عنوان مقاله [English]
In this paper a method for optimal digital beamforming in ground-based circular synthetic aperture radar in order to maximize the image signal to noise ratio (SNR) is proposed. In this method to maximize the image SNR, an array of receiver elements is used and the complex weighting coefficients of receiver channels are computed by solving an optimization problem and eigenvalue decomposition. The optimization problem is formed based on data modeling in each range and matched filter image formation and SNR computation in each image pixel versus excitation coefficients. Finally, optimal weighting coefficients of each range are computed as the eigenvector corresponding to the largest eigenvalue of a matrix related to the geometry and parameters of the system. Simulations illustrate the superiority of the proposed method in increasing image SNR over other digital beamforming methods, especially at long ranges.
 J. C. Curlander and R. N. McDonough, “Synthetic aperture radar- Systems and signal processing,” New York: John Wiley & Sons, Inc, 1991.
 I. G. Cumming and F. H. Wong, “Digital processing of synthetic aperture radar data,” Artech House, 2005.
 M. Soumekh, “Reconnaissance with slant plane circular SAR imaging,” Image Processing, IEEE Transactions on, vol. 5, pp. 1252-1265, 1996.
 H. Klausing, N. Bartsch, and C. Boesswetter, “A MM-Wave SAR-Design for Helicopter Application (ROSAR),” Microwave Conference, 1986. 16th
European, pp. 317,328, 8-12 Sept. 1986.
 H. Klausing and W. Keydel, “Feasibility of a synthetic aperture radar with rotating antennas (ROSAR),” 1990.
 Y. Luo, H. Song, R. Wang, Y. Deng, F. Zhao, and Z. Xu, “Arc FMCW SAR and Applications in Ground Monitoring,” Geoscience and Remote Sensing, IEEE Transactions on , vol. 52, no. 9, pp. 5989-5998, Sept. 2014.
 H. Lee, J.-H. Lee, K.-E. Kim, N.-H. Sung, and S.-J. Cho, “Development of a Truck-Mounted Arc-Scanning Synthetic Aperture Radar,” Geoscience and Remote Sensing, IEEE Transactions on, vol. 52, no. 5, pp. 2773-2779, May 2014.
 S. R. Samareh Hashemi and S. A. Seyedin, “Fast Imaging in Ground-Based Circular Strip-Map Synthetic Aperture Radar,” Journal of Radar, vol. 3, no. 1, pp. 57-72, 2015. (In Persian)
 A. Broquetas, R. De Porrata, L. Sagues, X. Fabregas, and L. Jofre, “Circular synthetic aperture radar (C-SAR) system for ground-based applications,” Electronics Letters, vol. 33, no. 11, pp. 988-989, 22 May 1997.
 M. Younis, C. Fischer, and W. Wiesbeck, “Digital beamforming in SAR systems,” Geoscience and Remote Sensing, IEEE Transactions on, vol. 41, no. 7, pp. 1735-1739, July 2003.
 W. Wang, “Multi-Antenna Synthetic Aperture Radar,” CRC Press, 2013.
 M. Suess, B. Grafmuller, and R. Zahn, “A novel high resolution, wide swath SAR system,” IEEE International Geoscience and Remote Sensing Symposium, 2001.
 N. Gebert, G. Krieger, and A. Moreira, “Digital beamforming for HRWS-SAR imaging: system design, performance and optimization strategies,” 2006 IEEE International Symposium on Geoscience and Remote Sensing, 2006.
 N. Gebert, G. Krieger, and A. Moreira, “Digital Beamforming on Receive: Techniques and Optimization Strategies for High-Resolution Wide-Swath SAR Imaging,” Aerospace and Electronic Systems, IEEE Transactions on, vol. 45, no. 2, pp. 564-592, April 2009.
 G. Krieger, M. Younis, N. Gebert, S. Huber, F. Bordoni, A. Patyuchenko, et al., “Advanced concepts for high-resolution wide-swath SAR imaging,” 8th European Conference on Synthetic Aperture Radar, 2010.
