We propose a technique for enhancing the angular resolution of a flat-base Luneburg lens antenna to enable it to detect multiple targets with arbitrary scattering cross-sections that are located in angular proximity. The technique involves measuring the electric field distribution on the flat plane of the Luneburg lens antenna, operating in the receive mode, at a specified number of positions, and correlating these distributions with the known distributions derived from the field distributions in the measurement plane generated by single target at different look angles. We show that the proposed approach can achieve enhanced resolution than the basis of the beam-width of the Luneburg lens antenna, and it is capable of distinguishing between two targets with different scattering cross-sections that have an angular separation as small as 1˚ for a Luneburg lens with 6.35λ aperture size, for Signal-to-Noise Ratio (SNR) better than 20 dB.
2. Lafond, O., M. Himdi, H. Merlet, and P. Lebars, "An active reconfigurable antenna at 60 GHz based on plate inhomogeneous lens and feeders," IEEE Trans. Antennas Propag., Vol. 61, No. 4, 1672-1678, 2013. doi:10.1109/TAP.2012.2237003
3. Mirkamali, A., J.-J. Laurin, F. Siaka, and R. Deban, "A planar lens antenna with circular edge inspired by gaussian optics," IEEE Trans. Antennas Propag., Vol. 61, No. 9, 4476-4483, 2013. doi:10.1109/TAP.2013.2269762
4. Luneburg, R. K., Mathematical Theory of Optics, University of California Press, 1964.
5. Demetriadou, A. and Y. Hao, "A grounded slim Luneburg lens antenna based on transformation electromagnetics," IEEE Antennas and Wireless Propag. Lett., Vol. 10, 1590-1593, 2011. doi:10.1109/LAWP.2011.2180884
6. Mosallaei, H. and Y. Rahmat-Samii, "Nonuniform Luneburg and two-shell lens antennas: Radiation characteristics and design optimization," IEEE Trans. Antennas Propag., Vol. 49, No. 1, 60-69, 2001. doi:10.1109/8.910531
7. Pfeiffer, C. and A. Grbic, "A printed, broadband Luneburg lens antenna," IEEE Trans. Antennas Propag., Vol. 58, No. 9, 3055-3059, 2010. doi:10.1109/TAP.2010.2052582
8. Bosiljevac, M., M. Casaletti, F. Caminita, Z. Sipus, and S. Maci, "Non-uniform metasurface Luneburg lens antenna design," IEEE Trans. Antennas Propag., Vol. 60, No. 9, 4065-4073, 2012. doi:10.1109/TAP.2012.2207047
9. Dockrey, J. A., M. J. Lockyear, S. J. Berry, S. A. R. Horsley, J. R. Sambles, and A. P. Hibbins, "Thin metamaterial Luneburg lens for surface waves," Physical Review B, Vol. 87, 125137, 2013. doi:10.1103/PhysRevB.87.125137
10. Mirkamali, A. and J.-J. Laurin, "Two-dimensional loaded wire grid for modelling dielectric objects and its application in the implementation of Luneburg lenses," IET Microw. Antennas Propag., Vol. 6, No. 15, 1728-1737, 2012. doi:10.1049/iet-map.2012.0344
11. Rondineau, S., M. Himdi, and J. Sorieux, "A sliced spherical Luneburg lens," IEEE Antennas and Wireless Propag. Lett., Vol. 2, 163-166, Feb. 2003. doi:10.1109/LAWP.2003.819045
12. Wu, L., X. Tian, M. Yin, D. Li, and Y. Tang, "Three-dimensional liquid flattened Luneburg lens with ultra-wide viewing angle and frequency band," Appl. Phys. Lett., Vol. 103, 084102, 2013. doi:10.1063/1.4819338
13. Wu, L., X. Tian, H. Ma, M. Yin, and D. Li, "Broadband flattened Luneburg lens with ultra-wide angle based on a liquid medium," Appl. Phys. Lett., Vol. 102, 074103, 2013. doi:10.1063/1.4793206
14. Ma, H. F. and T. J. Cui, "Three-dimensional broadband and broad-angle transformation-optics lens," Nature Communications, 2010, Doi: 10.1038/ncomms1126.
15. Dhouibi, A., S. N. Burokur, A. Lustrac, and A. Priou, "Compact metamaterial-based substrateintegrated Luneburg lens antenna," IEEE Antennas and Wireless Propag. Lett., Vol. 11, 1504-1507, 2012. doi:10.1109/LAWP.2012.2233191
16. Hua, C., X. Wu, N. Yang, and W. Wu, "Air-filled parallel-plate cylindrical modified Luneberg lens antenna for multiple-beam scanning at millimeter-wave frequencies," IEEE Trans. Microw. Theory Tech, Vol. 61, No. 1, 436-443, 2013. doi:10.1109/TMTT.2012.2227780
17. Ma, H. F., B. G. Cai, T. X. Zhang, Y. Yang, W. X. Jiang, and T. J. Cui, "Three-dimensional gradient-index materials and their applications in microwave lens antennas," IEEE Trans. Antennas Propag., Vol. 61, No. 5, 2561-2569, 2013. doi:10.1109/TAP.2012.2237534
18. James, G., A. Parfitt, J. Kot, and P. Hall, "A case for the Luneburg lens as the antenna element for the square-kilometre array radio telescope," Radio Science Bulletin, Vol. 293, 32-37, Jun. 2000.
19. Liang, M., X. Yu, S.-G. Rafael, W.-R. Ng, M. E. Gehm, and H. Xin, "Direction of arrival estimation using Luneburg lens," IEEE International Microwave Symposium (IMS) Digest (MTT), 1-3, Jun. 17-22, 2012.
20. Jain, S. and R. Mittra, "Flat-base broadband multibeam Luneburg lens for wide angle scan," IEEE Antennas and Propagation Society International Symposium (APS), Memphis, TN, 2014. doi:10.1155/2014/619304
21. Kendall, M. G. and J. D. Gibbons, Rank Correlation Methods, Oxford University Press, 1990.
22. Yu, W., X. Yang, Y. Liu, R. Mittra, and A. Muto, Advanced FDTD Methods: Parallelization, Acceleration, and Engineering Applications, Artech House, Norwood, MA, USA, Mar. 2011.