A coating composite is provided for a platform surface of an antenna array for, when applied to the platform, affording isolation of radiating and receiving antennas of the array. The coating composite includes a plurality of conductively coated elongate tubes dispersed in an insulating polymer matrix at a volume loading density approaching that at which the composite begins to conduct electrically over macroscopic distances, i.e., close to the percolation threshold. The tubes are preferably comprised of microtubules comprised of biologically-derived, high-aspect rod-shaped particles of microscopic dimensions having an electroless plated metal coating thereon.