 F. Feng, H. Dang, X. Tan, G. Li, and C. Li, “An improved scheme of digital beam-forming in elevation for spaceborne SAR,” IET International Radar Conference, 2013.
 F. He, X. Ma, Z. Dong, and D. Liang, “Digital Beamforming on Receive in Elevation for Multidimensional Waveform Encoding SAR Sensing,” Geoscience and Remote Sensing Letters, IEEE , vol. 11, no. 12, pp. 2173-2177, Dec. 2014.
 S. X. Zhang, M. D. Xing, X. G. Xia, L. Zhang, R. Guo, Y. Liao, and Z. Bao, “Multichannel HRWS SAR imaging based on range-variant channel calibration and multi-Doppler-direction restriction ambiguity suppression,” IEEE Transactions on Geoscience and Remote Sensing, vol. 52, no. 7, pp. 4306-4327, 2014.
 F. Bordoni, M. Younis, E. M. Varona, and G. Krieger “Adaptive scan-on-receive based on spatial spectral estimation for high-resolution, wide-swath Synthetic Aperture Radar,” IEEE International Geoscience and Remote Sensing Symposium, 2009.
 K. Schuler, M. Younis, R. Lenz, and W. Wiesbeck, “Array design for automotive digital beamforming radar system,” IEEE International Radar Conference, 2005.
 S. Huber and M. Younis, A. Patyuchenko, and G. Krieger, “A novel digital beam-forming concept for spaceborne reflector SAR Systems,” 2009 European Radar Conference (EuRAD), 2009.
 E. Varona, “Adaptive digital beam-forming for high-resolution wide-swath SAR system,” MA dissertation, Universitat Politecnica, De Catalunya, Spain, 2009.
 S. R. Samareh Hashemi, “Optimal Imaging in Ground-Based Circular Strip-Map Synthetic Aperture Radar,” Ph.D. Thesis, Ferdowsi University of Mashhad, 2015. (In Persian)
 S. R. Samareh Hashemi and S. A. Seyedin, “Model-Based Image Formation in Ground-Based Circular Strip-Map Synthetic Aperture Radar,” Journal of Radar, vol. 3, no. 2, pp. 23-44, 2015. (In Persian)
 M. Soumekh, “Synthetic aperture radar signal processing with MATLAB algorithms,” John Wiley & Sons, 1999.
 C. A. Balanis, “Antenna Theory Analysis and Design,” 3'rd Edition, John Wiley & Sons, 2005.
 R. A. Horn and C. R. Johnson, “Matrix analysis,” Cambridge university press, 2012.
 P. Comon and G. H. Golub, “Tracking a few extreme singular values and vectors in signal processing,” Proceedings of the IEEE, vol. 78, pp. 1327-1343, 1990.
 Y. Liao, M. Xing, L. Zhang and Z. Bao, “A novel modified Omega-K algorithm for circular trajectory scanning SAR imaging using series reversion,” EURASIP Journal on Advances in Signal Processing, vol. 2013, p. 64, 2013.
 Available at: http://www.sandia.gov/radar/complex-data/
 M. Lambers, H. Nies, and A. Kolb, “Interactive dynamic range reduction for SAR images,” IEEE Geoscience and Remote Sensing Letters, vol. 5, pp. 507-511, 2008.
 A. Gavrovska and I. Reljin, M. Samčović, A. Milivojević, G. Zajić, and V. Starovoitov, “High dynamic range mapping for synthetic aperture radar images,” Telfor Journal, vol. 10, pp. 56-61, 2018.
 S. Hisanaga, K. Wakimoto, and K. Okamura, “Tone mapping and blending method to improve SAR image visibility,” IAENG International Journal of Computer Science, vol. 38, pp. 289-294, 2011.
 A. Reigber and O. Hellwich, “RAT (Radar Tools): A free SAR image analysis software package,” in Proceedings of Eusar, pp. 997-1000, 2004.