Microwave induced upset of a digital flight control computer

Tests have established upset levels for a set of digital flight control computers exposed to microwave radiation. Upsets occur for unprotected computers above 10 W/cm/sup 2/ peak power over narrow frequency bands. The frequency range of upsets were from 1 to 4 GHz, no upsets were seen above these frequencies due to increased attenuation from circuit elements. Most vulnerable frequencies are at box resonance, which lie in the low single GHz for these types of avionics. Upset levels can be an order of magnitude lower at box resonance. The main point of entry of the microwave radiation is the I/O wire bundles. Box dimensions, wire runs, and internal board layout affect vulnerability. Almost all upsets seen were digital upsets. This is due to the very wide bandwidth of digital circuits being able to respond to narrow microwave pulses. The most important signal parameters to determine digital flight control computer upset potential are carrier frequency and peak power. Simple shielding techniques have the potential to eliminate any possible upsets seen.<
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