Development of Broadband Absorbing Materials for Frequencies as Low as 500 Mc. Phase I.
NAVAL RESEARCH LAB WASHINGTON DC
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Two new broadband absorbing materials have been developed at the Naval Research Laboratory for use in anechoic chambers to facilitate indoor antenna measurements at lower frequencies. Both are in the form of a loosely spun mat of animal hair which has been impregnnated with rubber containing carbon black to dissipate r-f energy. Reflection is minimized over a wide frequency range by gradually increasing wilth depth the amount of pigmented rubber applied from a very low value at the front face. The eight-inch-thick model absorbs well to below 500 Mc the four-inch version is for frequencies at low as 1000 Mc At angles near normal incidence these absorbers reflect less than 2 percent of incident energy from their low-frequency limit through the millimeter region. Both are now available commercially. The performance of these materials was determined from a measurement of VSWR in especially designed waveguide and coaxial line systems using samples as terminations. A 36 ft x 10 ft. x 13 ft anechoic chamber having one conducting wall has been constructed with the 500-Mc material.
- Radiofrequency Wave Propagation