • Exploit ambient radio signals • Detect reflections off targets using signals from Tx1 • Reference signal required for signal processing • Suppress interference • Direct signal (Null 1) • Jamming signal (Null 2) • Null placement is vital for electronic countermeasures • Receiver forms a single node of a netted radar system © CSIR 2006 www.csir.co.za

  4. Motivation4 • PCL would exploit ambient radio signal provided by the existing broadcasting infrastructure, the “illuminators of opportunity”. • PCL can be operated covertly. i.e. The receiver is not easily detected since it is only monitoring the ambient signals in the environment. • Effective null placement would be essential for the suppression of jamming signals. • A netted or multistatic PCL system can be used for counter stealth. • PCL is relatively inexpensive, mobile, versatile and suitable for rapid deployment. • The application of a PCL system would enhance air security. © CSIR 2006 www.csir.co.za

  5. Objectives and Methodology The core objective is to develop a single static PCL receiver node at UCT which will be accomplished by: • Mapping the signal environment of the Cape Town region • Determine the most favourable transmitter and its broadcast signal for the “illuminator of opportunity”. • An investigation in methods of pattern synthesis of an antenna array • Steer beam in the direction of a moving target • Place nulls in the direction of strong interference • Construction and testing of receiver node © CSIR 2006 www.csir.co.za

  6. Signal Environment of the Cape Town Region • A transmitter possessing the best characteristics of “illuminator of opportunity” is required • Transmitter list was provided by Sentech • Radio FM frequencies • Television VHF and UHF channels • Selection of transmitter was based on • Location • Illumination and beam width • Signal Strength © CSIR 2006 www.csir.co.za

  7. Selection of Illuminating Transmitter • Location of Receiver • UCT Menzies • Location of Airport • Location of Constantiaberg transmitter • 70° beam width (red lines) • Illuminates section just north of runway • Airplanes from JHB usually approach runway from the north (green line) © CSIR 2006 www.csir.co.za

  8. Selection of Signal Frequency • Each transmitter has multiple frequencies • FM radio to VHF and UHF TV • Selection based on direct reference signal strength • Friss equation • Physical antenna measurements • Simulation using AREPS3, a EM propagation tool • FM has greater signal strength © CSIR 2006 www.csir.co.za

  9. Pattern Synthesis of an Antenna Array • The method of designing an array of antennas such that it yields an acceptable radiation pattern is known as pattern synthesis1. • Pattern synthesis in general refers to: • Beam forming which ensures maximum gain in the direction of the target. • Null placement for the suppression of interference. • Applying methods of pattern synthesis aids us in determining: • Configuration of the antenna array • Dimensions of the antenna array • Excitation distribution of the array elements © CSIR 2006 www.csir.co.za

  10. Pattern Synthesis Methods • Pattern Synthesis methods can be split into three major categories1: • Beam shaping • Fourier • Narrow beam forming • Dolph-Tschebyscheff • Taylor • Binomial • Null placement • Schelkunoff © CSIR 2006 www.csir.co.za

  11. Locations of Interferring Signals • The receiver system is located at UCT (Menzies) • Suppress the direct signal from Constantiaberg with Null 1 • At a bearing of 212° • Suppress a jamming signal with Null 2 • Place the hypothetical jammer at a bearing of 20° • Maintain main beam in the direction of the airport © CSIR 2006 www.csir.co.za

  12. Schelkunoff Polynomial Method • Specify null postions and determine Schelkunoff polynomial zeros. • The subsequent coefficients of the Schelkunoff polynomial yield the element excitations • An array of 4 antenna elements will be used • The antenna array must be practically realisable • 4 elements make the array ~4.5m long at FM radio frequencies © CSIR 2006 www.csir.co.za

  13. Schelkunoff FEKO Simulation • The antenna arrays are simulated with FEKO2, a powerful antenna modelling program • Begin with 4 hertzian dipoles • Point sources (near-isotrophic) • This would illustrate a best case scenario • Next look at 4 folded dipoles • Structurally more stable than simple half-wave dipoles • Similar pattern to half-wave dipoles © CSIR 2006 www.csir.co.za

  14. Schelkunoff FEKO Simulation – Array Pattern Null 1 Direct Signal Constantiaberg Null 2 Jamming Interference Airport North © CSIR 2006 www.csir.co.za

  15. Schelkunoff FEKO Simulation – Array Pattern Null 1 Direct Signal Constantiaberg Null 2 Jamming Interference Airport North © CSIR 2006 www.csir.co.za

  16. Antenna Array Challenges Airport • Problem • Symmetrical Pattern about the array axis • Large back lobe • Solution • Addition of Reflectors and Directors • Increased complexity • In terms of application of synthesis methods Back lobe © CSIR 2006 www.csir.co.za

  17. Work in Progress • Adding directors and reflectors creates a Yagi-Uda antenna • Yagi-Uda antennas as elements of an array • What synthesis method can be applied to yield • Beam forming • Null placement © CSIR 2006 www.csir.co.za

  18. Conclusion • Investigating the signal environment and methods of pattern synthesis will form a good foundation for the development of a PCL receiver node. • Once the groundwork is in place construction of an antenna array and a PCL system node will begin. • The complete PCL system will eventually be able to: • Detect targets passively using FM radio signals • Steer nulls into desired directions to suppress interference • Form beams in the direction of targets © CSIR 2006 www.csir.co.za

  19. References & Acknowledgments • 1 Constantine Balanis. Antenna Theory and Design 2006 • 2 http://www.feko.info/ • 3 http://areps.spawar.navy.mil/ • 4 University College London and the Passive Bistatic Radar • For their supervision and guidance Professor Mike Inggs and Yoann Paichard © CSIR 2006 www.csir.co.za

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