The ambiguity functions of a kind of direct chaotic radar system are investigated. In this radar system, a microwave chaotic Colpitts oscillator is employed to generate the source signal that is directly transmitted through a wideband antenna without modulation. The auto-ambiguity function of this radar system shows many sidelobes which makes the unambiguous detection difficult. It is because the spectrum of the chaotic signal is not very flat and smooth, with pulsation peaks in it. The cross-ambiguity functions of the direct radar system have also been investigated to evaluate the electronic counter countermeasure (ECCM) performance and the "multi-user" characteristic. It is shown that rather excellent ECCM capability can be achieved in this radar system with transmitting chaotic signals generated by circuits with same parameters but at different time or with slightly different circuit parameters. In addition, several possible methods to reshape the spectrum of the chaotic signal from microwave Colpitts oscillators to improve the unambiguous detection performance are suggested at the end of this paper.
2. Zang, W., Z. G. Shi, S. C. Du, and K. S. Chen, "Novel roughening method for reentry vehicle tracking using particle filter," J. of Electromagn. Waves and Appl., Vol. 21, No. 14, 1969-1981, 2007.
3. Du, S. C., Z. G. Shi, W. Zang and K. S. Chen, "Using interacting multiple model particle filter to track airborne targets hidden in blind Doppler," Journal of Zhejiang University-Science A, Vol. 8, No. 8, 1277-1282, 2007.
4. Wang, S., X. Guan, X. Ma, and Y. Su, "Calculating the poles of complex radar targets," J. of Electromagn. Waves and Appl., Vol. 20, No. 14, 2065-2076, 2006.
5. Singh, A. K., P. Kumar, T. Chakravarty, G. Singh, and S. Bhooshan, "A Novel digital beamformer with low angle resolution for vehicleTracking radar," Progress In Electromagnetics Research, Vol. 66, 229-237, 2006.
6. Liu, G. S., H. Gu, and W. M. Su, "The development of random signal radars," IEEE Transactions on Aerospace and Electronic Systems, Vol. 35, No. 3, 770-777, 1999.
7. Soliman, M. S., T. Morimoto, and Z. I. Kawasaki, "Threedimensional localization system for impulsive noisesources using ultrawideband digital interferometer technique," J. of Electromagn. Waves and Appl., Vol. 20, No. 4, 515-530, 2006.
8. Lin, F. Y. and J. M. Liu, "Ambiguity functions of laser-based chaotic radar," IEEE Journal of Quantum Electronics, Vol. 40, No. 12, 1732-1738, 2004.
9. Shen, Y., W. H. Shang, and G. S. Liu, Ambiguity function of chaotic phase modulated radar signals, Proceedings of ICSP, 1574-1577, 1998.
10. Sobhy, M. I. and A. R. Shehata, "Chaotic radar systems," IEEE MTT-S Digest, 1701-1704, 2000.
11. Hara, Y., et al., Development of a chaotic signal radar system for vehicular collision-avoidance, Proceeding of IEEE Radar Conference, 227-232, 2002.
12. Flores, B. C., E. A. Solis, and G. Thomas, Assessment of chaos based FM signals for range-Dopper imaging, IEEE Proc.-R adar Sonar Navig., Vol. 150, No. 4, 313-322, 2003.
13. Venkatasubramanian, V. and H. Leung, A robust chaos radar for collision detection and vehicular ranging in intelligent transportation systems, IEEE Intelligent Transportation Systems Conference, 548-552, 2004.
14. Venkatasubramanian, V. and H. Leung, "A novel chaos-based high-resolution imaging technique and its application," IEEE Signal Processing Letters, Vol. 12, No. 7, 528-531, 2005.
15. Lin, F. Y. and J. M. Liu, "Chaotic radar using nonlinear laser dynamics," IEEE J. Quantum Electron., Vol. 40, No. 6, 815-820, 2004.
16. Lin, F. Y. and J. M. Liu, "Chaotic lidar," IEEE J. of Selected Topics in Quantum Electronics, Vol. 10, No. 5, 991-996, 2004.
17. Mykolaitis, G., A. Tamasevicius, and S. Bumeliene, "Experimental demonstration of chaos from Colpitts oscillator in VHF and UHF ranges," Electronics Letters, Vol. 40, No. 2, 91-92, 2004.
18. Shi, Z. G. and L. X. Ran, "Microwave chaotic Colpitts oscillator: design, implementation and applications," J. of Electromagn. Waves and Appl., Vol. 20, No. 10, 1335-1349, 2006.
19. Tamasevicius, A., G. Mykolaitis, S. Bumeliene, A. Baziliauskas, R. Krivickas, and E. Lindberg, "Chaotic Colpitts oscillator for the ultrahigh frequency range," Nonlinear Dynamics, Vol. 44, No. 1-4, 159-165, 2006.
20. Qiao, S., Z. G. Shi, K. S. Chen, W. Z. Cui, W. Ma, T. Jiang, and L. X. Ran, "A new architecture of UWB RADAR utilizing microwave chaotic signals and chaos synchronization," Progress In Electromagnetics Research, Vol. 75, 225-237, 2007.
21. Dmitriev, A. S., M. Hasler, A. I. Panas, and K. V. Zakharchenko, "Basic principles of direct chaotic communications," Nonlinear Phenomena in Complex Systems, Vol. 6, No. 1, 488-501, 2003.
22. Maggio, G. M., O. D. Feo, and M. P. Kennedy, "Nonlinear analysis of the Colpitts oscillator and applications to design," IEEE Trans. Circuits Syst. I, Vol. 46, No. 9, 1118-1130, 1999.
23. Shi, Z. G. and L. X. Ran, "Design of chaotic Colpitts oscillator with prescribed frequency distribution," International Journal of Nonlinear Science and Numerical Simulation, Vol. 5, No. 1, 89-94, 2004.
24. Shi, Z. G., Y. Zhang, H. W. Liu, and L. X. Ran, "Randomness test of signal generated by microwave chaotic Colpitts oscillator," Microwave and Optical Technology Letters, Vol. 49, No. 8, 1981-1984, 2007.
25. Dmitriev, A. S., A. I. Panas, and S. O. Starkov, "Ring oscillating systems and their application to the synthesis of chaos generators," Int. J. of Bifurcation and Chaos, Vol. 6, No. 5, 861-865, 1996.
26. Chen, G. R. and T. Ueta, Chaos in Circuits and Systems, World Scientific, 2002.