The Design of Broad-Band Resistive Radiation Probes

Thin-film resistive screens operated in free space above a critical frequency fc are shown to exhibit constant cross sections over extremely broad frequency ranges. Below fc, the cross sections decrease approximately at the rate of 12 dB/octave. Electrical equivalents to the screen in the form of thin-film gratings or grids are used to generate directly an output voltage proportional to the absorbed radiation. Probes with physical cross sections of 1-in diameter and absorptivities of 15-20 percent can be designed to operate from below 200 MHz to well within the millimeter range.