elements per unit volume, ot. is the total cross section (including absorption) of the individual chaff elements at the signal frequency, and £ is the total length of the signal path through the cloud, as illustrated in Figure C.4-1. For aluminum and aluminized-glass chaff dipoles, the absorption cross section is small relative to the scattering cross section, so that where a is the scattering radar cross section (RCS) of individual dipoles. For randomly oriented chaff dipoles, the scattering cross section of a single dipole averaged over all orientation is approximately where X is the wavelength (in meters) for the first resonant frequency of the chaff dipole. It is frequently useful to express attenuation in terms of decibels per unit path length. An attenuation factor, 3, for chaff may be expressed in decibels per meter (dB/m) as follows: where n is the number of effective chaff elements per cubic meter, and o is the e 4 radar cross section in square meters of the individual chaff elements. Chaff dipoles are frequently fabricated of aluminum coated glass fiber having a nominal coated diameter of one mil. Chaff provides a broad band frequency response so that chaff cut to a dipole length (approximately 2.36 inches long) corresponding to the SPS power beam frequency will provide near maximum RCS response at the sideband frequencies unless the carrier to sideband frequency separation is greater than about 100 MHz. Individual pod-type chaff dispensers available for Navy and Air Force air- craft can carry approximately 1.5 x 10^9 aluminized-glass chaff dipoles cut to the SPS frequency of 2.45 GHz. The chaff can be deployed in approximatley 2.5 minutes. Dipole damage, tangling, distortion, etc., associated with the dispensing process may be expected to reduce the effective number of dipoles to something like 60% of the total dipole count. Accordingly only about 9 x 10^8 dipoles loaded per pod will be effective. The wavelength at 2.45 GHz is 0.122 m so that the random average dipole cross section is
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