The French Aerospace Lab HYCAM : A Radar Cross Section Measurement and Analysis System for Time-Varying Targets Yoann Paichard

2 Contents 1. Introduction to Radar Cross Section measurement of time varying targets 2. Overview of the HYCAM system 3. Experimental results 4. Conclusion

3 Introduction to the Radar Cross Section measurement of time varying targets Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

4 Radar Cross Section (RCS) Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion unit : m² E i,H i E s,H s turntable Network Analyser Frequency Synthesizer H V H V reference channel test channel  Conventional measurement method (indoor measurements): Emission of several successive frequencies for different angles RCS depends on : - Shape and material of the target - Incident frequency - Direction of incident and scattered signals - Polarization -...

5  Scattering coefficients : ρ (F, φ, ) Time varying targets RCS is time - dependant Modulation of the emitted signal t  Target submitted to mechanical or radio-electrical deformations  Example : helicopter blades, jet engines, electronic devices Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

6 Measurements constraints c: wave velocity  x: range resolution B: frequency bandwidth  The measurement must be performed on a wide frequency bandwidth to obtain a fine range resolution : highest modulation frequency of the target  The measurement time must be short enough so that the target can be considered as stationary Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion = 100 kHz T < 5 μ s

7 Overview of the HYCAM system Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

8  Wideband architecture (> 1 GHz) with a high dynamic range (~ dB)  Emission and reception of the whole range of frequencies during a time lower than the stationary time (~ μs)  Real – time computation and display of the RCS (camera mode)  Use of digital technologies HYCAM (HYperfrequence-CAMera) system features Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

9 Transmitted waveform  Step frequency  Multi-carrier signal  Coded multi-carrier signal (OFDM) Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

10 Benefits of a multicarrier signal  Computation of the scattering coefficients by FFT Decrease of the cost of the receiver  Possibility of interleaving the test and the reference channel  Resistance against the linearity imperfections of the components Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

11 Computation of the scattering coefficients  Computation of the scattering coefficients on each frequency during a time lower than 5  s  High input data rate : 14.4 GB/s How to transfert the digitized data to the imaging unit ? Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

12 Real-time decimation  Use of polyphase filters + FFT to process the data Reduction of the data flow  Holes or " zeros " in the frequency spectrum  Frequencies of interest = carrier frequencies of the scattering coefficient. Decimation is performed without losing information Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

13 Polyphase Filter Bank  Decimation of the data before the FFT Polyphase Filter ADC 2 ADC 1 FFT 2048 CONCATENATION Polyphase Filter  No computation of the “zeros”  Same resolution than a 8192-points FFT in the frequency domain Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

14 Hardware implementation  Use commercial IP Cores for the polyphase filters – FFT structure Implantation on the FPGA Maximal computation power of 640 GMACS [Xilinx, Virtex 5]  Use of the new Vita 41 (VXS) standard for the data links: Max throuhput of 2.5 GB/s Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion  Acquisition board : 2 ADC 10 bits, 2.2 Gsps 1 FPGA Virtex 2 Pro -> Evolution towards Virtex 5

15 Experimental results Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

16  Frequency bandwidth : B = 800 MHz ( GHz) HYCAM experimental system Range resolution :  x = 19 cm  Emission of a multicarrier signal  Test and reference channels are interleaved Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

17 RCS measurement of a time-varying target Modulating signal Active transponder VEGA HYCAM system VEGA’s receiving antenna VEGA’s transmitting antenna Receiving antenna Transmitting antenna x 0 first echo Active response of the transponder Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

18 Extraction of an arbitrary modulation in anechoic chamber at x = 0.7 m Filtering  Modulating signal : period = 25  s  Sampling time for the modulation : T e = 1  s Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

19 Outdoor measurements on moving targets  Frequency shift : f m = 100 Hz  Range and cross resolutions :  x =  y = 19 cm  Doppler resolution : 5 Hz distance Doppler Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

20 Conclusion  An innovative digital system has been designed : Very short measurement time (a few μs) Wideband measurement (several GHz) High dynamic range (> 50 dB) RCS display in real-time  A new waveform has been used for the measurement and the analysis of the RCS of time-varying targets Instantaneous measurement of the scattering coefficients  An experimental system has been built Extraction of an arbitrary modulation in anechoic chamber Implementation of the "microwave camera“ mode (off-line processing) Extraction of an electronic modulation on a moving target Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion

21 Publications  Journals Y. Paichard, J.C. Castelli, P. Dreuillet, G. Bobillot, A. Mérigot, HYCAM : Un Moyen de Mesure et D’Analyse Fine de la SER des Cibles Scintillantes, in « la revue d’Electricité et d’Electronique (REE) » (in French), janvier Y. Paichard, J.C. Castelli, P. Dreuillet, G. Bobillot, A. Mérigot, "HYCAM : A RCS Measurement and Analysis System for Time-Varying Targets", to be published in IEEE Transaction on Instrumentations and Measurements.  Conference Y. Paichard, J.C. Castelli, P. Dreuillet, G. Bobillot, "HYCAM: A RCS Measurement and Analysis System for Time-Varying Targets", IEEE Instrumentation and Measurement Technology Conference, Sorrento, April “Giorgio Savastano” award for the best doctoral student paper. Y. Paichard, J.C. Castelli, P. Dreuillet, G. Bobillot, A. Mérigot, "First RCS Measurements Results on a Time-Varying Target with a Microwave Digital Camera “HYCAM”", AMTA European Symposium, Munich, May Best student paper award in the RCS Measurement session. Introduction to RCS meas. of time varying targets Overview of the HYCAM system Experimental results Conclusion