Transactions on Antennas and Propagation
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| B. Phase distortion and radome BSE Before studying the phase distortion caused by radome, it is necessary to first show the amplitude characteristics of T H and T V of inhomogeneous and homogeneous (VTR or CTR with constant permittivity) half-wave radomes. Flat radome made of the same glass composite material is employed, and the radome paint is included. The flat inhomogeneous radome has the aforementioned permittivity profile. It should be pointed out that, the conclusions hold well for half-wave wall radomes even if different materials or different permittivity are adopted or the radome paint is removed. Fig. a) plots t H and t V , the amplitude of parallel and perpendicular polarization transmission coefficients of mm flat inhomogeneous and homogeneous radomes, and Fig. b) plots the ratio of t H to t V of mm, mm and mm inhomoge- neous and homogeneous radomes. 8 mm is about the half-wave thickness for the used material at 0° incident angle. From Fig. a, it can be observed that the mm flat inhomogeneous radome has larger t H and t V than homogeneous radome, which is the crucial factor of the TL improvement of inhomogeneous radome, and other cases with mm and mm thickness, although not shown, have similar results. From Fig. bit can be seen that the amplitude ratio of inhomogeneous radome almost keep the same value when the thickness changes from 7 mm to 9.12 mm, whereas the amplitude ratio of homogeneous radome varies obviously. ab) Fig. 8 The amplitude characteristics of parallel and perpendicular polarization transmission coefficients of flat inhomogeneous and homogeneous radomes. (a) Amplitude t H and t V . (b) Amplitude ratio of t H to t V (t H /t V ). The maximum incident angle encountered in the employed radome is 71.26°. In the incident angle range [0, 71.26°], the amplitude ratio of the inhomogeneous radome has the same value, that is, about 1, which means that t H and t V have nearly the same amplitude. For an airborne radome with a sharper shape, the incident angle will increase and may exceed 80°. On this occasion, for inhomogeneous radomes, the amplitude ratio has just a slight increase, and t H and t V still have very similar value, whereas for homogeneous radomes, this may not hold. In Fig. b, when thickness varies during the interval [8 mm, 9.12 mm, the amplitude ratio lies within the range confined by the amplitude ratio curve of 8 mm and 9.12 mm. It can be found from Fig. b) that, in this case, the amplitude ratio of homogeneous radome is also close to 1 and t H and t V can be deemed as nearly identical. This characteristic can facilitate the phase distortion study of inhomogeneous and homogeneous radomes in the following. As t H and t V are very similar, it can be found from (3) that the radome insertion phase delay (IPD) M are mainly determined by H , V and polarization angle . Here we will take the IPD under two special scan angles, 6° and 16°, as examples to study the variation characteristics of IPD. Under 6° scan angle, the inhomogeneous radome has the maximum BSE, 3.143 mrad, which is larger than that of constant thickness radome (CTR, 2.143 mrad. Under 16° scan angle, the inho- mogeneous radome has a very small boresight error (BSE), X (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information DOI TAP, IEEE Transactions on Antennas and Propagation > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERETO EDIT) < 7 whereas CTR has a large BSE. Fig. 9(a)-(c), Fig. 10(a)-(c) and Fig. 11 show the corresponding IPD distribution of CTR, in- homogeneous radome and variable thickness radome (VTR) under 6° scan angle, respectively, while Fig. 9(d) and Fig. 10(d) show the corresponding incident angle distribution and po- larization angle distribution, respectively. All the polarization angle distributions in this work are plotted within the unified range [0°, 90°]. Table I lists the IPD variation interval under 6° scan angle, and Fig. 12 plots the interval of Download 1 Mb. Share with your friends:
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