The Linear Frequency Modulation (LFM) waveform is the most commonly and extensively used signal in practical radar system. However a compressed LFM signal at the receiver will produce the first sidelobe at a level of -13 dB to the peak of the main lobe. A weighting function is needed to apply in order to reduce the sidelobes. However, the penalty of mismatch loss is clearly evident. It may reduce output SNR, typically by 1 to 2 dB. Every single dB of additional SNR can have great effects in reducing false alarm rates in target detection applications. In an effort to achieve low autocorrelation sidelobe level without applying weighting function, Non-Linear Frequency Modulation (NLFM) signal has been investigated. This paper describes the sidelobe reduction techniques using simple two-stage FM waveform, modified two-stage FM waveform and tri-stage FM waveform. Simulation results of the proposed NLFM signal are presented. Sidelobe reduction of more than -19 dB can be achieved by this design without any weighting technique applied.
2. Chan, Y. K. and S. Y. Lim, "Synthetic Aperture Radar (SAR) signal generation," Progress In Electromagnetics Research B, Vol. 1, 269-290, 2008.
3. Skolnik, M. I., Radar Handbook, McGraw-Hill, New York, 1970.
4. August, W. R., High Resolution Radar, Artech House, Boston, 1996.
5. Fowle, E. N., "The design of FM pulse compression signals," IEEE Transactions on Information Theory, Vol. 10, No. 1, 61-67, 1964.
6. Mahafza, B. F., Introduction to Radar Analysis, CRC Press, New York, 1998.
7. Keeler, R. J. and C. A. Hwang, Pulse compression for weather radar, Record of the IEEE 1995 International Radar Conference, 529-535, 1995.
8. Barton, D. K., Modern Radar System Analysis, Artech House, Norwood, MA, 1988.
9. Skolnik, M. I., Introduction to Radar Systems, McGraw-Hill, New York, 1980.
10. Cook, C. E. and M. Bernfeld, "Radar Signals: An Introduction to Theory and Application," Artech House, 1993.
11. Jakowatz, C. V., D. E. Wahl, P. H. Eichel, D. C. Ghiglia, and P. A. Thompson, "Spotlight-mode Synthetic Aperture Radar: A Signal Processing Approach," Kluwer Academic Publishers, 1996.
12. Divito, A., A. Farina, G. Fedele, G. Galati, and F. Studer, "Synthesis and evaluation of phase codes for pulse compression radar," Rivista Tecnica Selenia, Vol. 9, No. 2, 12-24, 1985.
13. Harris, E. J., "On the use of windows for harmonic analysis with the discrete fourier transform," Proc. IEEE, Vol. 66, No. 1, 51-83, 1978.
14. Morgan, D. P., "Nonlinear chirp radar waveforms with improved tolerance to doppler shifts," IEE Colloquium on Physics and Device Applications of Acoustic Waves (Digest No. 69), 8/1-5, May 22, .
15. Collins, T. and P. Atkins, "Nonlinear frequency modulation chirps for active sonar," IEE Proceedings --- Radar, Sonar and Navigation, Vol. 146, No. 6, 312-316, Dec. 1999.
16. Johnston, J. A. and A. C. Fairhead, "Waveform design and doppler sensitivity analysis for nonlinear FM chirp pulses," IEE Proceedings F --- Communications, Radar and Signal Processing, Vol. 133, No. 2, 163-175, Apr. 1986.
17. Varshney, L. R. and D. Thomas, "Sidelobe reduction for matched filter range processing," Proceedings of the 2003 IEEE Radar Conference, 446-451, 2003.
18. Doerry, A. W., SAR processing with non-linear FM chirp waveforms, Sandia Report, Sandia National Laboratories, 2006.