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

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Abstmct -The wide hand rejection of superconducting thin film filters was investigated. The cross talk between input and output ports for thin film filters was degrading the wide baud rejection. We presented a thin film filter design based on a newly invented thin film resonator. The cross coupling between the input and output ports was reduced by a factor of more than ten. The fabricated thin film filter showed good performance and consistency with design and theory. The measured return loss in the passband was more than 23 dB. The insertion loss was 0.66 dB corresponding to a filter Q of 36,000. Steep rejection slopes at the band edges were obtained. The wide band rejection was 95 dB.