tailieunhanh - Giai đoạn mảng anten P11

The essential constituent of a conformal array is curvature. Authorities disagree on whether the array must be part of a curved metallic structure; in this chapter curvature alone is sufficient. Arrays of one or more concentric rings of elements, here called “ring arrays,” are treated first. The term “circular array” is not used, as it often means a planar array of circular perimeter. The following sections deal with arrays on curved metallic bodies. Most simple is the cylinder; Section treats cylindrical arrays with elements around the full circumference | Phased Array Antennas. Robert C. Hansen Copyright 1998 by John Wiley Sons Inc. ISBNs 0-471-53076-X Hardback 0-471-22421-9 Electronic CHAPTER ELEVEN Conformal Arrays SCOPE The essential constituent of a conformal array is curvature. Authorities disagree on whether the array must be part of a curved metallic structure in this chapter curvature alone is sufficient. Arrays of one or more concentric rings of elements here called ring arrays are treated first. The term circular array is not used as it often means a planar array of circular perimeter. The following sections deal with arrays on curved metallic bodies. Most simple is the cylinder Section treats cylindrical arrays with elements around the full circumference. Partial cylindrical arrays where only part of the perimeter has elements are the subject of Section . Finally arrays on surfaces with twodimensional curvature such as spheres and cones are examined. Many applications exist where the array occupies only a small part of a curved body and where the conformal effects are primarily on patterns and excitation rather than on impedance. For these applications the array can often be designed as a planar array but with proper conformal phasing with pattern perturbations predicted by techniques such as geometric theory of diffraction McNamara et al. 1990 . Smart skin flush-mounted antennas for aircraft and missiles often are of this type. One commom application of conformal array is an aircraft or helicopter satellite link where the signal is circularly polarized and zenith to horizon coverage is desired. Essentially all elements that radiate circular polarization at broadside radiate linear polarization at 6 90 deg or 3 dB directivity drop. Array directivity also changes. A rectangular planar array L x W has broadside directivity of 47r IF X2 where rj is the area taper efficiency. The same array at endfire in the L direction has directivity of 3jtW ky 2L k. Thus at the horizon the data link is worse