Transactions on Antennas and Propagation
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| M is mainly determined by H / V . The validation of such a law can be recognized by inspecting Fig. ab, c) and d. Along the line of x=0, is about 0°, and M is the same as H , whereas along the line of y=0.06 m, is about 90°, and M is the same as V . Otherwise M is a combination of H and V , and has a value between them. Just because H and V are similar as the incident angle distribution, these factors do not affect the similarity between M and the incident angle distribution. Although, as mentioned earlier, H and V always have a similar distribution, in Fig. 10, H and V of inhomogeneous radome seem distinctly different, which, in fact, is due to the difference of their value range. As Table I shows, inhomoge- neous radome introduces IPD less than 0.5 rad, whereas for CTR, more than 2 rad. Also, for CTR, intervals of H and V are similar in length and mainly overlap with each other, which ensure their similar distribution as shown in Fig. a) and (b. For inhomogeneous radome, interval of H and V has different length (the former, 0.086 rad, much less than the latter, 0.186 rad, and separate with each other, which lead to the phenomena in Fig. a) and (b, that is 1) H is nearly constant with the value close to the minimum (corresponds to blue color) while V nearly constant with the value close to the maximum (corresponds to red color 2) V is not as constant as V because it has a larger interval length, manifested as the color purity, i.e., H is almost just blue while V consists of more than one color (red, yellow, etc. The interval characteristics of H and V finally lead to the similarity between M and polarization angle. In addition, as H and V are greatly reduced, M of inhomogeneous radome has a corresponding obvious reduction, and a smaller interval length, as Table I shows. Table I also gives the jg of inhomogeneous radome, CTR and VTR, which is -0.03, 1.17 and 1.31, respectively. As pointed out in Section II (B, with the increase of jg, the distribution of M varies gradually from being similar with polarization angle (cf. inhomogeneous radome casein Fig. 10) to being similar with H and V (cf. CTR and VTR cases in Fig. 9 and 11). Then, consider the VTR case. As radome thickness is variable now, in Fig. a) and (b, the distribution of H and V , although similar with each other, is conspicuously different from that of the incident angle. Moreover, the interval length of M is even slightly larger than that of CTR whereas the BSE is tremendously reduced. By now, a preliminary summary can be drawn under 6° scan angle for inhomogeneous radome, CTR and VTR, their IPD distribution is similar with polarization angle distribution, similar with incident angle, dissimilar with either polarization or incident angle distribution, respectively their interval length of M increases in sequence whereas their BSE decreases in sequence. BSE depends on two characteristics of radome IPD: the distribution and the variation interval. On one hand, asymmetric distribution is immune to BSE irrespective of the magnitude of variation interval (consider the case of spherical ra- dome. On the other hand, for an asymmetric distribution, the BSE is proportional to the magnitude of variation interval. BSE is a synthesized production of these two factors. With CTR as a reference, VTR, although having a slightly larger variation interval, reduces BSE by changing the original IPD distribution, i.e., the distribution of incident angle, whereas inhomogeneous radome, although having an obviously smaller variation interval, increases BSE by the introduction of anew IPD distribution (the distribution of polarization angle. Evidently, under 6° scan angle, the distribution of incident angle is abetter one in the behalf of reducing BSE than that of polarization angle. Before making a meaningful conclusion of the characteristics of inhomogeneous radome, it is necessary to study more cases. Fig. ac) and Fig. ac) show the IPD distribution of CTR, inhomogeneous radome and VTR under 16° scan angle, respectively, while Fig. d) and Fig. d) show the corresponding incident angle distribution and polarization angle distribution, respectively. Table II lists the IPD variation interval under 16° scan angle, and Fig. 15 plots the interval of Download 1 Mb. Share with your friends:
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