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Heat can be transferred from an antenna’s surface by conduction, convection and radiation. Wind velocity over the antenna surface helps remove heat and is increased when the antenna is rotated. For instance, if an antenna is 8-ft wide and rotating at 6 rpm, the air velocity at the outer edge is 1.7 mph. The core temperatures for the test section of waveguide, taking into account solar heat, are shown in Fig. 6 in comparison with non-solar heat curves.

Temperature stability

Dimensional changes in the sample waveguide cross-sections were measured when the various samples were subjected to high temperature over a prolonged period.

Each sample was measured at room temperature across the central portion of both the “a” and “b” dimensions. The samples were then subjected to a temperature of 170°F for a period of eight hours, allowed to cool, remeasured and dimensional changes noted. The procedure was repeated in steps of 5°F until a temperature of 195°F was reached. The results are shown in Fig. 7a.

The sample of Eccofoam 8lb/ft3 was subjected to an additional heating cycle, ranging from 240°F to 260°F in steps of 5°F. This material was much more stable as shown.

Each sample was then heat cycled as previously described and dimensional changes noted. The non-heat-treated sample had relatively poor dimensional stability, while the heat-treated sample exhibited good stability as shown in Fig. 7b.