In this paper, the performance of a concentric hexagonal antenna array (CHAA) is investigated with the exploitation of a robust variable diagonal loading (VDL) technique in the presence of direction of arrival (DOA) mismatch. The performance of minimum variance distortionless response (MVDR) based CHAA is compared with the performance of existing MVDR based concentric circular antenna arrays (CCAAs), and it is found that the proposed MVDR based CHAA provides 25.54% narrow half-power beamwidth (HPBW) and lower side lobe level than the existing MVDR based CCAAs. When DOA mismatch occurs between main beam steering direction and actual signal-of-interest (SOI) direction, the performance of MVDR based CHAA is deteriorated. In the case of DOA mismatch, to ameliorate the performance of CHAA, this paper proposes VDL technique for the CHAA processor and compare the performance of proposed robust CHAA with existing robust CHAAs. The proposed VDL based robust CHAA delivers 88.37% and 78.56% higher output power for 2˚ DOA mismatch than existing fixed diagonal loading (FDL) and optimal diagonal loading (ODL) based CHAAs, respectively. Several tapering window functions are proposed to reduce the side lobe level of CHAA. Performance of the proposed beamformer is analyzed utilizing MATLAB environment in various scenarios.
2. Godara, L. C., Smart Antennas, CRC Press, 2004.
3. Fernandez-Olvera, A. D. J., D. Melazzi, and V. Lancellotti, "Beam-forming and beam-steering capabilities of a reconfigurable plasma antenna array," Progress In Electromagnetics Research C, Vol. 65, 11-22, 2016.
4. Khan, M. Z. U., et al., "Robust LCMV beamformer for direction of arrival mismatch without beam broadening," Wireless Personal Communications, Vol. 104, No. 1, 21-36, 2019.
5. Pappula, L. and D. Ghosh, "Linear antenna array synthesis using cat swarm optimization," AEU-International Journal of Electronics and Communications, Vol. 68, No. 6, 540-549, 2014.
6. Ram, Gopi, et al., IEEE Transactions on Antennas and Propagation, "Cat swarm optimization as applied to time-modulated concentric circular antenna array: Analysis and comparison with other stochastic optimization methods,", Vol. 63, No. 9, 4180-4183, 2015.
7. Reza, M. F. and M. S. Hossain, "Robust concentric circular antenna array with variable loading technique in the presence of look direction disparity," Progress In Electromagnetics Research M, Vol. 57, 35-43, 2017.
8. Ganz, M. W., R. L. Moses, and S. L. Wilson, "Convergence of the SMI and the diagonally loaded SMI algorithms with weak interference," IEEE Transactions on Antennas and Propagation, Vol. 38, No. 3, 394-399, 1990.
9. Gan, L. and Z. Yi, "Automatic computation of diagonal loading factor for robust adaptive beamforming based on Gaussian distribution," AEU-International Journal of Electronics and Communications, Vol. 67, No. 7, 570-573, 2013.
10. Li, J., P. Stoica, and Z. Wang, "On robust Capon beamforming and diagonal loading," IEEE Transactions on Signal Processing, Vol. 51, No. 7, 1702-1715, 2003.
11. Hossain, M. S., L. C. Godara, and M. R. Islam, "Efficient robust broadband beamforming algorithms using variable loading," IEEE Latin America Transactions, Vol. 10, No. 3, 1697-1702, 2012.
12. Li, J., P. Stoica, and Z. Wang, "On robust Capon beamforming and diagonal loading," IEEE Transactions on Signal Processing, Vol. 51, No. 7, 1702-1715, 2003.
13. Wang, W., R. Wu, and J. Liang, "A novel diagonal loading method for robust adaptive beamforming," Progress In Electromagnetics Research C, Vol. 18, 245-255, 2011.
14. Reza, M. F. and M. S. Hossain, "Performance investigation of robust concentric circular antenna array beamformer in the presence of look direction disparity," AEU-International Journal of Electronics and Communications, Vol. 82, 52-57, 2017.
15. Song, A., et al., "Widely linear generalized sidelobe canceling beamforming with variable diagonal loading," AEU-International Journal of Electronics and Communications, Vol. 76, 77-85, 2017.
16. Ali, M. Y., M. S. Hossain, and M. F. Reza, "Robust hexagonal antenna array with optimal diagonal loading in the presence of steering angle disparity," IEEE 4th International Conference on Electrical Information and Communication Technology (EICT), 1-5, 2019.
