Tham khảo tài liệu 'wave propagation 2010 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 262 Wave Propagation Fig. 24. Radiation pattern of the metamaterial tube waveguide antenna with the thickness d 5 mm at a frequency of 3 GHz. Fig. 25. Radiation pattern of the metamaterial tube waveguide antenna with the thickness d 10 mm at a frequency of 3 GHz. The thickness d 10 mm of the metamaterial waveguide tube corresponds to the negative total power flux S_ . the wave propagates in the backward direction 180 . This corresponds to an increase in the amplitude of the back lobe and the degeneration of the main lobe. Figures 26 27 are plotted for d 15 20 mm respectively. At a thickness of 20 mm Fig. 27 the difference between the back and front lobes of the radiation pattern is more than 15 dB and the antenna radiates predominantly in the backward direction 180 . Thus in the case of zero total power flux in the metamaterial waveguide the antenna radiates equally in the directions 0 and 180 . In the presence of the forward and backward wave fields the antenna radiates in the forward 0 and backward 180 directions respectively. Metamaterial Waveguides and Antennas 263 Fig. 26. Radiation pattern of the metamaterial tube waveguide antenna with the thickness d 15 mm at a frequency of 3 GHz. Fig. 27. Radiation pattern of the metamaterial tube waveguide antenna with the thickness d 20 mm at a frequency of 3 GHz. The backward radiation effect is observed only at the negative values of the real parts of permittivity and permeability. Figure 28 presents the radiation pattern of the metamaterial waveguide tube with the thickness d 20 mm at a frequency of GHz for which permittivity and permeability are positive according to Fig. 21. In this case the radiation pattern is usual with the main lobe greater than the back lobe. That is the antenna radiates mainly in the forward direction. To conclude we have experimentally demonstrated the effect of the backward electromagnetic radiation of the metamaterial waveguide tube antenna. We have shown that the effect is observed
