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The first part of this paper is concerned with finding an analytical expression for the scattering cross section of chaff oriented randomly within a vertical cone. The dipoles are allowed to take on all the angles within this cone. A vertically-polarized receiver is assumed off on the horizon and the transmitter on the ground below the chaff. The cross section is a function of the conical angle of the configuration and the angle between a normal to the ground and the incident electric field from the transmitter. Fig. 2 is a plot of the scattering cross section as a function of these two angles. Half-wave chaff randomly distributed within a conical angle about a vertical is not the most effective ensemble, but is a practical one at the lower frequencies. Cutting all these half-wave dipoles into very short ones makes it practical to place them in a horizontal position which has an ensemble gain over the conical but a reradiation loss, since short dipoles are less effective scatters than half-wave ones. The second part of this paper compares the reradiation loss and horizontal ensemble gain.
Date of Publication: March 1961