17. Mahmoud, K. R., M. El-Adawy, S. M. M. Ibrahem, R. Bansal, and S. H. Zainud-Deen, "A comparison between circular and hexagonal array geometries for smart antenna systems using particle swarm optimization algorithm," Progress In Electromagnetics Research, Vol. 72, 75-90, 2007.
18. Bera, R., et al., "Comparative study of circular and hexagonal antenna array synthesis using improved particle swarm optimization," Procedia Comp. Sc. (Science Direct), Vol. 45, 651-660, 2015.
19. Liu, C., Y. Liu, Y. Zhao, and D. Hu, "Robust adaptive wideband beamforming using probability- constrained optimization," Progress In Electromagnetics Research C, Vol. 52, 163-172, 2014.
20. Huang, Y., M. Zhou, and S. A. Vorobyov, "New designs on MVDR robust adaptive beamforming based on optimal steering vector estimation," IEEE Transactions on Signal Processing, Vol. 67, No. 14, 3624-3638, 2019.
21. Qin, L., M. Wu, and Z. Dong, "Robust adaptive beamforming using multi-snapshot direct data domain approach," AEU-International Journal of Electronics and Communications, Vol. 75, 124-129, 2017.
22. Gu, Y., et al., "Robust adaptive beamforming based on interference covariance matrix sparse reconstruction," Signal Processing, Vol. 96, 375-381, 2014.
23. Shen, F., F. Chen, and J. Song, "Robust adaptive beamforming based on steering vector estimation and covariance matrix reconstruction," IEEE Communications Letters, Vol. 19, No. 9, 1636-1639, 2015.
24. Huang, L., et al., "Robust adaptive beamforming with a novel interference-plus-noise covariance matrix reconstruction method," IEEE Transactions on Signal Processing, Vol. 63, No. 7, 1643-1650, 2015.
25. Mandal, D., S. P. Ghoshal, and A. K. Bhattacharjee, "Design of concentric circular antenna array with central element feeding using particle swarm optimization with constriction factor and inertia weight approach and evolutionary programing technique," Journal of Infrared, Millimeter, and Terahertz Waves, Vol. 31, No. 6, 667-680, 2010.
26. Robinson, J. and Y. Rahmat-Samii, "Particle swarm optimization in electromagnetics," IEEE Transactions on Antennas and Propagation, Vol. 52, No. 2, 397-407, 2004.
27. Reza, M., M. Hossain, and M. Rashid, "Robust centered element concentric circular antenna array with low side lobe using variable loading and tapering windows in the presence of array imperfections," International Journal of Antennas and Propagation, 1-10, 2017.
28. Nofal, M., S. Aljahdali, and Y. Albagory, "Tapered beamforming for concentric ring arrays," AEU- International Journal of Electronics and Communications, Vol. 67, No. 1, 58-63, 2013.
29. Dessouky, M., H. Sharshar, and Y. Albagory, "A novel tapered beamforming window for uniform concentric circular arrays," Journal of Electromagnetic Waves and Applications, Vol. 20, No. 14, 2077-2089, 2006.
30. Donelli, M. and P. Febvre, "An inexpensive reconfigurable planar array for Wi-Fi applications," Progress In Electromagnetics Research C, Vol. 28, 71-81, 2012.
31. Wang, Y.-F., et al., "Wideband circularly polarized magneto-electric dipole 1x2 antenna array for millimeter-wave applications," IEEE Access, Vol. 8, 27516-27523, 2020.
32. Donelli, M., T. Moriyama, and M. Manekiya, "A compact switched-beam planar antenna array for wireless sensors operating at Wi-Fi band," Progress In Electromagnetics Research C, Vol. 83, 137-145, 2018.
33. Yuri, N. and P. Ilia, "Probability of false peaks occurring via circular and concentric antenna arrays DOA estimation," 2016 39th International Conference on Telecommunications and Signal Processing (TSP), 178-181, 2016.
34. Sarkar, P. K. and M. F. Reza, "Performance analysis of uniform concentric circular antenna array beamformer using different DOA estimation technique," 2018 4th International Conference on Electrical Engineering and Information & Communication Technology (iCEEiCT), 320-324, 2018.
35. Diniz, P. S., E. A. Da Silva, and S. L. Netto, Digital Signal Processing: System Analysis and Design, Cambridge University Press, 2010.