Microwave bandpass filters constructed from materials exhibiting somenonlinearity, such as superconductors, will generate intermodulation distortion(IMD) when subjected to signals at more than one frequency. In commercialapplications of superconductive receive filters, it is possible for IMD to begenerated when a weak receive signal mixes with very strong out-of-bandsignals, such as those coming from the transmitter. A measurement procedure wasdeveloped and data were taken on several different types of superconductingbandpass filters, all developed for commercial application. It was found thatin certain interference situations, the 3-tone mixing can produce a spur thatis noticeable by the receiver, but that there are simple preventative designsolutions.
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