The output power of antennas is an important factor affecting the radiation performance of umbrella antenna arrays. Considering the power limit of very-low-frequency (VLF) umbrella arrays and the uncontrollable directivity, we propose a novel method for the spatial power-combining (SPC) of VLF umbrella arrays. Using multiple groups of feeders, the problem of phase shifting of the signals can be solved for VLF arrays. In the high-frequency portion of the VLF range (25-30 kHz), this novel method can improve the efficiency of VLF arrays by 26% in the special directivity. A model of a trideco-tower umbrella antenna array is established in the FEKO simulation software. The simulation results show that, compared with the in-phase feeding, the VLF transmitting antenna array forms the main beam in all directions. The array gain of the umbrella phased array in the 0° (180°) beam position is larger than 1.1 dB. The front-to-back ratio of the arrays is 3.7 dB. Compared with the in-phase feed mode, the directivity of the phased array enhances and the efficiency increases markedly. The simulation results demonstrate the effectiveness of the proposed method.
2. Madanayake, A., et al., "Energy-efficient ULF/VLF transmitters based on mechanically-rotating dipoles," Engineering Research Conference (MERCon), 230-235, Moratuwa, Sri Lanka, May 29–31, 2017.
3. Yan, Y. L., C. Liu, H. N. Wu, and Y. H. Dong, "Non-foster matching network design for VLF receive loop antenna," IEICE Electronics Express, Vol. 13, No. 12, 1-10, 2016.
4. Li, H.-Y., J. Zhan, Z.-S. Wu, and P. Kong, "Numerical simulations of ELF/VLF wave generated by modulated beat-wave ionospheric heating in high latitude regions," Progress In Electromagnetics Research M, Vol. 50, 55-63, 2016.
5. Rozhnoi, A., et al., "VLF/LF signal studies of the ionospheric response to strong seismic activity in the Far Eastern region combining the DEMETER and ground-based observations," Physics and Chemistry of the Earth, Vol. 85–86, 141-149, 2015.
6. Liu, Y. J., F. Liu, D. B. Yang, J. Xu, and Z. Zhang, "Type of active impulse noise suppressing method based on double-loop antennas in very low frequency/ultra-low frequency coupling communications," IET Microwaves, Antennas & Propagation, Vol. 11, No. 6, 867-873, 2017.
7. Liu, Y. W. and X. B. Su, "Analysis and design of a new 2×2 tapered finline array for spatial power combining," Journal of Electronics & Information Technology, Vol. 32, No. 2, 470-475, 2010.
8. Boaventura, A., A. Coallado, A. Georgiadis, and N. B. Carvalho, "Spatial power combining of multi-sine signals for wireless power transmission applications," IEEE Transactions on Microwave Theory and Techniques, Vol. 62, No. 4, 1022-1030, 2014.
9. Song, K., J. F. Zhang, S. Y. Hu, and Y. Fan, "Ku-band 200-W pulsed power amplifier based on waveguide spatially power-combining technique for industrial applications," IEEE Transactions on Industrial Electronics, Vol. 61, No. 8, 4274-4280, 2014.
10. Shan, X. Y. and Z. X. Shen, "An eight-way power combiner based on a transition between rectangular waveguide and multiple microstrip lines," IEEE Transactions on Microwave Theory and Techniques, Vol. 61, No. 7, 2557-2561, 2013.
11. Staiman, D., M. Breese, and W. Patton, "New technique for combining solid-state sources," IEEE Journal of Solid-state Circuits, Vol. 3, No. 3, 238-243, 1968.
12. Zhang, Y. S. and W. Hong, "A millimeter-wave gain enhanced multi-beam antenna based on a coplanar cylindrical dielectric lens," IEEE Transactions on Antennas and Propagation, Vol. 60, No. 7, 3485-3488, 2012.
13. Harvey, J., E. Brown, and D. Rutledge, "Spatial power combining for high-power transmitters," Microwave Magazine, Vol. 1, No. 4, 48-59, 2000.
14. Yin, K., K. Zhang, and J. Xu, "Characterization and design of millimeter-wave full-band waveguidebased spatial power divider/combiner," Progress In Electromagnetics Research C, Vol. 50, 65-74, 2014.
15. Ortega, B., J. Mora, and R. Chulia, "Optical beamformer for 2-D phased array antenna with subarray partitioning capability," IEEE Photonics Journal, Vol. 8, No. 3, 1-9, 2017.
16. Guo, L. T., et al., "Studies of a leaky-wave phased array antenna for high-power microwave applications," IEEE Transactions on Plasma Science, Vol. 44, No. 10, 2366-2375, 2016.
17. Wang, B. and K.-M. Huang, "Spatial microwave power combining with anisotropic metamaterials," Progress In Electromagnetics Research, Vol. 114, 195-210, 2011.
18. Lu, G., F. X. Wang, B. Chen, and L. Zhou, "Analysis of electrical properties of multi-VLF thirteentower umbrella antenna array," Journal of Navel University of Engineering, Vol. 26, No. 4, 46-49, 2014.
19. Chen, Q. J., Q. X. Jiang, F. L. Zeng, and C. B. Song, "Single frequency spatial power combining using sparse array based on time reversal of electromagnetic wave," Acta Physica Sinica, Vol. 64, No. 20, 0204101, 2015.
20. Chen, S. C., Y. L. Yan, and J. J. Ling, "Control technique of dynamic tuning of VLF transmitting antennas," Journal of Information Engineering University, Vol. 16, No. 4, 424-430, 2015.
21. Clive, P., G. Stuart, M. John, and J. R. Daniel, "Theory and practice of modern antenna range measurements,", The Institution of Engineering and Technology, London, 2014.
22. Fu, Z. H., "Constrained minimum power combination for broadband beamformer design in the STFT domain," Frontiers of Computer Science, Vol. 11, No. 3, 408-418, 2017.
23. Balanis, C. A., Antenna Theory: Analysis and Design, 4th Ed., Wiley Press, Hoboken, 2016.
24. Li, B., C. Liu, and H. Wu, "A moment-based study on the impedance effect of mutual coupling for VLF umbrella antenna arrays," Progress In Electromagnetics Research C, Vol. 76, 75-86, 2017.