Electromagnetic induced timing defects in the synthetic aperture radar of the Magellan spacecraft

Abstract

The Magellan spacecraft synthetic aperture radar experienced a failure when the receiver protect circuitry in the PRF/Timing subsystem failed. The receiver protect circuitry failed due to electromagnetic coupling from the ultra stable oscillator/clock generator circuit located on an adjacent board. Some ICs in this ultra stable oscillator/clock generator circuit had previously become detached from their traces when a thermal test caused the conformal coating to expand. The ICs were re-attached to the PCB traces using "smallwire loops" which apparently radiated significantly to cause the failure of the receiver protect circuits. The analysis which discovered the above failure mechanism is discussed. The analysis also includes the use of the method of moments to model the radiation from a portion of the noisy board and coupling into the susceptible circuits of another board. The analysis also derives expressions for the near field coupling between the radiating structure and the susceptible circuit. Only one of such models is discussed herein for brevity. The simple solution to the electromagnetic coupling problems is discussed in the conclusion of this work.