224 cones -/ * ' : ..' \rounded cones, r=O.la cone-spheres cone-spheres -----------___-----_ t ________ theory for cone-spheres io 15 -30 ka Fig. 1. Cross polarized radar cross sections.targets. The transmitted and received polarizat,ions were inclined & 4 5 O to the horizontal, and the resulting patterns were recorded over an angular range -30" _< 4 _< 30" about t.he axis. A thin horizont.al wire l.75X lohg was used for calibrat.ion, t.his length being chosen because the broadside return is relatively insensit.ive to the precise dimensions. The peak ret.urns of each pattern closest to, and on either side of, axial incidence were read and averaged to produce a dat,um point in Fig. 1.Four types of bodies were measured: thin disks; right circular cones, cones with rounded edges, and cone-spheres, where t.hese have been listed in the order of decreasing severity of edge. The peak values of t,heir cross polarized cross sections uccr are normalized wit.h respect to X* and plott.ed in Fig. 1 BS a function of ka = 2~a / x , where a is t.he maximum radius of the object. For a given ka, the returns decrease with decreasing edginess, with the effect. becoming more pronounced as Iza increases. Thus disks and sharply edged cones have t.he st.rong&t returns, conespheres the weakest, and cones with rounded edges have intermediate values. The differencebetween cones and cone-spheres is as much as 30 dB for Iza = 20.One can predict this behavior with reasonable.accuracy using the geometrical theory of diffraction. Consider, for example, a right circular cone of half-angle y. The formulas given by Senior and Uslenghi [ 2 ] are relevant, provided Iza is large enough to fix t,he peak of the cross polarized lobe within the backward cone (i,e.,+> 1,where now E = Z I i a cos y sin 4. The second term in (2) can be neglected for narrow cones, and the peak value of the resulting formula is plotted as a dashed line in Fig. 1. The agreement with experiment is reasonable in view of the extremely low levels measured, but the systematic discrepancy for...
